Prediction of full scale wake characteristics based on model wake survey

Article type: Research Article

Authors: Hoekstra, M.

Affiliations: Netherlands Ship Model Basin, Wageningen, The Netherlands

Abstract: This paper deals with the problem of the prediction of the effective wake distribution in the propeller plane of a ship, using the measured nominal wake of a model as a starting point. The chosen prediction method consists of two successive steps, viz. a scale effect correction to obtain the nominal wake field of the actual ship and the prediction of the difference between nominal and effective wake. With regard to the scale effect, a method is introduced based on a threefold contraction of the model nominal wake field in dependency of its harmonic content. An empirical approach is used to account for the scale effect on the diffusion of the wake peak in the centerplane which starts as soon as the flow has left the stern. Further, the scale effect on bilge vortices, assuming that they are generated near the same point on ship and model, is calculated. Application of the method shows promising results. It is felt, however, that our knowledge of the scale effect on generation of bilge vortices is unsufficient at present. The need for more correlation data is emphasized. Concerning the transition from nominal to effective wake, a rough estimate is made of the influence of the propeller-hull interaction on the flow by a.an approximation of the influence of the image of the propeller in the hull.b.a concentric contraction of the wake field to account for changes in the boundary layer profile andc.the calculation of the effect of screw race contraction on the axial velocity distribution in the bilge vortex, if present.

DOI: 10.3233/ISP-1975-2225002

Journal: International Shipbuilding Progress, vol. 22, no. 250, pp. 204-219, 1975