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Fluid is only flowing through the walls and not through the actual empty space

Posted 2024/02/15 7:49 GMT-5 1 Reply

Jason Collis
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Hi all, I'm new to COMSOL and designed a trayed vessel in Autocad. The walls of this vessel have a certain thickness (1-10mm), they are not just a plane, as it is modelling a real construction. I specified the inlet as a pipe coming in to the vessel, and likewise with an outlet. However, no matter what I try, the fluid always flows through the walls. I even made a cube and put it inside the pipe so it wasn't touching the walls, and set that as the inlet, but it still didn't work.

https://ibb.co/HVG3MyF (here is a picture) of what I mean, the fluid doesn't fill the space between, just goes up the walls.

Can I somehow set volumes where the fluid can go and where not?

Thanks!

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1 Reply Last Post 2024/02/15 13:30 GMT-5
Robert Koslover Certified Consultant
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Posted: 2 months ago 2024/02/15 13:30 GMT-5
Updated: 2 months ago 2024/02/15 13:47 GMT-5

There are a number of possibilities here, depending on how you've set up your geometry, physics, materials, domains, boundary conditions, mesh, etc, etc! Since it sounds like you imported the geometry, that's one of the first things that I would investigate for causing potential trouble. Comsol Multiphysics may not have interpreted, upon that import operation, what you consider to be solids, or solid walls, or unbroken/connected surfaces, or unbroken/connected edges, etc., in the way that you have in mind! Among other ways to test that, consider drawing directly within Comsol Multiphysics some alternative, but otherwise similar or simplified subset of your geometry of interest, and then see if that non-imported geometry exhibits the sort of same crazy behavior as what you imported. From your description, it almost sounds like you've modeled the inverse (like a photographic negative) of the geometry that actually matters. If you still can't figure out what is going on, then consider posting your .mph file to the forum so others can take a closer look. Oh, and by the way, if by "empty space," you intend to model the details of any fluids flowing there, then you might want to include that space as a computational domain in your problem. Aside from certain quantities computed in post-processing, most quantities of interest in Comsol Multiphysics are computed in/on locations (domains, surfaces, edges, and points) that are meshed with finite elements. E.g., if you are modeling fluid flowing in a pipe, you need to model (and mesh) the volume in which the fluid is flowing. By contrast, walls about such a volume are (for the most part) just boundary conditions, unless you are separately computing what is happening within that wall material (e.g., a structural deformation of the walls).

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
There are a number of possibilities here, depending on how you've set up your geometry, physics, materials, domains, boundary conditions, mesh, etc, etc! Since it sounds like you *imported* the geometry, that's one of the first things that I would investigate for causing potential trouble. Comsol Multiphysics may not have interpreted, upon that import operation, what *you* consider to be solids, or solid walls, or unbroken/connected surfaces, or unbroken/connected edges, etc., in the way that you have in mind! Among other ways to test that, consider drawing directly within Comsol Multiphysics some alternative, but otherwise similar or simplified subset of your geometry of interest, and then see if that non-imported geometry exhibits the sort of same crazy behavior as what you imported. From your description, it almost sounds like you've modeled the inverse (like a photographic negative) of the geometry that actually matters. If you still can't figure out what is going on, then consider posting your .mph file to the forum so others can take a closer look. Oh, and by the way, if by "empty space," you intend to model the details of any fluids flowing there, then you might want to include that space as a computational domain in your problem. Aside from certain quantities computed in post-processing, most quantities of interest in Comsol Multiphysics are computed in/on locations (domains, surfaces, edges, and points) that are meshed with finite elements. E.g., if you are modeling fluid flowing in a pipe, you need to model (and mesh) the volume in which the fluid is flowing. By contrast, walls about such a volume are (for the most part) just boundary conditions, unless you are separately computing what is happening within that wall material (e.g., a structural deformation of the walls).

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