Courant Number

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 January 11, 2012, 01:16 Courant Number #1 Member   Vaibhav Rai Khare Join Date: Jul 2011 Location: Jaipur Posts: 37 Rep Power: 7 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..

 January 11, 2012, 09:10 Re #2 Member   Domenico Join Date: Sep 2011 Location: Atlanta Posts: 39 Rep Power: 7 may be the mesh resolution is involved in the Courant number? regards

 January 11, 2012, 09:26 #3 Member   Vaibhav Rai Khare Join Date: Jul 2011 Location: Jaipur Posts: 37 Rep Power: 7 thnx doronzo...but there is no role of mesh resolution..

 January 12, 2012, 08:59 #4 Member   JP Join Date: Mar 2009 Posts: 57 Rep Power: 11 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. Last edited by srjp; January 12, 2012 at 09:12. Reason: to correct a spelling mistake + to add some more details.

 January 12, 2012, 09:23 #5 Member   Vaibhav Rai Khare Join Date: Jul 2011 Location: Jaipur Posts: 37 Rep Power: 7 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

 January 13, 2012, 01:34 #6 Member   JP Join Date: Mar 2009 Posts: 57 Rep Power: 11 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.

 January 13, 2012, 01:54 #7 Member   Vaibhav Rai Khare Join Date: Jul 2011 Location: Jaipur Posts: 37 Rep Power: 7 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..

January 13, 2012, 23:52
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Lucky Tran
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Quote:
 Originally Posted by vaibhavraikhare 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).

 January 14, 2012, 06:26 #9 Senior Member   shoeb khan Join Date: Nov 2011 Posts: 179 Rep Power: 7 Use a time step of 1e-7 to 1e-5 and then tell me what happens. shk

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