U.S. Air Force Summer Faculty Fellowship Program

U.S. Air Force Summer Faculty Fellowship Program

U.S. Air Force Summer Faculty Fellowship Program

U.S. Air Force Summer Faculty Fellowship Program

AFRL/RQ Wright Patterson AF Base, OH

SF.05.00.B0123: Mathematical Optimization in Multidisciplinary Design

Kolonay, Raymond (937) 713-7126

The basic objective of multidisciplinary design is to integrate the various disciplines that constitute the environment of an aerospace vehicle. The goal of modern design is to optimize the total system rather than the individual components, permitting the conflicting requirements of the subsystems to be handled much more effectively in getting optimal solutions. Aerospace Vehicle design is a large optimization problem consisting of libraries of variables, constraints, and performance functions. By expanding and contracting these libraries, we can explore the inherent coupling between subsystems and the disciplines and their impact on system level performance. Topics of interest include (1) simultaneous design with multiple constraints; (2) structural requirements derived from strength, stiffness, and frequency considerations; (3) static and dynamic aeroelastic requirements; (4) requirements from acoustic and thermal environments; (5) linear and nonlinear aerodynamic interactions with the structure and control system; (6) tailoring of composites and other new materials; (7) shape and topology optimization; (8) development and testing of efficient optimization methods; (8) sensitivity analyses; (9) Uncertainty Quantification for Design;(10)System Modeling and Discretization for Design, (11) Multi-Fidelity Analysis for Design.

SF.05.00.B0129: High-Fidelity Multidisciplinary Computational Fluid Dynamics

Visbal, M. (937) 713-7058

We conduct basic and applied research in multi-disciplinary high-fidelity computational fluid dynamics, a technology that is critical to the effective development of future Air Force systems. Mutually beneficial collaborations are sought in a broad range of research activities with the main objectives of advancing the state of the art, and complementing and/or expanding in-house capabilities. Opportunities for focused-research include (but are not limited to) the following topics:

(1) Development of high-order computational approaches, including structured and unstructured high-order spatial schemes, high-order implicit time-discretization methods, improved boundary treatments, as well as procedures for accurate solution of aero-acoustics and flows containing both fine-scale and sharp features (e.g. compressible turbulence).

(2) Simulation and improved understanding of vortex flows relevant to maneuvering combat unmanned air vehicles (UCAV) and small unmanned air vehicles (UAV) with emphasis on transition effects, dynamic stall and leading-edge vortex formation and breakdown, wake structure, and unsteady loads (e.g. gust).

(3) Direct (DNS) and Large-Eddy simulation (LES) of transitional and turbulent compressible flows, including improved sub-grid-stress models, inflow conditions for LES, and hybrid RANS/LES approaches extendable to complex configurations.

(4) High-fidelity simulation of active flow control of external and internal transitional, separated and vortical flows employing both traditional and novel techniques (e.g. synthetic jet and plasma-based actuators).

(5) Development of a high-fidelity computational framework for the analysis of aero-optical aberration in the near-field encountered in tactical laser weapon systems. Assessment of the role of aberrating flow structures on overall optical distortion pattern for relevant canonical flows. Investigation of flow control strategies to either regularize or break up large-scale coherent turbulent structures in order to mitigate overall aberration and enable/guide adaptive optic techniques.

SF.05.00.B2314: Development of Translaminar Reinforcement Techniques for Bonded Composite Joints

Ranatunga, Vipul (937) 656-8809

Delamination of adhesively bonded joints is one of the main causes of damage experienced in composite structures. Various translaminar reinforcement techniques such as stitching, pinning, tufting, weaving and braiding are commonly employed to improve the delamination resistance and provide a fail-safe adhesive joint. In order to design damage tolerant composite structural joints, it is necessary to have an in-depth understanding of the delamination growth under various loading conditions. Due to the complexity of loading conditions that exists under service conditions, the delamination growth is commonly studied under the idealized modes such as Mode I, Mode II, Mode III, and well defined combinations of these modes. Double-Cantilever Beam (DCB) and End-Notched Flexure (ENF) tests are the commonly used experimental techniques to understand the delamination behavior under Mode-I and Mode-II loading conditions, respectively. Edge-crack torsion test has been used to determine Mode-III delamination behavior, but the apparent fracture toughness is dependent upon the test geometry. Research opportunities exist in the area of experimental study and numerical modeling of delamination with translaminar reinforced composites. Proposals are solicited for the development of (1) test procedures to estimate the apparent fracture toughness of translaminar reinforced composites, (2) numerical modeling techniques to simulate delamination in translaminar reinforced composites under static and impact loading conditions.

Previous studies have successfully demonstrated the use of carbon fiber pins to improve delamination resistance of laminated composites. Proposed study may include other types of reinforcements applicable to fabric and woven materials.

Keywords: Bonded Joints, Translaminar Reinforcements, Composite Delamination, Finite Element Modeling, Multiscale Modeling.

*Eligibility: Open to US citizens only.

SF.05.00.B3817: Unmanned and Micro Air Vehicle Guidance, Control and Dynamics

Kingston, D. (937) 255-6301

We are committed to the aggressive development and transition of advanced air vehicle control technology to industry and the war fighter to improve total weapon system lethality, survivability, agility, performance, and affordability. Our long-term objective is to develop adaptive and autonomous control theories for the advancement of future Air Force flight vehicles.

Our current research focuses on autonomous and cooperative control of multiple unmanned air vehicles, flight control of flexible wing small UAVs, guidance and control of air-breathing hypersonic vehicles, and verification and validation of flight critical software. Specific research areas include (1) multi-objective optimization for cooperative mission planning involving heterogeneous unmanned vehicles interacting with one or more human operators; (2) cooperative ISR (intelligence, surveillance, and reconnaissance) techniques for multiple vehicles to locate, identify, and track dynamic targets; (3) cooperative strategies for multiple, heterogeneous unmanned air vehicles performing coupled tasks, including the effects of realistic network communication systems such as network latency and delays that result in different target state information on different parts of the distributed decision and control system; (4) autonomous and intelligent control algorithm development, including algorithms with the ability to learn improved responses to a dynamic environment; (5) control oriented modeling of flexible wing small UAVs; (6) control law development for small UAVs that use unsteady aerodynamic and mass property based control effectors; (7) experimental testing and validation of control laws for flexible wing small UAVs; (8) control law and trajectory generation for ground operation of small UAVs while perched, recharging, or operating as a ground based surveillance platform; (9) development of guidance and control laws for air-breathing hypersonic vehicles that provide optimum maneuvering performance while accommodating engine operability and aerodynamic heating constraints; and (10) flight control algorithms for hypersonic vehicles that prevent departure from controlled flight during inlet un-start. Our goal is to develop and validate control algorithms through real-time, nonlinear simulations and experiments, and transition technology to benefit the war fighter.

SF.05.00.B4614: Active Flow Control Modeling and Development

Tilmann, C. (937) 656-8782

Recent developments in small, powerful, and efficient flow control devices have made the application of active flow control systems on future aircraft a viable alternative. Modern flow control effectors and techniques show promise for localized adaptive control of boundary layer separation, laminar to turbulent transition, shear layer turbulence, and secondary flow features. They may also be used to create ‘virtual’ aerodynamic surfaces that can be tailored for changing operating conditions, or to provide flight control. To effectively use these devices in a system requires a multidisciplinary approach that includes further research in sensors, fluids, and adaptive control technologies. We must first acquire knowledge of the base flow to be modified, and determine which flow effectors can most efficiently modify it. We must also determine what flow properties can be sensed in a practical way, and how this information can be used to indicate the state of the flowfield. Then controllers to interpret sensor information, and direct the flow control effectors, can be developed.

Areas of interest include (1) new flow control methods and actuator devices with expanded frequency range, greater amplitude, and improved adaptability; (2) control systems that optimize performance in specific applications; (3) numerical simulation and experimental validation of devices to enhance understanding of the relevant flow physics; (4) integration of existing devices into air vehicle systems; (5) laminar to turbulent transition modeling, prediction, & control; (6) flow control enabled flight control; (7) aero/structure/controls interactions; and (8) development of rapid flow control modeling methods that allow designers to utilize the technologies in design trade studies. Research could involve developing new flow control methodologies, data base development, computational modeling, analytical modeling, and/or software integration.

SF.05.00.B4615: Hypersonic Boundary Layer Transition and Control

Kimmel, R. (937) 255-8295

Boundary layer transition from laminar to turbulent flow impacts hypersonic vehicles performance more profoundly than low-speed vehicles performance. Accurate prediction is difficult because of the sensitivity of transition to initial conditions. Although computational tools continue to improve, their use is limited largely to specialists. Ground testing continues to be a valuable tool; however, boundary layer transition is one of the most difficult fluid dynamic phenomena to replicate experimentally.

Basic research opportunities exist in the prediction and measurement of hypersonic boundary layer transition. Areas of interest include (1) linear stability, (2) parabolized stability equations,  and (3) hypersonic stability and transition measurements.

SF.05.00.B4616: Energy-Based Methods for Integrated Aerospace Systems Analysis & Design Optimization

Camberos, J. (937) 713-7151

Aircraft have evolved into extremely complex machines, posing a highly integrated design challenge. Some of the systems also generate by-products in the form of heat that must be carefully addressed. Methods exist for the design of all these systems based on evolutionary vehicle development. However, the more we depart from existing databases and experience levels, the less confident we are in an optimal design. In addition, many of the classical techniques remain constrained by the simplifying assumptions of quasi-steady, quasi-equilibrium, etc. If these assumptions are not considered, there is no guide as to when those classical techniques no longer give an energy-optimal solution. In particular, the total system and all its components need to be designed in the same energy-based framework. To realize the full potential of these new methods, they must allow design of all the aircraft subsystems to common system-level optimization criteria. Fundamental challenges remain that must be solved before such a vehicle becomes an affordable reality. The following are samples of the required research:

(1) Computational Capability for Loss-Analysis of Aerospace Vehicles. A coupled solution to the Second Law of Thermodynamics and the Navier-Stokes equations needs to be accomplished. Our primary focus will enable the analysis of configurations in terms of entropy generation (exergy destruction) in the wake in order to facilitate numerical experimentation. Theoretical analyses of minimum induced drag based on entropy generation will be studied and confirmed. We will assess the exergy balance of active flow control concepts, especially requiring energy input to the flowfield. In addition, a common framework will be defined for every aspect of vehicle design in exergy terms. It will be shown that mission and vehicle system requirements can be stated in terms of work to be done using the exergy (work potential) of the fuel. This computational capability in a system-level design framework will facilitate the discovery of revolutionary concepts able to achieve maximum performance per amount of work expended.

(2) Structures as an Energy Subsystem. Conventional high-speed vehicles are required to protect the structure from elevated temperatures or provide active cooling, a simple form of energy transfer. Current efforts utilize structural deformation as a flight control effector (i.e., wing twist for roll control), which requires actuation power. In hypersonic vehicles, the structure will have to be a fully integrated part of the system. In these vehicles, the structure may distribute energy between other subsystems, it may store energy for use as and when required, and it may be a user of exergy for tailoring different characteristics. For the future, with the advent of active structures technology, we need to understand the vehicle structure as an energy subsystem.

