Research Of Flow Around The Cylinder And Vortex Induced Vibration Under Multi-Factors

The flow around the cylinder is a common physical phenomenon,which exists widely in nature and engineering.In engineering applications,the flow characteristics of the cylinder are influenced by multiple factors,such as the cross section of cylinder,fluid flow form,natural vibration and so on.At the same time,under the action of fluid the cylinder is easy to occur vortex induced vibration and cause structural fatigue damages.Therefore,the research of flow around cylinder and vortex induced vibration under multiple factors is of important theoretical and practical significance for engineering design and optimization.And it can also lay the foundation of providing new methods of oscillatory suppression and drag reduction of cylinders.Researches and main results of this paper are as follows:Firstly,the flow characteristics and wake characteristics of four different cross-section cylinders,include circular cylinder,triangle cylinder,rectangular cylinder and hexagon cylinder,are compared and analyzed.The study found that the flow characteristics of the triangle cylinder,rectangular cylinder and hexagonal cylinder are related to the form of placement.The separation points of triangle cylinder,square cylinder,hexagonal cylinder are relatively fixed,and the separation point of circular cylinder is not fixed.The vortex shedding and the flow field characteristics of four cylinders are similar.Under the same Reynolds number,with the increase of the edge numbers,the fluid force and the vortex shedding period become larger.Then,numerical simulation of flow field around circular cylinder in pulsating flow is calculated(take circular cylinder as an example).By changing the pulsating frequency and amplitude of the pulsating flow at the entrance to analyse the control parameters and vortex structure of circular cylinder under different pulsating flowconditions,and the effects of pulsating frequency and amplitude on the flow around the circular cylinder are investigated.The study found that with the increase of pulsating frequency and amplitude,the pulsation of flow field is enhanced.There is a locking phenomenon of the vortex shedding frequency when the circular cylinder in pulsating flow field.Finally,under the conditions of single degree of freedom and two degrees of freedom the vortex induced vibration of circular cylinder is studied.It is found that the vortex shedding frequency is locked on the natural vibration frequency of cylinder when the cylinder is in the locked area,and the cylinder produce resonance.The flow parameter curves present a beat phenomenon(the alternation of high frequency oscillation and low frequency oscillation).Under the single degree of freedom,the mass ratio has little effect on the transverse amplitude of the vortex induced vibration of a circular cylinder.Under two degrees of freedom,the transverse amplitude of the circular cylinder increases gradually with the increase of mass ratio when the mass ratio is smaller.The mass ratio has little effect on the transverse amplitude of the circular cylinder when the mass ratio is larger.When the mass is relatively small,the influence of the flow vibration to the transverse vibration must be taken into consideration.When the mass ratio is relatively large,the influence of the flow vibration on the system can be neglected.