Modified Magnus effect and vortex modes of rotating cylinder due to interaction with free surface in two-phase flow

Abstract

When employing rotating cylinders as ship anti-rolling devices based on the Magnus effect, the cylinders are near the free surface. However, most of the previous studies on rotating cylinders considered single-phase (SP) flows, where the interaction between the free surface and rotating cylinders was missing. In this study, we explore a rotating cylinder in a two-phase flow using large eddy simulation. Given low submergence depths of less than one cylinder diameter, the pattern of vortices classified as mode A in the SP flow under the same operation conditions is altered to mode E. As regards depths below 1.5 diameters, mode E is changed to mode F′. These modes mentioned above were defined by previous researchers to identify the different wake patterns of rotating cylinders. Increasing the submergence depth in general enhances the lift generation, and this effect is more significant for the rotation with a higher spin ratio of 4 as compared to another spin ratio of 0.5. Nevertheless, the Magnus effect fails when the higher spin ratio is set at a depth of half of the cylinder diameter. As the depth is increased, the drag from the lower spin ratio decays. In contrast, the higher ratio rises significantly up to the depth of two diameters and then drops. This study clarifies the importance of the free surface in affecting the Magus effect. It is also the first time that the mode change of rotating cylinders owing to two-phase flows has been found.