The Aerodynamic Characteristics Of A Streamlined Box Girder In Sinusoidal Oscillating Flow At Large Angle Of Attack

This article is founded by the National Natural Science Foundation of China,“Aerodynamic admittance function of main beam section of mountain city long-span suspension bridge”(Project No.51778193).The aerodynamic characteristics of a streamlined box girder,subjected to uniform flow at different angles of attack and zero-angle sinusoidal oscillating flow,as well as sinusoidal oscillating flow at different angles of attack,is investigated by means of active controlled wind tunnel tests and CFD numerical simulation.The influences of angle of attack,oscillating frequency and amplitude on pressure coefficient,overall aerodynamic forces and flow characteristics are studied.The main contents and conclusions are as follows:Firstly,the wind tunnel tests and numerical simulations under the uniform flow at multiple angles of attack(-15°???15°)were carried out,and the accuracy of numerical calculation was verified.The smaller angles of attack do not cause significant flow separation and vortex shedding,and the surface pressure coefficient satisfies the Gaussian distribution.With the increase of angle of attack,there is obvious flow separation on the upper and lower surfaces of the box girder,meanwhile,vortex shedding occurs in the wake,and the range gradually enlarges.With the expansion of the separation bubble,the mean pressure coefficient recovers more slowly,and the fluctuating pressure coefficients is gradually increased.Then the active controlled wind tunnel tests and numerical simulations in sinusoidal oscillating flow are carried out at zero angle of attack,the effects of oscillating frequency(f_u=1.39~66.67Hz)and amplitude(U_m=0.5~2 m/s)are studied.The inflow oscillating frequency and amplitude have no effect on the average flow field and the mean pressure coefficient of the streamlined box girder,which are basically the same as the uniform flow.With the increases of oscillating amplitude and frequency,the wake vortex shedding phenomenon become more significant,and the shedding spacing decreases with the increase of oscillating frequency,but oscillating amplitude has no influence on it.Meanwhile,the fluctuating pressure increases significantly,the trend can be fitted to the linear relationship between the oscillating amplitude,the oscillating frequency and the flow distance.The correlation of pressure coefficient along the flow direction increases with the increase of oscillating frequency,but oscillating amplitude has no influence on it.When the amplitude is low,the overall aerodynamic force changes little with the oscillating frequency.As the oscillating amplitude increases,the overall aerodynamic force changes obviously.And the fluctuating coefficient increases linearly with the incoming frequency.Finally,the numerical simulations in sinusoidal oscillating flow at different non-zero angles of attack are carried out.The influence of oscillating frequency is studied under the condition of amplitude U_m=1 m/s.In the range of small angles of attack(-8°???8°),the inflow frequency has little effect on the average flow field,the mean pressure coefficient and the overall lift and drag coefficients,and the surface pressure coefficient satisfies the Gaussian distribution.In the range of large angles of attack(??-12°and??12°),the oscillating frequency has a great influence on the range of separation bubble,the mean pressure coefficient and the overall lift and drag coefficients,and the surface pressure coefficient exhibits non-Gaussian characteristics.In the range of smaller angles of attack(-8°???8°),the flucating pressure coefficient increases linearly along streamwise distance.But,in the range of large angles of attack(??-12°and??12°),the flucating pressure coefficient generally decreases or fluctuates along streamwise distance.In addition,under the angle of attack,the increase of the oscillating flow frequency has significant effects on the wake vortex shedding,causing significant vortex shedding in wake.