dnesity and phase separation
 

Hi .
I am working with a porous media simulating a drainage of oil in a porous media filled by water. But I found that if I use a low density oil, CFX hold the 2 phases segregated, but when I use an oil with a higer density (near of the water value) after some time ( in transient simulation), the 2 phases are mixed. What is happening? (the gravity is not defined)
Thanks
and sorry by my english

Model :
Laminar
B.C: Vel in, Pressure out
2D
Courant lower than 0.7