报告题目：Experimental studies on the control of vortex shedding from a circular cylinder using screen shrouds

主讲人：Tongming Zhou教授

报告时间：2021年12月17日周五下午13:30-15:30

报告地点：线上腾讯会议，会议号395-563-202

主讲人简介：Professor Tongming Zhou has been in the area of fluid dynamics for more than 20 years. He obtained his PhD in 1999 in the area of Fluid Mechanics from The University of Newcastle (Australia). After completing his PhD, he worked as a post-doc fellow for about 2 years and then joined Nanyang Technological University, Singapore, as an assistant/associate professor. Since July 2007, he has been working with School of Civil, Environmental and Mining Engineering, The University of Western Australia. His main research interests include manipulation of vortex shedding and vortex-induced vibrations of cylindrical structures, renewable energy harnessing based on flow-induced structural vibrations, resonance of waves in the gap between a floating LNG facility and a LNG carrier and liquid sloshing in a partially-filled tank by conducting experiments on the hexapod.

报告摘要：Vortex shedding from a cylindrical structure can be destructive as this will cause structural failure if the shedding frequency matches that of the natural frequency of the structure. In the present study, screen shrouds, made of stainless steel screen meshes with porositiesb= 37%, 48%, 61% and 67%, were put concentrically outside of a circular cylinder as control elements for vortex shedding manipulation. Two kinds of experiments were conducted using PIV in a water flume. In the first experiment, the wake characteristics of the above screen cylinders were studied. Depending on the porosity of the screen mesh, two vortex formation mechanisms were identified. One was associated with wake instability (for the screen cylinders withb= 37% and 48%) and the other was associated with shear-layer (Kelvin-Helmholtz) convective instability (for the screen cylinders withb= 61% and 67%). In the second experiment, the wake characteristics of a circular cylinder enclosed inside the above four screen cylinders were studied. Depending on the porosity of the screen shrouds, the wake vortices were developed through two kinds of processes. The first one was found forb=37% and 48% and was attributed to wake mode instability, or absolute instability, of the shear layers generated from the edges of the screen shrouds. The bleeding flow from the gap between the screen shroud and the bare cylinder delayed the interactions between the shear layers and elongated the vortex formation length. The second one was found forb= 61% and 67% and was associated to the merging of the shear layer vortices originated from the edges of the screen shrouds with the vortices shed from the bare cylinder due to the gap flow. The latter was due to absolute instability caused by the reverse flow immediately downstream of the bare cylinder. In the future, the effects of screen shrouds on suppression of vortex-induced vibrations will be examined.