Analysis Of Coupled Structural Characteristics Of Airfoil And Vortex Induced Vibration Cylinder

In coupled structures comprising multiple models,downstream models often exhibit different states due to the influence of wake,and the vortices generated by wake can also interact with each other.The impact of wake may lead to changes in the structural vibration,dynamic response,and subsequently alter the performance and stability.When the incoming flow is strong,flow separation is likely to occur at the blade root of wind turbines,and the tower may also face the issue of vortex-induced vibration(VIV)causing damage.To address such fluid-structure interaction problems,this paper investigates the two-dimensional foil-VIV cylinder coupled structure models for both blade and flexible tower,considering the coupling between the foil and cylinder in the structural field and the flow interference of the cylinder in the flow field.Specifically,the effect of vortex-induced vibration of small circular cylinder at the foil leading edge on foil aerodynamics is studied,and the vortex characteristics of the foilVIV cylinder coupled structure and the mechanism of the nonlinear energy sink(NES)on cylinder VIV mitigation are explored.Fluid-structure interaction problems consider the interaction between fluid and solid,where the solid deforms under the influence of fluid,and the deformation of solid,in turn,affects the flow field.The blade is susceptible to flow separation when strong winds occur,and a slender flexible cylinder structure at the blade leading edge can mitigate flow separation.The flexible cylinder generates vortex-induced vibration when the incoming flow passes,and this paper performs numerical simulations by adding single or double vortex-induced small circular cylinders at the blade leading edge.By analyzing the bi-directional fluid-structure coupling,the deformation of the flexible cylinder is closer to the actual situation,and the inhibitory effect on blade flow separation is studied,which is of great engineering significance for the practical design and safe operation of wind turbine blades.VIV of flexible towers at high wind speeds can cause fatigue damage or even structural failure.Typically,blades are located upstream of the flexible tower,and the interference of blade wakes under strong winds is more likely to induce larger-amplitude VIV downstream.Investigating the VIV characteristics of flexible towers is a prerequisite for the design and vibration control of flexible tower wind turbines.Clarifying the mechanism,vibration patterns,and influencing factors of flexible tower VIV induced by high winds is one of the important research topics in this paper.The study of coupled structural vibration and vibration reduction is more complex but more realistic.The basic principle of NES is to transfer energy from the main system to an energy trap to suppress the vibration of the main system.NES does not require external.energy supply,can achieve vibration control over a wide frequency range,and is easy to implement.Based on the various advantages of NES,this paper will simulate the effect of NES on the VIV control of flexible towers in coupled structures.This paper establishes two types of coupled structures and analyzes their fluid-structure coupling characteristics.The specific research contents include:(1)Based on the theories of structural dynamics and computational fluid dynamics,a two-dimensional foil-cylinder model was established.The accuracy of the foil’s aerodynamic performance and the cylinder’s VIV was verified by comparing it with experimental literature data,ensuring the reliability of NES for suppressing cylinder VIV.(2)Single and double vortex-induced vibration small cylinders-foil coupled structures were established to study the influence of vortex-induced vibration small cylinders at different positions on the aerodynamic performance of the foil.The suppression effect of single and double cylinders on flow separation under different angles of attack was analyzed,and the vibration response of cylinder displacement and frequency was observed.(3)A foil-VIV cylinder coupled structure was established to simulate the VIV response of the cylinder at different shutdown positions.NES was introduced into the coupled structure to observe its suppression effect and range on cylinder VIV.The flow characteristics,vibration patterns,and vibration reduction mechanism of cylinder VIV under different NES structural parameters were explored to provide a reasonable and effective vibration control scheme.Results showed that the introduction of small cylinders at the leading edge of the airfoil can effectively suppress flow separation and enhance aerodynamic performance.The optimal range of attack angles varies with the number and placement of the cylinders.Regarding the mitigation of VIV,the frequency and amplitude of cylinder oscillations are influenced by the distance from the airfoil and the rotational angle.The installation of appropriate parameters in the NES method proved to be effective in suppressing vortex-induced vibrations of the cylinder downstream of the airfoil wake.