The Channel Wall Confinement Effect on Periodic Cryogenic Cavitation from the Plano-convex Foil

Flow pattern of cavitation around a plano-convex foil, whose shape is similar to the inducer impeller of the turbo-pumps in the liquid fuel rocket engine, was observed by using a cryogenic cavitation tunnel of blowdown type for visualization. Working fluids were liquid nitrogen and hot water. The parameter range to be varied was between 20 and 60mm for channel width, 20 and 60mm for foil chord, -1.8 and 13.2 for cavitation number, 3.7 and 19.5m/sec for averaged inlet velocity, $8.5{\times}10^4$ and $1.5{\times}10^6$ for Reynolds number, -8 and $8^{\circ}$ for angle of attack, respectively. Especially at positive angle of attack, namely, convex surface being downstream, the whole cavity or a part of the cavity on the foil surface departs periodically. Periodic cavitation occurs only in case of smaller cavitation size than twice foil chord. Cavitation thickness and length in 20mm wide channel are larger than those in 60mm due to the wall confinement effect. Therefore, periodic cavitation in 60mm wide channel easily occurs than that in 20mm. These results suggest that the periodic cavitation is controlled by not only the hydrodynamic effect of vortex shedding but also the channel wall confinement effect.