| The interaction between impeller blades and diffuser vanes in diffuser pumps was investigated. Steady and unsteady pressure measurements were made on the diffuser vanes and on the front shroud wall of a vaned and a vaneless diffuser. Two different impellers were used, one half of the impeller of the double suction pump of the HPOTP (High Pressure Oxygen Turbopump) of the SSME (Space Shuttle Main Engine), and a two-dimensional impeller. The measurements were made for different flow coefficients, shaft speeds, and radial gaps between the impeller blades and the diffuser vanes (1.5% and 4.5% of the impeller discharge radius for the impeller of the HPOTP, and 5% and 8% for the two-dimensional impeller). The vane pressure fluctuations were larger on the vane suction than on the vane pressure side attaining their maximum value, of the same order of magnitude as the total pressure rise across the pump, near the leading edge. The resulting lift on the vane, both steady and unsteady, was computed from the pressure measurements at mid vane height. The magnitude of the fluctuating lift was found to be larger than the steady lift. For the impeller of the HPOTP, pressure measurements on the front shroud of a vaned and a vaneless diffuser showed that the front shroud pressure fluctuations increased with the presence of the diffuser vanes.; For the two-dimensional impeller, also unsteady impeller blade pressure measurements were made. The largest blade pressure fluctuations, of the same magnitude as the large pressure fluctuations on the vane suction side, occurred at the blade trailing edge. However, the dependence of those pressure fluctuations on the flow coefficient was found to be different; on the vane suction side, the fluctuations were largest for maximum flow and decreased with decreasing flow coefficient, whereas at the blade trailing edge, the fluctuations were smallest for maximum flow and increased with decreasing flow coefficient. Increasing the vane number resulted in a significant decrease of the blade pressure fluctuations.; Lift, vane and blade pressure, and front shroud pressure fluctuations decreased strongly with increasing radial gap. |
