Date of Completion
SIMD, SIMT, chemical kinetics, reactive-flow, analytical Jacobian
Field of Study
Doctor of Philosophy
This work details efforts to reduce the cost of using detailed chemical kinetic modeling in realistic reactive-flow simulations, utilizing analytical Jacobian evaluation and vectorized-computing on the central processing unit (CPU), graphics processing unit (GPU) and other hardware-accelerators.
The first part of this thesis investigated GPU-based ordinary differential equation (ODE) methods for stiff chemical kinetics. A fifth-order implicit Runge--Kutta method and two fourth-order exponential integration methods were implemented for the GPU and paired with the analytical chemical kinetic Jacobian software pyJac. The performance of each algorithm was compared with a commonly used CPU-based implicit integrator CVODEs. The implicit Runge--Kutta method running on a single Tesla C2075 GPU was equivalent to CVODEs running on 12-38 CPU cores for integration of hydrogen and methane kinetic models using a smaller global integration time-step, however the performance of the GPU-solver degraded at a larger time-steps due to thread divergence and higher memory traffic.
The second part of this work investigated the performance of vectorized evaluation of constant-pressure/volume thermochemical source-term and sparse/dense chemical kinetic Jacobians using single-instruction, multiple-data (SIMD) and single-instruction, multiple thread (SIMT) paradigms; the developed codes were additionally incorporated into pyJac. A new formulation of the chemical kinetic governing equations was derived and verified, resulting in greatly increased Jacobian sparsities. Significant speedups were found for shallow-vectorized OpenCL source-rate evaluation as compared with a parallel OpenMP code, increasing for sparse and dense chemical kinetic Jacobian evaluation. Further, the developed work was shown to be orders of magnitude faster than a simple first-order finite-difference Jacobian approach.
Finally, several CPU-vectorized linearly-implicit Rosenbrock solvers were adapted for use with pyJac, and validated against CVODEs. The open-source computational fluid dynamics code OpenFOAM was extended to utilize the vectorized solvers, and the eddy dissipation concept combustion model was adapted for their use. The OpenFOAM-coupled vectorized solver was validated over a range of zero-dimensional homogeneous ignition problem against Cantera, before its performance and precision were compared to built-in OpenFOAM solvers for a case modeling the Sandia Flame D; a speedup of 12-15x was found for the vectorized solver.
Curtis, Nicholas, "Accelerating Reactive-Flow Simulations via Vectorized Chemical Kinetic Evaluation" (2019). Doctoral Dissertations. 2044.