Observation of unsteady cavitating flow in flat plate cascades

For deeper understanding of cavitation instabilities arising in turbopumps, we have carried out an experimental study on unsteady cavitating flows in flat plate cascades. Visual observations using high-speed video cameras as well as pressure fluctuation measurements of unsteady cavitating flow were carried out in decelerating cascades with the solidity of 1.0 and 2.0 with and without a tip clearance. It was found that the overall cavitation performance of tested cascade had a strong hysteresis especially for the solidity of 1.0 due to the asymmetric development of blade cavities. The FFT spectrum of measured pressure fluctuations and cavity fluctuations extracted through the image analysis proposed in the present study revealed the unsteadiness of sheet cavity. It was found that the effect of tip leakage flow and tip leakage vortex cavitation did not have very strong impact on the unsteadiness of cavitating flow as well as the cavitation performance of cascades.