Microscale Kelvin-Helmholtz

Snapshots of the Kelvin-Helmholtz instability taking place on cavitation bubbles in a microchannel.

When we think of cavitation in a flow, we often think of it occurring at a relatively large scale — on the propeller of a boat, for example. But cavitation takes place on microscales, too, including around fuel-injection nozzles. In this study, researchers investigated submillimeter-scale cavitation using a flow through a tiny Venturi tube. What they found was something we usually associate with larger scale flows: the Kelvin-Helmholtz instability.

The Kelvin-Helmholtz instability takes place on this cavitation bubble.

The wavy shape of a Kelvin-Helmholtz instability forms when two layers of fluid move past one another at different speeds and the interface where they meet becomes unstable. Here, that happens along a cavitation bubble, where the bubble and the flow meet. Interestingly, at these scales, the Kelvin-Helmholtz instability seems to be the primary method of break-up, instead of shock wave interactions.

For those keeping track, we’ve now seen the Kelvin-Helmholtz instability from the quantum scale up to 160 thousand light-years. It’s hard to achieve a much wider range than that! (Image and research credit: D. Podbevšek et al.; submitted by M. Dular)

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