Effect of end-walls on the separated flow over a compressor blade at Re=20,000*

The effects of end-walls on the separated  flow over a compressor blade for a  chord based Reynolds number of Re=20,000 is investigated. The span of the blade is three times the chord length. The blade is bounded by end-walls on both ends. The blade is not twisted and is defined entirely by  a NACA 65(1)-412 airfoil cross section. Direct Numerical Simulation is conducted with a discontinuous Galerkin based Navier-Stokes solver. The airfoil is placed under an angle of attack of four degrees with respect to the free-stream condition.  Flow structures are  visualized with the finite-time Lyapunov  (FTLE) and Q-criterion. The FTLE visualizations show a pair of horse-shoe vortices next to the end-wall.  A major vortical structure  originates at the intersection of the airfoil and the end-wall and interacts with the nominally two-dimensional vortex street in the midspan region.  The vortex street arcs and breaks periodically which leads  to a low-frequency oscillation of lift and drag. The arcing further induces a flow  from the end-wall towards mid-span inside the separation region.