STUDY ON THE INTERACTION AND JET ENHANCEMENT EFFECT OF TWO OUT-OF-PHASE BUBBLES NEAR A RIGID BOUNDARY

Bubbles widely exist in nature and engineering applications. Bubbles usually do not appear in isolation and therefore more complex and interesting bubble dynamics and jet behaviors occur under multi-bubble coupling. The collapse of underwater pulsating bubble near rigid boundary will produce high-speed jet towards the structure, which will seriously threaten the local strength safety of the structure. The interaction of multiple bubbles can regulate and control the bubble collapse mode, jet direction, jet impact velocity, etc. in which the jet enhancement effect of out-of-phase double bubbles has a broad application prospect. In this work, a numerical model of nonlinear coupling of two out-of-phase bubbles near rigid boundary is established by combining bubble dynamics theory and boundary integral method. It can accurately simulate the dynamic behavior of the nascent, expansion and collapse jet of the bubble, and predict the coupling mode and collapse mode of the two bubbles. By comparing the numerical results with the experimental results, the favorable agreement is achieved which validates this numerical model. Using the numerical model as is mentioned above, the dynamic behavior of two bubbles is studied systematically in a large parameter space, and the enhancement effect of the jet is analyzed emphatically. With the aid of the pressure and velocity information of flow field, the mechanical mechanism is revealed. It is found that the delay time of bubbles formation τ greatly affects the jet enhancement degree of double bubbles coupling. The jet impact velocity of the near-wall bubble increases first and then decreases with the increase of τ , and reaches the maximum value nearby τ = 2. The effective parameter range of jet enhancement is obtained, which aims to provide new ideas and theoretical support for the attack strategy of multiple underwater explosive weapons.