Experimental investigation into passive control effect of micro vortex generator at various cavitation conditions

The objective of this study is to discuss a passive control method for different stages of cavitating flows. The passive flow control is implemented using micro delta-shaped vortex generator (mVG) inserted spanwise on the suction side of the NACA66 hydrofoil. A high-speed camera is applied to visualize the cavitating flow structures. The results show that for the inception cavitation, the mVG with different positions can cause different modes of inception cavity. The typical three-dimensional spot cavity, the fingerlike vortex cavity, and the patch cavity are respectively captured at the leading edge of baseline hydrofoil, mVG-1 hydrofoil, and mVG-2 hydrofoil. For the sheet attached cavity, a new cavitation mode is found on the mVG-1 hydrofoil which is the fingerlike vortex cavitation followed by the attached sheet cavity due to the vortex cavitation merging behavior. Furthermore, for the unsteady cloud cavitation, the two mechanisms of cavity quasi-periodic shedding caused by the re-entrant jet and shockwave are analyzed to reveal that the mVG-1 can enhance the instability while the mVG-2 can weaken it.