On formation mechanism of local cavitation in the near-wall flow field caused by an underwater explosion

In order to deeply understand the formation mechanism of local cavitation in the near-wall flow field caused by an underwater explosion, the optical images showing the local cavitation effect near the wall were obtained by using a self-developed rotating-mirror framing camera with high frequency and high resolution. Numerical simulations were carried out to present the flow-field pressure of shock wave propagation by giving the location of the cavitation area. The Taylor plane wave theory, an efficient method for describing the formation time of local cavitation, was applied to explain the reason that the cavitation did not form in the experimental case 1 that the explosive center was 120 mm from the wall. And the cavitation dynamics theory was used to analyze the local cavitation effect in the experimental case 2 that the explosive center was 80 mm from the wall, by calculating the motion laws of the cavities with different radii under different external environmental pressures. It is indicated that the existence of the rarefaction waves reflected by the interfaces and the expansion of the cavitation nuclei in the water result in the cavitation effects in the near-wall flow field. The external flow-field pressure hardly affects the initial stage of cavitation bubble expansion, but it exerts great influences on the movement behavior of the cavitation bubbles in the later stage. The cavitation bubbles with different sizes will take on different movement behaviors in the low-pressure environment. The cavitation bubbles with the small size less than 10 µm will expand and collapse rapidly in the low-pressure environment so that they have little effects on the flow field cavitation. While the cavitaion bubbles with the large size more than 10 µm may lose the stability, with the result that they have great influences on the flow-field cavition. The random spatial distribution of different-size cavitation nuclei in water is the main reason that the cavitation zone presents an irregular shape during the evolution progress. © 2023 Explosion and Shock Waves. All rights reserved.