Based on the theory of rigid body kinematics, a double slapping theoretical model is established for supercavitation projectile. And a parabolic simplification model is used for replacing the supercavitation equation in the part region of the cavity. Meanwhile, a time interval of two slapping impacts formula is derived from the parabolic simplification model. Then, the Logvinovich bubble expansion equation is discretized by using the Compound Simpson Formula and the cavity cross-section area of the projectile tail is solved in the condition that the projectile decelerates movement underwater. And, the cavity radius value of the projectile tail is obtained from Logvinovich bubble expansion equation, and it is substituted into the time interval formula. Compared with the experimental results, it demonstrates the rationality of the parabola simplification model and time interval formula. The projectile slapping impact, which is the main mode of motion in the cavity, is closely related to the stability of the underwater trajectory. This conclusion has a specific significance for studying the instability of the underwater trajectory.
To explore the effects of water entry angle on the cavitation flow field of high-speed revolution body, based on the finite volume method, VOF (Volume of Fluid) multiphase model, Schnerr-Sauer cavity model, SSTturbulence model, and dynamic mesh method, numerical simulation for modeling the oblique water entry of revolution body at high speed is performed. The evolution laws of cavity shape, motion characteristics, and hydrodynamic characteristics of revolution body at different water entry angles are analyzed. The results show that the numerical calculation method can effectively simulate the change of cavity shape during the water entry of the revolution body. With the increase of water entry angle, the uplift of liquid level decreases in the positive direction of the open cavity and increases in the negative direction. The angle of water entry has little effect on the velocity of the revolution body. The larger the angle of water entry, the greater the peak pressure and the faster the pressure decay at the moment of water entry.
To explore the effects of material density on the cavitation flow field of a projectile entering water at an oblique angle at 300m/s, numerical simulations were conducted. The model was based on the finite volume method, VOF (Volume Of Fluid) multiphase model, Schnerr-Sauer cavity model, SST(Shear Stress Transfer) k-ω turbulence model and dynamic mesh method. The evolution laws of cavity shape, motion characteristics and hydrodynamic characteristics of water entry are analyzed. The research results show that the numerical calculation method can effectively simulate the change of cavity shape during the water entry of the projectile. The larger the density is, the smaller the diameter of the cavity formed after entering water is; the longer the cavity is, and the smaller the diameter of the cavity opening is; The peak value of pressure on the surface of projectile with different density is the same at the moment of entering water, but the projectile with larger density experiences a slower rate of the surface pressure decline; Moreover, the larger the density, the smaller the acceleration peak value of the projectile at the moment of entering the water, the slower the velocity decay after entering the water, and the deeper underwater at the same time.
The presence of cavitation and turbulence in a diesel injector nozzle has significant effect on the subsequent spray characteristics. However, the mechanism of the cavitating flow and its effect on the subsequent spray is unclear. The initiation, development and collapse of the cavity are strongly influenced not only by the injection pressure and back pressure but also by the nozzle geometry. The numerical simulation of cavitating flow in nozzle holes of a vertical multi-hole injector with mixture multi-phase cavitating flow model was carried out. The effects of sac geometry, hole entrance curvature radius and hole inclination angle on the cavitating flow in nozzle holes were investigated. It is finally concluded that the performance of IMPROVED nozzle is better than that of STD nozzle and VCO nozzle and small inlet turning angle of the orifice can enhance the atomization of the spray.
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