Near-Wall Flow in Turbomachinery Blade Rows

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In the current project , the near-wall flow in turbine and compressor cascades is being investigated fundamentally. The work on turbine cascades has reached a natural end, but based on the results achieved, a number of research questions on flow in compressors have been raised which shall be answered in a two-year continuation phase to clarify important application-relevant aspects of the near-wall flow. While in the current phase the focus was on the single stage, especially the transferability of results for near-wall flow from linear cascades to rotating cascades, and only cylinder wakes were used as a model, this will now be extended to more complex near-wall rotor-stator interaction (RSI). To this end, in the continuation phase the transition to realistic inflow conditions of a real, multi-stage compressor will be accomplished. On one hand, this is done by experimental investigations with a streamlined, non-deflecting wake generator and a downstream rotor as well as considering the third stage of the four-stage low-speed axial compressor. On the other hand, high-resolution Large Eddy Simulations (LES) will be carried out, in which modularly designed inlet conditions specially designed for these configurations allow the effects to be clearly identified. The methodically closely coordinated procedure allows to clarify the role of the individual flow components in the inflow on near-wall flow, secondary flows and loss development in the rotor. A contribution to this is also made by the detailed analysis of the turbulence structure in the flow near the side wall under the influence of RSI. This is achieved by the combined use of wall-resolved LES and an innovative measuring technique, the laser Doppler profile sensor. The third topic is concerned with the transferability of the results obtained so far to off-design conditions, where it is to be expected that the RSI near the wall changes significantly with higher aerodynamic load. Current results also show ist influence on the triggering of rotating stall, i.e. the limitation of the operating range. Here, among other issues, the influence of the radial gap width is to be investigated, especially for large gaps. The work planned for the continuation phase will provide a detailed analysis of the flow near the wall under the influence of RSI and generate an improved physical understanding of fundamental issues, with the long-term vision of achieving a reduction of losses, increase of the efficiency and extension of the stable operating range.