Correlation Between Unsteady Loading and Tip Gap Flow Occurring in a Linear Cascade Produced by Simulated Stator-Rotor Interaction

The response of a compressor rotor blade tip to disturbances simulating unsteady stator rotor interaction in the casing region of a turbomachine such as an axial propulsion pump or axial compressor has been studied. The measurements were performed using 24 microphones embedded in the surfaces of two blades of a linear cascade with tip gap and single sensor-hot wire anemomemetry within the tip gap at a single tip gap (t_g/c = 0.033). The unsteady velocity measurements were made perpendicular to the blade camber line at the same locations at which the microphones were embedded. Relative motion of the blade tips and casing was simulated with a moving endwall. Unsteady periodic inflow from an upstream stator row was modeled using a set of vortex generators attached to, and moving with the endwall. The unsteady pressure was measured at eight tip gaps (t_g/c = 0.00825, 0.0165, 0.022, 0.033, 0.045, 0.057, 0.079, 0.129) along the chord and the span of the blades for a blade chord Reynolds number of 390,000. Upon initial investigations, the pressure fluctuations appear to be almost a linear variation with tip gap up to t_g/c = 0.057. With increasing tip gap past this, the pressure fluctuations begin to decrease. Both the pressure and velocity fluctuations increase significantly near the trailing edge of the cascade blade suggesting that the response involves both viscous and inviscid mechanisms.