
This
part contains further developments of the study of the Kelvin Helmholtz
instability to illustrate possibilities of Fluent:
A) 3 phasesThe mesh is an evolution of the mesh used in the time wave study. This time the height is 0.3m the additional space being occupied by the hid phase.A1 Mesh Click here for a picture of this mesh. As with the mesh, the used model is the same as in the time wave study. The third phase is liquid gasoil which is slightly lighter than fuel. The fluids are layered with heavier on the bottom an lighter on top. As we use 3 phases the vortexes are moving in most settings.A2 Model The interface 1 between water and fuel is perturbed whereas the interface 2 between fuel and gasoil is undisturbed The results showed that the oscillation at the interface 1 affected the interface 2. I seems like the interaction between both interfaces has a stabilizing effect.A3 Result For example with water 2
m/s, fuel 0 m/s, gasoil 2 m/s. .

at time 0.34s

With
a water 2 m/s, fuel 0 m/s, gasoil 2 m/s setting, the oscillation are moving
in opposite direction but there the same evolution occurs.
B) 3D InstabilityAs a 3D mesh uses a lot more computing power the domain is smaller: 0.1m in length (xaxis), 0.2m in height (yaxis), 0.1m in depth (new zaxis). We use a 4 mm space step size to keep the elements number down: 25*50*25=31250 elements.B1 Mesh The upper and lower faces are walls. The other faces are periodic ones. Click here to see a picture of this mesh
The model used and operating conditions are the same as for the time wave study. The initialization UDF init3d.c is an evolution of init.c. This time the is a perturbation on the xaxis and the zaxis. The wavelength in both direction is 0.1m. The fluid is flowing along the xaxis.B2 Model The image below show the result of the computation after 0.1s. The surface is the 0.5 isovalue of fraction of fuel (i.e. the interface). The color is the velocity magnitude.B3 Result 
Click here
to see an animation of the instabilities formation with a 0.01 time step.
This image shows the particular shape of the instability. 