[Nek5000-users] Robin boundary conditions for the velocity

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

Hi Nek's.

I would like to use the following boundary condition as my outflow condition
for the adjoint perturbation mode:

p = du/dz = dv/dz = 0
dw/dz = Re * Uz * uz

where Uz is the z-component of the base flow. I would be tempted to do
something like:

subroutine usrchk

[...]
common /mygrad/ gradwx(lx1,ly1,lz1,lelt)
             $             gradwy(lx1,ly1,lz1,lelt)
             $             gradw(zlx1,ly1,lz1,lelt)

call gradm1(gradwx,gradwy,gradz,vz)

[...]

and then in userbc

 subroutine userbc (ix,iy,iz,iside,eg)
     include 'SIZE'
     include 'TOTAL'
     include 'NEKUSE'

     common /mygrad/ gradwx(lx1,ly1,lz1,lelt)
    $              , gradwy(lx1,ly1,lz1,lelt)
    $              , gradwz(lx1,ly1,lz1,lelt)

     integer e,eg

     e = gllel(eg) ! global element number to processor-local el. #

c Assuming param(2)<0 in .rea, Re = 1./param(2) since in connect2 or subs1 I
do not remember there is first param(2) = -1/param(2)

     uz = (1./param(2)) * vz(ix,iy,iz,ie) * gradwz(ix,iy,iz,e)

However I am not sure how to handle the other boundary conditions on u, v
and p.

Regards,
JC

-- 
Jean-Christophe
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