Influence of rotation on the flow over a cylinder at Re = 5000

Abstract

The influence of the rotation ratio on the forces acting on a circular cylinder at Re=5000 has been investigated by means of direct numerical simulations (DNS). Spin ratios in the range 0⩽α=UT/Uref⩽5 have been considered. The results showed that rotation causes vortex shedding to cease for spin ratios α⩾2, in very good agreement with previous numerical and experimental research. Furthermore, as a consequence of the increased angular velocity of the cylinder the onset of Taylor–Görtler structures is also observed. Symmetry in the flow is broken as rotation ratio increases. This is specially evident in the shear layers as they start to curve towards the side with the lower pressure gradient causing the shrinkage of the vortex formation region. As these changes occur, both the stagnation point and the saddle point, formed in the closure of the recirculation region, shift in location coming closer to each other as the rotation ratio increases. For larger rotational speeds, the recirculation area behind the cylinder disappears and shear layers roll over the cylinder creating a “circumvolving” layer that greatly changes the wake topology. For α⩾4, the circumvolving layer forces the stagnation point off the cylinder surface, whereas for α=5, the accumulation of vorticity close to the stagnation point makes vortices to be shed on one side of the cylinder. Moreover, the changes that rotation cause on the aerodynamic forces on the cylinder are analyzed and discussed in detail.