[Nek5000-users] Problem with CHT: fluxes at the interface do not match

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

Dear all,

I was running a simple case with conjugate heat transfer. I managed to validate it against some analytic data.
I checked whether the heat fluxes at the interface between solid and fluid match or not. For any ratio of solid conductivity over fluid conductivity they match very well especially if the grid is very refined at the interface. The problem is that they match only if vtrans of solid is the same as vtrans of the fluid, else the ratio of the two fluxes is proportional to the ratio of vtrans, which is wrong.
I had a look into the code even though I am not very expert. I am using cvode. In fcvfun there is a call to makeq. In makeq, after the call to wlaplacian and add2, the rhs, which is bq, is divided by vtrans. When we are back to fcvfun, there is a call to dssum over ydot. I am not sure but I think that dssum mixes the properties of fluid and solid, therefore the transient equation which is solved for the temperature at the interface has a flux which is divided by vtrans of the fluid and another flux which is divided by vtrans of the solid, therefore the two fluxes can not match at the interface unless solid and fluid have the same vtrans.
If this is really the problem, I think it could be solved by dividing bq at the interface by vtrans of the solid only, before dssum is performed.
I'll check again my case to be sure that what I observed was not due to an error.

Thanks in advance for your help.

Regards,
Andrea.