Numerical Study of Horizontal Launch Free Motions of Powered Natural Supercavitating Vehicles

The unique force characteristics constrain significant improvements in the motion performance of supercavitating vehicles (SCAVs). To enhance stable motion performance, understanding motion characteristics is essential. Considering factors affecting the stable motion, the horizontal launch free motions of propelled vehicles are simulated by developing a numerical method based on the dynamic model of a natural SCAV, and analyses are conducted on the impacts of launch water depth, initial motion velocity, and propulsive force on motion characteristics. The study reveals that intense changes in vertical velocity cause motion instability and determine the instability mode by affecting the vehicle’s motion attitude and afterbody hydrodynamic force. Motion performance is enhanced using the optimized geometric characteristic model and initial motion parameters influenced by launch water depth. A balanced initial motion velocity, where propulsive force and resistance are comparable, promotes stable motion. In such cases, the vehicle maintain relatively stable motion with periodic contact with the supercavity’s lower surface; however, the immersion depth of the afterbody gradually increases until complete instability occurs. Both a small initial speed and propulsive force contribute to rapid instability. To ensure a stable long-distance navigation, in addition to equipping propulsion, control forces provided by the fin are essential to counteract the increasing swing of the afterbody. This study can establish a foundation for the hydrodynamic layout and initial motion parameter design of high-performance supercavitating vehicles launched underwater by combining computational fluid dynamics simulations and experiments. It also provides support for research on the vehicle’s motion stability and control in complex motions.