How can a flat rotating disk whip egg whites?

Question

The Bamix 'beater' attachment is just a flat disk which rotates on an immersion blender. When it rotates the disk stays mostly in place, it doesn't displace the liquid in a way that moving a traditional whisk would.

How does that beater attachment work? For example, this promotional video using the attachment shows egg whites from two eggs turn into foam in less than 30 seconds. I have the attachment and contrary to my expectations it's just a flat disk without any ridges to increase friction when spinning around in the liquid.

How does this form of whisking work?

Answer 1

The flat beater blade isn't quite flat.

At least, it's not flat with respect to the axis of rotation.

The beater blade is a smooth disk, but it's mounted at a slight angle so that when it spins, there's a "wobble." It doesn't spin in a flat/smooth circle.

The mounting angle works kind of like a fan, with a single, solid blade. The angle and the rapid speed combine with the solid blade to create a lot of turbulence. Unlike a fan that creates a single direction of flow, the solid blade is pushing and pulling as the "wobble" moves up and down.

That "wobble-induced turbulence" creates something very much like what a whisk does, just at a higher speed and smaller area.

Answer 2

It uses the boundary-layer effect

Just like a good old Tesla turbine.

In a Tesla turbine, a flat disc (or several flat discs) are propelled by a water flow (or any other liquid, or gas). Your attachment does, obviously, the "opposite thing"...no, it's isn't. In both cases, an energy transfer happens between the disc and the liquid.

https://en.wikipedia.org/wiki/Tesla_turbine

There are also a lot of videos on YouTube showing Tesla turbines being constructed and operated: https://www.youtube.com/results?search_query=tesla+turbine