Assessing the wall effects of backwards-facing step flow in tightly-coupled experiments and simulations

Backward facing steps are found in a range of engineering applications, including com-bustors, which is the main focus of the current work. Backwards facing steps promote shear generation and recirculation, as the boundary layer that develops ahead of the step separates and flow reverses behind the step. At the end of the recirculation zone, the shear layer impinges on the bottom wall of the step and the flow recovers, forming a new boundary layer downstream. When a flame is present in this configuration, it stabilizes in the shear layer, impinging on the wall downstream of the step. This flame configuration results in complex convective and radiative heat transfer to the wall. In this study, we begin investigations of these different heat transfer mechanism to the wall downstream of the backwards facing step using both experiments and large eddy simulations. In order to promote accurate comparisons between the experiments and simulation, we have first considered the spanwise variation of the velocity fields in the experiment. The experiment was designed such that the wall effects should be minimal along the centerline of the experiment, and large eddy simulations of the non-reacting flow show this is the case. Direct comparisons between these simulation results and preliminary velocity measurements from a particle image velocimetry technique show reasonably good agreement.