Non-axisymmetric endwall profiling in a highly loaded compressor cascade

Abstract

Very few studies of non-axisymmetric endwall profiling in compressor have been conducted in published literatures. This study investigates the control mechanism of non-axisymmetric endwall on the flow field of a highly loaded compressor cascade and the guidelines for the design of non-axisymmetric endwall. First, CFD method was validated with existing experimental data. Then, the design method of non-axisymmetric endwall based on trigonometric function and Bezier curve was introduced. The design strategies of non-axisymmetric endwall considering axial position effect, height effect and different patterns of concave/convex were investigated in detail. Results show that non-axisymmetric endwall is an effective way to control the near endwall flow field of the compressor cascade. With the optimal non-axisymmetric endwall in this study, the loss coefficient of the cascade is reduced by 5.5%, and the cascade exhibited suppressed corner separation, reduced passage vortex and more uniformly distributed outflow angles. The optimal axial position of the concave was at 0.22 axial chord, which was near the onset of corner separation, so the best control effect was obtained. There is an optimal height for the concave of the non-axisymmetric endwall. A lower concave will not have sufficient effect on the cascade, whereas a higher concave will be detrimental on the contrary. It is indicated that the influence mechanism of non-axisymmetric endwall on the compressor cascade is basically derived from the superimposed effect of reduced cross-passage pressure gradient and increased spanwise inward pressure gradient. The cross-passage pressure gradient can be reduced by both concave on the suction side and convex on the pressure side of the endwall. However, concave can introduce spanwise inward pressure gradient, whilst convex can introduce spanwise outward pressure gradient. For better improving the performance of compressor cascades, non-axisymmetric endwall is suggested to be a concave on the entire endwall, which introduces both reduced cross-passage pressure gradient and increased spanwise inward pressure gradient.