Effect Of Geometric Parameters Of Wind Fairing On Vortex-induced Vibration Of Π-section

Π-shaped beam is widely used in modern bridge construction due to Π-shaped beam’s reasonable stress,convenient construction,and good economic benefits.As typical bluff body section,the two side box Π-shaped beam is sensitive to wind load.Wind-induced vibration,especially vortex-induced vibration is a serious problem.In practical engineering,it is necessary to add vibration suppression measures to improve the aerodynamic performance of Π-shaped beam.Vortex-induced vibration is very sensitive to the aerodynamic shape.The aerodynamic measures improve the aerodynamic performance of the structure by changing the aerodynamic shape of the structure which change the flow field around the structure.Wind fairing is a commonly used measure to improve aerodynamic performance the Π-shaped beam.In this paper,pressure measurements and vibration measurements were used for the Π-shaped beam in wind tunnel.The influence of the wind fairing on the vortex vibration response of the doublesided box Π-shaped beam can be derived from comparing the vortex vibration response and surface pressure characteristics.The main research contents include:(1)Based on vibration test,the vortex response of the double-sided box Π-shaped beam under different wind speeds can be obtained,and the vortex response characteristics of the original section at different stages are analyzed.On this basis,the vibration test of sections which install wind fairing with different geometric parameters were tested.This study found that the vibration suppression effect of wind fairing is related to geometric parameters(l,h).(2)A few of sections with wind fairing are selected for further analyzed due to special vibration phenomenon.By comparing and analyzing the distribution of average pressure coefficient,fluctuating pressure coefficient,vortex-induced aerodynamic force,time-frequency characteristics of texted points,correlation and contribution of measuring point,it is found that,in the vortex-induced vibration range,the distribution trends of pressure and vortex-induced force are similar,the distribution of aerodynamic parameters in the static state and the fixed state of the model are basically consistent.In the vortex vibration range,the fluctuating pressure at each measuring point has the same predominant frequency as the fundamental frequency of the beam;improving the surface flow field under the structure is the key to the vibration restraint.(3)The original section and the section with different wind fairing measures were numerically simulated.By comparing and analyzing the changes of flow around the sections,it is found that the wind fairing measures change the airflow separation of the upper and lower surfaces of the front edge of the structure,especially the airflow separation of the front edge of the upper surface is significantly weakened.The flow around the structure of the ineffective vibration restraint measures is similar to the original section,but the vortex velocity and shedding time of the lower surface are changed.