are you trying to animate the flow front?
why not just plot 20ppm isoline and then do a transient animation of that plot? that should show 20ppm moving forward.
i'm actually not sure what you're trying to show in your attachment and if above isn't what you're looking for i'm a bit lost.
i doubt there are any 3rd party software to read the mesh. the best you'd get is creating all the screenshots for what you want and then build the animation in a program.
Thanks for the reply. I just tried this, and I think I can make it work. I didn't try it before because unlike isosurfaces, there is no way to define a single isoline in a cut plot. However, after thinking more about it, I tried to do it with two isolines, with the maximum value set much higher than what is in the simulation (1,000 ppm), and the minimum set at the desired value (20 ppm). I need to mess with this some more, but it looks like it might show what I need. Putting the lines on the same plot as requested would require being able to save the isolines as polylines, which I don't think Flow Simulation can do at the present.
I have been able to export the mesh to ASCII, and can combine everything into one file (Excel for the moment), so I may be able to do some visualization using Matlab or some other graphing tool - I'll post an update after I get that part figured out.