Discussion Forum

Hi everyone,

I'm actually struggling to find out what's the proper way to model a 'moving wall' at a fluid-structure boundary that is in fact a rotational movement. For example, imagine a tubular geometry filled with a fluid, where the geometry is continuously rotating. The main physical effect here is the transmission of the boundary velocity to the fluid (resulting flow depending on fluid properties like viscosity).

There are numerous examples that show this when demonstrating couette flow (but here only for planar boundaries with quasi-infinity movement directions) or when simulating rotating machinery (like stirrer elements within domains).

I tried to start with the simplest case possible (after failing with ALE/FSI setups for this) imho: A fully filled geometry, describing the boundary movement on the wall property by checking "sliding wall". However, COMSOL expects cartesian velocity components here and as far as I can see, positional variables (to just work with cos/sin math) do not seem to be supported here, hence I don't know how to tell COMSOL about the continuous rpm speed.

Note: I'm doing this in 3D space because I definitely will have to in the end (here I'm just trying to accomplish what I seem to misunderstand, however this model will be extended to phasefield within the geometry, thus symmetry will vanish)

Thanks in advance!