# Courant number selection

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 June 2, 2008, 21:29 Courant number selection #1 Woo Guest   Posts: n/a 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.

 June 3, 2008, 03:55 Re: Courant number selection #2 fadhil Guest   Posts: n/a try 0.1

 June 3, 2008, 04:04 Re: Courant number selection #3 Woo Meng Wai Guest   Posts: n/a 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

 June 3, 2008, 04:08 Re: Courant number selection #4 fadhil Guest   Posts: n/a try 0.1

 June 3, 2008, 04:24 Re: Courant number selection #5 fadhil Guest   Posts: n/a courant number is ratio of a time step to a cell residence time..so choose the small ratio.

 June 3, 2008, 04:42 Re: Courant number selection #6 fadhil Guest   Posts: n/a try 0.1 jn10hn likes this.

 June 3, 2008, 05:11 Re: Courant number selection #7 max Guest   Posts: n/a 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 jyothsna k likes this.

 June 3, 2008, 06:12 Re: Courant number selection #8 Woo Meng Wai Guest   Posts: n/a 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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