(3) Propulsion as an Energy Subsystem. In current aircraft, the engine obviously supplies the direct power and cooling air for all the aircraft subsystems. The definition of a jet engine as an energy component with airframe weight and drag has been done. A plasma-based vehicle will require new forms of propulsion/airframe integration. We need to understand how the hypersonic propulsion system, the various plasma-generating devices, and other subsystems can be designed to common metrics and optimization criteria based on the exergy/entropy analysis methods.

(4) Optimization Techniques for a System of Energy Systems. Conventional optimization techniques are not guaranteed to be the most appropriate for the envisioned system of energy subsystems. We must understand how to minimize total potential work loss in a complex integrated system subject to the appropriate constraints.

(5) Control Strategies for Energy Systems. A conventional flight control system is a user of exergy in the form of actuation power, and has an impact on vehicle drag, which consumes exergy. There are also multiple subsystems involved in the total vehicle control system, subject to (1) above. Now, the magnitude of the control design problem is magnified when we consider the control requirements and associated subsystems of future vehicles. First, we need to understand how the total vehicle control system can be designed to energy-based principles. Second, we need to understand how to control the distribution or transfer of energy between the different subsystems in order to produce an optimum system design.

Key Words: Systems integration, energy-based analysis, exergy-based methods, multidisciplinary systems analysis and design

Eligibility: Open to U.S. citizens

SF.05.00.B4617: Adaptive Computational Methods for Capturing Multi-Physics Interactions

Beran, P. (937) 713-7217

Aerospace systems are growing increasingly complex and are exhibiting a wider range of coupled physics phenomena. As a result, computational analysis of these systems is becoming more complicated, especially in an effort to capture important coupled physics earlier in the design process for the purpose of developing higher performance systems at lower cost. Several challenges exist, but many relate to the problem of integrating and orchestrating models of different levels of fidelity across a wide of physical phenomena while providing useful sensitivity analysis information and meeting accuracy requirements. Research opportunities include, but are not limited to, the following topics:

(1) Development of quantitative, goal-oriented methods to adapt mesh, time step, numerical order, level of physical coupling, and model fidelity for individual analyses to lower computational subject to constraints on error estimates; applicable to steady, time-periodic, and transient phenomena, especially those involving nonlinear interactions.

(2) High-order finite elements methods for solids and fluids featuring rich levels of adaptation with potential for hybrid approaches for multidisciplinary problems.

(3) Adjoint-based approaches for efficient adaptations and sensitivities, particularly for coupled-physics problems.

(4) Computer science approaches to integrating disciplines, facilitating on-the-fly adaptations, and parametrically enriching models, with emphasis on the automated exploration of large design spaces.

(5) Study of critical phenomena involving exchange of static and dynamic stability, and adaptation procedures seeking to minimize errors associated with these features.

(6) Machine learning algorithms and statistical approaches for making decisions about model selection, including the development of surrogate models enriched by sensitivities and informed by a number of different information sources.

(7) Model reduction strategies for reducing the reliance on high-fidelity models as another form of goal-oriented adaptation.

(8) Error estimation and analysis verification for large aggregations of models of arbitrary complexity.

(9) Applications to a wide range of coupled physics phenomena including, but not limited to, disciplines of incompressible and compressible aerodynamics, rigid-body and structural dynamics (with material nonlinearities), heat transfer including radiation, and acoustics. Applications of interest, whether system or component level, should demonstrate how physics drive the design and can be more effectively captured with an adaptive computational process.

SF.05.00.B4943: Computational Aeroelasticity and Fluid/Structure Interaction

Barnes, Caleb (937) 713-7103

The need to expand flight envelopes and mission requirements for existing aircraft, and the design of new highly flexible and maneuverable aircraft has driven interest in developing nonlinear aeroelastic analysis capabilities. Research opportunities focus on the simulation of complex fluid/structure interactions. Emphasis is placed on coupling high fidelity, nonlinear, fluid dynamics solvers with nonlinear structural mechanics. These simulation techniques will be used to investigate the response of flexible aircraft structural components to unsteady aerodynamic loadings and maneuvers. Research topics include (1) the development of algorithms to solve the nonlinear structural dynamics equations coupled with fluid dynamics equations; (2) applying computational tools for detailed investigations of fluid/structure interaction problems, including buffet phenomena, flutter, limit cycle oscillations, unsteady maneuvers and gust interactions; (3) novel techniques for grid deformation and fluid/structure interface treatment; and (4) development of multidisciplinary fluid/structure algorithms appropriate for a massively parallel computing environment.

SF.05.00.B5739: Computational Fluid Dynamics Research in Numerical Simulation of Turbulence Flows

Rizzetta, D. (937) 713-7104

Research opportunities exist to examine complex flow situations, employing direct numerical simulation(DNS) and large-eddy simulation(LES) in order to represent turbulent structures. Problems are considered which have both fundamental scientific and practical significance. Current efforts focus on developing high-order numerical procedures employing implicit LES techniques, as well as solutions of the Favre-filtered Navier-Stokes equations. For the later, improved subgrid-stress modeling is sought. Recent applications have been devoted to plasma-based flow control for low-Reynolds number airfoils and wings. Previous efforts have included simulation of supersonic compression-ramp flows with shock waves, acoustic suppression of aircraft weapons bay cavities using flow control, investigation of transitional flow past low-pressure turbine cascades, and roughness generated transition. We also have interest in applying the Reynolds-averaged Navier-Stokes(RANS) approach for practical computations. For this purpose, two-equation models and Reynolds stress formulations have been considered. Hybrid turbulence models for unsteady RANS applications and detached-eddy simulation(DES) are also being examined.

SF.05.00.B5740: Computation of Supersonic and Hypersonic Flow Phenomena and their Control

Nicholas Bisek 937-713-7101

Improved supersonic flight and space-access capability with air-breathing hypersonic trajectories are key elements of many future technology development programs because of their profound impact on commercial and military activities. Significant basic research challenges remain to be overcome in these areas, ranging from developing theories of transition and turbulence to predicting and managing the aerothermal and propulsion environment and determining non-continuum effects. Given the daunting difficulty of reproducing flight conditions in ground-test facilities, simulations necessarily have an integral role to play in design and development. High-fidelity computations of high-speed flows are very challenging because of the fundamentally multidisciplinary and three-dimensional nature of the problem. In addition to viscous fluid dynamics, it is often essential to consider turbulence and thermo-chemical non-equilibrium effects such as vibrational excitation, dissociation, ionization and combustion. Successful and affordable long-range hypersonic flight will also require breakthroughs in the understanding and implementation of revolutionary concepts such as plasma-based flow control. Formulations must therefore be extended to include variants of the Maxwell equations and sophisticated plasma models. The combined phenomena yield a large, stiff set of non-linear governing equations, which must be resolved with fine spatio-temporal discretizations. It is essential therefore to develop highly accurate physical models, and to couple them to advanced, robust numerical methods which can exploit massively parallel modern computational systems. Towards this end, broad research opportunities exist to (1) develop and implement highly accurate algorithms for a hierarchy of theoretical models of increasing fidelity with and without the continuum approximation, (2) utilize computational tools to investigate a variety of physical phenomena, including direct numerical simulations of supersonic and hypersonic transition and turbulence, plasma behavior in the aerospace environment and shock/boundary layer interactions, (3) develop, implement and validate models for state-to-state kinetics (4) explore drag reduction and thermal protection techniques through flow control.

SF.05.00.B5741: Numerical Simulation of Glow Discharges for High-Speed Flow Control

Nicholas Bisek 937-713-7101

The possibility of electromagnetic control of high-speed flow was first considered in the mid-1950's following the discovery of the high levels of ionization present during atmospheric reentry. Although this technology has been examined by a number of research groups during the intervening decades, practical implementation of the concept has remained ellusive. Recent advances in the production of very strong magnetic fields and in the generation of atmospheric pressure plasmas have led to a resurgence in interest in the technology, and the Air Force Research Laboratory Computational Sciences Center has developed computational tools for modeling candidate flow control technologies (Poggie and Gaitonde, 2002). In particular, recent study has focused on glow discharges immersed in high Mach number gas flows, including the effects of strong applied magnetic fields. In support of this activity, the following research opportunities exist: develop new, high-fidelity numerical algorthms for modeling these discharges, incorporate improved physical models in existing numerical codes, and utilize existing computational tools to explore potential electromagnetic flow control technologies.

J. Poggie and D. V. Gaitonde, "Magnetic Control of Flow Past a Blunt Body: Numerical Validation and Exploration", Physics of Fluids, Vol. 14, No. 5, pp. 1720-1731, 2002.

SF.05.00.B5742: Enabling Robust and Durable Aerospace Structures for Combined, Extreme Environments

Chona, R. (937) 656-8793

We are aggressively pursuing a computational framework for enabling high fidelity simulation of structures exposed to combined extreme environments. Examples include reusable vehicles exposed to launch, sustained hypersonic velocities, and atmospheric re-entry and stealth aircraft with buried engines and ducted exhaust. Scientific challenges include the nonlinear coupling between extreme environment/loads and the structural response, evolving material attributes and interacting failure modes that define the structural limit state, and the computational framework to support a future paradigm shift towards structural scale simulation. The framework must allow the limit state and material attributes to evolve and interact with the structural response as the simulation progresses. The long-term goal of the simulation is to predict with high confidence the life of a structure subjected to a combined fluid-thermal-acoustic-mechanical-vibratory environment throughout a high-performance aerospace vehicle trajectory.

To support the long-term goal, we have challenges spanning the disciplines of mathematics, computation, and engineering. Exciting research opportunities exist in the areas of (1) computational structural scale simulation for developing the necessary algorithms and data structures required for efficient parallel computing in support of long time record simulations, (2) methods and algorithms for variable fidelity modeling including a priori and/or a posteriori error estimators with convergence indicators, (3) fluid-acoustic-thermal-structure solver integration focusing on the stability and fidelity for loosely versus fully coupled solvers, (4) multiscale coupling techniques addressing and the computational algorithms for spatial and temporal issues associated with the inclusion of fine scale features into a coarse scale model supporting high fidelity simulations, and (5) identification of representative or benchmark extreme environment structures with levels of combined loading targeted toward exercising specific phenomena for verification and validation of multi-physics simulations.

SF.05.00.B6110: Design, Measurement, Modeling, Analysis, and Control for Optimal Weapon Integration

Stanek, M. (937) 656-8767

The addition of turrets, pods, external stores and tanks, and weapons bays to advanced air and near-space military flight platforms are required to turn these flight assets into practical weapon systems. Unfortunately, these additional features can compromise the overall weapon system performance, due to undesirable effects on unsteady aerodynamic loads, turbulence properties, heat transfer rates, optical signal transmission characteristics, and other factors. Advanced diagnostic techniques, computational analysis, flow control, and advanced modeling are all tools which need to be developed and aggressively applied to integrate advanced weapon concepts on future platforms.

