Flow separations often take place in the junction of blades and endwalls and limit seriously the aerodynamic loading increase of turbomachinery, which are caused mainly by mixing of the boundary layers on blades and endwall surfaces and the transverse secondary flow generated by the pressure difference between the pressure and suction side.
Firstly, focusing on a linear diffusion cascade with 42 degrees turning angle, it can be found that the transverse secondary flow can be reduced by inviscid hub and the flow separation is eliminated further through the numerical comparison between the viscous and inviscid hub cases. So the transverse secondary flow is the dominate factor for the flow separation in this cascade. We should try to control the transverse secondary flow to reduce the flow separation.
Secondly, based above analysis, the flow separation can be controlled effectively if we can cut off the secondary flow. So nine kinds of streamwise groove schemes are designed and analyzed. It can be seen that the streamwise grooves at the end wall inhibit obviously the transverse secondary flow but the flow structure change is different at different span. There is an optimum combination of width and height of groove, and the height is more important than width.
Thirdly, the detailed flow analysis of best scheme with smaller width, moderate height are carried out. It can decrease the separation zone scope at the corner zone, reduce the energy loss coefficient and also reduce the flow loss.