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Courant number and time step

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Old   March 7, 2012, 04:01
Default Courant number and time step
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Aditya
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How can we find for a fixed courant number the time step that fluent is using when an explicit density based solver is used?

I have looked in the manual of ansys fluent for the definition if CFL and it is given in some very complicated terms like flux and volume and etc.

SO can please someone tell me the way to know the time step for an explicit scheme when the courant number is fixed?

Thanks in advance!!
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Old   March 7, 2012, 04:36
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Hi,
as I know Courant number is u*deltat/deltax, where

u is the velocity
deltat is the time step
delta x is cell dimension

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Old   March 8, 2012, 19:35
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Hi

delta x = 0.025 mm; u = 595.40 m/s; C =0.12;

using the formula i get delta t = 5.0385 nano sec;

Therefore the physical time after 200 iterastions must be: t*200 = 1.00772 micro sec

Fluent simulation:

Since I am using an explicit formulation I couldnt think of any other way of finding out the time-step.

After 200 iterations the physical time shown by fluent is 10.191 micro sec.

I am assuming that as the the solution goes ahead in time the difference will become larger.

Can anyone tell me why this is happening? Am I doing any mistake?

Last edited by dsn2491; March 8, 2012 at 20:18.
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Old   September 18, 2012, 13:59
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have you activated time step print/plot from monitors panel? That will should unless your method of solution disables it.
Also the rough estimation you made using CFL will not be applicable always during simulation. So time step is not fix and fluent's result is correct since time step is changing every time step based on fixed CFL.
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