Advances in full-scale wake-field predictions and the implications for the propeller design

In the design of propellers for today’s advanced ships important design trade-offs have to be made regarding propulsion efficiency, cavitation-related vibration excitation, inboard noise and blade erosion. For some types of ships the design margins are extremely small and successful propellers can only be designed when the ship’s hull generates a wake distribution that is sufficiently homogeneous. Therefore, it is becoming increasingly important to have reliable, accurate information on the characteristics of the wake field.
Until now it has been common practice to base the propeller design on the wake field measured on model scale. In recent years, however, considerable progress has been made in the prediction of viscous wake fields both at model and fullscale Reynolds numbers. Due to the increased quality of the solutions and the reduced calculation times these methods have become viable tools for obtaining wake field information.
In this paper the results of calculations are presented obtained from MARIN’s viscous-flow solver PARNASSOS on the wake field of a high block product tanker and a large container vessel. The numerical results are compared to the results of model experiments and sea trials. Scale effects on the wake field characteristics were determined and the implications of the wake scaling on important quantities in the propeller design such as the hull pressure fluctuations and propeller forces are assessed in a tentative manner.