Cavitation in tip-leakage flows

Cavitation inception and the topology of developed cavities in tip leakage flow, for a hydrofoil with a square edged tip, have been investigated in a water tunnel using for the naturally occurring nuclei population. The experiments were performed for five tip gap to hydrofoil thickness ratios ranging between 0.07 and 1.4, and at Reynolds numbers based on the foil chord between 2 and 3.5 million. Inception was generally observed in the gap flow, however, the incipient cavitation number was found to have a stochastic character. Unlike the incipient cavitation number, the desinent cavitation number was found to be consistent across the range of investigated conditions. Hysteresis between the incipient and desinent cavitation number was observed. It was observed that for the cases with inception at low cavitation number a peak in overall noise level was often present as the cavitation number was increased from inception towards desinence. The topology of developed cavitation in the gap was found to vary with the gap size, from a laminar attached cavity observed for the smallest tip clearance towards an increasingly pronounced tip separation vortex as the gap was increased. Results from the square edge tip provide baseline data for comparison with more complex tip geometries in addition to validation data for CFD simulations with a simplified geometry.