[Nek5000-users] Fwd: Variable density flows

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

Hi Praveen,

If you want to follow the model of the Guermond paper that you
pointed out then I shouldn't think low Mach is necessary given
that, in their model, div U = 0.

I've not looked into this in detail, however, so I suggest
undertaking a bit of exploration and test.

To specify variable density in Nek, you set ifuservp=.true.
and ifstrs=.true. in usrdat, and then in uservp() you set:

      if (ifield.eq.1) then

         utrans = mydensity
         udiff  = my viscosity

      endif

You also need to set lx2=lx1-2, (same for ly2 and lz2 (if3d));
and set lx1m=lx1,ly1m=ly1,lz1m=lz1 in the SIZE file.

Paul


----- Original Message -----
From: nek5000-users at lists.mcs.anl.gov
To: nek5000-users at lists.mcs.anl.gov
Sent: Friday, October 11, 2013 11:54:38 AM
Subject: Re: [Nek5000-users] Fwd: Variable density flows




Hi Paul 

For variable density case do I need to use the low mach number version or some other way ? 


Thanks 
praveen 



On Fri, Oct 11, 2013 at 8:24 PM, < nek5000-users at lists.mcs.anl.gov > wrote: 



In principle, this should work with the Pn-Pn-2 STRESS formulation, but 
I don't think it has been thoroughly tested. 

Regarding large viscosity variations, work needs to be done on the 
preconditioners for the viscous terms. This hasn't been a traditional 
focus for Nek5000, which has been aimed at high Reynolds number flows 
where the viscous solves are essentially trivial (compared to the 
pressure, say). 

Certainly, there are things that could be done to be effective in 
this space. I would start by running some test problems with the 
STRESS formulation to see if you get the accuracy you're after. If 
so, then we can look into performance enhancement via better preconditioning 
strategies for the case at hand. 

HTH, 

Paul 



----- Original Message ----- 
From: nek5000-users at lists.mcs.anl.gov 
To: "nek5000" < nek5000-users at lists.mcs.anl.gov > 
Sent: Friday, October 11, 2013 9:16:24 AM 
Subject: [Nek5000-users] Fwd: Variable density flows 



Hello 





Can we solve variable density incompressible flows with nek5000 ? For e.g. see the model given by eq. 2.1 here 


http://www.math.tamu.edu/~guermond/PUBLICATIONS/guermond_quartapelle_JCP_2000.pdf 



Also, can nek handle variable viscosity with large variations ? 


Thanks 
praveen 

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