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Problem in convective flow simulation

Posted Aug 21, 2014, 4:48 a.m. EDT Fluid & Heat, Computational Fluid Dynamics (CFD), Chemical Reaction Engineering, Studies & Solvers Version 4.4 4 Replies

Leong
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I am now trying to solve magnetophoresis model by coupling CFD and transport of dilute chemical species modules together. I want to study the dynamical behaviour of the process and I used Time-Dependent solver in my study. However, I found that 'Nonlinear solver did not converge' when I used finer mesh in my computation. Also, I found that it is more difficult to converge when I want to do the simulation for a longer time range.
The solver does converge when I used a coarser mesh and simulate for shorter time range. Yet, solver gives different solution for each computation (or study) and I think that the solution is not reliable due to the extremely coarse meshing.
I know this is a highly non-linear model as it involves convective flow (due to buoyancy force) and transport of chemical species. Is it possible to improve the convergence of the solver in order to solve this highly non-linear model by using a finer mesh? Thank you.

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Leong
4 Replies Last Post Aug 26, 2014, 11:02 a.m. EDT
Nagi Elabbasi Facebook Reality Labs
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Posted: 10 years ago Aug 21, 2014, 1:19 p.m. EDT
Dear Leong,

The coarse mesh may be converging better because it is not capturing the flow accurately. A fine mesh, sometimes including a boundary layer mesh, is usually required for accurate results in a natural convection problem. I would start by adding (or increasing) consistent and inconsistent stabilization. You can then use that solution as an initial condition to another run with less stabilization.

Nagi Elabbasi
Veryst Engineering
Dear Leong, The coarse mesh may be converging better because it is not capturing the flow accurately. A fine mesh, sometimes including a boundary layer mesh, is usually required for accurate results in a natural convection problem. I would start by adding (or increasing) consistent and inconsistent stabilization. You can then use that solution as an initial condition to another run with less stabilization. Nagi Elabbasi Veryst Engineering
Leong
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Posted: 10 years ago Aug 25, 2014, 2:38 a.m. EDT
Hi Nagi，

Thanks for your reply. May I know in details how you carry out the simulation? Do you change the setting in the solver?

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Leong
Hi Nagi， Thanks for your reply. May I know in details how you carry out the simulation? Do you change the setting in the solver? -- Leong
Nagi Elabbasi Facebook Reality Labs
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Posted: 10 years ago Aug 25, 2014, 10:54 a.m. EDT
Hi Leong,

Stabilization is not in the Solver settings. It is in the main physics node. It is an advanced feature that may not show by default. If you don’t see it go to the “Show” icon and make sure Stabilization is selected.

Nagi Elabbasi
Veryst Engineering
Hi Leong, Stabilization is not in the Solver settings. It is in the main physics node. It is an advanced feature that may not show by default. If you don’t see it go to the “Show” icon and make sure Stabilization is selected. Nagi Elabbasi Veryst Engineering
Leong
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Posted: 10 years ago Aug 26, 2014, 11:02 a.m. EDT
Hi Nagi，

Thanks for your response and useful guide. The stabilization indeed does improve the convergence. However, I need to simulate for a much longer time range. Is there any other method to do this?

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Leong
Hi Nagi， Thanks for your response and useful guide. The stabilization indeed does improve the convergence. However, I need to simulate for a much longer time range. Is there any other method to do this? -- Leong

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