Aerodynamic Admittance Identification Method Based On Measured Spanwise Coherence Function And Its Application In Airfoil And Streamlined Box Girders

Streamlined box girder(box girder for short)are one of the main forms of stiffening girders for large-span bridges.However,the existing empirical model of the spanwise coherence function does not fully describe the distribution characteristics of the spanwise coherence function of the buffeting forces in box girder.In addition,the threedimensional effect of the real bridge is different from that of the wind tunnel test.Therefore,it is necessary to study the identification method of aerodynamic admittance of box girder considering the three-dimensional effect.In this paper,by combining theoretical analysis and pressure measurement tests,a method of identifying aerodynamic admittance based on the measured spanwise coherence function is proposed.And the one-wavenumber aerodynamic admittance and two-dimensional admittance of the NACA0015 airfoil section and box girder section are identified.The effects of different turbulent flow fields,different wind attack angles,and different scaling ratios on the identification results of two-dimensional admittance of box girder section are also considered.The main results and conclusions are as follows:(1)Five grid turbulence flow fields were developed in the wind tunnel,one group of turbulence flow fields have similar turbulence integral scales but different turbulence intensities,and the other group of turbulence flow fields have similar turbulence intensities but different turbulence integral scales,and the flow field characteristics of all turbulent fields are also given.(2)Based on the measured spanwise coherence function and the general recognition framework of two wave number aerodynamic admittance,a recognition method of aerodynamic admittance independent of the spanwise coherence function model is proposed.The concept of effective spanwise spacing is also used to demonstrate that the spanwise coherence function of buffeting lift of NACA0015 airfoil and box girder is greater than that of fluctuating wind velocity.(3)The one-wavenumber aerodynamic admittance of buffeting lift force of NACA0015 airfoil and box girder is less than the twodimensional admittance of the corresponding section.And the larger the turbulence integral scale is,the larger the one-wavenumber aerodynamic admittance is,while the turbulence intensity basically does not affect the value of the one-wavenumber aerodynamic intensity.In addition,the larger the wind attack angle,the smaller one-wavenumber aerodynamic admittance of the buffeting lift force of the box girder.The aerodynamic admittance of the buffeting lift force of the box girder decreases with the increase of scale ratio.(4)The two-dimensional aerodynamic admittance of the NACA0015 airfoil section identified by the test is accurate enough in a certain frequency range.But at the high-frequency range,due to the thickness effect,it is less than Sears function,and the two-dimensional aerodynamic admittance is not affected by turbulence integral scale and turbulence intensity.The feasibility of the aerodynamic admittance identification method is demonstrated and its applicability is given.(5)The identified two-dimensional aerodynamic admittance of buffeting lift force of box girder is greater than the value of Sears function in the low-frequency range and closer to the quasi-steady value.And with the increase of frequency,the decay rate of two-dimensional aerodynamic admittance of buffeting lift force of box girder is larger than the decay rate of Sears function,and the value of the former is less than that of the latter at a certain frequency.(6)The two-dimensional aerodynamic admittance of buffeting lift force of box girder is not affected by the turbulent fields,while the wind attack angle has an obvious influence on the two-dimensional aerodynamic admittance of buffeting lift force of box girder.In the case of a negative wind attack angle,the larger the wind attack angle is,the smaller the two-dimensional aerodynamic admittance is,but it is always larger than the result of the 0° wind attack angle.And the larger the absolute value of the negative wind attack angle is,the larger the lowfrequency range of the two-dimensional admittance close to the quasisteady value is.At the positive wind attack angle,there is no clear pattern of two-dimensional aerodynamic admittance values with changing wind attack angle.The two-dimensional aerodynamic admittance is smaller than the value at 0° wind attack angle,but it is still larger than the Sears function at low frequencies.In addition,the two-dimensional aerodynamic admittance of buffeting lift force of box girder increases with the increase of the scaling ratio,and the low-frequency range of the two-dimensional aerodynamic admittance that remains close to the quasisteady value is wider.(7)Based on the identified results of two-dimensional aerodynamic admittance of box girder models with different scale ratios,an idea of identifying the two-dimensional admittance of buffeting force of bridge by wind tunnel test with different scales is proposed.