Closing a Soft Valve
With a soft valve like those found in mammal hearts, passing flow can deform the valve. That change in the valve then feeds back into the flow, shifting it. This feedback loop between flow mechanics and structural mechanics can cause sudden and drastic changes, like the valve closing fully in the video below.
View through a soft conical valve under steady flow. The valve’s walls initially oscillate, then suddenly collapse inward to close the valve.We’re looking down a conical valve that widens slightly in the direction of the flow. (The flow is coming toward the camera.) Initial small oscillations in the valve’s shape grow into a sudden distortion that draws the valve walls together into full closure. In nature, this helps stop blood flow from reversing direction.
In experimenting with simple soft valves like these, researchers found that quite slight flow variations could trigger valves to close at one-tenth of the pressure needed to close the valve in steady flow. (Video, image, and research credit: M. He et al.; via APS)
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