Aerodynamic admittance functions of box girders based on hybrid RANS/LES methods

In order to study the applicability of hybrid RANS/LES method in unsteady aerodynamic forces and aerodynamic admittance functions of bridge sections in large-scale turbulent flow, three typical hybrid RANS/LES methods, namely SBES（stress-blended eddy simulation）, SAS（scale-adaptive simulation） and WMLES (wall-modeled LES）, were briefly summarized. Then they were used in the simulation of aerodynamic forces of a streamlined box-girder section and twin-box girder section in uniform flow. Finally, based on an improved turbulence synthesis method, a large-scale turbulent flow comparable to the actual bridge site was synthesized, and the aerodynamic admittance functions of the box-girder section were identified. The numerical results show that the SBES method is suitable for the simulation of aerodynamic forces of weak unstable flow and strong unstable flow.The SAS method is only suitable for the section with significant flow separation. The WMLES method has poor performance for both sections. For the box-girder section, the lift aerodynamic admittances identified in the large-scale turbulent flow is large than the result in the small-scale turbulent flow and the Sears function, and is also significantly larger than the wind tunnel test result of the segmental model. At high frequency, the results in the large-scale turbulent flow are in good agreement with the results in the small-scale turbulent flow and wind tunnel test. The results show that when the aerodynamic admittances identified in the traditional small-scale grid generated turbulent flow are used for bridge buffeting analyses, the buffeting forces at low frequency will be significantly undervalued. © 2023 Chinese Vibration Engineering Society. All rights reserved.