code_saturne User's Forum

Hello,

I am quite confused by the coupled Syrthes/Saturne result I get. I have a heating solid bar centered within a fluid domain. The solid bar is heated by Joule effect which I temporarily model by a handmade heating field.

What I am interested in is the thermal transfer between the solid bar and the surrounding air, and particularly the solid surface temperature.

Once I run the coupled simulation, I am very surprised to discover that my bar max. temperature is 26°C when the surrounding air is heated up to 59°C. Moreover, if I play with the power of the volumic heating field in the solid region, it affects the temperature of the bar, but does not change the evolution of the fluid (temperature, velocity, etc.).

Therefore, I suspect that my coupling is not complete and I am seeking some help to circumvent this difficulty.
Additionnaly, my syrthes mesh is 2D when the Saturne simulation is 3D. Could this be the reason? 
Thanks!

Hello,

It may be interesting on the code_saturne side to activate the visualization output of the thermal fluxes at walls (and wall temperature), to see what amount of heat exchange you have at the interface.

Depending on the mesh and turbulence model, the heat exchange might be underestimated even if coupling occurs.

Best regards,

Yvan

Here are the thermal Flux and Boundary_temperature at boundaries.

1. Why are these quantities given on the volumic mesh and not only at the boundary faces?
2. The input thermal flux is globally negative. Does it mean the heat is going from the fluid to the solid?
3. The heat exchange is not underestimated, since the solid is way colder than the fluid. I don't understand how a 26°C metal bar can heat air to 60°C.
4. What are the difference between all the Syrthes output results : resu.ensight.case, resu_rdt.ensight.case, resu_cplcfd.ensight.case, resu_cplcfd_rdt.ensight.case? I understand that '_rdt' means time varying, so that the non '_rdt' data are stricly present at the end of the corresponding '_rdt' file. What does '_cplcfd' corresponds to, then?

Hello,

1) The quantities should only be on boundary faces. Do you have separate writers for volume and boundary faces ? If not, using "extract block" under ParaView might help separate them.

2) Yes, this sign is chosen from a "finite volume" rather than user perspective. A negative flux means heat flows from the fluid to the solid.

3) What are you initial and other boundary conditions for the fluid ?

4) I am not sure. I have not used Syrthes in a while. Actually, I would like to update the tutorial so as too use the new CHT option in v9.0, based on a thermal solver which is part of code_saturne (so has a more consistent set-up).
But "cplcfd" probably relates to "coupled with CFD".

Best regards,

Yvan