Investigation Of Unsteady And Multiphase Flow Characteristics And Vortex Structures On Low Speed Oblique Water Entry Of A Cylinder

Water entry is a trans-media process which means the structure enters into water from air,involving multiphase flow,turbulence,wave and so on.So,the movement mechanism and flow field characteristics become very complicated during the process of water entry.In the present study,unsteady characteristics of low speed oblique water entry was analyzed.A three-dimensional simulation with a six-degree-of-freedom model was carried out,where the large eddy simulation(LES)model and the volume of fluid(VOF)technique were used for turbulence computation and air-liquid interface tracking,respectively.In order to provide validation data for numerical simulations,the corresponding experiment was carried out,in which a high-speed camera was used to record the cavity evolution.Numerical results are in agreement with experiment measurements in terms of cavity evolution,angular displacement and acceleration.Firstly,in the present work,the cavity evolution mechanism and flow pattern of water entry with calm water at a low speed were analyzed and it is found that water entry process can be divided into four stages,including impact water surface,cavity formation,cavity closure and cavity collapse.Moreover,parametric studies were conducted to analyze the effects of water entry angle and velocity on dynamic characteristics.Secondly,oblique water entry events of a cylinder under different waves were investigated.And a verification of the present model was carried out that it could simulate correct wave period,wave amplitude and steady fluctuation.Then,comparisons of cavity evolution mechanism and dynamic characteristics were predicted between water entry of calm water and wave.The cavity of water entry with wave closes more quickly than the calm water one.Besides,several parametric studies of water entry with different wave heights,wave lengths and water entry locations were carried out.Variables reflect similar trends and show fluctuations during the period of cavity closure.Finally,comparisons between vortex structures of a double-gyre flow described by Eulerian and Lagrangian method were analyzed.Then,vortex structures of oblique water entry with calm water and wave were predicted based on vorticity transport equation and Q criteria.It is found that vortex structures are closely related to cavity evolution.And the vortex intensity of water entry with wave is weaker than the calm water one while vortex areas are basically the same under these two conditions.