Investigation of endwall effect on transitional flow inside compressor cascade passage at low Reynolds number

Abstract

Laminar-to-turbulent transitional flow plays a key role in determining the overall aerodynamic performance of turbomachinery. In this paper, the physical mechanisms concerning transitional flow inside compressor cascade passages at low Reynolds number condition are investigated based on the large eddy simulations. Two categories of cascade flow simulations are conducted: one is for the quasi three-dimensional (3D) cascade flow without endwalls, i.e., the translational periodic boundary conditions are employed for hub and shroud surfaces, while the other focuses on the fully 3D cascade passage flow. Special emphasis is placed on the effect of endwalls on the laminar-to-turbulent transitional flow inside the compressor cascade passage. In addition, two levels of freestream turbulent intensity are set in these simulations. It is concluded that the endwall boundary layer flow has a non-ignorable influence on transitional flows in the lower-span region. Under the condition of low freestream turbulence intensity, the original laminar separation-induced transition pattern dominating the mid-span suction surface evolves to become natural and bypass transition flow when approaching the endwall region. With increase in the incoming turbulent intensity, the natural transitional flow disappears, and the cascade suction surface is dominated by the bypass transitional flow. Moreover, the blade loading near endwall is reduced and the aerodynamic loss on lower spanwise airfoil sections is substantially increased when compared to the cascade without endwall. The physical mechanisms concerning transitional flow described in this paper might provide some meaningful guidance toward developing advanced turbomachinery.