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March 27, 2000, 07:22 |
Restrictions on time steps
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#1 |
Guest
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Hi there,
I am working with Incompressible, viscous and time dependent flows. In recent days, I am implementing a Low-Reynolds turbulence model in a explicit code. If every one to know what is the restrictions on time steps in turbelent flows, or related papers, please let me know. Thank you. |
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March 27, 2000, 08:49 |
Re: Restrictions on time steps
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#2 |
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There are a couple of papers by Kunz and Lakshminariayana on the stability of explicit solvers using the Low-Re Chien model. Their conclusion was that the Chien Low-Re k-epsilon model does not lead to any additional requirements. My real-life experience is not the same though... I'd say that if you want to use low-Re models you should consider moving to an implicit solver. The explicit Runge-Kutta solvers are not very suitable to solve this type of source-term dominated equations, IMHO.
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March 27, 2000, 15:17 |
spelling correction
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#3 |
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look for Kunz and Lakshminarayana (Jonas got the second name wrong, but who can blame him)
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March 28, 2000, 21:52 |
Re: Restrictions on time steps
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#4 |
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Just a general observation, I don't have any particular references for you. The turbulence model introduces an eddy viscosity. If you already have a stability estimate based on viscosity considerations, that should work just fine with the combined eddy and molecular viscosity. The solver has no "knowledge" of any difference. This is how I have handled it before and it seemed to work just fine.
Also, a previous poster made reference to this being a "source term dominated" system. In what sense does \nu_t look like a source term? I had never conceptualized it as such. Bob |
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March 29, 2000, 03:02 |
Re: Restrictions on time steps
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#5 |
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I meant that the k and epsilon equations are source term dominated. The effect on the other equations is only through \nu_t, as you say.
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March 29, 2000, 03:24 |
Re: spelling correction
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#6 |
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Heh, my misstake... I even took out his excellent turbomachinery book to check the spelling and I still got it wrong. Btw, the papers are in J. Comput. Physics, vol 103, p 141 and AIAA J. vol 30, no 1 p 13.
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