NUMERICAL INVESTIGATION OF HEAT TRANSFER AND COOLING EFFECTIVENESS WITHIN A LPT-VANE CASCADE AND ITS COMPARISON TO EXPERIMENTAL RESULTS

Gaps between stationary and rotating parts in turbines have to be fed with cooling air to keep metal temperatures below material limits. Reducing the coolant mass flow and analysing its impact on the flow field concerning aerodynamic and thermal data were the objectives of experiments, performed within the European research project AITEB. As part of this project, measurements of cooling effectiveness and heat transfer on the endwall of a low pressure turbine nozzle guide vane were performed at a low speed cascade wind tunnel at DLR Gottingen. Higher cooling mass flow rates increase secondary flows and subsequently heat transfer whilst metal temperatures are reduced due to larger coverage with coolant. It was also shown that heat transfer varies significantly with different flow angles. According to the experimentally investigated flow fields numerical studies were performed using the DLR code TRACE, a RANS-Solver for turbomachinery flows. TRACE simulations were done using the Wilcox k-ω turbulence modelling. The boundary conditions were taken from the experimental setup. In this paper the numerical data was analysed and compared with the experimental results regarding thermodynamics. The simulations confirmed a high influence of the flow angle. Within the flow regime affected by the injected coolant a good agreement between the numerical heat transfer results and the experimental data was observed. The qualitative and quantitative values were met after finding the optimum calculation parameters. Only in the region downstream of the throat area a different behaviour became obvious. Concerning film-cooling effectiveness quantitative differences between simulation and experiment were found whilst qualitative good agreement was observed.