Numerical Analysis Of Mechanism Of Wake-generated Internal Waves

The internal waves generated by a moving body in stratified fluids can be divided into two types: one is the body-generated wave,and the other is the wake-generated wave.For the body-generated wave,theoretical studies based on kinds of shape bodies or stratified fluids become more mature after comparing with the results from experiments and CFD.For the latter,researchers have not reached the same conclusion on the generative mechanism successfully because of vortices,turbulence,shear flow and kinds of instabilities randomly appearing in the wake.In order to solve the problem,the thesis takes the moving ball in a linear stratified fluid as the object and analyzes the generative mechanism of wake-generated wave by LES-Mix multiphase flow numerical simulation.Firstly,the research methodologies and progress of the wake-generated wave were reviewed.The basic numerical simulation theory was also summarized and the LES-Mix multiphase flow model was chosen as the method to simulate the occurring of wake-generated wave.Secondly,the numerical simulation of body-generated wave at lower Froude numbers and flow field at medium Froude numbers based on Les-Mix multiphase flow model were carried out.The numerical results showing flow field agreed well with the experimental results at medium Froude numbers and the characteristics were also in line with the theory of body-generated wave that confirmed the model's reliability and practicability of simulating the wake-generated wave.Thirdly,the process of near-wake's mixing,collapsing under the effect of potential energy and generating of the wake-generated wave accompanied the wake's oscillating were numerically simulated based on the model.Through in-depth analysis of the results,including fresh water volume fraction's distribution vertically curve and the spatial decay of defect velocity,the thesis obtained the rule of the mixed wake's vertical height,the collapsing location with the Froude number.Finally,through analysis of the results,including the wake's fresh water volume fraction's distribution vertically curve,evolution of density contours and the vertical velocity's frequency spectrum,the mechanics of collapsed wave generating under the background fluid.