global courant number

hamid1 · June 11, 2012, 03:52

Hi
I would like to ask what is the appropriate global courant number for simulation of two phase flow inside the pipe via VOF?

Thank you
Hamid

ghost82 · June 11, 2012, 04:14

Taken from William reply on capeforum:

Global courant number: The default value of the Global Courant number is 2, but smaller value may be required for more accurate solution and more stable numerical calculation. In some cases, you need to reduce this up to 0.5 for accurate results. This is because the time step size (so, the CFL) should be small enough to get the accurate results. In some cases you may use CFL greater than 2 depending on the problem.

hamid1 · June 11, 2012, 05:08

thanks for reply,
im abit confused, the default global courant number for coupled explicit solver is 1 and for coupled implicit is 5 (no stability limitation),
but what about the segregated case, (which is my case)?
also what is the limitation for the courant number for the VOF model, is the limitation for that is 0.25?
thanks

ndabir · September 18, 2012, 13:53

Hi,

Have you found any good explanation about setting global courant number. Is it possible to reduce it to 0.1 or it might make numerical errors in simulation.

June 11, 2012, 03:52	global courant number	#1
hamid1 Senior Member hamid Join Date: Nov 2010 Posts: 185 Rep Power: 15	Hi I would like to ask what is the appropriate global courant number for simulation of two phase flow inside the pipe via VOF? Thank you Hamid chaitanyaarige and enass massoud like this.

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June 11, 2012, 04:14		#2
ghost82 Senior Member Rick Join Date: Oct 2010 Posts: 1,016 Rep Power: 26	Taken from William reply on capeforum: Global courant number: The default value of the Global Courant number is 2, but smaller value may be required for more accurate solution and more stable numerical calculation. In some cases, you need to reduce this up to 0.5 for accurate results. This is because the time step size (so, the CFL) should be small enough to get the accurate results. In some cases you may use CFL greater than 2 depending on the problem.

June 11, 2012, 05:08		#3
hamid1 Senior Member hamid Join Date: Nov 2010 Posts: 185 Rep Power: 15	thanks for reply, im abit confused, the default global courant number for coupled explicit solver is 1 and for coupled implicit is 5 (no stability limitation), but what about the segregated case, (which is my case)? also what is the limitation for the courant number for the VOF model, is the limitation for that is 0.25? thanks

September 18, 2012, 13:53		#4
ndabir Senior Member navid Join Date: Jan 2010 Posts: 110 Rep Power: 16	Hi, Have you found any good explanation about setting global courant number. Is it possible to reduce it to 0.1 or it might make numerical errors in simulation.