The two classes of weapon integration which are currently of most interest are weapons bays and optical apertures (for directed energy). Basic research opportunities include, but are not limited to the following areas: (1) design, analysis, and modeling of flow control devices to improve baseline integration characteristics; (2) optimization of the combination of aerodynamic shaping and flow control for best performance of the integration; (3) improvements to boundary conditions, turbulence models, physical effects models, and other specific computational aspects to enhance accuracy, fidelity, speed, and usefulness of advanced simulations; (4) the study of dynamic control techniques timed to the release of a store, to enhance trajectory properties; (5) modification of stability properties, turbulence properties, and separation characteristics of shear layers associated with cavities, turrets, or other integrations of interest; (6) development of models for prediction or scaling of flow control devices, and (7) development / use of innovative diagnostic techniques to allow for visual study as well as quantitative description of integration properties with and without flow control. Research could involve analytical modeling, computational simulation, design, experimental simulation, software development, or some combination of all the above.

SF.05.00.B6113: Residual Stress Engineering Technologies for Aircraft Structural Components

Langer, Kristina (937) 656-8814

Residual stresses – whether introduced via the manufacturing process or via surface treatment (e.g., laser peening or cold working) – alter the fatigue and fracture response of metallic airframe components. In many cases these stresses can be exploited to extend the life of the component with attendant benefits of increased safety, reduced operational costs, and improved performance. However, for full exploitation of these technologies for airframe life extension, in particular, the explicit consideration of residual stresses in determining non-destructive inspection intervals, validated design and analysis tools are required that can accurately and efficiently determine the effects of residual stresses on the design life of replacement and/or existing components. Validated tools will enable more cost effective developments of residual stress solution options by reducing the amount of experimental iteration required to field new applications. Further, such methods will allow designers to optimize residual stress treatments for specific lifing objectives, as well as study the effects of error and uncertainty.

To meet these objectives, research opportunities exist in the area of design, experimental validation, and life prediction for residual stress-enhanced aircraft structural components. Residual stress processes of interest include but are not limited to manufacturing processes such as forging, machining, and welding, as well as surface treatments such as laser peening, water jet peening, and UNSM (ultrasonic nanocrystal surface modification). Lifing approaches should include the prediction of crack growth rates and fracture paths compatible within a damage tolerance framework. Advances in validation techniques can include both destructive and nondestructive methods for quality assurance, stress evaluation, and crack growth tracking.

Specific topics include:

(1) Development of validated and efficient analysis techniques and design tools for predicting the fatigue characteristics of residual stress-enhanced airframe components under spectrum loading, including realistic initial conditions such as prior fatigue exposure, shot peening, and/or manufacturing-induced residual stresses.

(2) Development of stochastic analysis techniques for quantifying the effects of input uncertainties, such as processing parameters or material response, on the predicted fatigue response of a residual stress-treated component.

(3) Development of validated damage tolerance analysis methods for aircraft structural components to study the effects of deep residual stresses on fatigue crack propagation. Fatigue life prediction models should account for residual stress redistribution, work hardening, and/or surface deformation.

SF.05.00.B6114: Unsteady Aerodynamics, Gust Response and Maneuver

Ol, M. (937) 713-6650

Unsteady aerodynamics is relevant when there is no reference frame in which the bulk flow relative to a body is time-invariant. This is encountered in essentially all flight modalities, but is of principal import for maneuvering air vehicles, for operation in urban environments, for non-aeronautical applications such as wind-energy, for rotorcraft, and for any flight article where wind speed is comparable to cruised speed (such as vertical takeoff and landing). Engineering applications wax and wane, but the enduring point is understanding the relevant time-scales and transients in the flow (and especially in separated flows), in the “plant” (the airfoil/wing/airplane) and in the control system (flow control actuator, conventional-flap deflection and so forth). Ultimately we need to define, validate and codify reduced-order models that capture the flow-plant-controller, allowing us to quantify for example the limits of gust amplitude/frequency that the vehicle can tolerate, with or without clever new control strategies.

We are less interested in aeroelastic optimization, multi-disciplinary design or controller-optimization, than in understanding the constituent physics using abstracted problems. Recent work has ranged from airfoil pitch/plunge in steady and streamwise-oscillatory flows, to flat-plates in 2D and 3D undergoing periodic or transient accelerations with or without a free-stream, to bio-inspired problems of flexible wings undergoing articulated motions, to recrudescence of traditional helicopter-rotor dynamic stall.

Though a wealth of data has been amassed, basic questions remain nebulous. For example, when is a spring-mass-damper analogy sufficient to describe the lift/thrust/pitch history for a rigid flat plate in two dimensions, if the motion amplitudes/frequencies are not limited to a linearizable range? With decreasing Reynolds numbers the aeronautical engineer has more and more reason to consider biomimetic approaches based on the flight of insects, humming birds and bats, adopting nature's solution to cruise efficiency, flight agility and gust tolerance. But rational use of such approaches is predicated on rigorous study of the relation between the kinematics of flight-surface motions, the time-dependent aerodynamic and inertial loads, the mutual effect of loads on structural deformations, and the flowfield dynamics. This includes phenomena quite outside of the scope of traditional aeronautical engineering, such as manipulation of shed vortical structures to increase lift and thrust, and the phasing of vortex shedding to provide aerodynamic moments for maneuvering or gust rejection.

Areas of interest cover computations, experiments, and classical analytical methods of unsteady aerodynamics, from very low Reynolds numbers where the flow is identically laminar, to transitional and fully-turbulent flows. The focus is on incompressible problems, and primarily (but not exclusively) on rigid bodies or on bodies with a small number of degrees of freedom, such as hinged plates. Ideally, one would amalgamate all three approaches (computational, experimental, analytical), drawing on the respective strengths of each. For, example, high-resolution computations are adept at capturing fine details of boundary layer evolution and on local propagation of minute flow-control actuation, while particle image velocimetry can track and identify bulk coherent vortical structures in complex separated flow far from the body of origin. Analytical methods can capture time-evolution of lift/pitch/drag by tracking a small number (such as two) of vortices, in a format well-suited to large parameter studies or to investigation of control-strategies. On the experimental side, we are interested in evolution of quantitative flow visualization to track vorticity and its associated derived quantities, experimentally assembling the constituent terms of conservation laws and obtaining lift-history without direct force measurement. In unsteady flows, this approach delves into many potential pitfalls subtleties, which we seek to rigorously identify and to solve. And while the focus is not of development of flow control schemes per se, we are interested in system identification and controllability bounds for candidate schemes of actuation and control, specifically (but not solely) for gust response.

The eventual goal is a robust but low-order model of the complete vehicle state, useful for flight dynamics, control, and vehicle design.

SF.05.00.B8577: Adaptive Structures Applications to Aircraft

Reich, Gregory (937) 713-7138

Adaptivity of aircraft structures and systems can lead to improved performance across the flight envelope at off-design points for a given system. Adaptivity spans the entire range of vehicle size and speed scales, from super- and hyper-sonic systems down to SUAS, and can take many forms – from mechanized wing structures to adaptive devices that locally impact flow. Adaptive systems can utilize conventional materials and actuators, but most find improved chances of success with incorporation of adaptive materials due to the ability to create multifunctionality in the structure. Our research focuses on conception, design, and analysis of adaptive structures, demonstrating how those systems may be used, and quantifying the performance improvement possible. Topology optimization and other techniques are applied to numerical models in a multidisciplinary analysis environment to create new concepts and designs. Our work is focused in several areas: the integration and distribution of actuation into a structure in order to effectively move the structure using minimum energy; the design of novel structural layouts and mechanization concepts using topology optimization schemes tied to linear and nonlinear coupled multidisciplinary analysis; the development of secondary structures, sensors, or accompanying concepts that enhance the adaptivity benefit; and the application of adaptive technologies to unique aircraft systems.

Keywords: reconfiguration/morphing/adaptivity, adaptive structures, topology optimization, multidisciplinary design and optimization, multifunctional structures

SF.05.00.B8578: Multifunctional Structural Antenna Concept - Modeling and Simulation

Zeppettella, D. (937) 255-4277

The number of antennas on all air vehicles is increasing rapidly, as the need for larger antennas and large antenna arrays are necessary to meet range, and directivity requirements. As a result the installation of antennas with the airframe is becoming an important performance, cost and structural integrity consideration. Current antenna installations are limited to parasitic non-load bearing RF systems with radomes that protrude into the air stream and increase signature, drag, and supportability costs, or require complex support structures and integration schemes that add manufacturing cost and weight. The advent conformal load-bearing antenna structures (CLAS) technology presents a convergence of the structural and avionics disciplines. The multidisciplinary nature of this technology requires that researchers tackle the challenge of development in a truly collaborative fashion. This research topic is directed at modeling and simulation of advanced structurally integrated phased array structural antenna systems. Specific focus should be directed at the ability to develop an architecture that can be electrically reconfigured to provide wideband performance. Concepts to be explored should consider the use of RF MEMS devices, novel metamaterials along with the constraints associated with integration into a lightweight load bearing architecture. Modeling should provide accurate representation of the structural material electromagnetic interactions, losses associated with devices, and the conductive and dielectric materials. Analytic results should be validated based on the literature and from empirical testing conducted at AFRL where structural, S-parameter and near field chamber data will be developed.

SF.05.08.B6657: Sensitivity Analysis and Uncertainty Quantification for Multidisciplinary Systems Analysis & Design Optimization

Beran, Philip (937) 713-7217

Multidisciplinary design and analysis integrates components from various disciplines to synthesize aerospace systems. Modern design techniques are emerging that optimize the system as a whole rather than as individual components. This makes the entire optimization problem quite large and may consist of libraries of variables, constraints, and competing performance criteria. As multidisciplinary analysis and design methods evolve, primarily with the use of modern computer capabilities, we must account for cascading uncertainties in the various modeling and simulation tools for each discipline. Research opportunities exist in the general area of uncertainty quantification and sensitivity analysis for systems analysis and design optimization. Topics of interest include (1) Methods for quantifying uncertainty in selected disciplines; (2) The propagation of uncertainty within a discipline and across disciplines; (3) Control and reduction of uncertainty; (4) Verification and validation methods and techniques for the modeling and simulation tools used in selected disciplines; (5) Application of Design of Experiment techniques for modeling and simulation; (6) Efficient methods for calculating the sensitivities of key parameters in selected disciplines; (7) the impact of uncertainty on system robustness, reliability, and risk in context of each discipline and in multi-scale and multidisciplinary analysis and design.

SF.05.13.B1914: Trajectory Planning for Unmanned Aerial Vehicle Systems

Grymin, D.

(937) 713-7235

This research area is focused on the rapid generation of feasible trajectories for autonomous aircraft systems. General scenarios of interest involve position and orientation constraints on the vehicle, disturbance/environmental effects, and aircraft performance constraints. Mission planning may also be subject to various objective costs, and the tradeoff between optimality and computation time is a further area of concern. Examples of scenarios include, but are not limited to: (1) single vehicle planning between multiple tasks; (2) multiple vehicle planning subject to collision avoidance constraints; (3) multiple vehicle planning between tasks; (4) single and multiple vehicle planning incorporating aircraft performance constraints; (5) single vehicle planning in dynamic environments. We are interested in the development of new algorithms and approaches as well as novel applications and implementations of existing methods.

