Controlled oscillations of a cylinder: forces and wake modes

Abstract

The wake states from a circular cylinder undergoing controlled sinusoidal oscillation transverse to the free stream are examined. As the frequency of oscillation passes through the natural Kármán frequency there is a transition between two distinctly different wake states: the low-and high-frequency states. The transition corresponds to a change in the structure of the near wake and is also characterized by a jump in the phase and amplitude of both the total and vortex lift. Over the range of flow and oscillation parameters studied the wake states exhibit a number of universal features. The phases of the vortex lift and drag forces have characteristic values for the low-and high-frequency states, which appear to be directly related to the phase of vortex shedding. A split force concept is employed, whereby instantaneous force traces and images allow discrimination between the actual loading and the physics, and their conventional time-averaged representations. The wake states for the forced oscillations show some remarkable similarities to the response branches of elastically mounted cylinders. The equivalence between forced and self-excited oscillations is addressed in detail using concepts of energy transfer.

Three-dimensional flow past a fixed or freely vibrating cylinder in the early turbulent regime

“…The alteration of the flow length scales in the (x,y) plane is further discussed in Sec. V. Vortex formation tends to occur closer to the body when it vibrates, which corroborates prior visualizations of flows past oscillating cylinders [45].…”

Large Eddy Simulation of Flow Past a Stationary and Controlled Oscillating Circular Cylinder at Re=5500

“…The terms A and f e were defined after equation (9) while f K represents the Kármán frequency of the wake from a stationary cylinder. The parameters of the frequency ratios are based on the observations of [3] at Re=5000 with the goal of reproducing a close approximation of the experimental results measured by [3] and [7] at high Reynolds number. Figure 6 shows the force coefficients and the cylinder displacement y(t) for the frequency ratio f e / f K =0.80 and 0.85.…”

“…More recently, [6,7] performed controlled oscillation experiments at Re=2300, 4100 and 9100 with various amplitude ratios. They defined a transition state (2P mode equivalent to the upperbranch of the freely oscillating cylinder) between two distinctly different wake states, the low frequency wake state (2P mode equivalent to the lower-branch of the freely oscillating cylinder) and high frequency wake state (2S mode equivalent to the initial-branch of the freely oscillating cylinder), as the excitation frequency passes through the natural frequency.…”

“…The objective of the present study is to numerically examine the phenomenon of vortex switching from an oscillating circular cylinder observed in the experiments by [3,7] at high Reynolds number. The influence of this vortex switching on time-dependent forces acting on the cylinder and changes in wake mode are examined.…”

Optimal energy harvesting from vortex-induced and transverse galloping vibrations

“…Note how the 2 branch response is limited to A * = 0.6 which is closely related to the maximum value of oscillation expect for the lower branch. The vortex shedding structures downstream a circular cylinder under forced or free vibrations have been thoroughly investigated and classified in previous studies (Williamson and Roshko (1988), Brika and Laneville (1993); Govardhan and Williamson (2000) or Carberry et al, 2005). The most detailed map of vortex emission modes for forced vibration has been obtained by Morse et al (2009) at a Reynolds number of 4000 (Fig 3.2).…”