Flow-induced Vibration Of A Square Cylinder In The Vicinity Of A Plane Wall

Flow-induced vibration of a square cylindrical structure near the plane wall is of great significance in basic research and engineering applications.In practical,square cylinder structures near the wall are widespread,such as square suspension bridges,gravity platforms,etc.Naturally,it possesses significance to understand the effect on flow-induced vibration for the square cylinder in the vicinity of a plane wall.This study mainly aims at the vibration response mechanism of a square cylinder with varying incident angles near the wall.The cylinder is mounted at the horizontal mid-plane on the test section of the wind tunnel.The square cylinder,with diameter D=30mm and mass ratio m*=289.3,is elastically mounted on the spring system to promise the vertical 1-Dimensional oscillation.The incident angle a is defined as the angle between the incoming flow direction and the horizontal axis of the square cylinder.A plane wall is placed horizontally between the bottom test section wall and the square cylinder,here e indicates the gap widths composed by the wall and the bottom surface of the square cylinder,which is adjustable by rolling the lifting handwheel pairs.The gap ratio e*could be normalized as e/D.In the study,the selection of angles of attack a ranges from 0° to 45°,so does the gap ratio e*from 0.1 to 2.4,as well as the Re=0.174-1.93 x 104.The vibration response,vortex frequency and wake structure have been investigated.The result indicate that the vibration response of the cylinder classified into five regimes,i.e.,When ?=0°,regimes can be classified as(?)no vibration,(?)separated and(?)combined vortex excitation(VE)and galloping,and(?)galloping only.Yet as a=15°,300 and 45°,only two patterns appeared,which are regimes(?)and(?)VE only.Furthermore,the small e*reduces the vibration amplitude of the square cylinder,mainly because that the plane wall suppresses the vortex shedding from the square cylinder in the wake.Secondly,the vibration response significantly different from that at 0°and 5°,the galloping vibration will not occur at ?=15°,30° and 45°.