Abstract
The experimental study of vortex induced vibration needs to be carried out in water tunnel, but in previous associated simulation work, the water tunnel was treated as an infinite flow field in the depth direction with the effect of the free surface neglected. In the paper, the dynamic characteristics and physical mechanisms of a passive turbulence control (PTC) cylinder in a flow field with a free surface is studied, and the combined technique of a volume of fluid (VOF) method and vortex-induced vibration (VIV) was realized. In the range of Reynolds number studied in this paper (3.5 × 104 ≤ Re ≤ 7.0 × 104), the dynamic parameters (lift and drag coefficients), vortex structures, VIV response (amplitude and frequency ratios), and energy harvesting characteristics of a PTC cylinder under different flow conditions were obtained. The study found that: (1) the shear layer was made more unstable behind the cylinder by the free surface, which made it quicker to reach periodic stability, and the asymmetry shortened the initial stage of vibration of the oscillator, which made it easier to produce dynamic control of the motion of the oscillator; (2) the presence of the free surface only affected the positive amplitude ratio, but had almost no effect on the negative amplitude ratio; (3) the frequency ratio in the free surface flow was closer to the experimental data; (4) the presence of the free surface did not affect the detached vortex pattern in the flow around the stationary cylinder, but in the VIV, the lower the free surface height Z, the more vortices that were shed from the moving cylinder.
Highlights
The phenomenon of vortex induced vibration (VIV) widely exists in engineering, especially in the fields of oil, port, coastal, and offshore engineering
It can be seen from the two graphs that the separation points S on the upper surface and S’ on the lower surface of the passive turbulence control (PTC) cylinder developed backward with the increase of the flow velocity, which could be attributed to the fact that the turbulence intensity increased with the increase of the Reynolds number, and stronger turbulence delayed the boundary layer separation
Of the symmetrical flow field, the maximum value was obtained at Re = 5.3 × 104 (U = 0.6 m/s). It can be seen from the whole figure that the frequency of the free surface flow field was closer to the experimental data than that of the symmetrical flow field
Summary
The phenomenon of vortex induced vibration (VIV) widely exists in engineering, especially in the fields of oil, port, coastal, and offshore engineering. The existence of a free surface will affect the vortex-induced vibration phenomenon. Most experts and scholars have not considered the influence of a free surface on VIV performance. It is necessary to consider the influence of a free surface when studying the VIV phenomenon. Most of the experimental and simulation studies of vortex-induced vibration of blunt bodies use a uniform, symmetrical single-phase flow field. The researchers simplified the experimental conditions and studied the uniform flow field without considering the influence of the free surface.
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