Numerical study on unsteady propeller exciting characteristics considering shafting whirling vibration effect

In this paper, the unsteady exciting characteristics of a marine propeller influenced by the shafting whirling vibration effect are numerically studied by employing the dynamic sliding multi-region method and a Reynolds -averaged Navier-Stokes equation model. The propeller and shafting system inevitably vibrates during operation, where the multiple exciting forces can cause the shafting to rotate and whirl around different center lines at the same time, which is usually ignored in former studies on propeller exciting characteristics. To represent the complex whirling motion of the propeller, it is defined as a combination of revolution around its theoretical center line and rotation around its real center line. Firstly, a model for predicting the unsteady propeller exciting characteristics under different whirling motions is established, and an experiment of propeller transient forces is designed to validate the numerical model. Secondly, the influence mechanism of different whirling motions on the propeller exciting characteristics and propeller velocity field fluctuation are studied. Due to periodic fluc-tuation of the inflow velocity influenced by whirling, the propeller exciting fluctuates periodically. The linear relationship between propeller exciting and whirling amplitudes is found in the CFD and experimental results, which is caused by the linear increase of inflow velocity fluctuation amplitudes.