During last decades, many investigations have been done to find suitable solutions to reduce the drag force of underwater vehicles. These attempts can be divided into two main categories: supercavitating vehicles and unseparated flow patterns. In this study, a novel approach is introduced which uses hydrophobic surfaces for an underwater vehicle with an unseparated flow body profile. Fluid slippage on hydrophobic walls can lead to a considerable reduction of skin friction drag. The effectiveness of this approach for underwater hulls has been examined numerically. In this regard, first, the numerical procedure is validated by comparing the numerical results for the slip flow over a micron-sized spherical particle with the analytical results available in the literature. Next, numerical simulations are performed for an unseparated flow profile at various values of the sliding coefficients. Results show that the principal drag of such profiles is the skin friction drag which can be drastically reduced using hydrophobic surfaces. For the sliding coefficients smaller than 10, the drag coefficient of the underwater vehicle with an unseparated flow profile can be even lower than that of a supercavitating hull.
Numerical Study on Air-involved Cavity during Water Exit of Underwater Vehicle
