Excitation And Suppression Of Vortex Shedding In The Wake Of A Circular Cylinder

The study of the generation and suppression mechanism of vortex shedding is of significance both in theory and engineering practice, and it is also an important issue discussed over a long period of time by many numerical and experimental researchers.The paper contains two parts, the first part describes the impulse disturbance excitation of vortex shedding from a two-dimensional stationary circular cylinder at a Reynolds number Re=48.8, which is very close to, but still lower than the onset Reynolds number of vortex shedding. The second part demonstrates the suppression of vortex shedding from a stationary circular cylinder set in a current-wave stream environment. Both numerical and experimental methods are used in the study.In the first part, an impulse transient jection disturbance is applied to the static circular cylinder wake from a slit of width lmm on the side boundary of the flow field. The control parameters are the slit location and the non-dimensional instant blow velocity at the lip of the slit. Long time vortex shedding is excited at a certain blow velocity if the slit position is in an effective zone from the cylinder to a certain downstream distance. The influence of blow velocity on the effective zone is also investigated.In the second part, the current-wave flow velocity is u=V∞+V0sin(2πfet), the ranges of Reynolds number Re=V∞D/v=100～200, the non-dimensional wave frequency feD/V∞=0～3.0 and the wave amplitude V0/V∞=0～0.8, where V∞ is the time average velocity of the on-coming stream, v is the kinematic viscosity of the fluid, fe is the wave frequency, and D is the cylinder diameter. One non-lock-on mode and three lock-on modes of vortex shedding is observed in the undisturbed cylinder wake. A persistent jet spurts out from a slit of width 1mm at the rear stagnation point of the cylinder to control vortex shedding. Results show that all the modes of vortex shedding can be suppressed when the relative ejection velocity Vb/V∞ is in effective zones within the range of 0～14. The influences of Reynolds number, wave frequency and wave amplitude on the effective zones are investigated and the control mechanism is discussed.