Influence of Design Parameter Variations for Propeller-Boss-Cap-Fins on Hub Vortex Reduction

Abstract

The present study aimed to identify significant design parameters on the propeller open water efficiency and characteristics of the wake field of a propeller with propeller-boss-cap-fins (PBCFs), with special attention to hub vortex dynamics. A towed underwater stereoscopic particle image velocimetry system was used to measure the near wake fields of a five-bladed propeller and a PBCF model. Through model tests, it was confirmed that the disappearance of a low-pressure area behind a boss cap, i.e., a reduction of the hub vortex, was the dominant contribution to open water efficiency gains from PBCF rather than a decrease in net torque. Global force and wake fields were also measured in response to design parameter variations of PBCF, i.e., fin chord length, fin span height, pitch angle, and phase lag. In the cases of pitch angle and fin chord length variations, PBCF with a light loading configuration had better open water efficiency than the baseline PBCF. However, in the case of a short fin span height for light loading configuration, the hub vortex was not entirely prevented, and the total open water efficiency decreased. Under heavy loading configurations, excessive negative and torque degraded the open water efficiency. Phase lag variations were less effective with respect to the open water efficiency than other design parameter variations.