Investigation of the Unsteady Aerodynamics of an Annular Combustor Using PIV and LES

Abstract

Experimental measurements have been carried out which have been used for specifying both boundary conditions of CFD predictions and for validation of the results. Combustor aerodynamics were therefore investigated in the same geometry, using LDA, PIV and LES. Three different LES simulations were performed in order to assess the flow field sensitivity to different boundary conditions. In the first run steady state boundary conditions are specified; in the second run, unsteady conditions at the injector exit and steady conditions in the annuli entry are specified; and in the third run unsteady boundary conditions at both injector exit and annuli entry are specified. A standard RANS simulation is also performed for comparison. The different simulations gave considerably different results. LES results with white noise scaled to give correct inlet turbulence intensities agree reasonably well with experimental data. With steady inflow conditions incorrect prediction of combustor aerodynamics resulted. Introduction of unsteady inflow conditions at the fuel injector exit plane were shown to have a significant effect on the flow interaction between the injector and the primary ports. LES is thus shown to be a good predictive tool for unsteady combustor flow fields. It is still questioned what level of fidelity is required in representing the inlet conditions to best use the predictive ability of LES. It offers significant improvement over standard RANS techniques but LES is more costly and requires detailed experimental data, used carefully, to correctly specify the inflow conditions.