Experimental and numerical study of free surface effect on the ventilated cavitating flow around a surface vehicle model

In the current study, the ventilated cavitating flow for a model near the free surface is investigated experimentally and numerically. The experiments are performed in a towing tank equipped with a ventilation system, drag measurement interface and a photography system. The numerical simulation is performed by commercial CFD code ANSYS-CFX with the volume of fluid (VOF) method, the RNG k-e turbulence model, and effectiveness of the gravity. The ventilated supercavity and drag coefficient of the model under free surface effect is studied at different submergence depths and velocities. Both the experimental observations and numerical predictions show that with increasing the Froude number (Fr), the ventilated supercavity size increases and the drag coefficient decreases. The good agreement observed between the numerical predictions and experimental data, in terms of both the supercavity size and drag coefficient, has revealed the accuracy and capability of the applied numerical model. The numerical results reveal that with increasing the submergence depth, the drag coefficient increases due to existence of the cavitator at the front of the vehicle. Also, in the regions near the free surface, the variation of supercavity length with Fr is different from that of the regions away from the free surface.