Effect of pitch-to-diameter ratio and row-spacing-to-diameter ratio of venting holes on evolution process of air film around a vertically launched underwater vehicle

Equipping a slice of air film on a vehicle's exterior can realize the goal of load reduction and attitude control in the vertical water-emerging process. Similar to ventilated cavity, the performance of this air film depends on the venting structures and their arrangements. Based on the simulation of vehicle's water-emerging processes with exhaust, the effect of pitch-to-diameter ratio (s/d) and row-spacing-to-diameter ratio (l/d) of venting structures on evolution process of air film is investigated. Results indicate that the increase of s/d promotes the fast growth of air film, but makes the circumferential merging of adjacent air films slow. Two rows of inline-arrangement venting structures enhance the exhaust. And with the increase of l/d, the air film extends faster accompanied with its thickness enlarged. Further increase of s1/d1 for double-row-hole cases (based on the reasonable design of s/d and l/d) brings about little improvement to the air film, while, "more-smaller" hole1 can promote the circumferential coalescing of adjacent air films near venting structures, and provide more opportunities for hole2 being covered by air film considering the rotation of vehicle.