Abstract
The objective of this article is to investigate the flow structure of the ventilated cavitation around an under-water vehicle. In the experiments, a high-speed camera system is used to observe cavity evolution of the unsteady cavitation flow, the velocity field is measured by the particle image velocimetry technique, and dynamic pressure measurement systems are used to measure pressure fluctuations under different cavitation numbers. We seek to investigate the mechanism of the re-entrant flow and shock wave phenomenon during the cavity evolution. The study concludes that the ventilated cavity is insufficient to overcome the re-entrant jet intrusion and the re-entrant jet moves upstream straightly as well as curvilinearly. Then, the vortex structure rotating clockwise forms on the vehicle surface and the cavity area with low velocity represents the vortex. The re-entrant jet rolls back after the re-entrant jet reaches the front of the cavity. The experimental results also show that the pressure signals at different instants destabilize on the vehicle surface; fluctuant pressure peak is detected at the closure region of the cavity and pressure peak increases as the cavitation number is decreased. Surface pressure fluctuations travel on the vehicle surface from the collapse of cloud cavitation. The variation in shedding frequency for different cavitation numbers is discussed at the end of the article.
Highlights
Cavitation around the low-pressure region of the vehicle appears in under-water launch process of high-speed vehicle
The results revealed that the cavities fluctuated at specific frequencies associated with the oscillations of the cavity closure region
Fr = pVffiffiffi‘ffiffiffiffiffi gDn where p0 is the ambient pressure, pc is the pressure in the ventilated cavity, r is the water density, VN is the mainstream velocity, Q_is the volumetric gas rate at the pressure pc, and Dn is the diameter of the axisymmetric body
Summary
Cavitation around the low-pressure region of the vehicle appears in under-water launch process of high-speed vehicle. When the vehicle exits the water, the pressure fluctuates generated by the cavitation bubbles collapse, which has great influence on the trajectory and vibration of the vehicle. Most problems are related to the transient phenomenon of the cavitation structures. Rouse and Mcnown[1] studied a series of experiments on the cavitation flows around axisymmetric model. Measurements were made across a range of cavitation numbers and have been applied in a wide range of investigations. Arakeri and Acosta[2] made a large number of studies on the cavitating flow around axisymmetric bodies and found various types of cavities
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