Flow-induced rotation modes and wake characteristics of a circular cylinder attached with a splitter plate at low Reynolds numbers

Abstract

In this paper, the flow past a freely rotating cylinder-plate body is numerically investigated within a laminar flow region. The effects of Reynolds number and plate length on the rotary oscillation, wake flow, and hydrodynamic characteristics are examined. Numerical results indicated that the bifurcation phenomenon, i.e., the equilibrium position of the rotary oscillation deflects to a position which is not parallel to the free stream, is found in most cases. According to the variations of equilibrium position and root-mean-squared rotary angle (the root-mean-squared value of rotary oscillation obtained from sufficient stable rotary periods) against Reynolds number, three different rotation modes are identified: non-bifurcation regime without rotary oscillations (mode I), bifurcation regime with tiny rotary oscillations (mode II), and bifurcation regime with large rotary oscillations (mode III). Both the equilibrium position and root-mean-squared rotary angle increase first and then converge to a nearly unchanged value as Reynolds number increases. The splitter plate length has significant impacts on rotary oscillation responses. Generally, the cylinder with longer splitter plates possesses smaller deflection but larger root-mean-squared rotary angle. Moreover, a longer plate will push downstream the shear layer interaction, leading to a longer recirculation region and thus a smaller lift force. Due to the deflection, the upper and lower separation points of the rotatable cylinder-plate body are not symmetrical. The 2S vortex shedding pattern is recognized when the structure rotates, where two vortices are shed from the tip and the lower side of the plate, respectively. Additionally, three different reattachment behaviors are identified according to the position of the reattachment points: symmetrical reattachment (SR), asymmetrical tip-reattachment (ATR), and asymmetrical side-reattachment behavior (ASR). As compared with a bare cylinder, the rotatable splitter plate is helpful to reduce the drag and lift forces and meanwhile suppress vortex shedding.