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Modeling Tools for Hypersonic Flight


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Hypersonics The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 3.5 of the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. OBJECTIVE: To incorporate new mathematical constructs and high-fidelity design tools to predict time-accurate aerothermodynamics of hypersonic vehicles. DESCRIPTION: The United States Army has a need to develop high-fidelity, computationally efficient solvers for the aerodynamic analysis and design of vehicles ranging from rotary-wing aircrafts to medium/long-range hypersonic projectiles. The CREATETM -AV Kestrel team has been developing a comprehensive suite of codes with a combined on-body/off-body computational approach for the prediction of flows around such vehicles for over a decade. The Army has unique gaps in understanding the flight characteristics (e.g., flow structures, pressure distribution, thermal loading) of hypersonic vehicles at high Reynolds numbers, in small physical scales with geometrical uncertainty, and with configurational asymmetries. While robustness and accuracy of Kestrel computational fluid dynamic (CFD) solvers is under continuous improvement [2,4,5], recent advancements in hypersonic boundary layer transition and turbulence modeling [6] for on-body solvers and sub-filter-scale (SFS) vorticity-preserving methods for off-body solvers [3] are yet to be incorporated into Kestrel. Correct prediction of hypersonic boundary layer transition locations, turbulent heat fluxes and vortical structures of high-speed wakes are of paramount importance in enabling the prediction of a next generation Army hypersonic vehicle’s performance. For the near-body analysis, several mesh options are available in Kestrel including strand, structured, and unstructured meshes. The off-body dynamics of freely evolving vortical wakes are handled in Kestrel via a high-order block-Cartesian Adaptive Mesh Refinement (AMR) approach. In both the on-body and off-body domains, numerical dissipation decreases the effective resolution and overall fidelity of computations, in exchange for high degrees of robustness, especially with complex vehicle geometries [2,4]. The fidelity of the Kestrel suite needs to be augmented specifically to capture key features of hypersonic flight, namely: (a) boundary layer transition locations and hypersonic turbulent heat-fluxes and shear-stresses (on-body); (b) high-Reynolds-number high-speed vortex dynamics in the wake (off-body). More specifically: (a) In the near-body region, key fluid dynamic features to capture include ultrasonic acoustic waves trapped in the boundary layer responsible for hypersonic boundary layer transition to turbulence under canonical flow conditions. To improve Kestrel’s hypersonic transition modeling capabilities, verification and validation against high-fidelity numerical approaches capable of shock capturing and dynamic turbulence modeling [6], and experimental data from hypersonic quiet wind tunnels [1], respectively, are required. (b) In the off-body region, compressible coherent vortex structures, and their interactions with shocks, affect aerodynamic forces and moments of projectiles and lifting bodies. Kestrel’s off-body solver currently lacks adequate SFS -- or large-eddy-simulation (LES) -- closures for high-Reynolds-number compressible vorticity. Classic LES models rely on a local isotropic turbulent eddy viscosity closure for the SFS stresses; however, such approach is overly dissipative [4] if not equipped with a dynamic procedure [3]. This should leverage any related investments from partners such as the Air Force or NASA. This applies broadly to the energy category of efficiency because the utilization of hypersonic weapons may reduce the timeline of conflicts which ultimately reduces energy. PHASE I: The Phase 1 effort shall carefully assess the current hypersonic flow prediction capabilities of modern multi-physics solvers (e.g., Kestrel) [5] against benchmark-quality hypersonic quiet wind tunnel experiments [1] and state-of-the-art high-fidelity calculations [3,6] for flow conditions and geometries of interest to the Army. An uncertainty analysis of the predicted boundary layer transition location, and the on-body and off-body turbulent shear-stress and heat- flux levels, should also be carried out by exploring the currently available multi-physics solvers (e.g., Kestrel) model parameter space. Focus of the work will be with unstructured, finite-volume solver, KCFD, for near- and off-body predictions and the high-order, finite-volume Cartesian solver, e.g., SAMAIR, for off-body only predictions. However, methods developed will be applicable to other modern CFD solvers (e.g., Kestrel). Wind tunnel data should replicate natural transition dynamics under quiet conditions over the full extent of an Army reference vehicle, including on-body pressure sensor data and off-body wake surveys, for canonical flow conditions (e.g. low enthalpy and zero angle of attack). Reference boundary-layer-attached high-fidelity simulations need to capture the full range of boundary layer dynamics, from the modal transition process to the turbulent breakdown including the intermittency of the transitional region. One of the Phase 1 outcomes will be outline of Phase 2 schedule for implementation of augmented hypersonic transition and turbulence models in Kestrel, developed in coordination with the CREATE^TM-AV team. PHASE II: Phase 2 should involve direct modifications to the on-body and off-body source codes of the Kestrel solvers (or utilization of the external Python-API) executed under close supervision by the CREATE^TM-AV team. Once new functionalities are integrated and tested, re-assessment of Kestrel’s performance on the Phase 1 canonical benchmark cases should be completed to highlight and quantify improvements made. After re- assessment, the new implementation should be tested against larger-scale and more complex hypersonic test cases, which may include non-zero angles of attack and aerothermochemistry effects. PHASE III DUAL USE APPLICATIONS: Collaborate with model, software developers, and users on integration of products into a Long Range Precision Fires application. Optimize toolset to accommodate new advances in the technology delivering high-speed weapons in anti-access/area-denial environments. Transition the technology to an appropriate government agency or prime defense contractor for integration and testing. Integrate and validate the functional aerothermodynamic tools into a real-world development or acquisition program. REFERENCES: 1. T. J. Juliano, S. P. Schneider, S. Aradag, and D. Knight. "Quiet-flow Ludwieg tube for hypersonic transition research"". AIAA Journal, 46(7):1757–1763, July 2008 2. D. R. McDaniel, R.H. Nichols, T. A. Eymann, R.E. Starr and S. A. Morton, "Accuracy and Performance Improvements to Kestrel's Near-Body Flow Solver". AIAA SciTech Forum, p.1051, 2016. 3. J.-B. Chapelier, B. Wasistho and C. Scalo, "A Coherent vorticity preserving eddy-viscosity correction for Large- Eddy Simulation," Journal of Computational Physics, vol. 359, pp. 164--182, 2018. 4. R. H. Nichols, "A Summary of the Turbulence Models in the CREATE-AV Kestrel Flow Solvers," AIAA SciTech Forum, p. 1342, 2019. 5. R.H. Nichols, "Modification of the Turbulence Models in the CREATETM-AV Kestrel Flow Solvers for HIgh-Speed Flows, AIAA SciTech Forum, p. 1174, 2022 6. V. C. Sousa and C. Scalo, "A unified Quasi-Spectral Viscosity (QSV) approach to shock capturing and large-eddy simulation," Journal of Computational Physics, vol. 459, p. 111139, 2022. KEYWORDS: Hypersonics, aerothermodynamics, modeling, design, tools, air vehicles
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