SF.05.13.B1221: Multiscale, Multiphysics and Multifidelity Modeling of Aircraft Power and Thermal Systems

Patnaik, S. (937) 656-5452

Cross-domain, advanced physics based modeling and simulation tools have been identified by the Air Force as game changers that can significantly reduce development and deployment cycle time for acquisition. Our research focusses on development of computational methods, tools and models for design and performance-analysis of aircraft power and thermal management systems. We are developing an integrated power and thermal (P&T) modeling workspace to explore the multi-dimensional P&T trade space. Our research includes development of computational methods, numerical formulations and software with an integrated and unifying modeling framework. Aircraft P&T systems demand both static and dynamic response and include technologies that represent physical phenomena across a wide range of spatial and/or temporal scales involving multi-physics coupled interactions and requiring different output fidelity and response. Summer research opportunities include but are not limited to: P&T modeling toolset development; Dynamic modeling of multiphysics and multifidelity P&T systems; High fidelity thermodynamic analysis of aircraft P&T systems; Molecular and multiscale modeling of heat transfer and thermal energy storage; Molecular and stochastic simulation methods of nanoscale transport phenomenon; Reduced order modeling of thermal systems; Co-simulation of dynamic systems; Model verification and error estimation methods. Access to several commercial and in-house developed codes and computing resources at the AFRL DoD Super Computing Resource Center is available.

SF.05.14B0847: Electromechanical Actuation System for Aircraft Flight Control

Leland, Q. (937) 255-3060

This topic focuses on research and development of aircraft High-Performance Electric Actuation System (HPEAS) technologies. Specific areas include thermal management (TM) of electromechanical actuators (EMA) and motor control electronics; jam free or fault tolerance designs; innovative peak and regenerative power management; and prognostics and health management technologies. For TM, any solutions, liquid or air or other heat transport medium, active or passive, should be integrated with the actuation system as well as with the aircraft electric power system and air vehicle. For example, when implementing an air cooling solution, its heat sink requirement and electric power input should be in agreement with the aircraft’s flight envelope. The ultimate goal of this topic is an optimized HPEAS design fully integrated with thermal management solution and electric power system in an aircraft environment.

HPEAS offers considerable advantages over conventional hydraulic actuation system for air vehicles. Three technical challenges have to be addressed for a successful transition of EMA to aircraft flight critical control actuation: thermal management, fault tolerance, and peak and regenerative power management. EMA and its electronics operate under harsh environments, especially those for primary flight control and propulsion system controls for military fighter aircraft. Its environmental temperature ranges from -40o C to 125o C, its heat loads are highly transient and localized, making thermal management one of the critical challenges for HPEAS. The dynamic power level, both peak power draw and regenerative power, also poses a great challenge for the aircraft electric power system. Reliability or fault/jam tolerance has to be proven as good as conventional hydraulic actuation before its acceptance to primary flight control.

Keywords: Thermal management; Electromechanical actuator; HPEAS; flight control actuator; EMA; Power electronics cooling; Aircraft actuation; Regenerative power

*Eligibility: Open to U.S. citizens only.

SF.05.14B0848: High Capacity, Advanced Battery Development

Miller, R. (937) 255-2880

Next generation aircraft contain a host of system-level power and thermal challenges to enable capabilities such as: low-observable electronic attack and electrically-driven directed energy-based self-defense. Energy storage is among the critical technology challenges supporting aircraft power and directed energy weapons (DEWs). To this end, AFRL has the goal to develop a high capacity, advanced battery capable of operation as both an abuse tolerant, high-rate power dense source while maintaining high energy storage capability safely across a wide-temperature range. Current efforts focus on work, ranging from: the development of high capacity cathode materials for solid-state Li batteries; novel film processing techniques for the fabrication of solid-state batteries and fuel cells; power management/hybridization technology for small unmanned aerial vehicles (S-UAVs) and portable soldier power; and aircraft/DEW battery characterization and analysis.

The objective of this effort is to investigate methods for developing high capacity, advanced batteries for traditional aircraft and S-UAV applications. Solid-state lithium batteries have gained considerable interest as a next generation high energy-dense electrochemical power source. They offer not only the potential for high energy densities but also safe operation as compared to state-of-the-art Li-ion battery technology. In practice, the performance of these batteries falls drastically short of the potential theoretical values due to limitations in cathode diffusion/reaction kinetics and instability/decreased conductivity issues in the electrolyte. Advancing beyond these limitations is a function of two important but equal aspects: development of high capacity, safe cathode materials and introduction of novel cell processing/fabrication techniques.

Research interest includes exploring alternative novel cathode materials and utilizing advanced film processing techniques (ink jet and aerosol jet printing) to fabricate all solid-state cell configurations. In addition, energy and power densities in batteries typically have an inverse relationship, making it unlikely that one battery can provide both. Therefore, there is an interest to explore hybridizing different battery chemistries to produce an overall hybrid battery pack which can provide both high power discharge capability while maintaining high energy density storage.

Eligibility: Open to U.S. citizens only

SF.30.01.B0100: High-Speed Propulsion

Hagenmaier, M. (937) 255-7325

We conduct research on ramjet/scramjet and mixed-cycle propulsion components applicable to supersonic and hypersonic flight regimes. This includes fluid-dynamic studies of inlet, combustor, and nozzle components. We also pursue development of efficient computational methods, turbulent models, and kinetic schemes for reacting, high-speed flows. Our research approach necessitates the integration of experimental and theoretical methods to address challenges in (1) turbulent transport, entrainment, and mixing of multistream flows and/or two-phase flows including fuel injection, atomization, droplet transport and evaporation, flame stabilization, and blowout limits; (2) nonintrusive, multidimensional diagnostic instrumentation and concepts, including hardware and software, for applications to realistic combustor flow environments; and (3) time-averaged and time-dependent computational-fluid-dynamics codes for flow and combustion simulations in complex geometries. Available equipment includes extensive computer facilities (mini's to high-speed, mutiprocessor supercomputers), two combustor thrust rigs, a research combustor designed for a wide range of operations and applications of laser diagnostics, and a spray tunnel facility with associated optical and conventional diagnostic equipment. Also available is a stand-alone supersonic flow research facility, specifically designed for nonintrusive probing of the supersonic flowfield for simultaneous field measurements of pressure, temperature, velocity, and species concentration.

Eligibility: Open to U.S. citizens

SF.30.01.B0101: Combustion and Spray Studies and Diagnostic Development

Gord, J. (937) 255-7431

This research addresses the physics and chemistry of processes in gas turbine combustors and pulsed-detonation engines through the study of isolated and interacting droplets, sprays, jet premixed and diffusion flames, swirling flames, and bluff-body stabilized flames. Continuing work requires experimental and theoretical approaches related to the following: (1) turbulent transport, mixing, entrainment, evaporation, droplet drag, drop-spacing effects, atomization, finite-rate chemistry, flame stability, ignition, and blow-out; (2) development of laser-based diagnostic techniques to support combustion and spray experiments; and (3) studies using either time-averaged or large-scale, time-dependent simulations. Numerous well-equipped laboratories contain small- and large-scale combustion tunnels and advanced laser apparatus designed for two-dimensional imaging, coherent anti-Stokes Raman spectroscopy; laser Doppler anemometry; phase Doppler particle sizing; laser-induced florescence techniques; and femto/picosecond chemistry studies. Access to various combustion flow codes and the DOD ASC Major Shared Resource Center is available for theoretical studies.

Eligibility: Open to U.S. citizens only

SF.30.01.B0102: Model Development and Validation Experiments for Aircraft Fuel

Edwards, J. (937) 255-3524

Aviation fuels are not only the energy source for advanced aircraft; they are also used to cool airframe and engine components. Under high thermal loads, hydrocarbon fuels can react with dissolved oxygen or undergo pyrolysis to form gums and other deposits that reduce the efficiency of heat exchangers and cause fouling of fuel-system components. Computer models that can be used to estimate the thermal decomposition of hydrocarbon fuels in simple heat exchangers are in an early stage of development. The models are time dependent and include global chemistry, fluid mechanics, and thermodynamic effects. Many of the fundamental processes associated with thermal degradation of fuel are not well understood. One of the objectives of the models is to improve our understanding of selected issues in physics and chemistry. Of particular interest is experimental and theoretical research on the influence of dissolved oxygen content, turbulence, thermal loads, pressure, catalytic reactions, or heat-exchanger geometry on the thermal degradation of hydrocarbons found in jet fuels. Dedicated minicomputers and reacting flow codes are available for theoretical studies. This research includes current fuels (JP-5,7,8,10), as well as alternative (non-petroleum) fuels. Alternative fuels include those derived from coal or biomass through the Fischer-Tropsch process, as well as aviation fuels derived from oil shale and tar sands and direct liquefaction of coal. "Biojet" fuels, analogous to biodiesel, are also of interest.

Eligibility: Open to U.S. citizens

SF.30.01.B0103: Advanced Turbine Mechnical Systems

Rosado, L. (937) 255-6519   This research focuses on developing advanced engine mechanical system component technologies (bearings, gears, seals, and lubricants) for advanced aircraft turbine engines. We are developing novel mechanical systems technologies that enable higher loads, speeds, and temperatures in advanced engines while minimizing weight and complexity and maintaining safety and reliability. Finite element methods are used to model heat dissipation, stress fields, and shaft dynamics.  Continued research in high-temperature lubrication, fatigue life modeling, and tribological performance of advanced materials and lubricants is of interest. World class facilities equipped with unique test equipment and instrumentation are available for experimental and analytical bearing and gear performance, rolling contact fatigue, elastrohydrodynamic film, health monitoring and diagnostics, and oil-free technologies.  

 

Eligibility: Open to U.S. citizens

SF.30.01.B0104: Aero and Thermodynamics of Rotating Machinery

Sondergaard, R. (937) 255-7190

An improved understanding of internal flows and heat transfer under non-steady conditions is necessary for the continued advancement of turbine engine performance. Shortcomings in the ability to accurately predict aerodynamics and heat transfer of cooled and uncooled components in the hot section significantly impacts the design and development cost of new engines and component performance and durability. Improvements in specific fuel consumption are largely related to the ability to increase turbine inlet temperature and cycle pressure ratio, which are limited by the ability to model these flows. Important research areas include internal and external cooling of vanes, turbine blades, shrouds, platforms, broach slots, and disk cavities. Also important is the understanding and control of the aerodynamics and aerodynamic losses associated with these components. Nearly all of these flows are three dimensional and unsteady, and must be characterized over a large range of operating conditions, including low Reynolds number conditions at which flow separations become major contributors to aerodynamic losses. Strong pressure gradients, density gradients, curvature, rotation, and compressive effects are present in many of these flows. Non-steady shocks and shock boundary layer interactions can also be important.

Of interest are experimental and computational investigations studying methods of increasing film cooling effectiveness, techniques for selectively increasing or decreasing heat transfer coefficients, methods of flow control to increase blade loading, reduce passage, hub and tip losses, and techniques for controlling aeroelastic effects and damping. Characterization of aerodynamic, thermal, and structural effects requires non-steady two- and three-dimensional computational schemes and experimental techniques. The spatial and temporal resolutions need to approach wall flow scales in order to provide the accurate time-resolved blade vane interaction effects, as well as resolve loss mechanisms and heat transfer associated with other non-steady secondary flow phenomena that are present. Specific computational interests are three-dimensional non-steady, multidisciplinary approaches that are capable of optimizing aerodynamic, thermal, and structural designs.

