Learning Forum

[abhaymh]

I have the requirement of changing the input velocity based on the EWF thickness which is a result of the simulation, based on an equation. I wanted to know how I could read the value of the film-thickness into the UDF in order to manipulate it.

[Rob]

You may be better off using an expression as that can take the film thickness at a position as a Report. There will be an equivalent UDF macro, so check the manual. Expressions are a newer feature in Fluent (based on CFX technology) as a means to avoid needing UDFs for "simple" stuff.

[abhaymh]

I can use the expression, yes, but here's what I have to do: Use film thickness to calculate a value, then use that value to calculate the flow rate and subsequently the velocity at the flow inlet. For this, I think I will have to use a UDF since the value changes at every iteration. Is it possible to accomplish this using just expressions?

[Rob]

You can do that with expressions, that's one of the functions they're designed for. Just make sure the expression makes sense for a zero thickness film.

[abhaymh]

Thank you. While that works to define it, it says invalid expression. As you can see from the image, the expression does give a value in the plot. I'm not sure if I've made a mistake or something.
EDIT: I've also attached a plot for changing values of film thickness (it makes sense, realistically speaking)

[Rob]

What is evap_area?