I am trying to set-a flow in a 3D circular pipe based one the aneurysm bounceback case (especially for the boundary conditions).
I have a poiseuille flow at the inlet with a Reynolds number of around 400 and a pressure boundary at the outlet. I use bounceback boundary conditions for the wall.
The case runs but rapidly I get stability issues: non physical velocities appear along the wall and propagate in the flow until a got NANs !
I checked my stability parameters which seems right (U lb = 0.01). I run sensibilities for:
different lattices from around 1 to 40 millions (i. e. from 20 to 160 cells in a diameter)
different models: BGK or smagorinsky BGK model
different initializations: with default or poiseuille velocity initialization
Does everyone would have any idea of what is wrong, or what may set this right ? I am just out of ideas.
I already tried to reduce the inlet velocity (to values around 0.0005) but without success. Nevertheless I think I figured out why my computation crashes: It comes from the voxalization of my STL pipe which creates something like that:
So I have some bounceback nodes which are connected with almost only other bounceback node. This seems to be the problem since with a square pipe the computation runs without any trouble.
I will still post my sources so it may hep others.
Mmmm… I don’t know unfortunately I have very little experience in geometries from STL files. However, I work with porous media and I often encounter the situation you described. Sometimes, I have BB nodes which don’t see the fluid nodes at all!
It seems you were right, I made tests with different lattices I do not have BB nodes in from of one another anymore but the computation still crashes… So I try your idea of reducing the velocity and the computation runs smoothly for Reynolds under 160 but crashes for higher Reynolds number…
I open a knew post for this specific problem “Lattice requirement for wall driven flow” with my code.