Effect of Propeller Reynolds Number on Self-Propulsion Performance

Abstract

In sel f-propulsion test of large tanker models, the characteristics of the model propellers seem to be affected by laminar flow separation on the propeller blade. In consequence, the results of such self-propulsion tests often show peculiar features, especially in the relative rotative efficiency ηR, considerably declining at low Froude numbers. In order to eliminate this laminar-flow effect, an attempt at applying the following three kinds of propellers to self-propulsion models was made by the authors: (1) low-pitch propellers (2) a wide-blade propeller (3) propellers with turbulence stimulators. Moreover, some investigations on propeller open-water characteristics and some flow-visualization tests of the propeller surface flow were conducted. The results of the investigations are summarized as follows: (1) The boundary layer on model-propeller blade is a laminar-flow in substance up to at least ND^2/ν=8×10^5, and three-dimensional separation takes place before ordinary transition from the laminar boundary layer to the turbulent one occurs; needless to say that the flow is turbulent downstream from the separation line. (2) It cannot be expected that the favourable results are obtained by using the low-pitch propeller and the wide-blade one in the self-propulsion tests. (3) In order to make the flow over the blades turbulent, turbulence stimulators are required.