Flame Heat Transfer Measurements and Simulations in a Backward-Facing Step Combustor

The goal of this study is to measure and simulate both convective and radiative heat transfer in a backward-facing step combustor, which incorporates relevant flow features found in gas turbine combustors. A heat flux sensor and a radiometer are employed to measure total and radiative heat flux, respectively. High-speed CH* chemiluminescence images are taken to measure time-averaged flame shape. The heat flux is lowest in the recirculation region and increases as a function of downstream distance. Heat flux is most sensitive to the Reynolds number in the flame impingement zone and relatively insensitive to wall temperatures. Complementary large-eddy simulations of the combustor are conducted using a 16-species skeletal mechanism and the thickened-flame model. The flame shape agrees well with what is indicated by the chemiluminescence images. A Monte Carlo ray tracing solver with a line-by-line spectral database is employed to obtain spectral and directional statistics of radiation at the radiometer locations. Convective and radiative heat flux in the experiment are then separated using correction factors from the simulations. Convective and radiative fluxes agree reasonably well between simulation and experiment. Both show that convection is the dominant mode of heat transfer, although radiation is quite comparable to convection both locally and globally.