Experimental Validation Study of the BEM for Supercavitating Propellers

Abstract A systematic study was conducted to experimentally validate the performance prediction capabilities of the Boundary Element Method (BEM) for supercavitating propellers with truncated trailing edges (TE). The study focused on steady super cavitating conditions and utilized the propeller test data of TMB 3767. A mesh sensitivity analysis and point distribution study was conducted to determine an optimum mesh for the propeller geometry and the treatment of the blunt TE. The predicted performance parameters and cavitation patterns were compared to those from the experimental data. Additionally, a study was conducted to evaluate the influence of cavitation index on the predicted performance parameters. The BEM performance parameter and cavitation pattern predictions showed strong agreement with experimental data for the chosen operating conditions, especially at low advance ratios and at maximum propeller efficiency. INTRODUCTION Throughout the past century, rigorous efforts were made to increase the speed of marine transport. Even today, there is a rising demand for high-speed marine crafts which has led to an ever-growing demand for high powered outboard engines (The Staff, 2025; Armstrong, 2023). To reduce the overall size and mass of these engines, small propellers with the capability to rotate at very high speeds to generate a large amount of propulsive power are required. The combination of large rates of rotation and inflow speed place these propellers in the super-cavitating flow regime. Super-cavitation is defined on the basis of the length of the vapor-filled cavity that interests the suction side of the blade in ideal design conditions. When the length of the cavitation bubble exceeds the chord length of a propeller section and collapses downstream of the propeller blade, the propeller or its blade sections are said to be super-cavitating. Conventional propellers were often based on NACA profiles and designed to avoid (and if not possible, minimize) cavitation to reduce adverse effects such as thrust loss, surface erosion, noise, and vibrations which occur when the cavitation bubble collapses on the surface of the blade. On the other hand, when cavitation is unavoidable, such as in the case of powered outboard engines and motorizing high-speed marine crafts, supercavitating propellers (SCPs) and hydrofoils (SCHs) are the chosen technology. Such propellers are designed to operate in supercavitating conditions with more efficiency than conventional propellers (Allison, 1978) as can be observed in Figure 1.