Kelvin-Helmholtz instabilities in a shear flow in Elbe river.

Last week I talked about how I wanted to use the “Elbe” model in teaching. Here is another idea for an exercise:

On the picture below you see Kelvin-Helmholtz instabilities. They might be kinda hard to make out from the picture, but there is a movie below where they are a bit easier to spot.

Kelvin-Helmholtz instabilities the boundary layer of Elbe river

Anyway, this is what they look like: Kind of like the ones we saw off Jan Mayen in 2012.

Kelvin-Helmholtz instability off Jan Mayen

Kelvin-Helmholtz instabilities occur in shear flows under certain conditions. And those conditions could be explored by using a tool like Elbe. And once students get a feel for the kind of shear that is needed, why not try to reproduce a flow field that causes something similar to the instabilities seen in the movie below?