An overset RaNS prediction and validation of full scale stern wake for 1,600TEU container ship and 63,000 DWT bulk carrier with an energy saving device

Abstract

Two merchant ships (1,600TEU container ship, 63,000DWT bulk carrier with a type of pre-swirl duct energy saving device in the stern) are subjected to viscous CFD analysis aiming to investigate the capability of viscous CFD to estimate stern wake in full scale. Rigorous validations are made for the computational results of resistance, propulsion parameters and local flow fields using available measurement data both in model and full scale for the two vessels. The verification study for the container ship in full scale shows the difficulty to achieve grid convergence in propulsion parameters, yet the solution difference for these parameters are mostly below 1.7% of fine grid (~12M cells) solution. The effect of surface roughness becomes apparent not only in powering estimation but also in nominal and total wake distributions. The propeller rotation speed for the container ship in full scale is estimated well by the present CFD within 0.2% of difference compared to the measured data in full scale when the surface roughness is considered in the computation. The total wake in full scale in the vicinity of stern/ESD predicted by the present CFD simulation agree very well to the optical measurement data when the surface roughness is taken into consideration. Investigation of the total wake for the bulk carrier implies that the ESD should be designed based on the flow including both scale effect and the surface roughness. Throughout the validation and investigation of the present computational results in full scale, several common practices are suggested for predicting stern flow using full scale viscous CFD simulation together with the existing recommended procedures and guidelines by the ITTC.