[Nek5000-users] Heat/passive scalar solver - Helmholtz

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

Hi Marco,

If param(12) is positive, then it means that

        dt will not exceed param(12).

        and that

         dt will be chose such that CFL ~ CFL_target (specified in the .rea file).

Thus, if you have:


      .001              p12 DT
        :                :
      0.5000000         p26 COURANT/NTAU

then dt will be the min of (.001, dt_cfl ), where dt_cfl is such that CFL=0.5 (p26).

Note that there is some tolerance in resetting dt ... i.e., I think you can get to CFL=0.55
before it would reset dt to target CFL of 0.5

Similarly, it would not increase dt until CFL < 0.45.

ONE ADDITIONAL POINT:

If you are using characteristics, then COURANT (p26) takes on a different meaning.  

In that case, it means how many substeps the characteristics scheme takes for each
Navier-Stokes timestep. (1, 2 or 3 are most common values, but it can vary from 
case to case...)

See:   www.mcs.anl.gov/~fischer/new.pdf  , last section on timestepping, for a 
description of characteristics as implemented in Nek.

Paul

________________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Monday, August 22, 2016 1:19 PM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Heat/passive scalar solver - Helmholtz

Dear Neks,

I am a little confused by the setup in the rea file to run a simulation with a constant cfl. My understanding (from the Nek5000 archives) is that by setting p012 to a positive value in the rea file, it should be sufficient to ensure a constant cfl condition during the run. When I do so, my time step is constant and thus my cfl varies.

I tried to set p012 to a positive value in different rea file from the examples directory but none of them yield a constant cfl during the run.

If someone has an answer to this problem I would really appreciate the help.

Thanks,
Marco
_______________________________________________
Nek5000-users mailing list
Nek5000-users at lists.mcs.anl.gov
https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users