Effect of water injection on the cavitation control:experiments on a NACA66 (MOD) hydrofoil

The objective of this work is to investigate experimentally controlling cavitating flow over NACA66 (MOD) hydrofoils by means of an active water injection along its suction surface. The continuous water vertically jets out of the chamber inside the hydrofoil through evenly distributed surface holes. Experiments were carried out in cavitation water tunnel, using high-speed visualization technology and the particle image velocimetry (PIV) system to study the sheet/cloud cavity behaviors. We studied the effects of this active control on cavity evolution with four kinds of jet flow at two different jet positions. We analyzed the effect of water injection on the mechanism of the cavitating flow control. The results were all compared with that for the original hydrofoil without jet and show that the active jet can effectively suppress the sheet/cloud cavitation characterized by shrinking the attached cavity size and breaking the large-scaled cloud shedding vortex cavity into small-scaled ones. The optimum effectiveness of cavitation suppression is affected by the jet flow rates and jet positions. The water injection at flow rate coefficient 0.0245 with the jet position of 0.45Creduces the maximum sheet cavity length by 79.4% and the cavity shedding is diminished completely, which gives the most superior effect of sheet cavitation suppression. The jet blocks the re-entrant jet moving upstream and weakens the power of re-entrant jet and thus restrains the cavitation development effectively and stabilizes the flow field. Graphic