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Different Meshes for Different Physics

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Old   August 26, 2018, 17:59
Default Different Meshes for Different Physics
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Pi-Man
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Dear fellow cfd-online members,

I am using a modified icoFoam setup, that couples transient passive scalar transport to the momentum equations.

My issue is that my momentum equations don't require a fine mesh, while my scalar transport problem requires a relatively very fine mesh (due to high Peclet numbers). This further constrains my time step choice (due to the Courant number and viscous stability constraints) and adds a significant number of time steps to my problem. These time steps do not add significant physical information to my problem, but are rather there due to numerical stability requirements. Basically in one of the equations I have to use very fine mesh while the other one works OK with a coarser mesh.

I was wondering whether it would be possible to solve my coupled system on different meshes (one for each set of equations), and project the velocity results from the coarse mesh to the finer mesh to be used in solving my scalar transport equation.

Is there anyway that I can assign different meshes for each of these equations and thus save computational time?

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Pi-Man
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Old   August 27, 2018, 01:40
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Uwe Pilz
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You may always use a script which runs both simulations, one after the other. You need a tiny program in the programming language of your choice, which reads the velocity results of the coarse mesh and transfers it (with interpolation) to the finer one.
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Old   August 27, 2018, 02:43
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I'd be curious to see how you go, I suspect you will spend more time interpolating and IO operations than just solving on the fine mesh. Unless you do it inside the one solver with two meshes and keep the fields in memory while you solve I don't think you'll see the benefit.
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Old   August 27, 2018, 05:42
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It can be done, see this post of mine, which contains a screenshot.

I took inspiration from the multi-region solvers, and the mapFields utility.

I have no idea, when the additional effort (the second mesh, the mapping of fields each time step) is worth it.
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