An Experimental Investigation On A By-passing Passive Jet Flow Control On The Unsteadiness Of Wind Load Of A Long-span Bridge With Single Box Girder

The major developed countries had started building long-span bridges since the 19th century.Limited by the technology,there are a number of bridges destroyed by strong wind.And among them the most famous case was Tacoma Narrows Bridge destructing in American,induced by flutter.Afterwards as the levels of bridge design and construction,the span of modern bridge has been raised to a larger magnitude than ever before.According to historical engineering experience and research results,as the span of bridge increased,its rigidity was becoming smaller,and damping was also decreased.Wind effect of long-span bridge,especially wind effect of main beam was one of the most remarkable dynamic effect of bridge.How to reduce wind load and wind effectiveness that come along with it,are most concerned by researchers at present.Therefore,it will be of great importance in ensuring wind resistance safety of long-span bridge,to study wind effect of main beam and then to propose effective control method.The main research work is as follows:(1)The method of passive self-suction and jet flow is applied to suppress the unsteady flow of bridge box girder.In order to get the optimal method for the number of self-suction/jet holes in the main girder of the bridge,the experiment of force measurement,pressure measurement and PIV were used in this study.We found that it had a better inhibition effect on the fluctuating value of the aerodynamic force coefficients.And also through Linear stability analysis of wake flow field,it is found that the flow field near the wake of test model is more stable compared to uncontrolled case.(2)In order to facilitate the engineering application,after obtaining the optimal layout method of the suction/jet hole of the bridge section,the spacing optimal value of the suction/jet holes along the span-wise of main girder were also need to study.Through the experiment of force measurement,we found that the spacing of the suction/jet holes along the span-wise of main girder are smaller,the control effectiveness is more obvious.We found that the model of vortex shedding is changed by the PIV experiment.(3)In this paper,the flow field around the main girder of the bridge control effect of the suction hole at the windward stagnation point and the jet hole at the rear stagnation point of the main girder was studied.The root-mean-square of aerodynamic forces was decreased,and the pressure distribution on the surface of test model was reduced along the test model.The turbulence Kinetic Energy on the wake flow behind the test model was declined and the vortex shedding model was changed by the PIV experiment in the study.Through Linear stability analysis of wake flow field,it is found that the flow field near the wake of test model is more stable compared to uncontrolled case.