Cohn, Richard - 661-816-9084

The Air Force Research Laboratory Rocket Lab has been developing advanced technology rocket systems since 1947. In addition to being a leader in developing advanced technology, it is also a leader in supporting the community and being a diverse STEM workplace. In order to enhance and improve current research efforts the AFRL Rocket Lab encourages bringing in a diverse community of STEM graduates in order to bring in different workplace styles and backgrounds. However, we must work hard to recruit and retain top talent. This study seeks to help identify activities that will help improve recruitment and retention of STEM talent, particularly developing local, "home-grown" talent in order to ensure the AFRL Rocket Lab continues to be a world leader. Examples of potential activities include enhancement of internship opportunities, increasing opportunities for AFRL participation in student design projects and competitions, increased AFRL participation in faculty research and/or joint proposals, student club mentorships, lecture series, and other ideas of mutual interest.

Eligibility: Open to US citizens

Distribution Statement A: Approved for Public Release. Distribution Unlimited. PA# AFRL-2024-4365

Burr, Jason - 661-275-5175

Rotating detonation rocket engines (RDREs) harness detonative combustion, which offers benefits over the typical deflagration-based combustion process that is prevalent in propulsion devices today. As opposed to subsonic isobaric deflagration, detonation is a combustion-driven shock that generates a compact, isochoric heat release zone at elevated pressure and temperature; this allows more useful available work to be extracted from the propulsion cycle, leading to potential engine performance gains. Currently, the USAF/USSF are actively pursuing detonation-based propulsion as a means to develop rockets that are more compact, insensitive to thermo-acoustic instabilities and require lower injection pressure for equivalent performance to deflagration-based propulsion systems. In order to realize these benefits, we are currently exploring various research areas including the following:

• Multiphase detonation physics
• RDRE design optimization (e.g., nozzle/injection schemes)
• Thermodynamic systems analysis
• Advanced diagnostics for detonation characterization

Currently, we house multiple fundamental detonation facilities that are designed to study detonation propagation in both premixed and non-premixed configurations for gaseous and multiphase propellant systems. In addition, our group has two laboratory-scale RDREs for use in experimental studies for design optimization and advanced measurement diagnostic testing. Multiple research areas under this technology development topic are available, with the expectation that the selected individuals will work within our interdisciplinary RDRE group that is comprised of experienced research scientists and engineers in the fields of detonation physics and advanced propulsion.

Keywords: detonation, rotating detonation rocket engines, multiphase combustion, advanced propulsion

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

Harvazinski, Matthew - 661-275-5629

Large-Eddy Simulation (LES) has shown promise in modeling complex flow fields in liquid rocket engines (LRE) and rotating rocket detonation engines (RDRE). The flow environments in these devices involve multi-physics effects, including compressibility, multiphase flows, turbulence, reactions, high temperatures, and high pressures. These conditions challenge experimental measurements and motivate the use of simulations as a tool to gain insight. The flow fields also provide a rich dataset to study turbulent combustion because they contain regions of diffusive, deflagrative, and detonative combustion. AFRL is actively working to simulate these devices to better understand the complex physics influencing their performance. We are simultaneously working to further develop computational tools to deliver results that are more accurate and affordable. Topics of interest include:

1. Multiphase flows, atomization, and sprays
2. High-pressure effects
3. Wall models
4. Conjugate heat transfer
5. High-speed turbulent combustion
6. Numerical methods for multiphase chemically reacting flows
7. Uncertainty quantification and multi-fidelity ensembles
8. New paradigms in high-performance computing for these applications.

Keywords: rotating detonation rocket engines, multiphase combustion, high-fidelity simulations, wall models, liquid rocket engines

Eligibility: Open to U.S. citizens.

