Create simple mesh for conjugate heat transfer

[anshchaube]

• [x] Create solid mesh using same coordinates from the fluid mesh to obtain a conformal mesh.
• [x] Convert fluid and solid re2 files (w/ BCs ) to rea files using gen_rea(2) in usrchk()
• [x] Mesh solid and fluid rea files together using Prenek

[anshchaube]

Having trouble with step 3 : Nek's gen_rea(2) generates only the mesh data in its newrea.out file. The header and tail for the rea file that I need to add by hand are a bit of a mystery to me. I could take the top and the bottom of a 3d rea file from Nek5000/examples , but I am not sure how many parameters and logical flags I need to change from the original example.

Do the usr and par files overwrite everything in the rea file, so it doesn't matter what's in it? If not, is there a smarter way to do this, instead of changing several parameters by hand @dshaver-ANL ?

[dshaver-ANL]

You should blindly copy the head and tail to construct a complete rea file, then immediately convert it to an re2 file with reatore2. The re2 file doesn’t contain any of the extra info from the head or tail, so it doesn’t matter what you put there.

From: Ansh Chaube notifications@github.com Sent: Wednesday, June 26, 2019 4:30 PM To: arfc/sneks4me sneks4me@noreply.github.com Cc: Shaver, Dillon R. dshaver@anl.gov; Mention mention@noreply.github.com Subject: Re: [arfc/sneks4me] Create simple mesh for conjugate heat transfer (#6)

Having trouble with step 3 : Nek's gen_rea(2) generates only the mesh data in its newrea.out file. The header and tail for the rea file that I need to add by hand are a bit of a mystery to me. I could take the top and the bottom of a 3d rea file from Nek5000/examples , but I am not sure how many parameters and logical flags I need to change from the original example.

Do the usr and par files overwrite everything in the rea file, so it doesn't matter what's in it? If not, is there a smarter way to do this than changing several parameters by hand @dshaver-ANLhttps://github.com/dshaver-ANL ?

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[anshchaube]

Thanks! Kirk and I figured out that we need the head and the tail of an example rea file that is 3D and has thermal boundary conditions. We also removed the par file while running Nek in post-processing because Kirk was more comfortable with using rea files for this purpose.

The rea files generated were finally accepted by prenek as valid input.

[anshchaube]

Further steps:

• [x] Setup par file
• [x] Setup BCs again

[anshchaube]

I added test code to see if prenek was naming side sets correctly. I used this code in my userbc AND useric:

     do iel=1,nelv
          do ifc=1,2*ndim
              id_face = bc(5,ifc,iel,1)
              bc(5,ifc,iel,2) = id_face
              if (id_face.eq.100) then       ! Inlet
                  temp = 1.0
              elseif (id_face.eq.10) then   ! Inlet graphite
                  temp = 1.0
              elseif (id_face.eq.1) then   ! Inlet graphite
                  temp = 0.5
              endif
          enddo
      enddo

As the attached image shows, some sidesets have the temp 0.5, meaning there are some sidesets labelled "1", even though I never created any sideset with this ID in gmsh. It seems prenek is creating random sideset IDs.

[anshchaube]

What worked - changing all solid/graphite boundary conditions to insulated, having only one user-specified temperature BC (at the inlet). I can now see the inlet temperature being propagated along the flow.

[anshchaube]

@dshaver-ANL I tried to set the volumetric heat source in the fluid region in my usr file as follows:

     subroutine userq(ix,iy,iz,eg) ! set source term

c      implicit none

      integer ix,iy,iz,eg

      include 'SIZE'
      include 'TOTAL'
      include 'NEKUSE'

      integer e
c     e = gllel(eg)

      qvol = 10.0
      if (eg.gt.nelgv) qvol = 0.0 ! glob el id > no. of el in glob v mesh

      return
      end

Does this seem correct?

[dshaver-ANL]

looks right to me

[anshchaube]

Conjugate heat transfer works. I will post results that look physical once I have run a Nek simulation with the right non-dimensionalized thermal properties of the MSRE salt.

[anshchaube]

CHT is working. Inlet BC for temp is 1, which you can see propagating upwards. There's heat generation (qvol = 1.0) in the fluid which is also apparent. Mesh is functional.

Flow is not fully developed thermally. Future issues will focus on running a case with actual MSRE thermal properties until the flow is fully developed.