Vortex induced vibrations using Large Eddy Simulation at a moderate Reynolds number

This paper presents the results of a computational study on the vortex-induced vibration of a circular cylinder. We have performed a 2-D LES study of the VIV response of a circular cylinder at a Reynolds number of 8000 with a range of damping ratios and natural frequencies. A combined Dirichlet-Neumann outflow boundary condition was used to allow the wake vortices to pass through the outflow boundary, undisturbed by the boundary. In spite of the shortcomings of a 2-D representation, the results show the expected vibratory response of the cylinder for 0.555 < f(so)/f(N) < 1.59, where f(so) is the nonvibrating vortex-shedding frequency and f(N) is the natural frequency. For a solid cylinder with a mass factor (m*) of 7.85 and a material-damping ratio of 0.02, lock-on was observed for 0.793 < f(so)/f(N) < 1.39 with a peak at a reduced velocity of 5.5. Decreasing the value of material damping had the effect of increasing the extent of the lock-on range. A beating behavior in the oscillation was observed which diminished considerably as the damping value was increased. A decrease in the mass factor to 1.67 caused the lock-on range to broaden considerably as a function of reduced velocity. In addition, the amplitude of oscillation. increased by a factor of almost three for the lower value of mass factor. The standard 2S, 2P, etc. vortex structures observed at low Reynolds numbers for sinusoidal oscillations were not found in this self-excited case. Several reasons are suggested for this particular lack of agreement with some previous results. These results are seen to represent the VIV behavior of a cylinder reasonably well for the parameter values used in these calculations. (C) 2003 Elsevier Ltd. All rights reserved.