Research On The Method Of Simulating Submerged Body Wake In Stratified Fluid

Because of the heat radiation from sun and thermalhaline circulation, ocean usually is stratified whose density, temperature and salinity have obvious change along vertical direction.Wake with special characteristic would take place by submerged body moving in a stratified fluid causing convergence and divergence of free surface short gravity waves and capillary waves resulting characteristic of mall scale or micro scale folds lasting for a long time. As a typical form of stratification in ocean, continuous stratified fluids have been a hot and difficult spot in research for its special property from uniform fluids, especially lack simple and effective CFD method simulating stratified flow.Two numerical methods are established based on multiphase mixture model and temperature density flow model respectively with CFD software FLUENT. In the case of flow past a cylinder in linearly stratified fluid,LES was first used to simulate the stratified flow at high Fr number,and the characteristics of wake match corresponding results well for Fr=0.88,1.77, RANS was used to simulate stratified flow at low Fr(0.018,0.08,0.17), and for the first time quantitative descriptions upstream and downstream flow field are achieved for Fr=0.018, and numerical results match experimental result well. Based on the two models,numerical methods are established Fr range from low to high. The two methods are compared:for the multiphase method, volume fraction discrete format precision was analysed which may cause false diffusion base on the results of different Re and volume fraction discrete format; for temperature method, the suitable conditions are discussed in theory, and the minimum value of Pe was conclued on account of the working conditions of this article;selecting flow streams of different numerical moment for Fr=0.17 and 1.77,the two methods were compared to explore the advantages and disadvantages respectively. Finally,Another numerical method was discussed simply, namely the salinity density flow method.The method based on multiphase mixture model is invalid in simulating late wake due to its finite volume fraction discrete format precision which would cause false diffusion resulting in limited numerical simulation time lasting. Alternatively, mixture model and VOF model can’t use together, so it’s limited to simulate flow with the boundary condition of free surface.Without the limitation of multiphase and volume fraction discrete treatment , the large coherent vortex structure of late wake and free surface characteristic caused by stratified flow can be studied based on temperature density flow model for the method itself durable and stable.