STUDY ON THE WAKE VORTEX INSTABILITY OF THE PROJECTILE LAUNCHED UNDERWATER

In the underwater launch process, the wake of the first projectile has flow interference with the hydrodynamic characteristics of the second projectile. Therefore, the research on the evolution mechanism of the wake vortex is of great significance to solve the problem of flow interference in the single launcher and multiple vehicles launched successively. In this paper, the improved delayed detached eddy simulation model and energy equation, VOF (volume of fluid) multiphase flow model, and overlapping grid technology is used to simulate the wake vortex of the projectile launched underwater. Simulation results are in good agreement with the experiment, which verifies the effectiveness and accuracy of the numerical method. Taking the wake region of the projectile as the key research object, the transient flow field distribution in the wake area is analyzed, the wake vortex is identified and its evolution is analyzed by using the vortex identification method, and the effects of the crossflow intensity and Reynolds number on the evolution of wake vortex and fluctuating pressure distribution are discussed. The results show that the interaction between the high-speed fluid core and the low-speed free flow in the wake region causes obvious Kelvin-Helmholtz instability in the wake. Under the effect of crossflow, the vortex rings shed at the vehicle tail and the vortex leg form a hairpin arc-shaped hairpin vortex. At the same time, a plurality of hairpin vortices is arranged at intervals along the axial direction to form a hairpin vortex package, which exists in the wake. With the increase of crossflow intensity, forming a multi-stage hairpin vortex package. The main reason for the appearance of the secondary peak of fluctuating pressure is the evolution of wake flow. With the increase of Reynolds number, the secondary vortex structure composed of the cylindrical vortex and U-shaped vortex in the wake becomes more and more obvious, and the instability increases.