Coherent Structures in Trailing-Edge Cooling and the Challenge for Turbulent Heat Transfer Modelling

In the present paper, we test the capability of a standard Reynolds-Averaged Navier-Stokes (RANS) turbulence model to predict the turbulent heat transfer in a generic trailing-edge situation with a cutback on the pressure side of the blade. The model investigated uses a gradient-diffusion assumption with a scalar turbulent-diffusivity and constant turbulent Prandtl number. High-fidelity Large-Eddy Simulations (LES) were performed for three blowing ratios to provide reliable reference data. Reasonably good agreement between the LES and recent experiments was achieved for mean flow and turbulence statistics. For increasing blowing ratio, the LES replicated an also experimentally observed counter-intuitive decrease of the cooling effectiveness. In contrast, the model failed in predicting this behavior and yielded significant overpredictions. It is shown that the model cannot predict the strong upstream and wall-directed turbulent heat fluxes, which were found to cause the counter-intuitive decrease of the cooling effectiveness.Copyright © 2012 by ASME