Experimental Study On The Cavity Evolution And Motion Characteristics Of Sphere Entry Through A Viscous Fluid Layer Resting On The Water

The cross-media movement process from air to water involves the interaction between the three phases of solid,liquid,and gas.This process is accompanied by the complex flow phenomenon of the water entry cavity,including the splash crown above the free liquid surface and the cavity below the free liquid surface.The motion stability and slamming load during water entry are significant bottlenecks restricting the development of cross-media navigational bodies.The water entry environment and cavity evolution characteristics are closely related to the water entry movement and load of structures.Therefore,in this paper,by placing a high-viscous fluid on the water surface to change the water entry environment,the evolution of the cavity and motion characteristics of the sphere in the double-layer fluid with a viscous layer were explored.Through the research in this paper,we hope to provide a new idea for improving motion stability and reducing the slamming load of the structures in the water entry process.First of all,the cavity formation of the sphere vertically entered into the water after passing through a dimethicone layer that has a thickness of 2 mm was studied.By comparing the work condition that the sphere directly penetrates the water,it was found that the presence of the thin layer of dimethicone obviously modified the evolution process of the splash crown,and wave-like structures generated on the cavity wall.Besides,a parameterized study on the relationship between the Froude number and the characteristic values of the water entry cavity such as the splash crown interface height,the pinch-off time,the depth of the pinch-off position and the depth of the sphere at the pinch-off time were conducted,and the influence of the dimethicone layer on the above characteristic was studied.Secondly,by changing the thickness of the dimethicone layer,the effect of the thickness of the surface fluid on the vertical entry of the sphere into the stratified fluid was studied on the basis of considering the effect of Froude number.When the thickness of the dimethicone layer changes,there were obvious differences in the evolution characteristics of the splash crown,which can be divided into six evolution patterns.By analyzing the displacement curves of the sphere under different dimethicone layer thicknesses,the influence of the dimethicone layer and its thickness on the motion characteristic of the sphere was obtained.Meanwhile,parametric studies on the relationship between characteristic values of water entry cavity and the thickness of the dimmethicone layer were conducted.Finally,the experimental studies of the sphere with initial horizontal velocity falling into the dimethicone-water were carried out.In this case,the water entry cavity was asymmetry,but under the influence of the dimethicone layer,the double-layer splash crown phenomenon still occured,and the evolution characteristics of the splash crown also changed with the changing of the dimethicone thickness.The characteristic value of the splash crown changes from the interface height to the interface inclination angle.The relationship between this characteristic value and the thickness of the dimethicone layer and the initial horizontal velocity was studied.Besides,parametric studies on the cavity pinch-off time,the depth of the pinch-off position,and the depth of the sphere at the pinch-off time were also conducted.