Experimental investigation of the thermal effect on the unsteady cavitating flow structure

In order to investigate the influence of the thermal effect on the unsteady cavitation structure, the unsteady characteristics of cavitating flows under 6°C, 25°C and 45°C around Clark-y hydrofoil are investigated by experimental methods. A high-speed video camera is used to visualize the flow structures under different cavitation numbers. The digital particle image velocimetry (DPIV) is employed to measure the velocity and vorticity distribution. The results show that the cavity region becomes smaller and the cavity length is shorter with temperature increasing. But at the same cavitation regimes, the influence of the thermal effect on the cavity shedding cycle is small and the shedding cycle is basically the same. The region which shows larger influence of the thermal effect on the velocity and vorticity distribution is major in the cavitation region and the interface between the cavitation region and main free-stream region. The highfluctuating region with lower velocity becomes smaller and the specific velocity value increases slightly with temperature increasing. It results that the velocity gradient decreases and the turbulence fluctuating intensity decreases with temperature increasing. It can be also found that the vorticity region is corresponding to the region which has higher velocity gradient, the upper and lower vorticity region and its value decrease with temperature increasing.