速度场演化结构非定常气动力

EVOLUTION OF UNSTEADY AERODYNAMIC FORCES FOR BODIES FROM FLOW MAPS

从流体力学的基本公式出发,获得了结构受流场作用的非定常气动力公式。在积分降阶时,采用奥高公式使得非定常气动力公式不仅能够适用于单箱桥梁断面周围的流场,也能够适用于多箱分离断面周围的多连通流场。同时,由于试验流场数据的采样频率较低,因此给出了仅忽略时间项的简化公式以及忽略时间并仅依照有限区域流场进行计算的简化公式。采用数值模拟和粒子图像测速系统(PIV)获得了雷诺数为22000的方柱绕流的流场,由于能够与其他研究者的结果得到较好的吻合,因此取其流场数据用于验证上述气动力公式。结果表明,按照该文推导得到的气动力公式计算,得到的阻力系数的计算结果较好,而升力系数结果则存在一定的差别。采用简化公式计算时,仅忽略时间项的简化公式得到的结果较好,而更进一步的简化公式则差别较大。该文还以分离双箱断面周围的数值模拟流场为例进行了公式的验证,结果依然是阻力系数较好,而升力系数存在一定的差距。最后对于阻力系数和升力系数验证计算结果出现的这种差异进行了分析。

The equations of unsteady aerodynamic forces of the body emerged in fluids were derived from the basic equations of fluid mechanics. The equations were suitable not only for single connected fluid domain around bridge decks but also for multiple connected fluid domains around multiple separated box girders after using the Ostrovski-Gauss formula to change the integral from volume to surface. At the same time, the simplified equations were obtained for the sample rate of flow maps is low. The flow maps around the square cylinder were obtained in the Reynolds number of 22,000 using both numerical simulation and Particle Image Velocimetry which coincide with the results of experiments carried by other researchers. The aerodynamic forces were obtained using the flow map to validate the equations. The results show that it has a good agreement in damping force coefficient but poor in lifting force coefficient. When the equations were simplified to neglect the velocity difference in time, the results agree well. While the equations were simplified further to use only limited velocity data around only one segment, the results differs greatly with the results from original equations. Furthermore, the flow maps around the twin box girders from numerical simulation were also used to validate the equations. The results were the same with that of square cylinder, that is to say, good in damping force coefficient but poor in lifting force coefficient. At last, the reason of such discrepancies was analyzed.