Effect of Incoming Vortex on Secondary Flows in Turbine Cascades with Planar and Non-Axisymmetric Endwall

Non-Axisymmetric Endwall Profiling (NAEP) is commonly utilized in turbines to eliminate secondary flows. Nevertheless, most of the NAEP methods consider a single-blade row environment without incorporating the effect of the stage environment. This paper aims to investigate the influence mechanism of the incoming vortex on the endwall secondary flow structures of NAEP in a highly loaded turbine cascade. To model the incoming vortex in a stage environment, this study considers a half-delta wing as the vortex generator at the upstream of the turbine cascade. The NAEP is then carried out for a highly loaded turbine cascade with an in-house numerical optimization design platform subject to no incoming vortex. Numerical simulation is also carried out under the influence of the incoming vortex for the turbine cascades with both planar and non-axisymmetric endwall. This paper furthers investigated the pitchwise effect of the incoming vortex on the near endwall secondary flow. The results indicate that the NAEP effectively improves the endwall secondary flow of the turbine cascade, where the total pressure loss coefficient and the secondary kinetic energy (SKE) are reduced by 7.3%, and 45.7%, respectively. It is further seen that with the incoming vortex, the NAEP achieves a considerable control effect on the endwall secondary flow of the turbine cascade. With incoming vortex, the NAEP can still achieve considerable control effect on the endwall secondary flow of the turbine cascade; the averaged reductions of loss coefficient and SKE are 7.8% and 14.2%, respectively. Under some pitchwise locations, incoming vortex can suppress the convection of cross-passage flow toward the suction corner greatly and reduce the loss coefficient of the baseline cascade. The incoming vortex at 4/7 pitch impinged right at the blade leading edge, leading to the generation of low-momentum fluid, which increased the size and the strength of the horseshoe vortex. Under all the pitchwise locations, NAEP can suppress the secondary vortices, e.g., the passage vortex and the counter vortex, considerably.