Cavitating flow control and noise suppression using air injection

The cavitation phenomenon not only reduces hydrodynamic performance but also generates vibrations and noise, significantly compromising the operational stability of the system. In this study, we investigate the efficiency of air injection in controlling cavitation patterns and reducing noise on hydrofoil, both experimentally and numerically. The focus is to assess how the location of air injection on the suction side of the hydrofoil, the rate of air injection, and the cavitation number affect the cavitating flow. The hydrofoil has a span and chord length (C) of 100 mm. The air is injected from a column of multi-holes positioned at x/C = 0.05, 0.10, 0.30, and 0.40 separately and controlled through a flow meter. The cavitation number ranges from 3.65 to 1.62, while the air injection rates are set at 1, 3, and 5 standard liters per minute. The experiments are conducted at Chungnam National University's high-speed cavitating tunnel. Simultaneously, a high-speed camera is used to observe cavitating flow, and a pressure transducer is employed to measure noise levels. The results indicate that injecting air closer to the leading edge has the most significant impact on reducing vapor cavitation and noise. Injecting air at x/C = 0.05 reduces the length of the vapor sheet cavity by 27% compared to cases without air injection. Increasing the air injection rate increased the volume of ventilated cavitation. Noise reduction is primarily noticeable in the high-frequency region (>2 kHz) at a high cavitation number of 2.22. As the cavitation number decreases to 1.62, the noise reduction shifts mainly to the low-frequency region, and the effectiveness of air injection in suppressing noise is reduced.