Numerical Investigation of Unsteady Dynamic Characteristics of Discontinuous Gas Jets Emerging From Two Launch Tubes of Unmanned Underwater Vehicle

A three-dimensional numerical model was developed to investigate the dynamic characteristics of two discontinuous gas jets emerging from two launch tubes of an unmanned underwater vehicle (UUV), aiming to predict the complex multiphase flow and its effect on impact loads applied to the UUV. The accuracy of the developed model was verified through experimental validation. Furthermore, the unsteady behaviors of the two discontinuous gas jets under various launch conditions (including simultaneous launch, inconsistent chamber pressure, and launch timing) were obtained through comparative analysis. The results show that two discontinuous jets emerging simultaneously from two jet bubbles, and then undergo repeated cycles of expansion and contraction following their coalescence. Resultantly, negative drags on the UUV are substantial. Inconsistent chamber pressure in the two launch tubes results in differences in the pulsation period and dimensions between the jet bubbles. Consequently, asymmetric radial loads are imposed on the UUV. Moreover, inconsistent launch timing alters the evolutionary patterns, causing the two jet bubbles to evolve independently and leading to the disappearance of coalescence. In this case, the loads of the UUV are governed by the phase difference between the two jet bubbles.