[Nek5000-users] Problem with conjugate heat transfer + Low Mach number formulation

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

Dear all,

I am running a case with conjugate heat transfer + Low Mach number formulation, the domain is a 2D channel. The boundary conditions for the temperature are:
- fluid: constant inlet temperature equal to 1;
- solid: constant temperature equal to 2 at the outer side, at the inner side there is no boundary condition because the energy equation has to be solved, the other sides are insulated.
What I see is that the flow starts to accelerate almost immediately even though at the beginning the temperature of the fluid domain is almost 1. The outlet velocity becomes more than two times the inlet velocity.
The reason is that at the wall (and especially at the inlet corner) the thermal divergence is quite large, while it is almost zero in the rest of the fluid domain. 
In a conjugate heat transfer problem the derivative of the temperature is discontinuos across the wall because of the different thermal conductivities. Could there be a problem when "opgrad" and "opdssum" are evaluated in "subroutine qthermal"? I know that they are evaluated only on the fluid domain but maybe the discontinuity in the derivative of the temperature could give some problems.

Thanks a lot in advance for your help.

Regards,
Andrea