Influence of appendages on the wake field of surface combatant based on stereoscopic particle image velocimetry

Abstract

As the supporting structure of a ship shafting, the shaft bracket has a significant impact on the hydrodynamic performance of the ship, especially the propulsion. To determine the influence of the shaft bracket and bilge keel on the wake field, we performed a surface combatant wake field experiment. The flow field of the model with/without appendages was measured in three different sections, and the wake field characteristics on the propeller disk with/without appendages were compared. The influence of the shaft bracket was investigated, revealing that the bilge keel exhibited a slight influence on the flow field, the shaft bracket can influence the wake field in the entire installation space, the influence of the outer bracket arm was more significant than the inner bracket arm, and flow separation occurred at the outer bracket arm. The shaft bracket exhibited a more significant influence on the area above the propeller disk, resulting in an uneven flow field. The vortices generated by the shaft bracket were paired in opposite directions, and the vortices generated by the outer support arm were dominant. The shaft bracket improved the turbulent kinetic energy and fluctuation velocity, increasing their local maxima. Simultaneously, the velocity boundary layer gradually thickened from front to back at different cross sections. The installation angle of the shaft bracket is critical for the uniformity of the propeller disk plane flow field. If the angle is excessively large, cavitation readily occurs, which has an adverse influence on the propeller.