Cavitating flow evolution and restoring-moment generation mechanisms induced by wraparound fins on underwater vehicles

The attitude of high-speed underwater vehicles in the pre-exit stage is strongly influenced by cavitating flow structures and nonlinear hydrodynamic loads. Although wraparound fins (WAFs) provide a passive means of generating restoring moments under constrained spatial conditions, the coupling among WAF geometry, cavity evolution, and restoring moment generation remains unclear. This study investigates the restoring-moment response of WAFs under a prescribed fully submerged cavitating condition using computational fluid dynamics simulations and a surrogate-assisted design exploration method. A Gaussian process regression model optimized by a genetic algorithm is developed to characterize the nonlinear relationship between WAF geometric parameters and hydrodynamic responses, and is coupled with the Non-dominated Sorting Genetic Algorithm II to identify representative configurations balancing drag and nose-down restoring moment. The results show that WAFs modify tail pressure distribution and cavity structures, changing the pitching-moment response from nose-up to nose-down under the investigated condition. Sensitivity analysis indicates that the wrap angle dominates drag variation, while the deployment and wrap angles jointly control the nose-down restoring moment. Further flow analysis shows that, for the larger WAF configurations, the attached-cavity closure region and pressure center migrate upstream, accompanied by a reduction in the effective moment arm and a diminishing increase in restoring moment. These results support a time-averaged association among cavity closure, pressure redistribution, and restoring-moment response within the present steady Reynolds-averaged Navier–Stokes framework.