Vibrating in the Flow

Objects can obviously affect flows, but that’s not a one-way street. Flows can also affect objects, even ones as simple a circular cylinder. If you live somewhere with traffic lights mounted to a horizontal bar, you’ve probably seen this. On a windy day, the beam holding the traffic lights will oscillate up and down. This is an example of vortex-induced vibration, a coupling between the flow structures formed by an object and the motion of the object itself. With cylinders, engineers have mostly studied a situation like the traffic light – one where the motion of the cylinder is perpendicular to the direction of the flow. 

But it’s also possible to get vortex-induced vibration in the same direction as the flow. That’s what you see visualized in the images above. Notice how the oscillation of the cylinders is inline with the flow direction. As with the crossflow version of vortex-induced vibration, this inline example has several wake forms that vary based on flow conditions. (Image and research credit: T. Gurian et al.)

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