Eligibility: Open to U.S. citizens

SF.30.01.B1015: Nonequilibrium Processes in Hypersonic Flows

Josyula, Eswar

(937) 713-7100

The flight envelope of the next generation of hypervelocity aerospace vehicles powered by air breathing propulsive devices includes extended dwell time at relatively high altitudes. The design space of such vehicles can only be analyzed by acquiring a detailed understanding of a broad spectrum of spatio-temporal time scales inherent in the aerothermodynamics of the external flowfields. Hypervelocity flows are distinctive in the high temperature regime because of the finite rates at which the energy modes in the atmospheric air get excited and eventually dissociate. Since these processes take place at finite rates, their accurate computation impacts signal propagation and surface heat transfer prediction accuracy. Significant basic research challenges remain to be overcome in the areas, ranging from developing theories of transition and turbulence in the high temperature environment.

Given the daunting difficulty of reproducing flight conditions in ground-test facilities, simulations necessarily play an integral role in design and development. High-fidelity computations of high-speed flows are very challenging because of the fundamentally multidisciplinary and three-dimensional nature of the problem. In addition to viscous fluid dynamics, it is often essential to consider turbulence and thermochemical non-equilibrium effects such as vibrational excitation and dissociation. Therefore, formulations must be extended to include the master equation for treating the various energy exchange processes of the internal energy states in high temperature air. The combined phenomena yield a large, stiff set of nonlinear governing equations, which must be resolved with fine spatio-temporal discretizations. Thus, it is essential to develop highly accurate physical models to describe the external aerothermodynamic flowfields and to couple them to advanced, robust numerical methods which can exploit massively parallel modern computational systems. Broad research opportunities exist to (1) develop and implement highly accurate algorithms for a hierarchy of theoretical models of increasing fidelity of the aerothermodynamics; 2) develop, implement, and validate models using state-to-state kinetics for developing reduced order models; and (3) utilize computational tools to investigate a variety of physical phenomena, including direct numerical simulations of supersonic and hypersonic transition and turbulence, thermochemical nonequilibrium phenomenon, and shock/boundary layer interactions.

SF.30.01.B0112: Studies of Novel Combustion Concepts for Propulsion Systems

Schauer, F. (937) 255-6462

AFRL's Combustion Branch plans, develops, and transitions basic research and applied technology development programs for military air-breathing engines. We do this by executing in-house and contracted programs that enhance the capability of turbo-propulsion systems through design, analysis, development, and test of advanced combustion systems. Additionally, the branch explores novel propulsion concepts critical to meeting future Air Force requirements. Some of these novel concepts include pulsed-detonation engines, inter-turbine burners, and trapped vortex combustors. The branch has in-house activities associated with these concepts.

The branch evaluates and enhances component capabilities through the understanding and innovative use of chemistry, aerodynamics, heat transfer, materials, diagnostics, computational fluid dynamics, and design tools. Areas of fundamental research include fuel injection, fuel-air mixing, fuel atomization, chemical kinetics, flame stability, supercritical fuel injection, flame dynamics and ignition phenomena. A growing focus area is the understanding the chemistry and combustion characteristics of alternative fuels for new propulsion systems. Well-equipped laboratory laboratories and computational resources are available to carry out the research activities. The laboratories can operate at sub-atmospheric to 40 atmosphere conditions, and include a host of intrusive and non-intrusive diagnostic capabilities.

Eligibility: Open to U.S. citizens only

SF.30.01.B5437: Advanced Diagnostics for High-Speed Flows

Carter, C. (937) 255-7203

This research addresses technologies essential to high-speed, air-breathing propulsion, including fuel-air mixing processes in subsonic and supersonic flows and the role of turbulent transport on mixing and combustion in high-speed flows. Objectives include the following: (1) incorporation of science into preliminary design and advanced development of ram/scramjet combustors; (2) development and application of accurate CFD tools for the design and analysis of ramjet/scramjet combustors; (3) development and application of advanced non-intrusive optical diagnostic techniques for high-speed reacting flows; (4) study of ionized flows on a confined supersonic flow, especially for enhanced combustion; and (5) transition of basic research ideas, concepts, and findings to exploratory development programs. In particular, three areas of focus are supported: (1) Fuel Control and Fuel Injection, wherein fundamental aspects are studied for gaseous, supercritical, and multiphase fuels; (2) Ignition, Flameholding, and Flame Propagation in Supersonic Flows, wherein fundamental aspects are studied with a view towards improving performance in a high-speed combustor; and (3) Multidisciplinary Laser Measurements for benchmarking modeling and simulation and for elucidating the physics of high-speed flows. Both laboratory-scale (e.g., the stabilization of attached and lifted turbulent jet flames) and large-scale (e.g., stabilization of flames within a supersonic combusting ramjet engine) experiments are employed. Facilities include extensive high-speed wind tunnels, where conventional and advanced diagnostics can be employed, and a well-equipped optics laboratory, where techniques and ideas can be explored in small-scale flows prior to being employed in the large-scale facilities.

Eligibility: Open to U.S. citizens only

SF.30.01.B5438: Improving Structural Dynamic and Material Characteristic Understanding of Turbomachinery Components

Scott-Emuakpor, O.E. (937) 255-6810

To continue improving both performance and durability of gas turbine engines, a better understanding of the structural behavior of components is essential. Though structural capability of all engine componentry is assessed with rigor, critical components such as airfoils, disks, and integrally bladed disks (IBDs) are scrutinized more heavily than others. With advanced, sixth-generation engines requiring novel design concepts and non-conventional manufacturing methods to meet performance demands, the framework for structural assessment must be updated to define acceptable sustainment criteria for critical components. This research opportunity aims to address the need for improved structural characterization that will reduce the likelihood of legacy and developmental gas turbine engine components failing, Structural characterization requiring attention is based on vibration suppression, fatigue behavior analysis, and strength assessment.

Computational and experimental research to understand structural behavior of turbomachinery components is being conducted by the Turbine Engine Integrity Branch (RQTI) in the Aerospace Systems Directorate of AFRL. The research areas include mistuning, nonlinear vibration, applied damping prediction, system identification, damage detection, probabilistic analysis, fatigue life and crack growth predictions, additive manufacturing, thermomechanical fatigue, multiphysics lifing, and development of new structural design approaches. Within these areas are several key research topics that require the integration of experimentation and analysis. Ongoing work consists of modal characterization via finite element methods and bench experimentation, standard fatigue and fracture characterization using mechanical testing and physics-based modeling, novel component and material testing development leveraging reduced order modeling (ROM) and surrogate response prediction, and uncertainty quantification in analysis and experimental methods.

To support the aforementioned research, both experimental and computational facilities are available within RQTI. The Turbine Engine Fatigue Facility (TEFF) is a state-of-the-art research facility that performs structural and dynamic experimentation. The TEFF directly supports Air Force legacy fleets, as well as developmental programs through basic research in the areas of material characterization, vibratory assessment, life prediction modeling, and qualification of advanced measurement techniques. Experimental capabilities in the TEFF include scanning laser vibrometry, advanced geometric optical scanner, digital microscopy, triangulation displacement sensor, ping dynamic frequency analysis, large-to-small scale electrodynamic shakers, high-frequency/ultrasonic shakers, high-temperature induction and resistance ovens, single- and multi-axial servo-hydraulic load frames, traveling wave excitation system, and vacuum spin chamber for small IBDs. The Structural Analysis Group (SAG) is the high-performance computational research area leveraging physics-based understandings from finite element methods and computational fluid dynamics. The integrated work conducted by the SAG utilizes finite element software ANSYS, mathematical programming language MATLAB, executable programming languages Python and LabVIEW, computational fluid dynamics software STAR-CCM, mistuning ROM algorithm MAGMA, and digital twin solid model algorithm MORPH.

Keywords:
Turbine engine; Structural dynamics; Additive manufacturing; Fatigue; Mistuning; Damping; Prediction models; Airfoil; Material properties;

Eligibility
Citizenship: Open to U.S. citizens

Level: Open to Regular and Senior applicants

SF.30.01.B5439: Injection and Flameholding in Supersonic Flows

Gruber, M. (937) 255-7350

The success of a hydrocarbon-fueled scramjet depends on the ability of the combustor to sustain efficient combustion over a wide operating range. During a typical flight, the combustor will experience several transient events that, if not robustly managed by the flameholding system, could compromise engine performance and even vehicle life. For example, the flowfield that exists inside the combustor before ignition is significantly different than the flowfield after ignition. Also, as the engine accelerates from low to high flight velocity (e.g., Mach 4 to 8), the character of the flow within the combustor changes, the combustor fuel distribution may change, and the fuel itself may change (as a result of endothermic cracking). All of these changes may significantly impact the behavior and stability of the flameholder. Our research focuses on the understanding of flameholding in supersonic flows. We then strive to use that improved understanding to design and investigate more robust flame stabilization techniques for hydrocarbon-fueled scramjets. We have several experimental resources available to execute the research including two combustor thrust stands, a research combustor designed for a wide range of operation, and a stand-alone supersonic research facility specifically designed for non-intrusive probing of reacting and non-reacting flowfields to flameholding in a supersonic combustor. A wealth of conventional and advanced instrumentation is also available for measurements of pressure, temperature, velocity, and species concentration.

Eligibility: Open to U.S. citizens

SF.30.01.B5859: Gas Turbine Control Systems and Engine Health Management Research

Behbahani, A. (937) 255-5637

The development of control systems and software that can deal with the dynamic and uncertain nature of highly integrated turbine engine systems depends on a fundamental understanding of the physics of propulsion. Robust, distributed, model based, and model predictive control concepts must be explored to achieve the desired capabilities in new gas turbine engine designs. While advances in control system technology will impact system performance at a given instance in time, a focus on tracking engine degradation is required to optimize performance over the life of the system. Research is required to develop a greater understanding of performance degradation mechanisms, and the impact of component degradation on system behavior.

The Air Force Research Laboratories Propulsion Directorate has established a Turbine Engine Dynamic Simulator (TEDS) as a real-time test bed for the development of advanced engine controls, diagnostics and prognostics. This simulator, data acquisition equipment and comprehensive engine models are used to explore simulation-based approaches for real-time, physics-based controls and health management algorithms. In a simulation based approach, a model of the propulsion system is embedded within the control system and tracks engine performance to continuously adjust to changes in the engine or operating environment. The use of a simulation based approach is also useful both in the context of virtual test where testing with actual systems is cost or time prohibitive and as embedded control system software to predicted sensed values where actual sensors could not be used.

As a result of this work, researchers gain a better understanding of the complex system interactions that exist in new propulsion systems and apply this knowledge in the development of future high performance, highly integrated systems.

