Research On The Characteristics Of Wake Field Generated By Submerged Body Moving In Pycnocline

Because of the heat radiation from sun and thermohaline circulation,there are many pycnoclines in the ocean.When a submerged body travels near the pycnocline,internal wave wakes will be excited because of volume effect and turbulent wake effect.The internal wave wakes involve wide range,long duration and can modulate with the microscale waves and capillary waves in the free surface.Folds with different roughness will be generated because of the change of convergence and divergence of flow field.Synthetic Aperture Radar(SAR)can get the location and motion of the submerged body by capturing the signal of roughness and forming an image.The characteristics of wake fields are studied by viscous CFD method when the submerged body travels in stratified fluids.Firstly,the continuous stratification of density is formed based on thermal density current model.Large Eddy Simulation method is used to simulate the flows past a sphere at different Froude numbers and Reynolds numbers.The results show due to the stratification of density,the wake fields are approximately quasi two-dimensional at low Froude numbers.The vertical motions of fluid particles are become obvious at high Froude numbers.The numerical results are consistent with experimental results,which proves the feasibility and accuracy of viscous CFD method on solving wake fields generated by submerged bodies moving in stratified fluids.Secondly,based on the above research,the form of density stratification is changed to mixed stratification which is more close to the actual condition from continuous stratification.Large Eddy Simulation method is used to simulate the wake fields of a moving sphere.The influence of density stratification form on internal wave wakes is studied when the Froude numbers and Reynolds numbers keep same as the continuous stratification.The results show the form of density stratification has more influence on the horizontal motions of wake fields at low Froude numbers when the vertical motions are influenced more at high Froude numbers.Once again,the mixed stratification with free surface is established according to the distributions of pycnoclines of China seas.Reynolds Average Navier-Stokes method is used to simulate the wake fields of full-scale Suboff model traveling in mixedly stratified fluids.The free surface is captured by solving the volume fraction of each grid.And the influence of speed,diving depth and density gradient on the characteristics of wake fields is studied.The results show Kelvin waves are generated on the free surface.Mutation regions or thick regions are formed in the pycnoclines of wake fields.At the same time,speed and diving depth have more influence on the wake fields than density gradient of pycnoclines.Finally,the true environment of sea surface is get based on wave spectrum by using numerical boundary method.The modulating action of flow fields excited by moving steadily full-scale Suboff model and irregular waves on the free surface is studied.The characteristics of wake fields are also studied when surface tension and propeller are considered.And the change of convergence and divergence of surface is get.