Experimental and numerical study on hydrodynamic characteristics in water-exit of slender body

The water-exit process of a vehicle involves severe gas-liquid mixing,and the flow field is unsteady and highly nonlinear.To understand the characteristics of the process,the water-exit process of high speed slender body is studied by experimental and numerical simulation.The experiment was operated in a two-dimensional water tank,and the flow field of the water-exit of a slender body with different velocities was photographed by a high speed camera.The water-exit process according to the experiment was simulated,the Volume of Fluid(VOF)model was used to simulate the interface between water and air,and the dynamic mesh and UDF technology were adopted to simulate the movement of the slender body.The growing process of the cavity,the mechanism of the cavity collapse,and the way of the slender body affecting the free surface when the slender body moving in the water have been investigated.The experimental result indicates that:(1)there is a sudden increase in velocity when the slender body completely leaves water;(2)as the velocity increases,the cavity phenomenon begins to appear at the end of the slender body,and subsequently appears at the head of the slender body;(3)if the velocity is not large enough to generate local cavity at the head of the slender body,the free surface uplifts obviously as the slender body exits from the water.If the local cavity appears at the head of the slender body,the free surface uplift phenomenon is unobvious,and the “splash”phenomenon appears. The numerical result indicates that the free surface uplift phenomenon endures for the whole water-exit process,and the extent of free surface uplift is larger when the tail leaves water than the head.The numerical result was found to be in agreement with the experimental results.