Collaborative Research: Theoretical prediction of wake lock-in for fluid-structure interactions with phase-reduction analysis

当流体与非流线型物体(如桥梁、烟囱或电缆)相互作用时，会产生由周期性脱落的漩涡组成的尾迹。这些涡流对物体施加不稳定的力，导致结构振荡，在某些条件下有可能损坏或造成破坏。当旋涡脱落频率接近物体的共振频率时，会产生特别危险的情况。在这种情况下，涡旋脱落与物体的固有频率同步，并发生锁定。目前，还没有一种理论方法能够预测锁定的开始。这项实验和理论研究的目的是通过关注涡旋相对于圆柱体运动的脱落阶段来预测在流体流动中振荡的圆柱体发生锁定的条件。这项研究工作将使高中生、本科生和研究生接触到实验和计算流体力学研究。此外，研究结果将通过会议和研讨会向国内外研究团体传播。本项目的目标是利用振动圆柱体平移和旋转耦合运动的相减分析来预测锁定的发生。该项目将涉及补充的实验和理论工作，重点是：(I)产生预测同步条件所需的相响应函数，(Ii)从理论上预测和验证扩大或收缩同步区域所需的平移和旋转强迫振荡，以及(Iii)在分析中考虑高阶非线性项，以更准确地捕捉较大幅度振荡所发生的同步。这些任务将通过使用热膜热风速法测量小扰动和大振荡强迫运动引起的旋涡脱落频率的变化的实验工作来进行。在计算方面，将进行直接的数值模拟，以捕捉在强迫振动下的尾迹动力学和对物体的力历史。计算得到的力历史将被用来揭示同步特性，然后与测量的脱落频率进行比较，以验证理论预测。预计总体努力将通过消除同步区和抑制涡流诱发的振动来支持控制锁定的发生。此外，它将允许扩大同步区，这将导致更有效的流动控制、化学混合和能量收集。高中学生，目的是激励他们追求科学和工程领域的职业生涯，并增加他们的科学研究知识。本科生研究活动将提供独特的机会，培训学生为在行业、政府和学术界的高级工程职业做准备。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

When a fluid flow interacts with a non-streamlined object, such as a bridge, smokestack, or cable, a wake is created consisting of periodically shed vortices. These vortices exert unsteady forces on the object resulting in structural oscillations with the potential to damage or cause destruction under certain conditions. An especially dangerous situation results when the vortex shedding frequency is close to the resonant frequency of the object. In this case, the vortex shedding synchronizes with the object’s natural frequency and lock-in occurs. Currently, there is no theoretical approach capable of predicting the onset of lock-in. The objective of this experimental and theoretical study is to predict conditions when lock-in occurs on a cylinder oscillating in a fluid flow by focusing on the shedding phase of the vortices relative to the cylinder motion. This research effort will expose high-school, undergraduate, and graduate students to experimental and computational fluid dynamics research. Moreover, the findings will be disseminated to domestic and international research communities through conferences and workshops.The goal of this project is to predict the occurrence of lock-in using the phase reduction analysis for an oscillating cylinder undergoing coupled translational and rotational motion. The project will involve complementary experimental and theoretical work focusing on (i) generating the required phase-response functions needed to predict the synchronization condition, (ii) theoretically predicting and verifying the required translational and rotational forced oscillations required to expand or collapse the synchronization region, and (iii) consider higher-order nonlinear terms in the analysis to more accurately capture synchronization that occurs for larger amplitude oscillations. These tasks will be undertaken through experimental efforts using hot-film thermal anemometry to measure changes to the vortex shedding frequency caused by small perturbation and large oscillatory forced motions. On the computational side, direct numerical simulations will be performed to capture the wake dynamics and force history on the body under forced vibrations. The force histories from computations will be used to reveal the synchronization properties and then be compared to the measured shedding frequencies to verify the theoretical predictions. The overall effort is expected to support controlling the occurrence of lock-in by eliminating the synchronization region and suppress vortex-induced vibrations. Furthermore, it would allow the expansion of the synchronization region which would result in more efficient flow control, chemical mixing, and energy harvesting. High school students with the aim to motivate them to pursue careers in science and engineering fields and to increase their knowledge in scientific research. The undergraduate research activities will provide unique opportunities to train students to prepare for advanced engineering careers in the industry, government, and academia.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.