Distribution Statement A. Approved for public release, distribution is unlimited. AFRL-2024-3177

Sedano, Nils - 661-275-5972

The fluid flow associated with the truncated aerospike nozzles are accompanied with free shear layers that are known to introduce instabilities and unsteadiness. These unsteadiness and instabilities can couple with the vehicle aerodynamics and create control and instability problems in flight. The severity of these issues vary with the altitude.
The research focuses on the high fidelity numerical simulation of the flowfield associated with the aerospike engines operating at various altitudes. The topics and issues of interest are: (1) secondary combustion of the plume gases with the ambient fluid. (2) Investigation of the free shear layers in the external jet boundary and in the near wake surrounding the circulating flow in the base region, and the interaction of the free shear layers with nozzle and its effects on the aerodynamic performance of the vehicle.
Key words: aerospike, free shear layer, base region, aerodynamics performance, high fidelity numerical simulation

Vaghjiani, Ghanshyam - (661)-275-5657

Our research centers on fundamental chemical kinetics and applications in combustion chemistry of energetic propellants. The rates of elementary reactions are measured using various direct time-resolved techniques such as pulsed laser photolysis, coupled with laser-spectrometric or mass-spectrometric probing of the short-lived species in the gas phase. We also use rapid-scan FTIR absorption spectroscopy to probe the formation of stable products in these reactions. Heterogeneous processes, such as the reactions of aerosolized propellant fuel in various oxidizing gaseous environments, are studied using the VUV-PI-TOFMS experimental set-up of the Chemical Dynamics Beamline 9.0.2.3 at the Advanced Light Source Synchrotron Facility at the Lawrence Berkeley National Laboratory in Berkeley, CA. Direct molecular dynamics simulations are also performed to identify pertinent chemical processes in the combustion of propellant mixtures. Chemical models of these processes are constructed using ab initio quantum chemical, TST and RRKM theories to understand the mechanisms. The laboratory data is extrapolated to operational conditions in the prediction of ignition delay times, a quantity of significant importance in the design of rocket engines.

*References:

Sun H, Vaghjiani GL: J. Chem. Phys., 142, 204301 (2015).

Newsome DA, Vaghjiani GL, Sengupta D: Propellants, Explosives & Pyrotechnics, 40, 759 (2015).

Perez JPL, Yu J, Anderson SL, Sheppard AJ, Chambreau SD, Vaghjiani GL: Appl. Mat. Interfaces. 7, 9991 (2015).

*Keywords:

Combustion chemistry; Propellant ignition; Reactions kinetics; Time resolved laser spectroscopy; FTIR spectroscopy; TOF mass spectrometry; Chemical mechanisms; Quantum chemical calculations; Molecular dynamics simulations;

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

Sankaran, Venke - (661) 275-5534

This research focuses on the exploration of novel meshing paradigms for computational fluid dynamics simulations of internal rocket flowfields. Current meshing paradigms have both strengths and weaknesses. Cartesian meshes are efficient and accurate, but are not suitable for capturing near-wall boundary layer phenomena; curvilinear structured meshes are efficient, accurate, and suitable for boundary layers, but the grid generation is complex and tedious; unstructured meshes are much easier to generate and are well-suited to boundary layers, but they are relatively inefficient and are typically restricted to second-order accuracy at best. The technical approach is to combine different mesh types within a single flowfield simulation so that the domain is effectively mapped by the grid-types best suited to the local requirements. Thus, the off-body region can be represented by Cartesian meshes, while the near-body region is governed by body-fitted structured or unstructured meshes. Connectivity between the different mesh systems is usually accomplished using overset grid technology. We anticipate that the judicious combination of such mesh types can lead to over two orders of magnitude savings in computational time and provide significant enhancements of solution accuracy. The specific topic of interest is the development of such a multiple-mesh infrastructure for internal flowfields that are representative of rocket propulsion flowfields. Additional areas of interest include (1) automated adaptive mesh refinement technology, (2) effective domain decomposition and load balancing algorithms, and (3) improved overset interpolation and/or conservative flex-exchange methods for inter-mesh information transfer. Research and development will be conducted within an existing code infrastructure and the methods applied to rocket propulsion flowfields including solid motors, liquid engines, cryogenic turbomachinery and/or electric thrusters.