Eligibility: Open to U.S. citizens

SF.30.01.B6706: Unsteady Aerodynamics and Heat Transfer in Turbines

Clark, J. (937) 255-7152

An accurate accounting of unsteady flow phenomena is critical to the successful design of turbine components. This is especially true for future systems, where it is desirable both to increase engine performance and to reduce operating costs. Phenomena of current interest include vane-blade interactions, unsteady shock boundary-layer interaction, boundary-layer transition, separation control, and unsteady heat transfer and cooling as a result of the passage of turbine blade tips over outer air seals. Research opportunities in the turbine branch of the Turbine Engine Division typically have combined design, analysis, and experimental aspects. A complete design, analysis, and optimization system is in place to create advanced turbine components for validation testing in the laboratory. For example, by capitalizing on advances in transition modeling made at the laboratory, the system was used successfully to define exceptionally high lift low pressure turbine airfoils. High pressure turbine components with low heat load have also been defined and validated and we anticipate that further advances in the state-of-the-art in turbine aerothermodynamics are achievable with these design tools. Therefore, we are particularly interested in analytical work to improve the design system, including improvements in optimization techniques. In addition, a hybrid Reynolds-Averaged Navier Stokes/Large Eddy Simulation code is now being developed for incorporation into the system. It is also possible to access computational resources at the US Air Force Shared Resource Center to support projects. Experimental facilities available for design system validation and other research run the gamut from low-speed wind tunnels suitable for the assessment of fundamental flow physics on flat plates and cylinders in cross-flow, to low- and high-speed linear cascades (with and without heat transfer and/or cooling) and full scale, rotating transonic turbine rigs.

Eligibility: Open to U.S. citizens

SF.30.01.B9931: System Integration Optimized for Energy Management

Yerkes, K. (937) 255-6186

On demand systems require attention to issues of system integration and energy management for optimal performance and capability. Integrated system modeling and simulation spans a broad range of technical expertise such as thermal management, power generation, power distribution, and load management in a highly dynamic environment. Energy conversion is critical in the efficient design of on demand systems. For aircraft applications, the majority of energy conversion takes place in the gas turbine. Therefore, significant opportunities exist for optimizing this process, especially the consideration of auxiliary systems and how they interface with the hot gas engine sections. Gear boxes and starter/generators are key components of power generation leading to power distribution which is then connected to load management. Methods of storing and dissipating energy such as high-energy density batteries, super-capacitors, and heat exchangers are also vital for on demand system optimization which has regenerative energy capability. Underlying these system integration issues is the basic energy management issue of on demand highly dynamic thermal management. Depending on the on demand energy rates, fundamental assumptions such as thermodynamic equilibrium are violated. Therefore, research into various fundamental non-equilibrium thermodynamics methods such as mesoscopic thermodynamic descriptions of non-equilibrium thermodynamics, quantum thermodynamics, and extended irreversible thermodynamics is being accomplished. From an experimental view, hardware in the loop (HIL) system integration optimization for energy management will continue to be pursed. In particular, remote HIL system integration is vital to advancements in aircraft system integration. Finally, research into integrated system health management will continue to be utilized to optimize the complete system.

Keywords: System integration; Thermal management; Power handling; Energy conversion; Gas turbines; Non-equilibrium thermodynamics; Hardware in the loop (HIL); Health management; Heat exchangers

Eligibility: Open to U.S. citizens

SF.30.02.B0109: Physics of Electric Discharges

Adams, S. (937) 255-6737

Basics atomic, molecular, and optical physics of electrically excited non-equilibrium gases are studied in a number of excited gas configurations including direct current, radio frequency, and microwave discharges, as well as laser excited gases. Research is primarily experimental and includes studies of ionization cross sections and ion-molecule reaction rates, excitation processes, energy transfer processes under non-equilibrium conditions, and gas breakdown mechanisms. Experimental facilities include a high resolution Fourier-transform mass spectrometer, modified for ionization cross section measurements, pulsed inductively coupled plasma source, laser excitation sources, plasma diagnostics including optical emission and absorption spectrometers, microwave interferometer and Langmuir probes. Applications include plasma processing and decontamination, control of plasma characteristics, and laser control of spark ignition.

Eligibility: Open to U.S. citizens

SF.30.02.B0110: Applied Atomic and Molecular Spectroscopy

Scofield, J. (937) 255-5949

Spectroscopic methods are developed and applied for quantitative measurements in nonequilibrium plasmas and high-temperature reacting flows. Well-defined low to medium pressure discharges using CW and pulsed direct current, low frequency to radio frequency, microwave excitations, and tandem pulsed-microwave excitations are investigated for their application to flow control in hypersonics, plasma enhanced etching, surface modifications, and dielectric breakdown. Experimental and theoretical studies are being conducted to characterize homogeneous and heterogenous processes in plasmas including plasma-surface interactions, plasma assisted ignition, and the creation and influence of self-ordered nanoparticles in plasmas. Power deposition scaling of atmospheric and near atmospheric pressure plasma properties including microplasmas are quantified by Stark spectroscopy, one- and two-photon allowed laser-induced fluorescence, Raman scattering, and photo absorption measurements using tunable visible to near-infrared, narrow line width diode laser sources. Experimental results are supported by theoretical modeling of electron kinetics and heavy particle interactions in nonequilibrium plasmas. A triple stage differentially pumped mass spectrometer is used to study transient discharge phenomena and photocatalytic reactions at medium to high pressure. We are also investigating the flux scaling properties of atmospheric pressure or near atmospheric pressure DBD plasma jet excited by short pulse duration, high reduced electric field dielectric barrier discharges for both vacuum ultraviolet/ultraviolet light source and low-cost surface coating applications.

Eligibility: Open to U.S. citizens

SF.30.02.B4272: Research and Development of Efficient and Novel Thermal Management Approaches for Airborne Vehicles

Yerkes, K. (937) 255-6186

Heat acquisition, transport, storage, and rejection represent fundamental limitations for future high-power, high-energy missions and for high-performance aerospace vehicles. Basic and applied heat-transfer and thermodynamic phenomena are examined analytically and experimentally with emphasis on their adaptation to airborne power-systems, electronic component thermal management, and directed energy weapon thermal management. Areas of interest include, but are not limited to single-phase, two-phase, multiphase systems, and high-performance rapid-responding thermodynamic systems; novel working fluid approaches for low and high temperatures (-55oC to >300oC for high-performance dielectric materials); nano and micro scale thermophysics; concurrent and countercurrent heat-transfer devices; capillary and other augmented heat-transfer methods for variable gravity applications; novel thermophysical and heat-transfer phenomena characterization; high- and low-temperature heat-transfer fluid-properties verification; unsteady heat transfer in pulsed and transient-phase change processes; analysis and verification of direct and indirect liquid cooling for electronic component temperature control; and the solution of the conjugate problem associated with this configuration for silicon carbide applications.

Eligibility: Open to U.S. citizens

SF.30.02.B4833: Lithium-Ion Conducting Channel

Scanlon, L. (937) 255-2832

Rechargeable lithium polymer batteries are of interest because of the very high-energy densities achievable relative to that of current generation batteries such as nickel-hydrogen. A key problem associated with the development of this battery has been the poor performance of the polymer electrolyte at ambient and subambient temperatures. Recent developments within our laboratory have demonstrated that a solid-state lithium ion conducting electrolyte (lithium ion conducting channel) can function over a broad temperature range from + 100 C to -50 C with very high specific conductivities on the order of 10 to 100 mS/cm. This electrolyte is particularly attractive since the transference number for lithium is one. The electrolyte was designed by computational chemistry with this feature as the anion matrix provides a constant negative electrostatic potential throughout the molecular system. This characteristic is important for operating over a broad temperature range since lithium ion transport no longer depends on polymer segmental motion but on the electric field gradient created by the potential difference of the electrodes within the electrochemical cell. Our goals are to simulate the electric field gradient using computational chemistry and applying it to the lithium ion conducting channel molecular system in order to correlate molecular structure with ionic conductivity. In addition, we intend to investigate the electrolyte/electrode interface through computational chemistry. We conduct research on ramjet/scramjet and mixed-cycle propulsion.

Eligibility: Open to U.S. citizens

SF.30.02.B4834: Wide Temperature Range Power Semiconductors

Scofield, J. (937) 255-5949

Research opportunities exist in the areas of power device design, development, and reliability assessment as they relate to wide bandgap power switch and diode performance in harsh environments. In addition to a consideration of carrier transport phenomena over wide temperature operational ranges, current research is focused on the thermo-mechanical aspects of device packaging to minimize CTE-related stresses and enhance reliability while providing the requisite electrical functionality. Novel composite and metallurgical materials are being investigated in module designs which aim to functionally optimize heat transfer efficiency and temperature distributions to minimize the stresses which drive conventional packaging failure modes. FEA modeling and simulation are extensively used to drive component designs which are subsequently validated empirically. In conjunction with this area of research is an interest in developing thermal models of heat transport across small-dimensional layers and interfaces that are not accurately described by Fourier conduction theory. A closely related area of research is in improving our understanding of the fundamental physics and chemistry of device failure in these emerging wide bandgap material systems. Efforts to determine activation energies and correlate device failure data with resident dislocations, inclusions, micropipe, and other defects is an area of high priority. Research interest also exists to develop sensors and optical interrogation techniques that are capable of providing accurate, repeatable, high-resolution response to small changes (<5%) in pressure, temperature, electrical current, voltage, and fluid flow under similar thermal environments.

Eligibility: Open to U.S. citizens

SF.30.02.B4962: Superconductors, Thermoelectrics, Carbon Nanotubes, and Magnetic Materials for Advanced Power Applications

Haugan, T. (937) 225-7163

The discovery of high-temperature superconductors (HTS), carbon nanotubes, thermoelectrics, and advanced magnetic materials offers many possibilities for their application in energy, power, and thermal applications and systems. However, a basic understanding of these materials, uniquely engineered structures, or the discovery of new materials (for superconductors, thermoelectrics, and magnetic materials) with their associated development is necessary to realize these applications. We are interested in both experimental and theoretical work, and modeling and simulation to accomplish these goals. Also the design and development of power devices is of interest to understand and demonstrate new capabilities. The following discusses each area as well as relevant general capabilities needed. In HTS, current emphasis is placed on the search for new superconductors at higher temperatures or more isotropic in current transport, and preferably operating above liquid hydrogen temperatures. Basic research is performed for the development of wire conductors, with emphasis on magnetic flux pinning enhancement, ac loss understanding and minimization, and stability and quench. Development of advanced superconducting wire is acceptable and can include conductor or cable configurations and coil windings. Thermoelectrics explore properties either at higher temperature for waste heat applications or as a means for cooling through the Peltier effect. Material emphasis is placed on multilayers and other nanostructures, oxides, and carbon nanotubes. Carbon nanotubes and composites are studied with an eventual goal to either achieve long lengths for electrical wiring/data transmission, or for thermal transport and structural support in a variety of electro-thermal environments including cryogenic. Magnetic materials research focuses on developing improved permanent magnets, such as high saturation and nanoparticle composite materials, and on soft magnetic material. Pulsed laser deposition, MOCVD, and MOD are the principal processes for thin-film growth in addition to the different materials for study of superconductors and thermoelectrics. Bulk growth of the magnetic materials and superconductors is of primary interest. CVD (both thermal and microwave) is typically used for growth of the carbon nanotubes.

