Numerical Simulation Of Supercavity Flow Property Induced By High-Speed Projectiles Into Water

When high-speed projectile motion in the liquid,ambient pressure is lower than the saturated vapor pressure of the liquid,the body will be around the vaporization to produce steam,reducing the projectile and the wet area of the liquid,thus greatly reduce the resistance of sailing,this kind of phenomenon is the phenomenon of supercavitation.Supercavitation theory has very important application in drag reduction of the submarine body and high-speed motion.Supercavitation flow phenomenon is also a more complex flow phenomenon,and high-speed projectile water entry process supercavitation flow is a kind of extremely complex flow phenomenon.Previous study of supercavitation is mainly based on the experimental research method,however,due to the supercavitation flow with high speed,complex and changeable characteristics,experimental study has certain limitation;In recent years,due to the development of computer simulation technology,making use of the method of numerical simulation study of supercavitation more convenient,to a certain degree complement and expansion of experimental contents.The present simulation investigates the water entry process of high speed projectiles by using the CFD software and selecting the VOF model of multiphase flow.The models of projectiles are cylinders,whose diameters are 6mm and the aspect ratios are 12.The projectiles with a flat head,conical head and spherical head respectively produce supercavitating flows in water at a speed of 100m/s.By comparing the supercavity's shape from the simulation results with the results from Logvinovich's semi-empirical formulas,it is indicated that the front half of the supercavity's shape is in a good agreement between the simulation and the Logvinovich's result;the back half of the supercavity's shape is bigger than the Logvinovich's result,which is because of the air entrainment.In addition,comparing the phase diagram of the three kinds of head shape supercavitation projectiles,it is found that the amount of air entrainment of the conical head cylinder is the most,and the flat head cylinder is in the second,the spherical head cylinder at the last;the air entrainment volume fraction of the spherical head cylinder is the largest,and the conical head cylinder is in the second,the flat head cylinder at the last.For the projectile with spherical head,the flow fields at 500m/s,900 m/s and 1500 m/s entry speed are simulated and discussed.In addition,also analyzed the head type's influenceon the maximum pressure,the water entry velocity's influence on the maximum pressure;The head type's influence on the maximum velocity,the water entry velocity's influence on maximum speed;The head type's influence on the pressure coefficient,the water entry velocity's influence on the pressure coefficient;The head type's influence on the surface friction coefficient,the water entry velocity's influence on the surface friction coefficient;the head type's influence on the vorticity,the water entry velocity's influence on the vorticity;The Mach number's influence on isobar distribution;A series of conclusions.And used for naval engineering university professor Hou Jian experimental projectile model,using the static grid technology is simulated to the process of the horizontal water entry of the projectile,air entrainment in cavitation was analyzed.