Shock and Vibration

Volume 2016 (2016), Article ID 5298687, 10 pages

http://dx.doi.org/10.1155/2016/5298687

## Vortex-Induced Vibration Suppression of a Circular Cylinder with Vortex Generators

^{1}Key Lab of Structures Dynamic Behavior and Control, Harbin Institute of Technology, Ministry of Education, Heilongjiang, Harbin 150090, China^{2}School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China^{3}College of Architecture and Civil Engineering, Xi’an University of Science and Technology, Xi’an 710054, China

Received 30 November 2015; Revised 24 May 2016; Accepted 9 June 2016

Academic Editor: Carlo Trigona

Copyright © 2016 Shi-bo Tao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The vortex-induced vibration is one of the most important factors to make the engineering failure in wind engineering. This paper focuses on the suppression method of vortex-induced vibration that occurs on a circular cylinder fitted with vortex generators, based on the wind tunnel experiment. The effect of the vortex generators is presented with comparisons including the bare cylinder. The experimental results reveal that the vortex generators can efficiently suppress vortex-induced vibration of the circular cylinder. Vortex generator control can make the boundary layer profile fuller and hence more resistant to separation. The selections of skew angles and the angular position have a significant influence on the vortex generator control effect. By correlation analysis, it can be concluded that the vortex generators can inhibit the communication between the two shear layers and produce streamwise vortices to generate a disturbance in the spanwise direction.

#### 1. Introduction

The stay-cables and hangers are the key components of long-span bridges. They are prone to vortex-induced vibration (VIV) due to their high flexibility and low damping ratio. Although the VIV is self-limiting, it may induce violent structural vibrations and stresses that eventually lead to considerable fatigue damage and reduction in the structural lifetime of stay-cables and hangers [1]. Therefore, strategies aiming at reducing vibration amplitudes for stay-cables and hangers are of great concern for industry and academia [2, 3]. Most of the algorithms of fatigue analysis of stay-cables and hangers subjected to VIV consider that the flow around an inclined circular cylinder can be considered equivalent to the one in which the free stream velocity is projected onto the direction orthogonal to the circular cylinder axis [4]. In the present work, we referred this simplification.

Flow control involves active and passive devices [5]. Active devices require energy expenditure. Kim and Choi [6] studied a forcing scheme for cylinder drag reduction by blowing and suction of fluid through two slits located on the surface of the cylinder. Muralidharan et al. [7] designed a suction control strategy for a circular cylinder and implemented it to assess its efficacy. Bigger et al. [8] applied open-loop control in the near wake of a disk in subsonic air and water flows. Passive devices require no auxiliary power and no control loop [9, 10]. Adachi [11] considered the influence of different surface roughness values for a circular cylinder wake. Chen et al. [12] investigated passive jet flow control technique to manipulate the vortex shedding process from a circular cylinder. Oruç [13] studied flow control around a circular cylinder with a screen that had a streamlined shape. Bao and Tao [14] used dual plates to control the wake of a circular cylinder.

Vortex generators (VGs) are effective at controlling boundary layer. This control method can stimulate vertical motions confined in the boundary layer and its close surroundings, hence, providing momentum enhancement in the vicinity of a wall [15]. The simple geometrical properties of passive VGs can provide relatively practical and low cost effective solutions to complex flow separation phenomena. Therefore, VGs are commonly used as flow control devices, especially in aerodynamic applications. Many results of using VGs to control stationary cylinders were available at present. Ünal and Atlar [16] used VGs to control the wake flow of a cylinder. Their study shows that vortex generators enforced the shear layers to bend towards the centreline and decrease the width of the wake. Shur et al. [17] show that VGs can produce a significant delay of separation and drag reduction in flows past smooth bluff bodies in the transcritical flow regime, with turbulent boundary layers ahead of separation.

In the present investigation, a vortex generator control method was adopted to mitigate the VIV of a circular cylinder. The Reynolds numbers in the present work were in the range of 10^{4}~10^{5}, which is within the subcritical regime.

#### 2. Vortex Generator Design

Based on the literature survey review, the triangular VGs are adopted in this paper. This is a thin plastic plate vortex generator with a 0.2 mm thickness as suggested by Godard and Stanislas [18]. Figure 1 shows the geometrical parameters. is the distance between the trailing edges of two triangular plates of one pair; is the height of the triangular plates; is the length of the triangular plates; is the distance between two passive devices; and is the skew angle. Before the experiment, we conducted computational simulations to determine the boundary layer thickness () of the circular cylinder. The boundary layer thickness was approximately 1.5 mm–1.9 mm near the separation line (Re = 10000). The height of the VGs can be greater than that of the boundary layer thickness. Therefore, the VGs used in this experiment were -scale, with . In the experiment, the heights of the VGs were set at mm. The sizes of the VGs were determined according to the suggestion given in [18]. In this way, , , and . Configurations of the VGs are shown in Figure 2, where is the free stream, and the positive and negative skew angle are shown in Figures 2(a) and 2(b).