紊流场中流线型箱梁的自激气动力

The wind field of the bridge in the service state is the near-earth atmospheric boundary layer and the turbulent flow is the basic characteristic. One of the primary issues of long-span and super long-span bridges in the future is to evaluate the flutter characteristics of the bridge in the natural wind. A large number of wind tunnel tests indicate that the turbulent flow has uncertainty influences on the streamlined box girders, which are commonly used for the long-span bridges. However, the current self-excited aerodynamic force models are based on the uniform flow condition and cannot explain the flutter characteristics in the turbulent flow. Using the classical aerodynamic theory, the forced vibration section model wind tunnel tests and PIV measurements will be conducted in this project. The unsteady self-excited aerodynamic forces and the spanwise distribution characteristics of the airfoil, 1:5 rectangular section and streamlined box girder section will be studied in three kinds of flow fields, including the uniform flow, the sinusoidal flow and the isotropic homogeneous turbulent flow. An empirical self-excited aerodynamic force model of streamlined box girder will be established for flutter analysis and the corresponding verification tests will be conducted in the turbulent flow. The formation mechanisms of self-excited aerodynamic forces and flutter in turbulent flow will be revealed preliminarily. The research results of the project can provide a scientific basis for the evaluation of the flutter performance of long-span bridges under the atmospheric turbulent flow.

桥梁服役状态所处的流场为近地大气边界层流动，紊流是流动的基本特性。如何评价桥梁在自然风作用下的颤振特性，是未来面向更大跨越能力的特大和超大跨度桥梁必须解决的首要问题。大量风洞试验业已表明，紊流对大跨度桥梁常采用的流线型箱梁断面颤振特性的影响具有不确定性。然而，现行的自激气动力模型是基于均匀来流的，无法合理阐释紊流中的颤振特性。本项目研究借鉴经典空气动力学理论，采用强迫振动节段模型风洞试验和PIV流动显示，研究翼型、1:5矩形及流线型箱梁断面在均匀来流、顺流向正弦阵风和均匀各向同性紊流等三种流场中的非定常自激气动力及其跨向分布特性，建立紊流来流下流线型箱梁自激气动力经验模型，开展紊流下颤振计算分析和验证试验，并初步揭示紊流中自激气动力和颤振的形成机理。项目成果可为大气紊流风作用下的大跨度桥梁颤振性能评估提供科学依据。

如何精确评估桥梁在自然风作用下的颤振特性，是未来大跨、超大跨度桥梁必须解决的关键问题。作为桥梁颤振分析的前提条件和基础，自激气动力模型是桥梁颤振问题的核心研究内容之一。为此，本项目通过理论与试验相结合的方法，对紊流下的自激气动力开展了一系列研究工作。首先，利用多风扇主动控制风洞和强迫振动装置研究了两种典型断面在单频纵向正弦阵风场中的自激气动特性，试验验证了Greenberg公式，完善了经典平板气动力理论，为紊流下自激气动力模型的建立提供了理论上的指导；其次，利用常规风洞和强迫振动装置研究了翼型在格栅紊流场中的自激气动力特性。基于Greenberg和Theodorsen平板气动力理论，深入考虑纵向脉动速度与结构运动共同作用将产生附加气动力以及结构在紊流中发生颤振时其过程为单频窄带的特点，揭示了紊流对自激气动力传递函数的影响，由此提出了可以量化紊流参数作用的自激气动力理论模型；然后，基于Scanlan自激气动力半经验公式，研究了5:1矩形和流线型箱梁在格栅紊流场中的颤振导数特性，并结合PIV研究了纵向脉动来流下5:1矩形的周围流场特征。通过考虑钝体表面的流动分离，对紊流下自激气动力理论模型进行了修正，进而提出了适用于桥梁断面的紊流下钝体自激气动力模型； 最后，基于所提出的自激气动力模型，结合现有的均匀流颤振分析方法，分析了紊流对典型断面颤振稳定性的影响，定量揭示了颤振临界风速与紊流参数的关系，为准确预测桥梁在紊流下的颤振临界风速，实现自然风作用下桥梁颤振特性的精确评估提供了方法和依据。