Conjugate Heat Transfer Predictions of a Combustor Heatshield Containing Pedestals

This paper reports an investigation into the use of CFD methods for modelling the combined fluid flow and heat transfer in a generic combustor heatshield geometry typical of current aeroengine designs. The study describes the development and testing of a conjugate heat transfer methodology, to allow the CFD code to predict the heat exchange in both fluid and solid regions of the solution domain simultaneously; special attention is given to continuity of heat flux at the fluid/solid interface. The heatshield cooling air is supplied via rows of jets that flow through holes in the backplate and impinge on the heatshield backside. An interesting phenomenon associated with these jets is investigated. It is noticed that under some conditions of heatshield flow, jet impingement leads to the model predicting a minimum in heat transfer coefficient, rather than a maximum, at the impingement point. It is shown, by predicting the measured Nusselt number distribution in a single impinging jet experiment, that this is a correct simulation, associated with the combined effects of low impingement height and low turbulence levels in the jet cores. The presence of pedestals on the impingement surface removes this effect by creating extra turbulence and enhancing conductive paths for heat transfer. A model for including the pedestals in both flow and heat exchange processes as a sub-grid-scale model in the CFD simulation is described. An illustrative calculation of the performance of the overall model for a realistic heatshield geometry is provided, indicating the predicted spatial variation of temperature on heatshield surfaces.