Effects Of Reynolds Number On Aerodynamic Characteristics Of A Bowl Steel Box Girder

The bowl steel box girder has a slender and beautiful shape,which is suitable for municipal bridges or landscape bridges.Because bowl box girder is curved in appearance,and surface flow characteristics are greatly affected by Reynolds number,which determines the aerodynamic characteristics and wind-induced vibration response of the section,it is necessary to study the effect of Reynolds number on the aerodynamics and wind-induced vibration of bowl section to guide the wind-resistant design of bridges.At present,scholars who study bridge wind resistance draw lessons from classical theory and experimental results of Reynolds number effect on the circular cylinder,carry out a lot of tests and put forward some instructive simulation methods,such as increasing turbulence of incoming flow and changing surface roughness of model to simulate Reynolds number effect.In order to reflect the actual bowl-type box girder aerodynamic characteristics more truthfully in low Reynolds number wind tunnel tests,obtain its static three-force coefficient more accurately,predict the wind speed and amplitude of vortex-induced vibration of bowl-type steel box girder,this paper realizes the simulation of different Reynolds numbers by changing the surface roughness of the model and the test wind speed.Then the effect of Reynolds number on static three-force coefficient and vortex-induced vibration characteristics of bowl steel box girder is studied.In this thesis,bowl-shaped steel box girder of a cable-stayed bridge design scheme is taken as the research object,and a section model with 1:60 geometric scale ratio is used for wind tunnel test research.Specifies include the following aspects:(1)Reviewed the domestic and international research status on Reynolds number effect of circular and rectangular sections,and summarized the relevant laws according to the previous research.The theory of flow separation of blunt body and the simulation of Reynolds number effect are introduced.Wind tunnel tests of cylinders with different surface roughness are carried out according to the theory.The flow separation points of cylinders with different surface roughness are observed.It is verified that the flow separation points of cylinders can be changed by wrapping special roughness sandpaper on the surface in the wind tunnel test of cylinder model.To achieve the purpose of simulation of flow around a curved cylinder in a low Reynolds number wind tunnel towards a high Reynolds number.(2)The three component test of the segmental model of bowl box girder was carried out.By changing the wind speed and surface roughness of the wind tunnel,the Reynolds number effect of the static three component coefficient of the main beam is studied.The results show that the drag coefficient and lift coefficient of bowl steel box girder have significant Reynolds number effects,which decrease with the increase of Reynolds number,but when they are in the high Reynolds number range,their Reynolds number effects can be ignored;The Reynolds number effect of the section lifting moment coefficient of bowl steel box girder is not obvious,and there is only a small floating in the low Reynolds number range.(3)The vortex induced vibration test of the segmental model of bowl box girder was carried out.Based on the dynamic characteristics of the cable-stayed bridge calculated by ANSYS software and combined with the wind tunnel test of segment model,the effects of different Reynolds numbers(by changing the wind speed and surface roughness of the wind tunnel)on the vortex induced vibration of the main beam are studied.The results show that with the increase of surface roughness,that is,the effective Reynolds number,the dimensionless amplitude of vertical vortex vibration of bowl box girder increases;in addition,the increase of effective Reynolds number can reduce the amplitude of torsional vortex vibration,but the influence of wind attack angle needs to be considered comprehensively.According to the results of all test conditions,the amplitude of torsional vortex vibration decreases in varying degrees with the increase of effective Reynolds number at 0 ° and + 3 °;however,there is no significant difference in the maximum amplitude of torsional vortex vibration at-3 °.Finally,the increase of effective Reynolds number will affect the eddy vibration range to some extent.According to the experimental results,there are delays in both vertical and torsional eddy vibration ranges at an angle of attack of +3degrees.Therefore,the Reynolds number will have an obvious and complex impact on the vortex induced vibration starting wind speed,locking interval width and maximum amplitude of the bowl box girder,which needs to be comprehensively judged according to the Reynolds number interval and wind angle of attack.