Problem with constraintIB validation

[Sagar G Nayak]

Hello,

I am trying to validate constraintIB code by simulating flow through a packed bed of spheres. I am comparing the pressure difference across the bed predicted by IBAMR with that predicted by Ergun equation. IBAMR is giving a much higher pressure difference than expected (~7 times) and I am unable to figure out why. Can someone help me with this? I have attached the figure. Its a 3d channel with only one layer of spheres in z-direction.

Problem2: If I simulate a flow though constricted channel, the velocity rise at the throat is much higher than expected (figure attached). A_in = 1.2, V_in = 1, A_out = 0.3. V_out should be ~4 units but it is almost twice. I think both problems are related.

I would appreciate any help. Thanks

[Boyce Griffith]

For IB methods that use regularized delta functions, the numerical size of the immersed structures is slightly larger than their physical size. I would suggest running at a higher resolution to see how the results depend on grid resolution, and also using a narrower delta function (perhaps BSPLINE_3 or the poorly named DISCONTINUOUS_LINEAR) at the current resolution.

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[Sagar G Nayak]

Thank you very much Dr. Griffith. That actually helped.
But when I increased the grid resolution, a patch of high pressure appeared at a corner near the inlet (figure attached). Can you please comment on that? Also, when I switch-on AMR (max_levels = 2), it refines the mesh near the left top and left bottom corners even though there are no structures at those places. I suppose it is because of velocity gradients. How can I overcome that?

Thanks again,

[Boyce Griffith]

Sagar —

Did you ever sort out this pressure issue?

(It is probably obvious, but I am working my way back through my inbox. 😬)

— Boyce

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