3. An Experimental Study on the Stern Bilge Vortices of Full Hull Form

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At the bilge of full ordinary hull form, a pair of vortices is generated. To study the scale effect of the bilge vortices, the flow observations and velocity measurements on a small model of oil tanker were carried out in the circulating water channel, by means of boundary layer suction. The methods employed for flow observations were tuft grid, twin tufts, and chemical film. A small total head tube and a static head tube were utilized for velocity profile measurements, and a small blade wheel current meter for wake distribution. Consequently, it is cleared that, by the boundary layer suction at the fore part of run, the axes of bilge vortices come near the center plane and to lower position, the wake reduces considerably, the resistance coefficient induced by stern bilge vortices is nearly constant with various suction rate, and the large values of effective Reynolds number for stern bilge vortices are obtained. And, by the results of observations of limiting streamlines with twin tufts and chemical film, it is considered that the three dimensional flow separation occurs at stern bilge. In addition, the visualizations of flow at the stern bilge were carried out by means of electrolysis of water and injection of aluminium powder suspension. As a result, it is observed that the flow separates at the stern bilge, so bilge vortices are generated.
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