Working mechanism of pre-swirl stator based on stereoscopic particle image velocimetry

Abstract

The pre-swirl stator (PSS), as a type of energy-saving device, has garnered increasing attention due to efforts aimed at global energy-saving and emission reduction. Owing to the influence of the stern profile, the wake field at the stern is complex, and the installation of such energy-saving appendages further increases its complexity. To explore the flow mechanism of a ship's wake field and the working principles of energy-saving appendages, this study used a scale model of a bulk carrier as its research object and conducted a wake field experiment with the help of the large underwater stereoscopic particle image velocimetry system at Harbin Engineering University. The wake field data of several sections were obtained, including the axial velocity, tangential velocity, average kinetic energy, vorticity, swirl strength, streamline, pulsating velocity, turbulent kinetic energy, and axial velocity at different radii. The wake field data with or without a PSS in the bare hull condition and with or without a PSS in the self-propelled condition were compared. The time-averaged flow field clearly demonstrated a “hook-like” velocity profile, bilge vortex, hub cap vortex, and other flow structures, as well as the flow details around the PSS. The results showed that the PSS could destroy the contour structure of the axial velocity, which mainly affects the range of 0.5–0.8R, making the flow field more uniform. The PSS has a certain influence on the flow field on the side without the stator blade and a great influence on the tangential velocity by producing a pre-swirl flow in a direction opposite to the propeller rotation in front of the propeller plane. This pre-swirl flow can increase the inflow of the propeller disk and improve the working conditions of the propeller. The PSS also has an influence on radial velocity; however, the influence degree and range are smaller than that on the tangential velocity. The PSS changed the water inflow direction, increased the interaction angle between the water flow and propeller blade, improved the wake conditions and propulsion performance, and was conducive to improving the working efficiency of the propeller. Moreover, the existence of a PSS reduced the local pulsating velocity and turbulent kinetic energy, benefiting the structural strength of the propeller.