Experimental Study And Numerical Simulation Of Underwater High Pressure Gas Jet Bubble

With the continuous depletion of natural resources on the land,the abundant and wide varied deep-sea resources are gradually drawing extensive attention.The exploration and exploitation of deep-sea resources have been placed in a more important position.Due to its stable performance,the highly automated and economic air guns have become the most widely used method of seismic exploration.The jetting process of high pressure gas inside the air gun is an extremely complicated physical process.Generally,the evolution process of air gun bubble is complicated,except that high-speed jets are often accompanied by the formation of turbulence and eddies,which increases lots of difficulties to the study of air gun bubble.The current theories of air gun bubble are mainly based on the spherical bubble theory,ignoring the influence of the strong nonlinear process such as bubble collapse,jet,and rebound on the field pressure.The current researches mainly focus on the researches of far-field pressure wavelets.While few studies focused on the evolution of air gun bubble,and the air gun bubble experimental researches are also insufficient.In this paper,experimental study and numerical simulation are carried to study the characteristics of air gun bubble and pressure wavelet of the air gun.The effects of different air gun design and initial conditions on evolution of the air gun bubble and characteristics of pressure wavelet are explored in order to improve the structure of the air gun.It provides new ideas for performance optimization of the air gun.In the experimental investigation,two kinds of air guns with port design and no port design were discussed in this research,and experiments were carried out in an open water tank with a size of 2m ×2m ×2.5m.The high-speed camera is used to capture the bubble evolution;the PCB series pressure sensors are used to record the pressure change of the flow in the field.In this paper,a series of experiments are designed to study the effects of different air gun initial pressure,depth of air gun placement and the form of air gun port on bubble evolution and the characteristics of pressure wavelet.In the numerical study,the Finite Volume Method(FVM)is used to simulate the bubble evolution and field pressure during the air gun working process.The Finite Volume Method is good at predicting the complex fluid processes such as bubble collapse and rebound.By simulating the movement of the shuttle valve,the air gun bubble and the complex gun structure are well simulated.The key parameters such as the size of the port,initial pressure and deflation time are explored.The impact on the characteristics of air guns has a greater significance.Firstly,the validity of the numerical model is verified by the experimental researches.The results show that the numerical model results agree well with the experimental ones.Then,based on the established Finite Volume Method model,the effects of air gun parameters such as the size of the port,initial pressure and deflation time on bubble pressure wave characteristics are studied.Simultaneously,the pressure wavelet characteristics of the two air guns were compared,and the influence of the port design on the pressure wave characteristics of the air gun was explored.In addition,this paper explores the interaction between underwater high-pressure jet bubble and free surface and floating structure through the combination of experimental study and numerical simulation.