Numerical Simulation of Ventilated Cavitation Evolution with an Insight on How Ventilation Influences Pressure Fluctuation and Cavitation Noise

Abstract

Cavitation occurred in hydraulic machines can generate severe pressure fluctuations and induce high-pitched noise. Ventilated cavitation (inject air into the cavitating flow) is one of the most effective ways to control cavitation and then alleviate the noise and fluctuations. Thus, the evolution of ventilation cavitation around a NACA0015 hydrofoil was numerically investigated with a modified model. The results indicated that the ventilated cavitation consists of two parts: the attached cavity which attached to the leading edge of the hydrofoil and the detached cavity which detached from the hydrofoil surface. With the air injection increased, the detached cavity becomes larger. Besides, the ventilated cavity evolves periodically along with two opposite vortexes which fall off in turn near the tailing edge of the hydrofoil. Among three ventilation volumes, an air injection of 250 L/min presents the best alleviation on pressure fluctuation induced by cloud cavitation. The acoustic analysis indicated that air injection is an effective way to alleviate the cavitation induced noise. With air injected into the flow, two new types noises induced by the ventilated cavitation has been detected by monitoring points along the upper side and behind of the hydrofoil: the lower frequency noise induced by the waving of attached cavity and the higher frequency noise induced by the shedding of the detached cavity. While with the air injection increased, both of the two types noises increased. The acoustic and dynamic patterns under different air injection conditions are able to provide guidance in engineering application.