Perforated shroud is one of the techniques for suppressing vortexinduced vibrations (VIV). In this study, we investigate the effect of a screen cylinder rolled from a screen mesh on the suppression of vortex shedding and VIV. The screen mesh was enfolded into a cylindrical form of required diameter. In measuring the VIV response, the amplitude of VIV of a bare pipe and a pipe inserted in a screen cylinder i.e. a screen shroud, was measured in a wind tunnel. It was shown that the screen shroud can suppress VIV by about 50%. In exploring the mechanism on VIV reduction, two sets of experiments using two Xtype hot wire probes were conducted on the screen cylinder and the solid cylinder separately. In the first experiment, the two probes are located at y/d = 0.5 (where y is counted from the wake centreline and d is the diameter of the cylinder) and separated in the spanwise direction to quantify the cross-correlation of the vortex structures in various downstream locations of the wakes. In the second one which was conducted at x/d = 10, one X-probe was fixed to provide a reference signal at the edge of the wake while the other probe was moved across the wake so that phase-average analysis can be used to examine the vortex structures in the two wakes. The result indicates that small-scale vortices are generated in the mixing layers of the screen cylinder wake, which merge to form the large structures at about x/d = 20. This result is in consistent with flow visualizations obtained previously. This is also supported by the velocity spectra obtained in the two wakes.
It is well known that a cylinder exposed to a steady current experiences vortex shedding for Reynolds number, Re, greater than 40.
