Numerical Study On Vortex-induced Vibration Of Rigid Cylinders

Cylinders are one of the common structures in the field of engineering.When the fluid flows past the cylinder at a certain velocity,alternate vortices will be formed in the rear of the cylinder.When the vibration frequency of the cylinder is close to its natural frequency,it will cause the resonance and even the damage of the structure.Therefore,the ?? and its suppression of cylinders have always been a hotspot in the field of engineering.In this paper,the ?? of a cylinder at low Re was systematically studied,which lays a foundation for uncovering the coupling mechanism of the transverse and streamwise motion.On this basis,the transverse only ?? of an elliptical cylinder with different aspect ratios,the?? of a cylinder downstream of an elliptical cylinder with different aspect ratios and the transverse only VIV of cylinders with additional rectifiers are studied,which provides a novel idea for the suppression of VIV.The main research contents and conclusions are as follows:Firstly,the transverse,streamwise and 2DOF ?? of a circular cylinder at low Re are calculated.The results show that for 2DOF ?? the streamwise motion of the cylinder is derived from the non-linear coupling of the transverse and streamwise motion,instead of the fluctuation of drag or vortex shedding.Alternate vortex shedding gives rise to the periodic fluctuating pressure in the transverse,which further causes the vibration of the cylinder in the transverse.And due to the non-linear coupling of the system,the streamwise vibrates.Secondly,the ?? of an elliptical cylinder with different aspect ratios(corresponding to the inclined cylinder in 3D)at low Re and the ?? of a cylinder downstream of an elliptical cylinder with different aspect ratios are systematically studied.In the study of the motion response and wake modes of the elliptical cylinder,it is found that for elliptical cylinder with small aspect ratios,it is analogous to a circular cylinder equipped with an additional rectifier,which reduces the intensity of the flow.For elliptical cylinder with large aspect ratios,the response amplitude and forces acting on the cylinder increase significantly.Meanwhile,P+S and 2T*vortex shedding modes are observed in the wake.Finally,the VIV of a cylinder equipped with fairing at different top angles or splitter in different lengths are calculated.The results show that the parameters of the rectifying device calculated by a fixed cylinder are not accurate enough to describe the effect of the rectifying device on the ?? suppression of an elastically-mounted cylinder.