Swirling turbulent flows in a combustion chamber with and without heat release

Abstract

This paper presents experiments and numerical simulations of swirling turbulent flows with and without combustion in a laboratory gas turbine combustor. Three approaches, particle image velocimetry (PIV), laser Doppler velocimetry (LDV) and large eddy simulation (LES) are employed to minimize the uncertainties of the results. The aim is to characterize the main flow structures and turbulence in a combustor that is relevant to gas turbines. Isothermal flows with different outlet geometry and lean premixed preheated natural gas/air flames with equivalence ratio of 0.47 are considered to demonstrate the effect of heat release and combustor geometry on the flows. At the combustor inlet the swirl numbers are about 1.4 and the Reynolds numbers are about 20,000 for all cases. The PIV, LDV and LES show consistent agreement on the mean flow field, whereas for the velocity variances the results from LDV and LES agree each other but the PIV data show considerably lower turbulence level. The mean flow field is characterized by three large-scale recirculation zones resulted from sudden expansion of the combustor geometry and vortex breakdown due to inflow swirl. Combustor outlet geometry exhibits great impact on the vortex breakdown structure. Heat release enhances the production of turbulence near the axis of the combustor, but it does not alter the fundamental vortex breakdown structure. A mechanistic explanation of the underlying flow physics is presented to describe the effect of swirl, heat release and outlet contraction on the flow field.