Non-Dissipative LES Design Tool for Turbulent Combustion and Acoustics Analysis of Gas Turbine Combustors

Combustion Large Eddy Simulation (LES) is a very promising approach for resolving acoustics in turbulent-reacting flows. CFD Research Corporation (CFDRC) has successfully developed and validated state-of-the-art Combustion LES software (CFD-ACE+) to analyze gas turbine acoustics, using unstructured grids with second-order temporal and spatial differencing. Still, unstructured LES has not yet matured to a practical design tool with an affordable turnaround time because very small time-steps and cell-sizes are needed to accurately resolve the small-scale acoustics physics. If the time-step or cell-size is increased in an attempt to reduce the run time, the code becomes too dissipative. Typical run times with CFD-ACE+ for accurate acoustic analysis are 40-50 days for 2M cells on 16 PCs. To make the code less dissipative, CFDRC proposes to develop a fourth-order accurate solver for unstructured grids. To our knowledge, a fourth-order solver has never been successfully developed for unstructured meshes. In Phase I, a fourth-order time-integration scheme and a fourth-order pressure interpolation will be implemented in CFD-ACE+. Significant reduction in run-time (~ 5-10 times) and numerical dissipation will be demonstrated. To further increase the accuracy and decrease run time, fourth-order spatial discretization and dynamic grid adaptation will be implemented in Phase II. At the end of Phase II, accurate combustion LES run times on 16 PCs will be 1-2 days. The software will be thoroughly validated and delivered to the Air Force.