The effect of the wake on the separated boundary layer in a two-stage compressor

Abstract

This experimental study provides striking examples of the separated boundary layer development resulting from blade-wake interaction in a multistage turbomachine. Particle image velocimetry measurements are performed within the second-stage rotors of a two-stage compressor. Phase-lock results confirm that wake impingement greatly changes the passage flow, as well as affecting the boundary layer flow. The high turbulence level and the negative jet behavior of the wake dominate the interaction between the unsteady wake and the separated boundary layer on the suction surface. By correlating the flow state of the boundary layer with the spatial position of the wake, the influence of the wake on the blade boundary layer flow is revealed, and the mechanism restraining boundary layer separation on the suction surface is studied. It is found that the wake itself does not inhibit separation, and instead, the boundary layer of the region swept by the wake is thickened and separation is strengthened. However, the wake impingement produces a turbulent spot, and the calmed region behind this spot inhibits separation, as well as making the boundary layer thinner. As a consequence, the periodic sweeping of the wake makes the boundary layer exhibit a clear periodicity.