A Study into Surface-Piercing Propellers at Different Immersion Depths using a Towing Tank and a Numerical Method

Abstract

Surface-Piercing Propellers (SPPs) are essential categories of high-performance propulsion systems usually used for high-speed boats, which are designed to operate in semi-submerged conditions. In such conditions, a propeller performs in a two-phase mixed environment, consisting of water and air concurrently. Due to the intrinsic complexity of the working environment, describing the performance of an SPP is complex and cannot be recognized with the traditional submerged propellers. The present study aims to assess the effect of immersion depth on semi-submersible propellers. Accordingly, experimental tests in a towing tank were used along with a numerical method to achieve reliable results. In the numerical method, a sliding mesh was used to simulate the propeller's motion, and the volume of fluid was used to model the free surface. The hydrodynamic coefficients of the SPP, measured in the towing tank, were used to validate the numerical method. The outcomes of the numerical method were revealed to be in good agreement with the experimental data. The results showed that the critical advance coefficient decreased with the rise in the immersion depth. In detail, altering the immersion depth from 0.4 to 0.75 reduced the critical value of the advance coefficient from 0.8 to 0.7. The ventilation pattern also changed with increasing the immersion ratio. For a constant advance coefficient, the amount of ventilation increased at shallower depths of immersion.