INVESTIGATION OF CAVITIES SHEDDING CONDITION ON UNDERWATER VEHICLES IN THE VERTICAL LAUNCH PROCESS

Shedding phenomena of cavitation bubbles can change the characteristics of collapse pressure. Thusly, it is very important for structural design to investigate the influence of launch conditions on the shedding and evolution of cavitation bubbles. Firstly, the re-entry jet was affirmed as the control factor through the analysis of bubbles shedding. A dimensionless number S_ul was conducted as the ratio of periods of the re-entry jet motion and the vehicle motion. S_ul can describe the condition of bubbles at the moment when the vehicle is running through the free surface. Moreover, a series of numerical simulations were carried out to obtain the evolutions of flow fields and cavities in typical launch processes with different depth. CFD results verified theoretical results and calculated the parameters in the formula of S_ul by nonlinear fitting. Finally, the influence of important factors on shedding of cavities was discussed, such as cavitation number, Froude number, launch speed, and depth.