Hydrodynamic performance of a highly-skewed propeller in ventilated flow conditions near the free surface

This study investigates the performance of the INSEAN E1619 propeller—a seven-bladed generic submarine propeller designed by Consiglio Nazionale delle Ricerche–Istituto Nazionale per Studi ed Esperienze di Architettura Navale (CNR-INSEAN), the Italian Ship Model Basin—under near-surface conditions through experimental and numerical approaches. Experiments were conducted for semi-submersion and full-submersion scenarios at varying water depths to evaluate how proximity to the water surface influences propeller performance. Additionally, numerical simulations employed a Large Eddy Simulation model combined with a dynamic mesh technique. A two-phase flow, simulated with the Volume of Fluid method, provided insight into free surface effects, with a User-Defined Function governing the propeller's forward motion. A sensitivity analysis of the propeller model was performed using simultaneous grid and time refinement, validated against open-water test results obtained from the National Cheng Kung University towing tank. The simulation results indicated reductions in thrust and torque as the propeller approached the water surface. The ventilation effect was particularly pronounced at lower immersion ratios (hi) and advance coefficients (J). Subsequently, the combined effects of varying propeller immersion ratios (hi) and advance coefficients (J) on hydrodynamic performance and the flow structure around the propeller were thoroughly investigated.