Rotor/Stator Unsteady Pressure Interaction

Abstract

This paper describes an investigation of rotor/stator interaction in centrifugal pumps with radial diffusers. Steady and unsteady diffuser vane pressure measurements were made for two impellers, one half of the double suction pump of the High Pressure Oxygen Turbopump (HPOTP) of the Space Shuttle Main Engine (SSME) and a two-dimensional impeller. Unsteady impeller blade pressure measurements were made for a second two-dimensional impeller with blade number and geometry identical to the two-dimensional impeller used for the diffuser vane pressure measurements. The experiments were conducted with different flow coefficients and different radial gaps between the blade trailing edge and the diffuser vane leading edge (5% and 8% of the impeller discharge radius for the two-dimensional impellers, and 1.5% and 4.5% for the impeller of the HPOTP). The largest pressure fluctuations on the diffuser vanes and the impeller blades were found to be of the same order of magnitude as the total pressure rise across the pump. On the diffuser vanes, the largest pressure fluctuations were observed on the suction side of the vane near the leading edge, whereas on the impeller blades the largest fluctuations occurred at the blade trailing edge. The resulting lift on the diffuser vane was computed from the pressure measurements; the magnitude of the fluctuating lift was found to be larger than the steady lift.