Unsteady side wall flows and heat transfer in a linear turbine cascade

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Current efforts in turbomachinery to increase pressure ratio, reduce blade count, decrease the aspect ratio, intense part load operation, etc. lead to increasing influence of flows near the side walls on the overall engine performance. Especially the operating range, losses and heat transfer are influenced by these flows. The occurring mechanisms are not fully understood although being investigated since decades. Thus the current technological progress strongly requests adequate basic research activity. This deficit will be addressed by a joint research program of four research groups at TU Dresden, UniBw München und RU Bochum, by carefully coordinated simulations and experiments to produce relevant results. Beside the investigation of heat transfer and the development of methodical tools a major goal of this joint program is the detailed analysis of the effect of system rotation. Therefore a number of specially planed and adjusted configurations will be investigated and compared with each other.Within the framework of the project part (TV3) at the Institute of Jet Propulsion of the University of the Federal Armed Forces Munich, the endwall flow and heat transfer will be analyzed in a low pressure turbine cascade. The array of investigated aspects of the unsteady endwall flow include the endwall boundary layer, the formation of the horse shoe vortex, influence on suction surface transition near the endwall, loss production in the endwall region, as well as heat transfer to the endwall and blade surfaces and its effect on potential cooling methods. A new and improved setup, featuring an additional inserted endwall, will be implemented in the High Speed Cascade Wind Tunnel in order to produce more realistic endwall flow, which is a critical factor in attaining significant results. The experiments will be conducted utilizing a multitude of flow measurement methods with high spatial resolution (PIV), high time resolution (CTA, Kulite), as well as surface measurements (TSP, Thermo-LC, Shear-LC). The experimental investigations will be supported by numerical simulations (URANS) with high fidelity heat flux modeling, using the flow solver TRACE. The scientific goal of the research project part is to improve the understanding of the interaction mechanisms of the periodically unsteady inflow with the endwall flow, the endwall boundary layer and heat transfer as well as to evaluate the capabilities of the RANS method to predict these flow phenomena. Furthermore, comparisons of the investigation results with the project partners (especially TV4) provide information regarding the similarities and differences of flow phenomena in linear cascades and axial turbines.