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

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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.