Vortex structures in the wake of a buoyant tethered cylinder at moderate to high reduced velocities (Q597695)

The authors report a computational study of the flow past a tethered circular cylinder with mass ratio \(m^*= 0.833\). The Navier-Stokes and dynamic equations of motion of the cylinder are solved using a Galerkin spectral-element/Fourier method. The fluid forces acting on the cylinder, as well as the tension in the tether, are computed and used to determine the resulting cylinder motion. A large peak in the cylinder oscillation is noted for a reduced velocity \(u^*\) of about 19 corresponding to a negative maximum in the mean lift and a positive maximum in the RMS drag force. Analysis of vortex structures in the wake of the cylinder, for the cases of \(u^*= 15.4\), 19 and 21, reveals a subtle asymmetry in the shedding process which may provide a mechanism to explain this peak in oscillation amplitude.