Investigation of the dihedral angle effect on the boundary layer development using special-shaped expansion pipes

The corners between the blades and end walls are common geometric structures in turbomachinery, where boundary layers on the blade and end wall surface interact with each other. This boundary layer interaction enlarges the region of low momentum fluid which leads to the boundary layers grow thicker at the corner region. Then the corner separation is likely to occur, and even worse by the adverse pressure gradient along the streamwise as well as secondary flows along the pitchwise. The key issue to design the geometric structures of the corner region is to control the dihedral angle between the blade and end wall surface. However, from the current published literature, few researchers have studied the influence of dihedral angle on the flow structures at the corner region in detail. In this paper, a series of expansion pipes with different cross sections which represent different dihedral angles are simulated. Then, some useful conclusions about how the dihedral angle affects the flow structures at the corner region are drawn. Moreover, a new method to predict the boundary layer thickness at the corner region is introduced, and the predicted results are in good agreement with simulation results.