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<p>Indeed traction boundary conditions are suitable. However it is
unclear which NEKUSE variable I should set. From bdry.f lines 1101
to 1103 :</p>
<p> V1(IX,IY,IZ) = TRN<br>
V2(IX,IY,IZ) = TR1<br>
V3(IX,IY,IZ) = TR2<br>
</p>
<p>it seems that I should set TRN, TR1 and TR2 for (shear horizontal
local) 'shl' BC. <br>
</p>
The end goal here is to compute a friction velocity locally for
which loglaw - velocity at the first grid cell is zero.<br>
<br>
For now whether I set 'shl' or 'SYM' I get the same results.<br>
<br>
<br>
<div class="moz-cite-prefix">Le 18/07/2018 à 11:07,
<a class="moz-txt-link-abbreviated" href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> a écrit :<br>
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<blockquote type="cite"
cite="mid:mailman.6481.1531904884.86639.nek5000-users@lists.mcs.anl.gov">Hi,
<br>
<br>
there are so-called traction boundary conditions (or mixed
traction-velocity boundary conditions), see the documentation
<a class="moz-txt-link-freetext" href="https://nek5000.github.io/NekDoc/theory.html">https://nek5000.github.io/NekDoc/theory.html</a>
<br>
(it is in the section about passive scalars, which is perhaps not
ideal). The conditions should work for both PnPn and PnPn-2, but
for some cases you need the stress formulation. I am not sure
whether Nek is properly catching all impossible (or unimplemented)
combinations.
<br>
<br>
There are some Nek examples that use these conditions, so you can
get some guidance from there.
<br>
<br>
Hope this helps,
<br>
Philipp
<br>
<br>
On 2018-07-18 09:38, <a class="moz-txt-link-abbreviated" href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> wrote:
<br>
<blockquote type="cite">Dear Neks,
<br>
<br>
<br>
I have been looking into the different boundary conditions
available by default in bdry.f. However, I haven't seen any
mixed conditions. I would like to impose a no slip condition and
specify the shear stress at the boundary. The boundary is flat
and aligned with the mesh.
<br>
<br>
Moreover it seems that shear stress boundary conditions are
applicable only to the Pn-Pn-2 formulation. Is there a way I can
specify the wall normal streamwise velocity gradient u_y as well
?
<br>
<br>
<br>
Best regards,
<br>
<br>
Armand.
<br>
<br>
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