基于RANS/LES混合方法的箱梁气动导纳函数研究

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

为了研究RANS/LES(Reynolds-averaged navier-stokes/large eddy simulation)混合方法在桥梁非定常气动力的应用以及大积分尺度湍流中桥梁断面的气动导纳函数,首先选取3种典型的RANS/LES混合方法,即SBES(stress-blended eddy simulation)方法、SAS(scale-adaptive simulation)方法、WMLES(wall-modeled LES)方法,分别对3种方法的特点和适用性进行简要的概述,然后在均匀流中将其用于箱梁断面和分离式双箱梁断面气动力的计算,最后在提出的改进湍流合成方法基础上,实现了与实际桥位处积分尺度类似的大积分尺度湍流模拟,在此流场中识别了箱梁断面的气动导纳函数。数值计算结果表明,SBES方法适用于弱流动不稳定和强流动不稳定流场气动力的模拟,SAS方法仅适用于显著流动分离的断面,而WMLES方法对两种断面整体表现都较差。对于流线型箱梁断面,大积分尺度湍流场中识别的升力气动导纳在低频处大于Sears函数和小尺度湍流场中的结果,并显著大于节段模型风洞试验结果。在高频处大积分尺度湍流场的结果与小尺度湍流场以及风洞试验结果吻合较好。研究结果表明,将传统小尺度格栅湍流场风洞试验识别的气动导纳用于桥梁抖振分析时,会导致低频处的抖振力显著偏小。

In order to study the applicability of the hybrid RANS/LES(Reynolds-averaged navier-stokes/large eddy simulation)method in unsteady aerodynamic force analysis and the aerodynamic admittance functions of bridge sections in large-scale turbulent flow field,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 a twin-box girder section in uniform flow.Finally,based on an improved turbulence synthesis method,a large-scale turbulent flow similar to that at 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 in weak unstable flow and strong unstable flow field.The SAS method is only suitable for the section with significant flow separation.The WMLES method has poor performance for both sections.For the streamlined box-girder section,the lift aerodynamic admittances at low frequency identified in the large-scale turbulent flow field is larger than the results identified in the small-scale turbulent flow field by the Sears function,and are also significantly larger than the wind tunnel test results of the segmental model.At high frequency,the results in the large-scale turbulent flow field are in good agreement with the results in the small-scale turbulent flow field and in the wind tunnel tests.The results show that when the aerodynamic admittances identified in the traditional small-scale grid generated turbulent flow field are used for bridge buffeting analyses,the buffeting forces at low frequency will be significantly undervalued.