Helping energy convergence with conjugate heat transfer and tet mesh
For conjugate heat transfer problems with tetrahedral mesh, and especially with widely varying thermal conductivities, sometimes the energy equation
is difficult to converge at the start of the calculation.
Turning off the secondary gradients for temperature calculation helps with the energy equation convergence. The
command for doing this is;
(rpsetvar 'temperature/secondary-gradient? #f)
This command from the Fluent console window turns off the secondary gradient calculation for temperature, thus helping the energy equation to converge. Once the solution has progressed for a few hundred iterations and the
temperature field established, the secondary gradient calculation can be turned on again for better accuracy.