ABSTRACT

Many kinds of Energy Saving Devices (ESD) have been installed on commercial ships to reduce fuel consumption. Among them, a fin attached to the hull surface is one of the simplest ESD. A fin installed on stern hull is focused in this paper. A fin controls the inflow velocity field to a propeller and the effect to self-propulsion factors is observed in the model test. However it is typically difficult to predict the effect by Computational Fluid Dynamics (CFD) because a fin is considerably smaller than the hull and there is a distance between a fin and a propeller. To clarify the mechanism of fin effect, not only the flow field but also the turbulence kinetic energy are measured and compared with CFD at the downstream of the model fin which is composed of the flat plate and the small fin.

INTRODUCTION

To improve propulsion efficiency of a ship, various kinds of Energy Saving Devices (ESD) have been developed and installed on commercial ships. For example, a duct, a fin, a rudder bulb, a propeller boss cap fin and etc. are installed for a real ship (for example, Dinham et. al.2017). A fin is one of the simplest and effective ESD among them. Sumitomo also has installed the fin at the upstream of the propeller (Fig. 1). The effect for self-propulsion factors can be measured on a model ship test and an actual ship speed trial. The effect can be predicted by Computational Fluid Dynamics (CFD) about the fin near upstream from the propeller. On the other hand, about the fin far upstream from the propeller, the estimation by CFD is difficult.

The fin which is installed on stern hull far upstream form the propeller is hardly affected by the propeller, so the direct interaction between the propeller and the fin is small, and the fin tip is usually in the boundary layer that has developed from the bow. It means the fin do not influence the non-viscous flow outside the boundary layer but influence the viscous flow in the boundary layer or its boundary, so the cause of the effect for the self-propulsion factor seems to be the distortion of the inflow velocity field to the propeller due to vortex shed from the fin.

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