Hi CFX 5.6 world! I've modelled the following problem successfully for the stationary case but have no idea how to work in some transient modifications:

Object: Rectangular Parallelepiped (20* 20* 50 mm(height)) with a capillary tube (right-angled to one side wall) some millimeters above the bottom.

Fluid domain - so far only one,

Fluid model : variable mole fraction, isotherm

2 Inlets (Bottom, Top) 1 Outlet (Capillary tube)

The composition at the two inlets differs (otherwise no diffusion due to concentration gradient - okay?!)

Result:A relative sharp z-gradient on the level of the capillary tube. Also transport occurs in x and y direction.

Now the real problem: The bottom inlet isn't usefull anymore. But I would like to start the simulation with an initial concentration distribution (only depending on the z-coordinate). A step function (any height from the bottom th the top should be possible) would be enough for the first guess. How can I implement this? - even sleeping on the manual wasn't successful!

Thanks for all helpful hints!

Volker

Step functions are easy with CEL. The bump tutorial has an example of using a step function to initialize variables (in that case, it is used to initialize volume fraction for a free surface calculation).