Numerical study on motion of the air-gun bubble based on boundary integral method

Abstract

To simulate the motion of the non-spherical bubble generated by air gun, boundary integral method is used in conjunction with the basic theory of the air gun. The time length of the bubble aeration τ (i.e., the close time of the air gun), the utilization efficiency of the gas inside the air gun chamber η, the heat transfer coefficient α and other key parameters of the air gun are employed to control the motion of the bubble. In the simulation of a single air gun bubble with buoyancy, the vortex ring model is used to simulate the motion of the toroidal bubble after jet impacts, and it is extended to the multiple vortex rings in the simulation of the interaction between two clustered air gun bubbles. Some new findings are summarized as follows: (i) Under the effect of the buoyancy, the shape of the bubble becomes non-spherical at later phase of bubble collapse, but the deformation seems to have little effect on the far-field pressure. (ii) For the clustered air gun bubbles, the primary-to-bubble pulse ratio will reach a maximum when the standoff distance d is about 1.6 times maximum radius of a single bubble. (iii) Primary-to-bubble pulse ratio is relative large at a small firing depth of the air gun H (the vertical distance from the bubble center to the free surface).