[sarrazs]

Hi!
I'm simulating a bubbly flow using cfx. I want to use a user drag coefficient for that I'm trying to use the pt_drag_factor.F file in the cfx expemles directory.
The input argument are the reynold number and the volume fraction.
I created the expressions in the cfx_pre to calculate Re and the air velocity :
Rep = air.density*airvelocity*air.mean particle diameter/air.viscosity
airvelocity = sqrt(air.u^2+air.v^2+air.w^2)
then in the drag coefficient box I call the function : UserDrag(Rep,air.vf)
UserDrag is the name of the subroutine.
I always have this error, I can't figure out how to fixe it :


Fatal bounds error detected
---------------------------
Variable: air | water.Drag Coefficient
Locale : Default Domain

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine ENFORCE_BOUNDS |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| An error has occurred in cfx5solve: |
| |
| The ANSYS CFX solver exited with return code 1. No results file |
| has been created. |
+--------------------------------------------------------------------+

[Opaque]

Perhaps your drag coefficient is negative. Adding a write statement to your function to check it is computing a valid value ?

[sarrazs]

Originally Posted by Opaque

Perhaps your drag coefficient is negative. Adding a write statement to your function to check it is computing a valid value ?

Thank you for your reply Opaque. All the parameter on the CD expression are positive.
My questions are?
is this the right way to calculate the reynold number Rep = air.density*airvelocity*air.mean particle diameter/air.viscosity
airvelocity = sqrt(air.u^2+air.v^2+air.w^2)?
and when I call the function UserDrag(Rep,air.vf) should I put only two input arguments?
I'm using the pt_drag_factor.F without doing any modification.

[sarrazs]

I found out where the error is. The pt_drag_factor.F can be used for the particle transport fluid model(Euler-Lagrange). And in my simulation, I was using the MUSIG model (Polydispersed model).
My question now is can I use a User drag coefficient for polydispersed and dispersed fluid (Euler-Euler)

[ghorrocks]

The user fortran evaluates a CEL variable and you use that variable as the drag coefficient.

[sarrazs]

it works with the particle transport model but not with dispersed and polydispersed models.


Fatal bounds error detected
---------------------------
Variable: air | water.Drag Coefficient
Locale : Default Domain

+--------------------------------------------------------------------+
| Writing crash recovery file |
+--------------------------------------------------------------------+

+--------------------------------------------------------------------+
| ERROR #001100279 has occurred in subroutine ErrAction. |
| Message: |
| Stopped in routine ENFORCE_BOUNDS |
| |
| |
| |
| |
| |
+--------------------------------------------------------------------+

[ghorrocks]

That error message suggests your drag coefficient has a bounds error, which means that is a value which is not allowed. That could be a negative number, maybe zero or maybe larger than some upper bound.