Keywords:

Computational fluid dynamics; Overset grids; Internal rocket flowfields; Adaptive mesh refinement;

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

Sankaran, V - 661-275-5534

Rocket propulsion flowfields offer significant challenges to computational modeling because of the complex turbulent reacting multiphase physics, the presence multiple length and time scales, and the unsteady nature of the flow phenomena. This topic concerns the investigation of numerical algorithmic aspects to address these challenges from the viewpoint of ensuring solution accuracy, robustness, efficiency and scalability. Specific areas of interest include improved flux schemes that can preserve uniform accuracy at all Mach, Reynolds, and Strouhal numbers; high-order accurate spatial and temporal discretizations; enhanced implicit solution techniques; and automated time-step control for the robust solution of stiff and highly nonlinear problems. The technical approach will involve the use of numerical analysis tools such as von Neumann stability, asymptotic theory, and the method of manufactured solutions as well the development and implementation of the algorithms in candidate computational fluid dynamics codes. Particular emphases will be placed on unsteady flow simulations with DES or LES models for turbulence, generalized equations-of-state for high-pressure super-critical problems, finite-rate chemical kinetics, and stochastic-PDF methods for turbulent combustion. Verification and validation will be targeted towards canonical spray and combustion problems, as well as practical rocket flowfield simulations involving solid motors, liquid rocket engines, cryogenic turbomachinery, and/or electric thrusters.



Keywords:

Computational fluid dynamics; Algorithm development; Propulsion flowfields; Liquid rocket engines; Solid rocket motors; Cryogenic turbomachinery;

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

Mabry, J - (661) 275-5857

The chemical synthesis of novel molecules and reactive monomers, as well as their use in thermoplastic and thermosetting polymer nanocomposites, has resulted in significant improvements in a wide variety of polymer composite systems. Property improvements enabled by these materials have resulted in their use in several rocket propulsion and other defense-related applications. In addition to property improvement, synthesis of functional molecules and compounds at reduced cost is also desired. AFRL/RQ is a leader in the field of reinforced polymer composite research. An opportunity exists in the Air Force Research Laboratory at Edwards AFB for research in the synthesis of novel molecules, compounds, and polymer composites. A qualified candidate will have experience in organic, inorganic, organometallic, or polymer synthesis, or a combination of these areas. The Rocket Propulsion Division, Propellants Branch conducts both basic and applied research, leading to the development of advanced materials for use in rocket propulsion and other defense applications. Chemical aspects of the research involve the synthesis and characterization of new materials and polymer composites. These materials can be utilized for the modification of polymer properties, such as resistance to wetting by water and hydrocarbons, oxidation-resistance, thermal stability, and ease of processing. Aspects of this work involve the design and synthesis of monomers and polymers, as well as functional nanomaterials with novel architectures and composite resin development. Research is performed by both scientists and engineers, working together as an interdisciplinary team. US citizenship is required for this position. Please state prominently in any correspondence that you are a US citizen.

References:

Tuteja A, Choi W, et al: Science 318: 1618, 2007

Mabry JM, et al: Angewandte Chemie, International Edition 47: 4137, 2008

Mabry JM, et al: Langmuir 27, 10206, 2011

Mabry JM, et al: Journal of the American Chemical Society 133, 20084, 2011

Keywords: Synthesis; Polymer; Oleophobic; Nanocomposite; Nanomaterial; Composite; Hydrophobic

Eligibility: Open to U.S. citizens

Koo, Justin - 661-275-5908

This research topic in applied physics and mathematics focuses on the development and application of advanced numerical methods and physical models applied to plasma dynamics for conditions relevant to various applications of interest to the Air Force, particularly electric propulsion systems. Physical regimes range from rarefied plasma to ideal MHD, weakly to fully ionized, and with temperatures up to 100 eV. We are particularly interested in multiscale methods, hybrid methods, and innovative mathematical and numerical approaches to solving plasma kinetics. Fluid (MHD) and multi-fluid models, collisional-radiative (CR) kinetics, particle-in-cell (PIC), and Monte-Carlo collisions (MCC) methods are of typical interests, as well as Vlasov/Fokker-Planck approaches and their combination.

