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Old   June 2, 2008, 21:29
Default Courant number selection
  #1
Woo
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Dear all,

I am using the pressure-based coupled solver. This pressure-velocity coupling method requires input of the Courant number. the default value in FLUENT is 200. I think i need to lower this value for better convergence. Any idea how to select a proper value?

Best regards, Woo

P.S. I have gone through the archives. It seems that 0.5 is always referred as a low value. Not sure why it is so.
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Old   June 3, 2008, 03:55
Default Re: Courant number selection
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fadhil
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try 0.1
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Old   June 3, 2008, 04:04
Default Re: Courant number selection
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Woo Meng Wai
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Hi Fadhil,

Thanks for the advice. May I know the reasoning in choosing 0.1 or perhaps thre is a calculation that we can use?

Best regards, Woo
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Old   June 3, 2008, 04:08
Default Re: Courant number selection
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fadhil
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try 0.1
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Old   June 3, 2008, 04:24
Default Re: Courant number selection
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fadhil
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courant number is ratio of a time step to a cell residence time..so choose the small ratio.
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Old   June 3, 2008, 04:42
Default Re: Courant number selection
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fadhil
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try 0.1
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Old   June 3, 2008, 05:11
Default Re: Courant number selection
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max
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Hello Woo,

the Courant-Number limit < 1 must be adhered to for explicit time discretitation schemes, especially for Vof-applications or certain high Mach-number flows with shocks where one should use density-based coupled solvers. For single-phase flows or incompressible fluid dynamic problems I met no stability problems using a Courant-number of 20 with the pressure-based coupled solver, provided that you have a good quality grid.

cheers

Max
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Old   June 3, 2008, 06:12
Default Re: Courant number selection
  #8
Woo Meng Wai
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Hi Max,

Thank you for the advice. No wonder my model failed to converged at the default value of 500. Will try the lower number and see what happens.

cheers, Woo
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