Development of a Modified RANS-Model for the Computational Investigation of Cooling and Heat Transfer on an Endwall

he thermal load on the endwalls of the hot gas path of gas turbines, in particular those of the nozzle guide vanes (NGV), has increased considerably over the last decades. Therefore, cooling concepts have been the focus of R&D efforts for some time. Dedicated cooling, i.e., film-cooling holes in the most thermally highly-loaded areas, can be applied. This requires both additional cooling air and costly mechanical efforts. When using purge air, neither of these two disadvantages comes into play. For this reason, cooling the endwalls with purge air is very attractive. In order to establish and evaluate this cooling concept, dedicated tests are normally performed. Both the required time and financial resources preclude testing every possible geometry. Hence CFD is used. The thermal load consists of both the film-cooling effectiveness and the heat transfer on the endwall. Combined, these yield the Net Heat Flux Ratio (NFHR). In an industrial environment, RANS solvers are used to carry out CFD-analyses. These have difficulties in modelling shear stresses and turbulence and thus an existing k--SST-model was modified. The model was developed based on film-cooling experiments and validated on experiments of endwall cooling in a linear cascade. In this paper, these experiments, the CFD-model and its validation will be presented and discussed in detail.