Reynolds Number Effects On The Flow Characteristics And Its Control Of Twin-box Girder

With the rapid development of emerging economies,it has become a universal phenomenon that long-span bridges are constantly being built in these areas.With the increase of bridge span,wind load becomes the dominant control load of long-span bridge.The Reynolds number effect of wind load has been a key scientific issue in the field of structural wind engineering.It is a challenge to investigate the Reynolds number effects on flow and aerodynamic characteristics of a twin-box girder,owing to complicated aerodynamic configurations of bridge decks.Up till now,the research on the Reynolds number effects of twin-box girder in the flow field has mainly focused on the rules changing with the Reynolds number of some individual typical parameters in the flow field,while the in-depth research on flow field parameters and its internal hydromechanics mechanism is still extremely insufficient.Thus,it is urgent to research on the basic theoretical aspect of the Reynolds number effects mechanism of twin-box girder.In addition,the wind-resistant design and research of bridges is mainly based on wind tunnel tests.However,the Reynolds number of conventional wind tunnel tests is quite different from the Reynolds number of prototype bridges.It is impossible to guarantee the similar Reynolds number,which causes that the flow field structure and aerodynamics have markable disparities between wind tunnel test and prototype bridges.Therefore,it is of great theoretical and practical significance to study h ow to achieve the flow field and aerodynamic characteristics of high Reynolds number under wind tunnel test at low Reynolds number.Based on the research of Reynolds number effects,this thesis conducted the numerical simulation on the Reynolds number effects of twin-box girder.Firstly,the thesis offered the variation law of flow field and aerodynamic force with Reynolds number,and revealed the mechanism of Reynolds number effect of twin-box girder from the perspective of flow field structure change.Secondly,the research on the Reynolds number effect control of twin-box girder is carried out through wind tunnel test.After that,this thesis proposed the global and local flow field disturbance control method,and then high Reynolds number's flow field and aerodynamic characteristics of twin-box girder are realized in the wind tunnel test at low Reynolds number.The research contents of this thesis are as follows:I.The thesis figures out the flow and aerodynamic characteristics of twin-box girder in a broad range of Reynolds number.It points out that significant Reynolds number sensitivity exists in the flow field structure and aerodynamic parameters of twin-box girder.Then,it presents the change of flow patterns on the leading edges,around the gap and in the wake of the downstream box girder of the twin-box girder at various Reynolds numbers.Next,it indicates the Reynolds number effects on pressure distributions on the surface and around the gap of the girder model,and explains the mechanism of the Reynolds number effect.Finally,it explains the variation characteristics of aerodynamic parameters of twin-box girder at various Reynolds numbers.In general,the above analysis forms complete the Reynolds number effects mechanism of a twin-box girder;II.Based on the Reynolds number effects mechanism of twin-box girder,and aimed at the pressure coefficient distribution characteristics of twin-box girder at high Reynolds number,this thesis studies the control effects of different aerodynamic control measures on Reynolds number effects by changing the turbulence intensity and the flow field.In this thesis,the similarities and diffe rences between global and partial control measures for Reynolds number effects are compared and analyzed.Furthermore,the thesis puts forward the effective turbulence intensity range to control Reynolds number effects of twin-box girder on the basis of the test results.And eventually,it obtains the control measures to simulate high Reynolds number's characteristics of twin-box girder in normal wind tunnel at low Reynolds number.