Simulation research on water-entry impact force of an autonomous underwater helicopter

Autonomous Underwater Helicopter (AUH) is a novel dish-shaped multi-functional submersible vehicle in the autonomous underwater vehicle (AUV) family. Numerical study of launch and recovery system for AUVs from a research vessel is significant in the overall design. Single-arm crane and air-launch way are the important ways of launching AUVs with the high expertise and security. However, AUVs are still easily subject to a huge impact load which can cause the body damage, malfunction of electronic components, and other serious accidents when AUVs are launching into water. In this paper, unsteady, incompressible, two-phase flow with identified boundary conditions was modeled in the computational domain using Volume of Fluid (VOF) technology, and different overset-grid sizes were set and analyzed to ascertain the accuracy of computational fluid dynamics (CFD) simulation first due to the setting of the grid which will directly affect the accuracy of the calculation results, especially the overset-grid convergence validation. Then, the change of water-entry impact force and velocity of AUH with different water-entry velocities and angles were calculated by CFD analysis software STAR-CCM + solver. The proper immersion angle of the AUH should be 75° under comprehensive analysis and comparison. Besides, the variations of pressure distribution of the AUH in the whole water-entry process were also obtained, which provides reference for the shape optimization in the future work.