Flow around cylinders oscillating in transverse or in-line direction to the main stream has long been in the focus of attention. In real life, however, both transverse and in-line motions occur simultaneously, resulting in a two-degree-of-freedom (2-DoF) motion. Studies dealing with 2-DoF motions usually fall into two groups: (a) when the oscillation frequencies are identical in transverse and in-line directions (fx=fy) leading to an elliptical path and (b) when the oscillation frequency in in-line direction is double that of the transverse direction (fx=2fy), resulting in a figure-eight or a distorted figure-eight path depending on the phase angle difference between the two motions.
Forced figure-eight cylinder motion is investigated here against frequency ratio FR=fy/St0 (where St0 is the Stouhal number for a stationary cylinder at the given Reynolds number) for different Reynolds numbers Re with both clockwise (CW) and anticlockwise (ACW) orbit of the cylinder on the upper loop of the figure-eight path. It is found that both Re and direction of orbit have a major effect on energy transfer E between the fluid and the cylinder and on the time-mean of lift. The time-mean (TM) of lift is mainly zero when plotted against FR for the ACW orbit, and mainly positive and increases with Re for the CW orbit. Below a certain Re value the time-mean TM of lift becomes zero, leading to bifurcation of the results.
E values are mainly positive for the ACW orbit and increase with Re. Positive energy transfer values mean a potential risk of vortex-induced-vibration (VIV). Interestingly, E values remained negative in the investigated parameter domain for the CW orbit (no VIV danger).
Prof. Baranyi works at the Department of Fluid and Heat Engineering at the University of Miskolc (Hungary). He lectures primarily on fluid mechanics, heat transfer, and computational fluid dynamics. His field of research centers on fluid-structure interaction and numerical simulation. He spent two years as a visiting professor at Nagaoka University of Technology (Japan), and has given talks at universities around Europe. He is an editor of the Journal of Computational and Applied Mechanics, a regular reviewer for several leading journals, and a regular co-developer of sessions of the ASME Pressure Vessels and Piping conferences.