OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Computing and Software OBJECTIVE: Develop an innovative hybrid hardware/software system, based on Lattice-Boltzmann aerodynamic modeling techniques, capable of accurately modeling interactional aerodynamic effects on rotary-wing vehicles in the shipboard environment that is suitable for real-time, blade element-based rotary-wing aircraft flight simulations of urban and shipboard launch and recovery operations. DESCRIPTION: Rotorcraft operations near obstacles (e.g., buildings, revetments, and ships) are characterized by complex aerodynamic interactions between the flow field created by the passage of air over the obstacle (airwake) and the flow field created by the air vehicle (rotor wake). Typically, real-time piloted simulations use simplified aerodynamic models in order to meet real-time execution requirements. The effects of obstacle proximity and unsteady, non-uniform wind flow (airwake) are accounted for using separate, precomputed models that are superimposed on the rotor inflow model. While this approach works well in many situations, important interactional aerodynamic effects that occur when a rotorcraft is operating in close proximity to obstacles are neglected. This compromise in fidelity is a barrier to using modeling and simulation for launch and recovery envelope development or for pilot shipboard certification. Coupled rotor/obstacle aerodynamics can significantly affect handling qualities; therefore, modeling these effects accurately is essential for predictive ship launch and recovery, and urban environment flight simulations. Interactional aerodynamics can be modeled using high fidelity Navier-Stokes (N-S) computational fluid dynamics (CFD) methods; however, the computations are significantly slower than real time. Lattice-Boltzmann CFD methods (LBM CFD) offer the possibility of calculating the evolving flow field in the loop with the piloted simulation because the equations set is reduced (as compared to N-S), and the algorithms are highly scalable on GPU computer hardware. This STTR topic seeks to leverage ongoing research related to modeling-coupled aircraft/ship environments with LBM CFD methods to develop and demonstrate an aerodynamic coupling compute on the fly flight simulator. A combined hardware/software LBM CFD capability that captures average and standard deviation of rotor thrust to within 90% of N-S CFD and executes at speeds sufficient to model the evolving physics in a real-time piloted simulation environment is sought. The final system must be demonstrated in the Manned Flight Simulator environment at NAVAIR, NAS Patuxent River, Maryland. PHASE I: Demonstrate accuracy of helicopter rotor thrust prediction for in-ground-effect hover ladder and for stationary hover behind a ship or ship-like structure for no-wind and with-wind conditions by comparing to GFE data. If the model does not execute fast enough to meet real-time simulation requirements, determine technical feasibility and develop a plan to achieve execution speed requirements. Demonstrate execution of LBM CFD integrated into a flight simulation environment for an (auto) piloted rotary-wing vehicle attempting to hold a hover in the wake of a bluff body obstacle. Create a plan to develop and demonstrate a deployable module. The Phase I effort will include prototype plans to be developed under Phase II. PHASE II: Extend the Phase I approach to model shipboard launch and recovery operations for a single-main-rotor and a multiple-main-rotor aircraft as specified by the Navy Technical Point of Contact (TPOC). Demonstrate desktop (auto-piloted) simulations using contractor or university hardware. Develop and implement an approach to interface with the Controls Analysis and Simulation Test Loop Environment (CASTLE) operating environment. Implement the software and models in the NAS Patuxent River Manned Flight Simulator (MFS) CASTLE environment on a GFI GPU cluster at the MFS. Demonstrate integration of hardware/software system in real-time flight simulation for at least one Navy relevant ship/aircraft combination. Accuracy of the results will be judged through comparisons with GFI experimental and/or high-fidelity, fully coupled, Navier-Stokes CFD simulations. The ship configuration, the aircraft model, and CASTLE will be provided GFI. PHASE III DUAL USE APPLICATIONS: Enable application for future Navy ship and aircraft configurations by developing methods to expedite new aircraft and ship model development and implementation. Determine and document best practices required to assure accuracy requirements are achieved for new aircraft and ship models. Developments from this STTR topic are marketable to both commercial and private sectors to improve fidelity of helicopter flight simulators for shipboard, urban environments, and mountainous terrain. REFERENCES: 1. Syms, G. F. Simulation of simplified-frigate airwakes using a Lattice-Boltzmann method. Journal of Wind Engineering and Industrial Aerodynamics, 96(6-7), 2008, pp. 1197-1206. https://www.researchgate.net/profile/S-Shukla-3/post/Why-cant-the-lattice-Boltzmann-method-be-used-in-high-Reynolds-number-simulation/attachment/59d6256ac49f478072e9a449/AS%3A272164027076609%401441900368541/download/2007-Simulation+of+simplified-frigate+airwakes+usinga+lattice-Boltzmann+method.zip 2. Ashok, S. G. and Rauleder, J. NATO generic destroyer moving-ship airwake validation and rotor ship dynamic interface computations using immersed boundary Lattice Boltzmann method. Proceedings of the 79th Vertical Flight Society Forum, West Palm Beach, FL. May 2023. https://scholar.google.com/scholar?hl=en&as_sdt=0%2C14&q=NATO+Generic+Destroyer+Moving-Ship+Airwake+Validation+and+Rotor%E2%80%93Ship+Dynamic+Interface+Computations+using+Immersed+Boundary+Lattice%E2%80%93Boltzmann+Method&btnG= 3. Ashok, S. G. and Rauleder, J. Towards real-time coupled ship rotorcraft interactional simulations using GPU-accelerated Lattice-Boltzmann method. Proceedings of the 80th Vertical Flight Society Forum, Montr al, Canada, May 2024. https://scholar.google.com/scholar?hl=en&as_sdt=0%2C14&q=Towards+Real-Time+Coupled+Ship%E2%80%93Rotorcraft+Interactional+Simulations+using+GPU-Accelerated+Lattice-Boltzmann+Method&btnG= 4. Forrest, J. S. and Owen, I. An investigation of ship airwakes using detached-eddy simulation. Computers & Fluids, 39(4), 2010, pp. 656-673. https://www.academia.edu/download/39854358/An_investigation_of_ship_airwakes_using_20151109-9413-136wwwl.pdf 5. Yuan, W., Wall, A. and Lee, R. Combined numerical and experimental simulations of unsteady ship airwakes. Computers & fluids, 172, 2018, pp. 29-53. https://doi.org/10.1016/j.compfluid.2018.06.006 6. Polsky, S. A.; Wilkinson, C.; Nichols, J.; Ayers, D.; Mercado-Perez, J. and Davis, T. S. Development and application of the SAFEDI tool for virtual dynamic interface ship airwake analysis. 54th AIAA Aerospace Sciences Meeting, 1771, 2016. https://www.cobaltcfd.com/pdfs/2016/AIAA_2016_1771.pdf 7. Forsythe, J. R.; Lynch, E.; Polsky, S. and Spalart, P. Coupled flight simulator and CFD calculations of ship airwake using kestrel. 53rd AIAA Aerospace Sciences Meeting, 0556, 2015. https://arc.aiaa.org/doi/pdf/10.2514/6.2015-0556 8. Nichols, J.; Magyar, T. and Schug, E. The platform-independent aircraft simulation environment at manned flight simulator. AIAA Modeling and Simulation Technologies Conference and Exhibit, 4179, 1998. https://doi.org/10.2514/6.1998-4179 KEYWORDS: Lattice-Boltzmann Methods; LBM; Rotorcraft; Shipboard; Computational Fluid Dynamics; CFD; Flight Simulation; Coupled Aerodynamics; Real-Time; Dynamic Interface; DI; Launch and Recovery Envelopes; LRE
