Grid configuration
We first choose to study the RayleighBenard
instabilities in a two dimension case. Practically, it is the kind of flow
that we could observe in a fluid between two horizontal flat walls of large
dimension, compared to the fluid thickness.
The dimensions of the simulated zone are 2 cm
in the horizontal direction (x) and 1 cm in the vertical dimension (y).
The grid is composed of 5000 squared cells
(50x100).
The boundaries conditions are:
 symmetry on the vertical boundaries
 Temperature given on the wall
next
Conditions of the Calculation
In all the cases we studied, the Rayleigh number stay
close enough to the critical Rayleigh number to stay in laminar flow. That
is why we always choose the laminar model.
Define=>Models=>Viscous...


For the buyancy resulting from the difference of density, we have to
change one parameter in the Materials menu. (Define=>Materials...).
We change the density from constant to Boussinesq.
A new field appears under the viscosity, it is the thermal expansion
coefficient. It has to be filled. We have chosen the value of 0.00012.
All others parameters where not modified.