GPU Acceleration of an Adjoint Enabled Real Gas Hypersonic Flow Solver

The objective of this Phase 1 proposal is the Graphical-Processing-Unit (GPU) acceleration of a two-dimensional, unstructured, viscous Navier-Stokes (NS) solver for aerothermodynamic applications. The subject code employs a multi-species two-temperature chemically reacting real gas model and incorporates the exact discrete tangent and adjoint systems for the real-gas system, which has been used for uncertainty quantification in past work. Our approach is based on a hybrid OpenACC-CUDA strategy, which seeks to extract maximum performance while minimizing code re-writing with an eye towards code maintainability and portability. In the Phase 1 project, the entire 2D code will be ported to V100 or A100 GPUs using OpenACC directives. This will be followed with the development of specific optimized CUDA implementations for the most critical components of the code. In particular, we will investigate CUDA implementations of the implicit line solver, the chemical source term, and a representative real-gas adjoint kernel from the 2D code. The effect of the number of species and reactions, and solver block sizes will be investigated in these component CUDA implementations. Phase 1 will also investigate alternate solver approaches with reduced memory requirements for their suitability for use on GPUs. The CUDA optimized kernels will in turn be used to further optimize corresponding portions of the simpler OpenACC implementation in order to investigate the potential for performant implementations with minimal code disruption. In Phase 2, the most promising component implementations and solution techniques will be extended to three dimensions and incorporated into a fully functional three-dimensional multi-species aerothermodynamics CFD solver optimized for GPU architectures.

There is a strong requirement within NASA for more accurate and efficient predictive numerical simulation tools for entry, descent and landing (EDL), particularly in view of the difficulties in testing at the extreme conditions and harsh environments associated with spacecraft re-entry. Efficient use of GPU architectures offers the possibility of lower cost simulations at higher resolution, using more complex and realistic physical gas models, and incorporating other effects such as ablation.

The development of a GPU accelerated aerothermodynamic simulation capability which lowers the cost and inreases the accuracy of hypersonic flow simulations will open new markets for commercial CFD in high speed flows. GPU implementation of chemically reacting gas species will also have application in combustion problems with the potential to open new markets in the aerospace propulsion industry.

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