Discussion Forum

I have set-up a simple rectangular geometry that consists of a rectangle, an inlet and an outlet. As a flow-medium I use air. Next, I have solved for the stationary velocity field, using the laminar-flow module.

As a next step, I put a concentration of a species at the inlet and want to investigate how the fluid field transports the species across the geometry. I solve this in a stationary study as well.

Next, however, I want to take into account that the concentration of my species varies across the geometry. In the x direction, this variation is given by

(change in concentration) = -(some constant) * exp(some constant) * dx / (velocity in x direction)

, where dx is a small step in the x direction. The change in the y direction is the same, only with x substituted for y.

Clearly, this is a function of my computed velocity field. Now the question is: how can I setup such a function so that I can use it for further studies in my COMSOL model?

I have tried to this with adding an analytic function, but I cannot figure out how to access the components of the computed velocity field as an input to a function.