Study On Development And Stability Of Ventilation By Flat Plate

Ventilated bubble flow is widely used for its easily realizable and effectively in the drag reduction of ventilated cavitation of underwater vehicles.The flow structure of ventilated cavitation is different from natural cavitation because of the non-condensable gas.As the changes of different factors such as the ventilation volume and flow speed,it will have a greater impact on the flow patterns,dynamic characteristics,kinetic characteristics and flow stability.In this paper,by using the numerical simulation method which based on the experiment of ventilated bubbles,the bubble flow structure and stability of the different flow parameters and structural parameters are discussed.The main results are shown as follows:Numerical simulation methods on three-dimensional plate ventilation are established,and the flow structure of porous plate ventilation are discussed.The application of plate ventilation in different multiphase model and turbulence model are evaluated,then finally Level Set method and RNG k-? model is selected for simulation.The law of flow structure of the ventilated flow under general conditions is discussed,the general bubble flow is a progress that bubbles are transformed from dispersed air cavity into continuous bubble layer by the movement and expansion of the inner gas.The surface morphology and internal motion become more stable as the bubble layer develop.The influence of different flow parameters on the development and stability of flat plate is discussed.As the Eu number changing,the pressure distribution of the plate is changed,but it has little influence on the development and stability of the bubble layers.The ventilation rate Qv change the width and height of air cavity,and impact on not only the position and height,but also stability of bubble layers.As the Re number changing,the air phase velocity are changed with the changing of water velocity in the flow field,and the stability of the bubble layer are then affected.When the water velocity decreases gradually in the flow field,the height of the bubble layer increase,and both air velocity and the internal motion stability of the bubble increases.It is the most stable when the water is in constant speed.The influence of different structural parameters on the development and stability of flat plate is discussed.Both transverse and flow direction of the air cavity development will be affected by different hole arrangements,the air cavity will cover plate faster while the surface and internal motion will be poor in cross arrangement compared with parallel arrangement.It will shorten the gap and change the transverse distance of air cavities with small hole spacing,small hole spacing can form the stable continuous bubble layer more favorable,but it may cover less plate region.Different hole patterns make less effect in the development of air cavity,but it has much influence on the surface morphology and little influence on internal motion of bubble layer.What's more,compared with square hole,the bubble layer surface of circle hole is more stable while the internal motion is not so far different.