Measurement of Heat Flux in Reacting Flow in a Backward-Facing Step Combustor

Heat flux to the combustor liner in gas turbine engines is increasing as core sizes shrink and flame temperatures increase. In addition to the presence of a flame, gas turbine combustors have a wide range of flow features including recirculation, shear layer separation and impingement, and boundary-layer recovery. These all impact the heat transfer to the wall, making modeling and prediction through these different flow features challenging. The current work seeks to quantify total and radiative heat transfer from a flame to the wall in a backward-facing step combustor over a range of operating conditions. Backward-facing step combustors have been used in combustion studies due to the combustor-relevant flow features in a relatively simple two-dimensional geometry. In this study, a heat flux sensor and a radiometer are mounted in the combustor floor to measure total and radiative heat flux, respectively. The Reynolds number and plate temperature were varied and heat flux measurements were conducted through the different combustor zones: recirculation, shear layer impingement, and recovery. High-speed CH* chemiluminescence images were also collected for evaluation of the flame heat release. Radiative and total heat flux increased downstream of the impingement zone, and the temperature of the bottom plate and limited impact on the measured heat flux. Chemiluminescence data showed little impact of Reynolds number and plate temperature on the time-averaged flame shape and proper orthogonal decomposition highlighted the vortical structures shedding from the combustor step.