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-   -   Courant Number (http://www.cfd-online.com/Forums/fluent/96038-courant-number.html)

vaibhavraikhare January 11, 2012 01:16

Courant Number
 
I am using VOF model for simulating..but within 1 or 2 time step courant number reach its limit and iteration stops..i reduced the time step size from 1 to 0.05 but there is no result of it..and i have to simulate it for around 1hour..
how can it be possible to increase courant number..or what is its concept..

doronzo January 11, 2012 09:10

Re
 
may be the mesh resolution is involved in the Courant number?
regards

vaibhavraikhare January 11, 2012 09:26

thnx doronzo...but there is no role of mesh resolution..

srjp January 12, 2012 08:59

Did you check the flow velocity? If it is too fast through the system, it may give a problem.
Courant number = velocity * delta t / delta x
It is a measure of the ratio of simulation time step to the system time scale.
You can edit the Courant number limit in the solver settings.

vaibhavraikhare January 12, 2012 09:23

i have checked..there is no velocity in my model..i didn't give any..
how can i change courant number in solver? i have gave its value to 1 in VOF model solver setting but its not working

srjp January 13, 2012 01:34

No velocity? What are your boundary conditions?
Also, you can still try reducing your time steps.

It is always good practice to start with extremely small time steps and gradually increase it.

vaibhavraikhare January 13, 2012 01:54

Actually i am working on a water filled (30% by volume) box which is packed. there is only a pressure outlet on its upper face. The heat is given to the box by its lower surface..
Boundary Conditions Are:
Fluid (water)
outlet(pr outlet)
plate (heat is given)

i reduced time step to very small number as in VOF model the time step size should be in the form of 1e7.
But after some time (10 sec) it always increase suddenly at a particular point..and its courant number reaches very high..

LuckyTran January 13, 2012 23:52

Quote:

Originally Posted by vaibhavraikhare (Post 338803)
thnx doronzo...but there is no role of mesh resolution..

May not be directly related to the problem but, interval size plays a direct role in the calculation of the Courant number so the role of mesh resolution cannot be thrown out. Mesh resolution definitely has an impact (it is in the definition of Courant number).

shk12345 January 14, 2012 06:26

Use a time step of 1e-7 to 1e-5 and then tell me what happens.

shk


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