Dynamics of spark-generated array bubbles near a free surface

In this study, we systematically focus on the coupling mechanism between the free surface and array bubbles. The method of underwater electric discharge was utilized to synchronously generate the array bubbles. The current array design consists of three collinear bubbles arranged horizontally beneath the free surface. High-speed photography shows distinct bubble dynamics and water spike evolution patterns for different bubble-free surface stand-off distances of γb and γf. Numerous distinct and novel phenomena were identified. Quantitative analyses are performed on the jet velocities of array bubbles and the width and rising velocity of the water spikes at different stand-off distances. It is shown that for small γb less than 1.0, the bubbles would merge as well as the water spike being formed. As γb increases, the integrated water spike is observed to be separated, resulting in three water spikes arising on the free surface. Rich shapes of water spikes with the required width or height can be produced by controlling the stand-off distances associated with the array bubbles. The findings can provide a probable reference for predicting dynamics of the water spikes caused by array oscillating bubbles.