Learning Forum

[f.lindner]

I'm having trouble calculating swirl number in a 2D axisymmetrical swirl case. I need to access the swirl component of the velocity, which is not possible in the named expressions window. The velocity.z component (in my case corresponding to the circumferential component) is zero at every point in the domain. The Fluent User Guid (5.5 Appendix: Supported Field Variables) says 'TangentialVelocity' should be accessible. This is not the case for me.

On the other hand, 'Swirl Velocity' is accessible for a contour plot. So it is actually calculated by the solver. Do I need to transfer or save the results to be able to use them in an expression?

If this is not possible, what are my alternatives?

[Rob]

It's possible the Expression function doesn't see the tangential component in the same was as post processing does.  What do you need the expression for? 

[f.lindner]

I want to calculate the swirl number:

(9–15)

(from User Guide 9.3.2)

[Rob]

Have a look at Custom Field Functions (under User Defined), the interface is a little more clunky and all units are SI. 

[f.lindner]

I don't see how a custom field could help me here. I still have to calculate two integrals separately. Also, I dont want to calculate the values in my whole domain but just at a defined location (a line in my 2d case). It seems a bit over the top to me.

If this is not possible directly in Fluent without a lot of effort, I do the post-processing in CFD-Post. Not my favourite option, but at least it does the job somehow.

[Rob]

Having checked it's not available at present. So, I'd use a CFF and then report on the line. 

[f.lindner]

Note to other users facing similar problems: Using Fluent in 3D mode with a periodic 3D mesh (1 cell thickness) gives you full control over all variables in the expression calculator.