Department of Mechanical Engineering, The University of Texas at Dallas, Richardson, Texas 75080, USA.
Department of Mechanical Science and Engineering, University of Illinois, Urbana, Ilinois 61801, USA.
Phys Rev E. 2019 Dec;100(6-1):063106. doi: 10.1103/PhysRevE.100.063106.
The flow and drag induced by active pitching of plates in the wake of a cylinder of diameter d were experimentally studied for various plate lengths L as well as pitching frequencies f_{p} and amplitudes A_{0} at Reynolds number Re=1.6×10^{4}. Planar particle image velocimetry and a load cell were used to characterize the flow statistics and mean drag of a variety of cylinder-splitter assemblies. Results show the distinctive effect of active pitching on these quantities. In particular, flow recovery was significantly modulated by L, f_{p}, or A_{0}. Specific pitching settings resulted in a wake with dominant meandering patterns and faster flow recovery. We defined a modified version of the amplitude-based Strouhal number of the system St_{A} to account for the effect of the cylinder in active pitching. It characterizes the drag coefficient C_{d} across all the cases studied, and reveals two regions intersecting at a critical value of St_{A}≈0.035. Below this value, the C_{d} remained nearly constant; however, it exhibited a linear increase with increasing St_{A} past this critical point. Inspection of the integral momentum equation showed the dominant role of velocity fluctuations in modulating C_{d} past the critical St_{A}.
在直径为 d 的圆柱尾流中，对不同长度的板（L）、不同的俯仰频率（f_p）和不同的俯仰幅度（A_0）进行了主动俯仰板引起的流动和阻力的实验研究，在雷诺数 Re=1.6×10^4 下进行。平面粒子图像测速和负载单元用于描述各种圆柱分裂器组件的流动统计数据和平均阻力。结果表明主动俯仰对这些量有显著的影响。特别是，L、f_p 或 A_0 显著调节了流动恢复。特定的俯仰设置导致尾流中存在主导的蜿蜒模式和更快的流动恢复。我们定义了一个改进的基于系统振幅的斯特劳哈尔数 St_A，以考虑圆柱在主动俯仰中的影响。它描述了所有研究案例的阻力系数 C_d，并揭示了两个区域在临界值 St_A≈0.035 处相交。在这个值以下，C_d 几乎保持不变；然而，在这个临界点之后，它随着 St_A 的增加呈线性增加。对积分动量方程的检查表明，速度波动在超过临界 St_A 时对 C_d 的调制起着主导作用。
