[Nek5000-users] Effect of CFL number.

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

Hi Kamal,

In my view, you are trying to run in a regime that is actually not reproducible.
You are right at the transition Re, which implies strong sensitivity to initial
conditions and under such circumstances you should not expect two simulations
at two different resolutions to converge to the same result, just as you would not
expect two turbulent simulations to follow the same trajectory point-by-point, only
on average. 

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: Tuesday, May 27, 2014 11:23 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Effect of CFL number.

Dear Neks,

I would like to know what is the effect of CFL number on a turbulence
simulation in SEM.

I use polynomial order of lx1 = 5 and lxd = 8 and get a C = 0.176 for a
Re = 2000 with dt = 0.001  in pipe flow where I find a transition to
turbulence. when I decrease my time step 'dt = 0.0001 ' further my pipe
becomes fully turbulent for the same mesh.

When I increase the order lx1 = 7 and lxd = 10, I find a completely
steady solution, instead of a transition to turbulence.

It would be nice what if some could please tell me what parameter
determines the accuracy of the simulation in terms of a turbulent flow
because I am not able to reproduce the result with a different mesh or
with higher order.

Thank you,

Kamal
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