Effect of Hole-to-Hole Spacing and Row-to-Row Spacing as well as Inclined Angle of Venting Holes on the Pressure-Equalizing Film along the Surface of a Vertical Launched Underwater Vehicle Free

Pressure-equalizing film is a slice of air layer attached to vehicle’s exterior with nearly uniform inner pressure. Similar to ventilated cavity in composition, it is generated through exhaust process via venting holes as vehicle travels from launch tube to water surface, and could significantly weaken the pitching moment and environment disturbance that vehicle suffers. Depending on the venting structure, the forming speed of this film as well as its covering range on vehicle’s exterior are the key factors that determine the improvement effect of vehicle’s trajectory stability. In this article, the emerging process of vehicle through the water layer with pressure-equalizing film is simulated. Based on previous work, single-row holes with different hole-to-hole spacings and double-row holes with different row-to-row spacings as well as inclined angles are chose to investigate the influence of geometry parameters and arrangements of holes on the evolution of air film and the hydrodynamic characteristics of vehicle. Discussions about the distribution of phase and pressure, mass flow rate, and vortices motion near venting holes indicate that, as the value of pitch to diameter ratio (s/d) increases with the same total exhaust area, film length grows faster with the inner vortex structures further development. As for the double-row hole cases, reverse flow between different rows of holes is induced which has enlarged the size of film covering the exits of back holes, leading to the faster exhausting of back holes. Besides, the decreasing of row-to-row spacing inhibits the growing of film length, and simplifies the flow structures that dominate the reverse flow. While as the venting holes gradually incline to the gravity direction (inclined angle changes from 90°/90°to 90°/45°to 45°/45°), the shearing action and impeding effect of surrounding water decrease, which have weakened the reverse flow and promoted the axial extension of air film in some degree.