[Nek5000-users] Warning : DIV(V)-QTL too large

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

I guess you are using PNPN with Boussinesq. What's your reason not to use PNPN with LowMach?
-Stefan

-----Original message-----
> From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
> Sent: Tuesday 19th September 2017 16:21
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Warning : DIV(V)-QTL too large
> 
> In an incompressible flow, QTL (thermal divergence) is ZERO. In this case the error in divergence is essentially the divergence in velocity.  The error depends on your spatial resolution (typically dominates), dt and pressure solver tolerance. You may want to visualize the error in divergence to get a feeling about the spatial location.
> 
> Hope this helps
> Stefan
> 
> 
> -----Original message-----
> > From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
> > Sent: Tuesday 19th September 2017 16:09
> > To: nek5000-users at lists.mcs.anl.gov
> > Subject: [Nek5000-users] Warning : DIV(V)-QTL too large
> > 
> > Dear Nek experts,
> > 
> > I'm trying to simulate a differentially heated cavity with a Rayleigh 
> > number of 10e9 (turbulent convection).
> > I modified the tutorial of the Rayleigh Benard cell to build my case.
> > I increased progessively the Rayleigh number. As my Ra increase, I get 
> > this warning "DIV(V)-QTL is too large" so I refined the mesh and the 
> > timestep as proposed in this thread 
> > https://lists.mcs.anl.gov/pipermail/nek5000-users/2016-January/003553.html.
> > 
> > I have now still this warning even if my courant number is very low 
> > (around 0.05).
> > So I would like to know if I could use a bigger time step keeping C 
> > below 0.5.
> > 
> > My other question is the meaning of QTL, the thermal divergence. In my 
> > simulation it is equal to 0, this is partly why DIV(V)-QTL is too large. 
> > Should I specify a QTL ?
> > 
> > 
> > Thank you in advance for your answers,
> > Best,
> > Samuel
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