Experimental Study On VIV Of Two Cylinders In Tandem Arrangement

This paper firstly carried out the experiment of vortex-induced vibration of a single cylinder in air,and studied the influence of the mass ratio and spring stiffness on the vibration amplitude and vibration range of the cylinder.Then,the vortex induced vibration of two cylinders in tandem was carried out,and the influence of the restriction method of the upstream and downstream cylinders and the change of the spacing ratio on the vibration amplitude and frequency of the cylinders was analyzed.The range of the spacing ratio is 3D?s?14D.There are three ways to restrict the upstream and downstream cylinders,namely,the upstream cylinder is elastically restricted and the downstream cylinder is fixed;the upstream cylinder is fixed,and the downstream cylinder is elastically restricted;both upstream and downstream cylinders are elastically restricted.The main conclusions are as follows:For the vortex-induced vibration of the single cylinder,the smaller the mass ratio of the cylinder and the larger the spring stiffness,the larger the maximum amplitude ratio of the cylinder,and the larger the vibration range.For the vortex-induced vibration of two cylinders in tandem,the restriction method and spacing ratio of the upstream and downstream cylinders have a great influence on the vibration amplitude of the cylinder,but it has no effect on the vibration frequency.When the upstream cylinder is elastically restricted and the downstream cylinder is fixed,the upstream cylinder still maintains vortex-induced vibration within the spacing ratio of 3D?s?7D,but the maximum amplitude ratio and the vibration range have been improved.When the upstream cylinder is fixed and the downstream cylinder is elastically restricted,the vibration pattern of the downstream cylinder changes under a specific spacing ratio.When s =3D,the downstream cylinder is a combined vortex-induced vibration and galloping phenomenon.After the amplitude reaches the maximum,it continues to increase with the reduced velocity until the maximum reduced velocity that can be achieved in this experiment.When the spacing ratio increases,the influence of the upstream cylinder on the downstream cylinder decreases,and the vibration of the downstream cylinder approaches a single cylinder.When both the upstream and downstream cylinders are elastically restricted,the existence of the downstream cylinder has no effect on the upstream cylinder,but the downstream cylinder is deeply affected by the wake of the upstream cylinder.The downstream cylinder beats under the coupling action of the oscillating wake of the upstream cylinder and its own vortex-induced vibration.