Objectives  In order to study the precise flow field of rudder cavitation and its related laws of unsteady hydrodynamic performance,

  Methods  a propeller and rudder model of a certain ship is established, and a structure grid, SST k-ω turbulence model and VOF method are used to calculate the rudder cavitation. In order to understand the phenomenon of rudder cavitation, an observation experiment is carried out with a real ship. The calculated results are compared with the experimental results, proving the reliability of the numerical method. The periodic changes in rudder cavitation are then discussed and analyzed, and rudder cavitation is calculated on the basis of cavitation and non-cavitation under the two states of three kinds of rudder angles.

  Results  The results show that when the cavitation range is small, it has little effect on average rudder force. As the cavitation range increases, its influence on average rudder force increases significantly while lateral rudder force decreases significantly. Once cavitation occurs, the amplitude of unsteady force increases greatly; the greater the cavitation range, the greater the amplitude of unsteady force.

  Conclusions  The results of this study can provide technical support for assessing the hydrodynamic performance of rudders under cavitation conditions in the pursuit of optimal rudder design.