We limite our study to influence of the boundaries conditions.

__- Geometry :__

We choose to take 1 centimeter in Z direction. So,
we have same length in Z direction and X direction. We 'll see consequence
below.

__- Meshing :__

We choose cartesian mesh. There are two reasons : first,
the geometry is enough simple, then we can't use an classic unstructured
mesh because to study Rayleigh Benard instabilities with FLUENT, we must
activate option !*PRESTO *but this option doesn't exist with
an unstructured mesh.

Moreover, in order to avoid prohibitive computation, we
take 20 x 40 x 40 nodes.

__- Boundaries conditions :__

In order to study the "same" problem of 2D study,
we take boundaries conditions showed below :

__- Convergence's behaviour :__

Due to number of nodes relatively limited, CPU time is
not important (see below).

__- Results :__

We obtain comparable results with 2D study.

(temperature for DT=0.5)

(velocity for DT = 0.5)

__- Boundaries conditions of symmetry :__

We change the boundaries conditions of the two horizontal
plans which had wall conditions and we applicate symmetry conditions. We
obtain following results :

We should be obtain a similar solution with 2D solution
(indeed, we take same boundaries conditions :symmetry) but the result is
totally different. It seems there are two symmetric planes.

How come we obtain such as results ?

We have take same lengthes in X direction and Z direction,
this can explain why the solution has this particular form. A idea to break
these symmetric plans could be to take differents lengthes for X segment
and Z segment. So, the geometry have not more symmetric planes, and the
solution too.