Influence of periodic wakes on the unsteady flow near endwalls in full annular axial turbine cascades

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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. Therefor a number of specially planed and adjusted configurations will be investigated and compared with each other.Within the project part at the Chair for Thermal Turbomachinery at Ruhr-Universität Bochum the interaction between near end-wall flow and selected unsteady phenomena should be evaluated by means of detailed experimental investigations in axial full annular axial turbine cascades. Particularly effects, which cannot be reproduced in simplified linear cascades and which are thus limited to full annular cascades are in the focus of attention. Non-uniform pitch across span, curvilinear and rotating end-walls as well as skewed inlet boundary layers are among these. With the aid of time-resolved and optical measurement techniques the impact of the detected mechanisms on transition and separation behavior in the end-wall region is to be clarified to support the urgent validation of involved numerical models. In two consecutive setups the effect of an additionally induced tip clearance vortex on the identified interactions should be analyzed. To separate the opposing effects of pressure-gradient driven tip flow and of the relative-motion of the passage end-wall, measurements will be conducted with fixed as well as rotating passage hub contour. Subsequently the transferability of the results regarding blade tip flow conducted in compressor cascades with the ones from turbine cascades is to be evaluated with the research partners. To simulate the impact of upstream shed blade wakes, a rotor equipped with cylindrical bars creates periodically unsteady stator inflow conditions. The experimental data is complemented by additional (U)RANS simulations.