The current trend towards more compact aeroengines, resulting in smaller blade aspect ratios, leads to higher relevance of secondary flow effects, with an increased influence of endwalls. The study of rotating blade rows is difficult due to the reduced geometrical size combined with the rotating operation of these machines. A commonly used surrogate to rotating rows are&nbsp; linear cascades, where the geometrical configuration is simplified. In this process the effects of rotation and relative motion between blade and endwall do not appear. In order to transfer results from the linear cascade back to the rotating rows, it is necessary to gain insight into the effects of rotation and relative endwall motion on the flow structure in compressor cascades.&nbsp;&nbsp;&nbsp;&nbsp; With this aim, the present work analyses these effects in a rotor stage representative of a high pressure compressor. 
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&nbsp;&nbsp; &nbsp;The analysis is performed&nbsp; on a low speed compressor rotor at engine-relevant Reynolds number&nbsp; and is based on three flow cases simulated with a wall-resolving Large Eddy Simulations approach. The reference case features the true geometry, but without endwall motion nor rotation, the second case includes the relative motion between casing and blade, and the third case accounts for rotation, through the Coriolis force in a frame rotating with the blade.The juxtaposition of the results enables discerning the contribution of each of the effects to the overall flow structure. In the analysis, the third case will be assessed against experimental data of a low speed compressor under the same conditions to validate the numerical simulations. 
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&nbsp;&nbsp; &nbsp;The final paper will provide detailed results on the change of the Tip Leakage Vortex (TLV), the pressure distribution on the blade, the mean flow and turbulence statistics inside the passage, as well as the losses. Some of the essential findings are 
&nbsp;&nbsp; &nbsp;a drastic change in the flow field through&nbsp; the gap caused by the relative motion between endwall and blade, which is the key element in the shift of the TLV away from the endwall. Furthermore, the roll-up process of the TLV near the blade leading edge is markedly different. Without relative motion the roll-up takes place following the blade profile suction side, while on the other hand the roll-up is observed closer to the leading edge. The radial pressure gradient along the blade is also affected by this relative motion, showing a smaller variation in spanwise direction when relative endwall motion is accounted for.&nbsp; Incorporation of rotation, achieved through a Coriolis force term in the momentum equations, reveals a significant effect on the hub boundary layer. The results show a significant change in the secondary flow structure when rotation-related effects are accounted for. By its results, the study highlights the relevance of accounting for them in studies of secondary flows involving linear cascades.

Effects of Rotation on the Flow Structure in a Compressor Cascade

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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