[Nek5000-users] Linear Advection Equation

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

Technically Nek solves convection-diffusion (CD).

CD with nu=0 is invalid because it's a singular perturbation --- the number of
boundary conditions is different for the 1st-order convection eqn than for the
2nd-order CD equation, so Nek checks to make certain nu \ge 0.

I usually set nu=1.e-31....  it won't show up in the calculation (assuming
your other quantities are O(1)).

Best,

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: Sunday, March 08, 2015 9:17 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: Re: [Nek5000-users] Linear Advection Equation

Thank You, Paul.

Why does the conductivity/diffusivity (i.e. param(08)) have to be small and non-zero positive?  Can nek5k solve the linear advection equation without the discrete diffusion term?

On Sat, Feb 28, 2015 at 10:31 AM, <nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>> wrote:



Set ifflow to false and ifheat to T and ifadvc = F T F F F F...

in the .rea file.

Then, supply your velocity field in useric  (ux, uy, uz), or, if you want time-varying velocity,
do so in usrchk by over-writing the velocity field arrays, vx(), vy(), and vz() at each step.


Paul
________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov<mailto:nek5000-users-bounces at lists.mcs.anl.gov> [nek5000-users-bounces at lists.mcs.anl.gov<mailto:nek5000-users-bounces at lists.mcs.anl.gov>] on behalf of nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov> [nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>]
Sent: Saturday, February 28, 2015 9:24 AM
To: nek5000-users at lists.mcs.anl.gov<mailto:nek5000-users at lists.mcs.anl.gov>
Subject: [Nek5000-users] Linear Advection Equation

Dear Users,

Is there a way to solve a linear advection equation in nek5k without computing the Navier-Stokes equations?  I am simply interested in advecting a profile according to the following:

D(phi)/Dt = d (phi) /dt +  v.grad(phi)= 0

where v.grad(phi) = u.d(phi)/dx + v.d(phi)/dy + w.d(phi)/dz

and v is a prescribed velocity (for example v = (1,1) in 2D)

Best,

Saumil


_______________________________________________
Nek5000-users mailing list
Nek5000-users at lists.mcs.anl.gov<mailto:Nek5000-users at lists.mcs.anl.gov>
https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users




--
Saumil S. Patel
Ph.D. Candidate
Department of Mechanical Engineering
Computational Multiphase Fluid Dynamics Group<https://sites.google.com/site/leeccny/>
The City College of New York
Telephone: 1 (212) 650-7134
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20150308/7d56510a/attachment.html>