Eligibility: Open to U.S. citizens

SF.30.13.B0910: Advanced Catalysis for Hypersonic Vehicles

Reitz, T. (937) 255-4275

Significant progress has been achieved to date in the development and demonstration of hypersonic engine technologies. These vehicle demonstrations currently utilize very basic power and thermal management subsystems whose only role is to provide limited operation for the short duration of the test flight. Advanced hypersonic vehicles, however, require sustained hotel power and cooling loads which may last several hours. Additionally, these vehicles operate in an extremely challenging environment making subsystem design a considerable challenge. Amongst the greatest of these subsystem challenges is long-duration (>10 min) thermal management of the vehicle, engine, and onboard electronics. Current research has focused on using the energy contained within the chemical bonds of the fuel to effectively store these aggressive heat loads prior to combustion. However, challenges associated with carbon fouling of the fuel lines due to non-selective fuel decomposition reactions currently limits operational life.

The objective of this effort is to explore advanced catalysis and reactor designs to promote selective endothermic fuel decomposition of relevant operational fuels. Interest areas include catalysis, kinetic, and reaction modeling studies of elevated temperature (200-700°C), high-pressure (20-60 bar) pyrolysis and partial-fuel reforming reactions.

Eligibility: Open to U.S. citizens

SF.30.13.B0911: Design and Verification of Autonomous Systems

Humphrey, L. (937) 713-7032

The USAF has called for a dramatic increase in the use of autonomous systems. However, due to their complex and adaptive nature, new methods for design, verification, and validation of autonomous systems are needed before they can be used in practice. This includes methods that take into account interactions with human users, supervisors, and/or collaborators. Toward this end, we are investigating methods for requirements, architecture, and design formalization and analysis; “correct-by-construction” synthesis of architectures, designs, and implementations from higher-level requirements; synthesis of analytical proofs of system correctness; compositional verification of systems-of-systems; alternative methods of assurance for systems that cannot be fully verified; methods for analyzing and improving human-automation interaction and human trust in automation; and construction of “safety cases” or “assurance cases” for certification. Some examples of specific topics in these areas include:

  • Formal methods
  • Runtime assurance
  • Assume-guarantee contracts
  • Architecture design and analysis with AADL
  • Reactive synthesis of system designs from LTL GR(1) specifications or from probabilistic specifications
  • Developing and incorporating models of human behavior and performance into the system design process
  • Methods that enable system adaptation while maintaining guarantees
  • Increasing transparency of autonomous systems, both for certification and for real-time use
  • Improving the usability of verification and validation tools, e.g. by explaining counterexamples

Application domains of particular interest include:

  • Cyber-physical systems
  • Multi-agent systems
  • Systems for human-automation mission planning

*Eligibility: Citizenship: Open to U.S. citizens only.

SF.30.13.B0912 Camber Morphing and Continuously Reconfigurable Wing Structure Design and Analysis

Joo, James (937) 713-7137

Conventional wings using a discrete control surface system (e.g., ailerons or flaps) suffer from aerodynamic inefficiency due to non-smooth outer mold lines and gaps/holes that can create unwanted vortices and flow separations, which increase drag. The discrete nature of these systems also creates structural inefficiency due to limited ability to control induced stresses during the performance of maneuvers. Competing economic and flight performance requirements drive aircraft design to consider aeroservoelastic solutions to balance these requirements, and in some instances attain performance beyond traditional capabilities. Enhanced maneuverability decreased structural weight, reduced drag, reduced noise, and maximized mission range are benefits that may result from replacement of traditional control surfaces with camber morphing and continuously reconfigurable wing designs. AFRL recently developed a Variable Camber Compliant Wing (VCCW) and tested it in the vertical wind tunnel at Wright-Patterson AFB. This demonstrated that a wing with a single continuous and non-stretchable composite skin can be designed, fabricated, and tested to achieve a large, predefined camber change using a compliant mechanism. This achievement of shape reconfiguration with minimum actuation was possible due to an inherently flexible substructure that is strong enough to withstand aerodynamic loads while meeting acceptable deformation constraints. The VCCW design team in Aerospace Systems Directorate is interested in exploring Camber Morphing and Continuously Reconfigurable Wing Structure technologies that enable maneuvering without using a discrete control surface system (e.g., ailerons or flaps) in terms of the aerodynamic benefits and developing advanced enabling technologies such as control laws, planforms that are more inherently synergistic with VCCW, hybrid system, engineered material, and fabrication. The research focus includes but is not limited to: (1) understanding the 2D/3D aerodynamics of a camber morphing and continuously reconfigurable wing structure; (2) evaluating the benefit of the conformal wing system compared to a conventional wing system with a discrete control surface system (e.g., ailerons or flaps) in terms of efficiency, flight control effectiveness, fuel consumption, and so on; (3) increasing vehicle range and/or flight performance by modifying wing characteristics in flight, such as continuous camber shape optimization at different flight conditions during flight; (4) novel hybrid morphing multi-functional structure design combining compliant mechanism, smart structures, traditional mechanism design and actuation inspired by avian flight; (5) aeroelastic behavior of a camber morphing and continuously reconfigurable wing structure; (6) control allocation for optimization or balance of sub objectives, such as aerodynamic efficiency, structural loading, and maneuverability; (7) flexible/corrugated skin; (8) novel actuation system; (9) novel wing mechanism/structure design methodologies such as topology optimization; (10) advanced fabrication and bonding; (11) verifying the benefits and performance using wind tunnel test; and more.

*References:
https://www.youtube.com/watch?v=F-PVtlQCr5w
https://www.youtube.com/watch?v=o76UZ4ZX1i0
Joo JJ, et al: "Variable Camber Compliant Wing - Design," 23rd AIAA/ASME/AHS Adaptive Structures Conference, Kissimmee, FL, 5-9 January 2015
Jo, Y., et al: "Aerodynamic Characteristics and Shape Optimization of a Variable Camber Compliant Wing," AIAA AVIATION 2016, AIAA-2016-3010, Washington DC, VA, 2016

*Eligibility: Citizenship: Open to U.S. citizens

SF.30.13.B0913: Cooperative Control of Autonomous Systems in Uncertain Information Environments

Casbeer, D. (937) 255-4895

This research focuses on cooperative control problems involving autonomous agents in uncertain environments with communication restrictions. Typical scenarios of interest involve different modalities of communication, e.g., high-bandwidth, high-rate communications for short range peer-to-peer interactions and low-bandwidth, low-rate communications over larger distances. Agents must be able to intelligently adapt to the situation at hand and base decisions on the locally available (and uncertain) information, while still guaranteeing success of the overall mission. To accomplish this, the agents must be able to ascertain what information is important to ensure correct and appropriate decision-making for success of the overall mission objective. Furthermore, with the necessary information for mission success determined, the agents must be able to keep this information accurate and up-to-date given the changing (possibly distributed) communications restrictions. With such systems, analytical tools are needed to guarantee overall mission success given that decision-making is distributed with uncertainty. The overarching topics of interest for this research effort can be summarized as follows: value-of-information, distributed estimation, and distributed decision-making/control.

*References:

K. Krishnamoorthy, M. Pachter, S. Darbha, P. Chandler, Optimization of Perimeter Patrol Operations using UAVs, AIAA J. Guidance, Control and Dynamics, 2011.

K. Krishnamoorthy, D. Casbeer, P. Chandler, M. Pachter and S. Darbha, UAV Search & Capture of a Moving Ground Target under Delayed Information, IEEE Conf. Decision and Control, 2012 (to appear).

D. Casbeer, K. Krishnamoorthy, A. Eggert, P. Chandler and M. Pachter, Optimal Search for a Random Moving Intruder, Proc. AIAA Infotech@Aerospace Conf. 2012.

*Keywords:

distributed and robust decision-making, (partially-observable) Markov decision process, intelligent control, distributed estimation, sensor fusion, value-of-information, multi-agent

*Eligibility:

Citizenship: Open to U.S. citizens only.

SF.30.13.B1109: Two Phase Heat Transfer

Byrd, L. (937) 255-3238

Next generation aircraft have a significant increase in thermal loads due to a transition to more electric aircraft, more powerful electronics, and the use of more composite structures. Two phase heat transfer is being used to provide thermal management for these aircraft. This can provide energy transfer that is orders of magnitude more efficient than single phase cooling thus allowing increased heat fluxes with almost isothermal surfaces at 1% of the mass flow rate. Vapor compression cooling systems utilizing two phase heat transfer are seen as essential components for the INVENT program to reach its goals.

Toward this end, we are investigating the limitations of two phase heat transfer. This includes the critical heat flux and heat transfer coefficient for a number of configurations including pool boiling, thin film evaporation, spray cooling, and jet impingement. Pressure drop and stability are also of concern for situations where there is two phase flow and in systems with multiple evaporators or condensers.

Examples of research in this area include:

*Increasing heat transfer and critical heat flux through the use of surface enhancements such as porous coatings or nanoscale features that promote early bubble release and good rewetting.

*Nonlinear control and stability of two phase systems with transient loads and multiple heat exchangers. This includes system level as well as component level response.

*Energy optimization control schemes for two phase thermal management systems that can be integrated into a platform level energy optimization manager.

*Two phase systems that use working fluids that can reject heat at higher temperatures than current refrigerants.

*Eligibility: Citizenship: Open to U.S. citizens only.

SF.30.16.B0001: Control Techniques for Aircraft Energy Management

Hencey, Brandon (937)-255-0375

Current and next generation of aircraft are faced with increasingly critical power and thermal requirements despite decreasing footprint (i.e. weight, volume, and external sinks). These challenges involve large transient loads and strenuous mission environments. The siloed and steady-state design paradigms have reached a point of diminishing returns for expanding system capabilities. Instead, techniques are needed that dynamically allocate energy resources over the mission and across the aircraft to vastly expand capability. This necessitates coordinating energy conversion, distribution, storage, and dissipation among subsystems. Specifically, there are tremendous opportunities for employing cyber-physical systems concepts applied to power and thermal systems. Potential techniques include optimal control, predictive control, distributed control, Bayesian estimation, formal synthesis, and machine learning.

Keywords: System integration; optimal control, predictive control, distributed control

*Eligibility: Open to U.S. citizens

SF.30.16.B0002: Analysis of Low-Velocity Impact on Laminated Composites

Vipul Ranatunga (937) 656-8809

Finite element method (FEM) and finite difference method (FDM) are two of the widely used numerical methods that require the discretization of problem domain with a mesh or a gird. Fracture and fragmentation will present challenges to both of these methods in handling newly created surfaces and forcing the numerical scheme to regenerate the mesh frequently. Formation of discontinuities in an undamaged material is a sudden event, and the knowledge of the location and the external conditions for such an event is not available in advance. The mathematical framework used in the classical theory of continuum mechanics requires the use of partial derivatives to calculate the displacement field and these derivatives are undefined along the discontinuities. In order to overcome this difficulty, geometry of the continuum has to be redefined so that the discontinuity becomes a new boundary for the continuum body. The redefinition of boundary requires the location of the discontinuity in advance, limiting the possibility of predicting the formation of spontaneous discontinuities such as dynamic cracks. Therefore, new techniques are necessary to reformulate the equations of the continuum mechanics to utilize the same set of equations for the calculations at discontinuities and elsewhere.

Basic research opportunities exist to develop advanced analysis methods (Peridynamics, Smooth Particle Hydrodynamics, etc.) to predict the behavior of composites under low-velocity impact. Current state-of-the-art analysis methods fall short in the area of capturing damage during an impact event. Sub-surface delamination is the predominant mode of failure observed in experiments, but matrix cracking, fiber breakage and ply-splitting also take place during an impact. Development of advanced numerical tools to capture these failure mechanisms and predict the remaining strength after impact is expected.

