Research On Supercavitation Flows Characteristics Of Projectiles With Complex Structure Water Exit And Entry

The supercavitation phenomenon can make underwater moving objects be wrapped by large steam bubbles,thus achieving the purpose of greatly reducing drag.Due to this advantage,supercavitation technology is widely used in various military weapons,such as the supercavitation underwater torpedo,supercavitating underwater bullets,etc.the birth of these supercavitating weapons overcomes the shortcomings of traditional underwater projectiles with large resistance and short range.On the other hand,there are still many difficulties to be solved in the technology of supercavitation,such as maintaining the appropriate size of supercavitation underwater for a long time?the ballistic stability control of supercavitating underwater weapons?and moving the supercavitation of underwater projectile across the medium(high-speed water entry and exit).Based on the above background,in this paper mainly studies a series of underwater high-speed projectile supercavitation problems through numerical simulation method,theoretical analysis and experimental comparison.The main contents are divided into the following parts:(1)In order to study the influence of the projectile empennage on the supercavitation,the VOF multiphase flow/Schnerr-Sauer cavitation model was used to simulate the three-dimensional supercavitation of the complex structure projectile with different empennage numbers.The effect of the cavitation number,the number of empennage of the projectile on the morphological characteristics of the three-dimensional supercavity,the perturbation of the supercavitation and the hydrodynamic characteristics was analyzed.The numerical simulation results are compared with the Logvinovich theoretical formula.The numerical simulation results are consistent with the Logvinovich theoretical formula.(2)High-speed projectile cross-medium motion has always been a difficult problem in the research of supercavitation.In this paper,two-dimensional axisymmetric numerical simulation of high speed underwater projectile wanter entry and exit supercavitation is carried out using dynamic mesh technology.The influence of the initial velocity of projectile on the development of supercavitation,the characteristics of projectile resistance and the flow field structure in the process of projectile water entry was analyzed;at the same time,the effects of velocity and the cone Angle of the warhead on the hydrodynamic characteristics of the water exit supercavitation,supercavitation morphology and the hydrodynamic characteristics of the projectile was analyzed.The numerical simulation results are in good agreement with the semi-empirical formula.(3)In order to study the influence of the shape of the underwater projectile head cavitator on the water exit of the projectile across the medium,based on the RNG k-? turbulence model and the Schnerr-Sauer cavitation model,the three-dimensional water exit supercavitating numerical simulation of the projectile with discal-nose,conical-nose and hemispherical-nose was carried out,the influence of cavitator shape of projectile nose on the three-dimensional morphological characteristics of water exit supercavitation,kinematics characteristics(velocity,displacement)of projectile water exit process and hydrodynamic characteristics of projectile water exit supercavitation were analyzed.In the numerical simulation,the phenomenon we captured is the same as that in the experiment,especially the cavity that gradually shrinks below the free surface of the projectile water exit process and projectile completely out of the water exit instantly tail out of water column,etc.,the three-dimensional numerical simulation results of the water exit supercavitation are compared with the existing analytical and experimental results,it is found that the numerical simulation results are in good agreement with the experimental results and theoretical formulas.