Wake of a Compressor Cascade with Tip Gap, Part 2: Effects of Endwall Motion

Abstract

The effects of relative motion between the blade tips and endwall on the flow downstream of a linear compressor cascade have been studied. Endwall motion was simulated by using a 0.25-mm-thick Mylar belt propelled ove ra sliding surface beneath the tips of the cascade blades. Three-component mean-velocity and turbulence measurements made in cross sections downstream of the cascade reveal that the wall motion flattens and shears the turbulence and mean-velocity distributions of the vortex. Mean-helicity density plots also show that endwall motion smears the vortex center from a single point (when seen in cross section) into a ribbon that makes an angle of some 30 deg with the endwall. Despite these effects, many critical features of the vortex are almost unaffected by the endwall motion. The vortex produces almost the same magnitude of streamwise mean-velocity deficit, and this deficit still dominates both the mean velocity field and the production of turbulence. Thus, although endwall motion distorts and displaces the leakage vortex it does not fundamentally alter the mechanisms that govern the development of its mean flow and turbulence structure.