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.