[Nek5000-users] Warning Message : L1/L2 DIV(V)

[nek5000-users at lists.mcs.anl.gov]

Well I cannot tell you if you resolution is large enough. As you know this depends on the scales you need to resolve. Is this a DNS resolution?

If you do some large scale runs I recommend to run with lx1=8 and a larger number of elements. A high polynomial order N is typically not needed for engineering type problems. In addition there are several reason why you don't want to increase N more than needed:

- CFL scales with 1/N^2 so with a higher N you have to use a smaller dt
- the number of pressure iterations may depend on N (depending on your mesh and preconditioner)


Are you using IFCHAR=T?
Filtering?
Dealiasing?
 
You may want to post the logfile.


Stefan

On May 3, 2010, at 10:15 PM, nek5000-users at lists.mcs.anl.gov wrote:

> Hi Stefan,
> 
> I have 23k elements and an lx1=11, so I am guessing my resolution is reasonably good (32 Mil Nodes) . As regarding the boundary conditions, yes I do add some divergence at the outflow. I am running it at CFL of close to 2 with 2nd order time stepping. Would you recommend lowering the Courant to say 0.5 ? Even though the warning pops up, I don't see any crazy stuff happening in my flow . 
> 
> 
> Regards
> Shriram Jagannathan
> 
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