Experimental and numerical study on the effects of sweep angle on cavitation around a wedge-section hydrofoil

Abstract

The influence of sweep angles on cavitation characteristics and mechanisms of a wedge-section hydrofoil is investigated experimentally and numerically. Four hydrofoils with sweep angles of 0 degrees (straight), 30 degrees, 45 degrees, and 60 degrees are considered across a range of cavitation numbers from 2.00 to 0.48 and angle of attack (AOA) of 0 degrees, 5 degrees, 10 degrees, and 15 degrees. Two high-speed cameras are used to visualize the cavitation flow in a highspeed cavitation tunnel. The numerical simulation is conducted using unsteady Reynolds-averaged Navier-Stokes equations through OpenFOAM. At an AOA of 0 degrees and 5 degrees, vortex cavitation first appears in the wake region of all models at a cavitation number of 0.98. However, at higher AOA values of 10 degrees and 15 degrees, tip-vortex cavitation (TVC) begins first for the straight foil, and this is followed by sheet and wake cavitation. In contrast, the swept foil does not succumb to TVC. Instead, as the sweep angle increases, sheet cavitation develops into root leading-edge vortex cavitation (LEVC). The inclination angle of the LEVC from the leading edge is observed to be between 6 degrees and 15 degrees, depending on the sweep angle, and it is independent of the cavitation number and AOA. The wake vortex changes from eddy vortex shedding at the wake region of the straight hydrofoil into two root trailing-edge vortices as the sweep angle increases. The swept hydrofoil reduces the average cavity volume by more than 45% compared with the straight foil. The lift coefficient of the straight hydrofoil increases as sheet cavitation is generated and reaches a maximum value of 0.6 when cavitation covers the suction side of the hydrofoil before dropping sharply when it extends to the wake region. However, there is only minor deterioration in the lift coefficient of the 60 degrees swept-angle foil when the cavitation occurs. The drag coefficient reduces when cavitation forms for both foils. However, the drag coefficient of the swept hydrofoil is lower than that of the straight foil. These findings offer valuable insight into the design and optimization of foils for various applications where cavitation affects their performance and stability.