Grid
The hypothesis is that the upper
rolls need more room to developp, so we mqde a higher mesh.
Viscosity
/*user define function*/
/* udf pour viscosite*/
#include "udf.h"
DEFINE_PROPERTY(viscosite,cell,thread)
{
real nu;
real temp;
temp=C_T(cell,thread);
if (temp<300.5)
nu=0.1;
else if (temp<300.75)
nu=-0.396*temp+119.098;
else
nu=0.001;
return nu;
}
Initial Velocity, |v|=1, delta T=1
If we simulate this case without
any viscosity gradient, the convergence is to 2 rolls, one above the other.
Velocity
We can notice the developpement
of the lower roll and the motion of the fluid above, but still not one
real roll.
Velocity, |v|=10, delta T=1
Even with a greater velocity initialisation, the convergence is similar to the last one.
Velocity, |v|=10, delta T=10
The solution could have been to take a bigger Rayleigh number, but , as we can see, the researched case is unstable and with a greater Rayleigh, the case converges to one single roll.
Velocity, |v|=1, delta T=5
