[tinhtt]

Hi cfd-online community,
In axisymmetric system (base on cylindrical coordinate), the strain rate magnitude is defined by |S|=sqrt(2S:S), which includes the term (v_r/r)^2.
I wonder how this term in Fluent can be treated in vicinity of z-axis, where v_r is not equal zero, but r is very very small (r is radial direction, z is axial direction).

I intend to impose v_r/r=0 if r<epsilon_value (for example 10e-8) by using Custom Field Function. But there are no place to impose if ... else ...

Or which function of User-Defined Function is useful in this case.

Thank you for any ideas or suggestions.

PS: Attached figure is strain rate tensor for axisymmetric system

[tinhtt]

For more information, I have compared the strain rate magnitude provided by Fluent and by Custom Field Function |S|=sqrt(2S:S)
- For Cartesian coordinate, the strain rate magnitude of both cases are similar.
- For axisymmetric (cylindrical coordinate), the results are totally different. Strain rate magnitude provided by Fluent ~ O(10e5). The one by Custom Field Function ~ O(10e9). It means that Fluent has special treatment for (v_r/r)^2 term at vicinity of z-axis.