Comprehensive Investigation of Flow Dynamics around Rotating Cylinders

Paper in proceeding, 2024

The study addresses the intricate dynamics of flow around rotating cylinders, a classic problem in fluid mechanics known for the Magnus effect. This research delves into unconventional yet compelling aspects of rotating cylinders, investigating the influence of rotational speed, incoming flow velocity, geometric shape, free surface, and angle of attack on lift-drag characteristics and wake flow fields. To begin with, fully parametric three-dimensional modelling of rotating cylinders was carried out using the Sobol design optimisation method coupled with computational fluid dynamics. The Sobol method efficiently explored the design space, focusing on critical parameters such as cylinder end diameters and lengths. The results revealed several local optimum values for lift and drag, showing the effect of the Magnus effect on vortex separation points and leading to significant variations in pressure and velocity distributions. Furthermore, the investigation was extended to the mode change of rotating cylinders in twophase flows through large eddy simulation. The findings showed that increasing the submergence depth generally improves lift generation, especially for rotations with higher speeds. At low submergence depths of less than one cylinder diameter, the pattern of vortices in the single-phase flow is altered under the same operating conditions. Surprisingly, the effectiveness of the Magnus effect diminishes at a depth of half the cylinder diameter. This study represents the first exploration of the mode change in rotating cylinders induced by two-phase flows. Additionally, the hydrodynamic performance of rotating cylinders at different angles of attack was investigated using an improved delayed detached eddy simulation method. The focus here is on the end effect of the rotating cylinder. The study identified an optimal spin ratio that maximised the lift-drag ratio while emphasising the profound influence of the angle of attack and spin ratio on the streamwise and crosswise vortex structures. In conclusion, this study not only sheds light on the intricate dynamics of flow around rotating cylinders and provides new insights into Magnus effect-induced phenomena, but also paves the way for future advances in engineering applications, such as optimising the performance of rotating structures in various fluid environments. Further exploration of these findings may contribute to the development of more efficient and robust engineering solutions in the fields of energy harvesting, aquatic robotics, and fluid transport systems.