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-   -   Courant number and CFL number (http://www.cfd-online.com/Forums/star-ccm/111278-courant-number-cfl-number.html)

 snandish13 January 2, 2013 10:55

Courant number and CFL number

Hello Friends,

I know that the Courant number has to be increased to reduce the number of iterations and for faster convergence. But what is the influence of CFL number?
We have the option of giving both CFL and courant number as input for the simulation. Also, under expert initialization (solver settings) we can increase or decrease the maximum grid levels. What is the influence of grid level on the solution obtained.
Please can anyone clarify these doubts?

 abdul099 January 5, 2013 18:30

Stationary or transient simulation?

Don't worry about the max levels.

 LuckyTran January 7, 2013 01:32

Quote:
 Originally Posted by snandish13 (Post 399760) I know that the Courant number has to be increased to reduce the number of iterations and for faster convergence. But what is the influence of CFL number? We have the option of giving both CFL and courant number as input for the simulation. Also, under expert initialization (solver settings) we can increase or decrease the maximum grid levels. What is the influence of grid level on the solution obtained. Please can anyone clarify these doubts?
High courant number will affect solution accuracy. CFL refers to a condition imposed on the courant number, above which, the solution will be affected by numerical oscillations that make the solution unstable. CFL really only applies to explicit solvers. For implicit solvers, your courant number can exceed the CFL number and not run into these oscillations, but that does not mean the solution will be accurate (just oscillation free).

Quote:
 Originally Posted by snandish13 (Post 399760) Also, under expert initialization (solver settings) we can increase or decrease the maximum grid levels. What is the influence of grid level on the solution obtained. Please can anyone clarify these doubts?
The maximum grid levels refers to the maximum number of grid levels allowed in the multi-grid solver. For most cases you don't need to ever worry about this unless you really know what you are doing (hence the reason it is listed under expert). If you have to ask what this is, then don't touch it. If you want to learn more, read about multi-grid solvers.

 snandish13 January 7, 2013 05:14