Mitigation On Wind Loads Girders Of Longspan Bridges By Pulsed Plasma With Dielectric-Barrier-Discharge Plasma Actuator

Convenient transportation is the basic project for the development of economy.Bridge is an important tool for crossing obstacles in land transportation.With the deepening of long-span bridge theory,the progress of bridge construction technology and the urgent demand of national economic construction,the span of long-span bridge has been constantly refreshed.But the history of bridge development is never plain sailing.In the history of the development of technology,human beings always take the loss of a large number of financial resources and even lives for exploration.For example,in 1940,the Tacoma bridge was damaged due to severe wind-induced vibration at the wind speed of 19m/s in the United States.This reshaped the bridge engineer’s cognition of the stability under the dynamic load of the bridge,which gave birth to the new discipline of bridge wind engineering.Up to now,bridge wind engineering is still combining with the needs of the times,constantly improve the theory and technology and it has opened up a new situation of modern bridges.After the long-span bridge has reached a certain degree of grace,it is easy to produce the common dynamic effects such as flutter and vortex-induced vibration due to its characteristics of fineness and softness.Flutter often causes violent shock to the bridge or even collapse of the whole structure.However,the amplitude of vortex-vibration is limited.Even so,it will affect the traffic comfort and cause structural fatigue to affect the safety.The primary problem of bridge wind engineering is how to reduce the dynamic response of bridge structure in wind.Based on previous studies on pulsed DBD flow control,this paper attempts to explore the feasibility and specific scheme of applying this method to the main girder for flow control,including the following contents:Firstly,based on the section size of main girder of the Danish Great Belt Bridge,an experimental model was made according to a certain scale ratio,and dielectric barrier discharge electrode was affixed to the model at the appropriate position.The DBD actuator system and the 3D printing wind tunnel experiment platform were built,and the test conditions were determined.Secondly,the pressure coefficient distribution on the upper and lower surfaces of the model was measured under different wind attack angles.Different starting positions of electrodes and different input parameters,and the aerodynamic force of the model was obtained by integrating.It was found that DBD had better flow control effect on the model under the condition of positive angle of attack,and the expected phenomena of reduced drag coefficient and pulsating lift coefficient appeared.Although the negative angle of attack still has a certain control effect,not as obvious as the positive angle of attack.This is caused by the asymmetric geometry of the upper and lower surfaces of the bridge section.In most cases,starting electrode no.2 at positive angle of attack and starting electrode no.3 at negative angle of attack can achieve better results.Pulsed excitation frequency is the parameter that has the greatest influence on the control effect.Finally,by analyzing the characteristics of the flow around the model at typical angles of attack and different frequencies,it is found that reasonable electrode arrangement and starting mode can effectively reduce the turbulent kinetic energy at the tail of the model and inhibit the vortex shedding at the tail.The turbulent kinetic energy and vorticity distributions at different frequencies are consistent with the results of pressure test.The excitation frequency is an important factor affecting the flow field characteristics.