References: Kapper MG, Cambier JL: Journal of Applied Physics 109: 113308, 2011

Kapper MG, Cambier JL: Journal of Applied Physics 109: 113309, 2011

Keywords: Plasma; Nonequilibrium; Collisional-radiative; MHD; PIC; Vlasov

Eligibility: Open to U.S. citizens

Miller, Timothy - 661-275-5323

Solid propellants are a unique class of materials that behave in a viscoelastic manner but also develop damage as an effect of aging. Methods for characterizing propellant mechanical properties have been adapted from linear elastic, small strain experimental methods, but these approaches are lacking in fidelity. We are interested in developing advanced experimental methods to determine the mechanical behavior parameters of solid propellants in various stress states so that the results can be used to predict the mechanical response of the propellant grain. Properties such as Prony series, Williams-Landel-Ferry (WLF) parameters, fracture parameters (J-integral and fracture toughness KIC), and damage parameters are considered important. Linear and nonlinear viscoelasticity can both be considered, although nonlinear viscoelastic models are now being used to characterize damage due to particulate debonding and other microstructural failure phenomena. Although time and temperature dependence are important, other environmental factors such as pressure and relative humidity may also be investigated. Using techniques such as Digital Image Correlation or Dynamic Mechanical Analysis, we would like to develop experimental test methods that successfully improve the characterization of propellant mechanical properties and that give additional insight into the nature of solid propellant mechanical behavior under conditions experienced by solid rocket motors. Keywords: solid rocket propellant, digital image correlation, dynamic mechanical analysis, viscoelasticity, damage mechanics, fracture mechanics

Munipalli, Ramakanth - (661) 275-5647

The objective of this work is to investigate atomization and combustion of liquid propellants at high pressures including supercritical pressures. Current understanding of spray combustion processes is based mostly on low pressure, subcritical mechanisms, whereas future Air Force propulsion and other combustion applications will increasingly emphasize high pressures. Atomization and spray combustion mechanisms may be different in these regimes. At pressures exceeding the critical point of the propellant (731 psi for liquid oxygen), the sharp distinction between gas and liquid phases can entirely disappear, and we can question whether droplets can even exist. Such flows will likely exhibit properties, which at some times are like those of turbulent jets and at other times are more like those of sprays. Even subcritical high pressures pose substantial challenges for combustion diagnostic techniques, most of which were developed for low-pressure applications. To be overcome are obstacles such as dense sprays, beam steering, molecular quenching, and spectral line broadening. Numerous research opportunities are available to work with an established team of scientists and engineers to improve technology in this area.

Keywords: Liquid propellants; Supercritical fluids; Drops (liquids)

Eligibility: Open to U.S. citizens

Mabry, J - (661) 275-5857

The development of polymer nanocomposites and fiber-reinforced polymer matrix composites has resulted in significant improvement in thermal, mechanical, and physical properties in many aerospace applications. The property improvements enabled by these materials have resulted in their use in many defense-related applications. In addition to property improvement, production of functional composites at reduced cost is also desired. AFRL/RQ is recognized as a leader in the field of composite materials research. An opportunity exists for research in the area of polymer nanocomposites and fiber-reinforced polymer matrix composites. The Rocket Propulsion Division, Propellants Branch conducts both basic and applied research, leading to the development of advanced materials for use in various applications. Chemical aspects of the research involve the synthesis and characterization of monomers, polymers, resins, and composites. Research is performed by both scientists and engineers, working together as an interdisciplinary team. US citizenship is required for this position. Please state prominently in any correspondence that you are a US citizen.

References:

Mabry J, et al: Angewandte Chemie International Edition 47: 4137, 2008

Chhatre SS, Mabry JM, et al: ACS Applied Materials & Interfaces 2: 3544, 2010

Moore BM, Mabry JM, et al: Journal of Organometallic Chemistry 696: 2676, 2011

Guenthner AJ, Mabry, JM, et al: Macromolecules 454: 211, 2012

Keywords:

Polymer; Resin; Composite; Nanocomposite

Eligibility: Open to U.S. citizens