[Nek5000-users] Stress formulation

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

Hi Andrew,

I checked into this... I think what is happening is that the 'O  ' bc for the stress formulation
means stress-free, which is not guaranteed to yield  a parabolic profile at the outlet.

If you increase your Reynolds number I'm guessing that you'll recover the parabolic
profile because the viscous stresses will diminish -- this is what I observed.

>From my perspective, the outlet boundary is not a region where I would count on accurate
physics --- it is, after all, a truncated domain, so I don't generally worry too much about
the behavior there.

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, December 01, 2015 2:44 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Stress formulation

Hi Neks,

    I have one question about stress formulation in NEK5000.
    I tried to make a simulation for Poiseuil flow with stress formulation. In inlet boundary condition use was made of parabolic profile. If IFSTRS=false the outlet profile is exactly the same as inlet one but in case of IFSTRS=true the outlet profile changes significantly (both the maximum value and profile shape). Could you tell me how I can get the parabolic profile at outlet, please?
     The same thing occurs with pressure values. The maximum pressure value with IFSTRS=true is three times higher then the one with IFSTRS=false.

     I found that the difference comes from subroutines where the stiffness matrix is calculated (axehlm for IFSTRS = false and axhmsf for IFSTRS = true) but I don't undestand what is happening exactly.

Thanks in advance for your help,
Best regards,
Andrew
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