Upstream wake-secondary flow interactions in the endwall region of high-loaded turbines

A detailed experimental and numerical investigation of the unsteady interaction of secondary flow vortices in turbine endwall region was performed with the effect of upstream periodic wakes. The flow field was investigated respectively in a linear turbine cascade and a turbine rotor. The study revealed the physical mechanisms of unsteady interaction between upstream wake and secondary vortices. The influence of the upstream wake on the performance of turbine endwall region was also discussed.The flow field at the exit of the turbine blade row showed a decrease in passage vortex strength and loss due to the upstream wake transport. Two interaction mechanisms are proposed whereby passage vortex loss decreases. They are the upstream wake-pressure side leg of the horseshoe vortex interaction and the upstream wake-passage vortex interaction. The transport of upstream wake can suppress the development of pressure side leg of the horseshoe vortex and passage vortex because of the " negative jet" influence of the wake.