CFD study of propeller tip vortex cavitation

Abstract

Tip vortex cavitation (TVC) caused by a marine propeller is a complex cavitating flow phenomenon, often featured by long helical trajectories making it challenging to simulate numerically. This paper presents a study on the CFD simulation of TVC with the focus on four key influence factors: mesh size, turbulence modeling, gas content, and Reynolds number. For the effect of mesh size, the simulations with different mesh refinement strategies show that the TVC is highly sensitive to mesh sizes and it is crucial to refine the mesh in the propeller wake. The adaptive mesh refinement method used in this study is shown to be effective in refining the mesh where the tip vortex locates. Compared with RANS (Reynolds averaged Navier-Stokes equations) method, IDDES (Improved Delayed Detached Eddy Simulation) method produces a noticeably better result since the dissipation of the tip vortex in the IDDES simulation is weaker. To suppress the dissipation of the tip vortices, vorticity confinement (VC) method is applied. The VC method significantly improved the TVC trajectory prediction for IDDES simulation, even with a less refined mesh, but it is not effective for RANS simulation. The effect of gas nuclei in water is considered by utilizing an Euler-Lagrangian method combined with a modified Schnarr-Sauer cavitation model in which a group of Lagrangian gas bubbles are used to model the non-condensable gas. The improvement on the TVC trajectory is notable by considering the air bubble effect. The effect of Reynolds number on TVC simulation is discussed by modifying the propeller's rotational speeds. Results show that the high Reynolds number gives a stronger tip vortex thus resulting in a longer TVC trajectory, but the improvement is limited compared with the effect of the other three influence factors.