Keywords: Mesh-Free methods, Peridynamics, Smooth Particle Hydrodynamics, Impact Damage, Delamination, Finite Element Modeling.

*Eligibility: Open to US citizens only.

SF.30.16.B0003: Extreme Light Matter Interactions

Roquemore, William (937) 255-6813

The goal of this program is to gain a fundamental understanding of the interactions of ultra-short pulse, ultra-intense laser (extreme light) interactions with matter. Experimental and computational studies of the interaction of a 10 mJ, 1 kHz, 35 femtosecond pulse laser with micron diameter water jets are being performed. Experimental studies have demonstrated the production of MeV electrons and gamma rays from the interaction of the laser, focused to an intensity of 10^18 W/cm^2, with a 25 um diameter water jet when a significant pre-pulse is present. Simulations of laser/water jet interaction have provided considerable insights into the processes responsible for producing electron and gamma rays and the role of the pre-pulse. Experiments using a laser intensity of 10^19 W/cm^2 and eventually at near-IR wavelengths are being planned. Also, laser/heavy water jet interaction experiments are in preparation to produce neutrons by a laser fusion process. The fundamental understanding gained from these types of experiments will aid in determining the feasibility of using similar types of extreme light/target interactions to produce fundamental particle and radiation as a source for nondestructive inspection of weapon system components. We are interested in faculty and graduate students with experience in conducting or simulating extreme light/target interaction experiments similar to those outlined in this topic.

Keywords: Extreme Light; Femtosecond Lasers; MeV Electron Production; Gamma Ray Production; Laser/Target Interactions

Eligibility: Open to U.S. citizens

SF.30.16.B0004: Combustion Enhancement in High-Speed Flows

Ombrello, T. (937) 656-5950

Presently, the harsh and restrictive reactive environments within high-speed propulsion systems, such as scramjets, can be limiting factors for their development and practical implementation. Typically, these limitations lie in the ability to ignite, propagate, and stabilize a flame near flammability limits, at low temperatures and pressures, and within short residence times, therefore necessitating some form of energy addition, with one promising solution being plasma. There is a need to better understand the fundamental interactions involved in enhancement with different forms of energy addition, such as the effect of specific plasma-produced species or how to efficiently couple energy into a high-speed and highly-turbulent reactive flow. A range of systems are available to interrogate these problems, including simple bench-top experiments (such as in a variable pressure combustion platform), to wind-tunnels (including direct-connect scramjet facilities). A host of optical and laser diagnostic assets are available, including, but not limited to planar laser-induced fluorescence (PLIF), particle image velocimetry (PIV), intensified high-frame-rate imaging (chemiluminescence and schlieren at >100,000 frames per second), and absorption and emission spectroscopy, to study these phenomena.

Keywords: Supersonic combustion; Scramjets; High-speed flows; Plasma; Plasma-assisted combustion; Advanced optical diagnostics; Reactive flow energy coupling

Eligibility: Open to U.S. citizens

SF.30.17.B0001: Fan and Compressor Aerodynamics Experimental Research and Data Analysis

List, Michael (937) 255-7047

Collection and analysis of experimental datasets from transonic fan stages benefits the design and analysis processes of modern fans and compressors. The Compressor Aero Research Lab (CARL) investigates gas turbine aero engine fan and compressor aerodynamic/aeromechanic performance to impact future designs. To support the synthesis of experimental results into design guidance and models, CARL collects high-fidelity experimental datasets and implements/develops state-of-the-art post-processing techniques.

Topics of interest include but are not limited to: (1) data reduction and analysis techniques for unsteady pressure measurements, including over-the-rotor kulites; (2) stall detection automation; (3) reduced order modeling, linear and non-linear analysis, and multivariable analysis of complex 3-D flows; (4) flow feature detection and model development; (5) assessment of novel and low-intrusion instrumentation and measurement techniques; (6) experimental planning for design tool calibration and CFD validation; (7) uncertainty quantification and error analysis; (8) formulation of generic and calibrated models for assessment of derivative airfoil designs.

SF.30.17.B0002: Fan and Compressor Aerodynamics Design and Analysis

List, Michael (937) 255-7047

Aerodynamic design and analysis of modern compression systems uses meanline, throughflow, and CFD to generate flowpath and airfoil shapes. The Compressor Aero Research Lab (CARL) investigates gas turbine aero engine fan and compressor aerodynamic/aeromechanic performance to impact future designs. CARL is developing meanline and throughflow capabilities in-house for design, and CARL applies a range of academic, government, and commercial CFD tools for analysis. Collaboration is possible through implementation of plug-ins – discrete, focused code modules – for everything from loss models to blade parameterization to file exports.

Topics of interest include but are not limited to: (1) implementation of loss, mixing, and other generally applicable models; (2) development or implementation of post-processing tools to assess off-design operation, e.g. Gong and Tan model; (3) novel blade shape parameterization for optimization; (4) integration with MDAO frameworks; (5) efficiency improvements in the design-to-CFD process; (6) early design phase aeromechanics, such as Campbell diagram generation.

SF.30.17.B0003: High-Order Finite Element Methods for Computational Fluid Dynamics in Aerospace Vehicle Design

Shrock, Christopher (937) 713-7138

The development of future Air Force systems requires the development of flexible and efficient, high-fidelity, multi-physics, simulation capabilities. To be applicable within the design cycle, such capabilities must be capable of handling complex, full-configuration geometry and enable the designer to interchange vehicle components at-will, without substantial labor in grid re-generation. Additionally, the approaches must be computationally efficient to be relevant in the design process. The computational benefits of high-order techniques are being demonstrated in both fluids and structures simulations; namely, for a specified level of accuracy, significant reductions in computational time are achievable over traditional second order methods.

Multiple finite element discretization techniques such as Discontinuous Galerkin (DG), Hybridized Discontinuous Galerkin (HDG), Streamwise Upwind Petrov Galerkin (SUPG), and Flux Reconstruction (FR) schemes have been developed. Broad research opportunities for the advancement of such approaches to both fluid and multi-physics simulations encountered in aerospace system design exist. Areas of interest include: (1) Extension of techniques to overset framework, (2) Stabilization of high-order methods in presence of sharp gradients and discontinuities (e.g. shock waves, etc.), (3) Application to RANS turbulence modeling, (4) Quantitative evaluation/comparison of computational efficiencies of various high-order discretization schemes, (5) Development/exploration of multi-physics solver & domain couplings, (6) Development of multi-fidelity approaches to improve efficiency, (7) Theoretical analysis and development of numerical schemes, (8) Efficient linearization strategies, (9) Development of high-order mesh motion and deformation techniques.

SF.30.17.B0004: Turbulence Measurement and Characterization

Guyton, Robert (937) 713-6680

Measurement of turbulence intensity in low turbulence wind tunnels requires new and possibly multiple approaches in order to produce dependable results. Traditional instruments and approaches are vulnerable to the weak signal strength and signal noise. The lack of standardized configuration control on signal content and signal processing leads to free set of arbitrary choices that produce results that are incomparable to other wind tunnels given the same general method. Sensitivities to fixtures, signal conditioning, data acquisition, processing and data reduction are strong players in the outcome as well. Research proposals are solicited that will quantify the issues and resolve them in order to produce dependable turbulence intensity measurements when the turbulence intensity magnitude is below 0.1%. Proposals are solicited in the following topic areas as they relate to measurement of turbulence intensity in the AFRL/RQ SARL wind tunnel located at WPAFB, Ohio: (1) Development and demonstration of refinements to traditional turbulence measurement, data acquisition, and signal processing. (2) Development and demonstration of non-traditional turbulence measurement methods, data acquisition, and signal processing. (3) Development and demonstration of a comparison basis for a representative set of medium scale low turbulence wind tunnels using the same fixtures and instrument/signal processing suite.

SF.30.17.B0005: Advanced Aeronautical Design Methodologies

Zeune, Cale (937) 713-6657

Advanced aerodynamic technologies enable development of potentially revolutionary vehicle configurations for Air Force needs. But progress is contingent upon synthesis of design tools, engineering level aerodynamic analysis tools, and the associated disciplines of wind tunnel testing and traditional computation. A wide range of mission areas and vehicle concepts is of interest, including: small UAS, air dominance, long dwell ISR, tankers, transports, UCAVs, and VTOL. In the aerodynamics discipline, research-interests include laminar flow and laminar to turbulent transition, flow control for drag-reduction and lift-enhancement, unsteady aerodynamics, low Reynolds numbers flows, efficient transonic design, high lift generation, aero design methodologies, and potential/panel methods. Vehicle design and configuration maturation topics of interest include: integration of large diameter propulsors, distributed propulsion, propeller/rotor mechanics, rapid geometry and mesh generation, stability and control assessments, unconventional power and propulsion integration (hybrid/electric vehicles), structural layout, performance modeling, mass properties estimation, etc. Partners are sought to conduct practical analyses, develop tools and methods, research configurations and aerodynamic phenomena, and design exploratory campaigns linking wind tunnel testing and computation.

Key Words: conceptual design, laminar flow, potential flow, stability and control, distributed propulsion

SF.30.17.B0006: Application of Similarity Laws in High Speed Viscous Flows

Miller, James (937) 255-7212

Complex flowfield interaction regions, caused by control surface deflections, wing-body junctures, structural gaps, or large angles of attack, often become design drivers for high speed vehicles. Recent research in AFRL has demonstrated a more practical approach to characterizing these regions, which are usually characterized by shock interactions that cause large pressure gradients to exist in the vicinity of viscous boundary layer flows. With AFRL’s discovery of a new similarity parameter for the Navier-Stokes equations that represents the ratio of pressure forces to viscous forces, it is now appropriate to explore analytical approaches to characterizing external flows with bounding values of this new parameter. For example, viscous flow regimes that could be explored include flows that are dominated by large pressure forces, but small viscous forces; or have small pressure forces but are dominated by large viscous forces. In addition it may now be possible to fruitfully explore closure equations for turbulent flows and develop new closed-form approximations to the Navier-Stokes equations. With the intent of focusing on high speed flows, the present research opportunity hopes to address research questions as follows (listed in priority order): 1) Explore the impact of pressure force / viscous force ratio on existing boundary layer theories, with eventual application to high speed external viscous flows including computational results and experimental measurements 2) Explore feasibility of pressure force / viscous force ratios to developing turbulence models to close the Reynolds stress equations either through turbulent viscosity models or stress-equation models for high speed viscous flows. 3) Explore basic physics of shock / boundary layer interactions or 3D viscous interactions to characterize ratios of pressure forces / viscous forces for fundamental fluid interactions using LES or DNS methods. This could include exploring the feasibility of improving filtering methods for LES/DNS using the aforementioned pressure / viscous considerations.

AFRL/Aerospace Systems

Dr. Frank S. Gulczinski III
AFRL/RQ
2130 Eighth Street
Wright Patterson Air Force Base, Ohio 45433-7542
Telephone: (937) 938-4805
E-mail: frank.gulczinski@us.af.mil