Investigation of the Influence of the Methods for Estimation of Scale Effects on Wake Distribution on the Prediction of Excitation Forces from Propeller

Abstract

The scale effect on the wake distribution at the propeller plane has an important influence on the prediction of the shaft horsepower, the designing of the propeller and the ship vibration excited by the propeller. The authors have two purposes mainly in this study. One is the experimental investigation of scale effects on wake distributions by use of geometrically similar models of fine form and full form ship. So the authors examine the problems of various methods for estimation of wake distrubutions within the range of the Reynolds numbers at these experiments. The other is the investigation of the influence of the methods to estimate the full scale wake distribution on the theoretical prediction of propeller excitation forces. It confirms experimentally that the peak values of the wake fraction decrease as the dimensions of the models become larger in both full form and fine form ship models. This scale effect can not be explained by Sasajima-Tanaka's method, but can be represented by Tanaka's and Himeno's method. Calculated bearing forces, moments and pressure fluctuations induced by a cavitating propeller are strongly influenced by the estimated wake distribution of a ship. Their predicted values in the estimated wake distrubution by Sasajima-Tanaka's method are higher than by Tanaka's and Himeno's method.