Effect of radial ventilation on drag reduction characteristics of underwater axisymmetric vehicle

With the growing demand for underwater vehicles in complex aquatic environments, drag reduction technology plays an increasingly critical role in enhancing vehicle performance and energy efficiency. This paper employs numerical simulations to investigate the drag characteristics and drag reduction effects of an underwater vehicle under radial jetting conditions, analyzing the flow field variations and drag mechanisms at different speeds and ventilation rates. The study reveals that, under low-speed conditions, radial ventilation leads to an increase in drag; however, under moderate- to high-speed conditions, the friction reduction becomes apparent as ventilation intensity rises, with a maximum drag reduction rate of 45.5%. Analysis of the drag components shows that an increase in speed contributes to a reduction in pressure drag, while frictional drag is effectively reduced with the increase in both speed and ventilation rate. Flow field analysis indicates that the gas layer formed by radial jetting significantly reduces frictional drag by decreasing surface shear stress. Furthermore, the expansion of the gas layer, along with the gas–liquid mixture effect, reduces the high-shear stress regions, thereby enhancing the friction reduction. In conclusion, the drag reduction effect of radial jetting is mainly achieved through the optimization of the gas layer distribution, shear stress modulation, and regulation of gas pocket behavior, with a clear dependence on both speed and ventilation rate.