How to calculate grad Electric Potential?
 

Hi all1

If I want to usr user subroutine to calculate the gradation of electric potential which is a scalar. How can implement it into CFX5.5.1? Thank you!

Miko

Re: How to calculate grad Electric Potential?
 

Hi Miko,

There is no need to implement this yourself. Have a look through the doc on User Fortran and you will see that gradients can be accessed directly within your user subroutine through the USER_GETVAR call.

Regards, Robin

Re: How to calculate grad Electric Potential?
 

Hi Robin,

Thank you! I will read it at once! Thank you!

Miko

Re: How to calculate grad Electric Potential?
 

I just want to know how do you imply electro potential modeling in your simulation, a simple user scalar or more complex model? what is the difference between CFX 5.5.1 and cfx 4.4 in this part.

THx

Re: How to calculate grad Electric Potential?
 

Electric potential is simply a laplace equation (i.e. diffusion only). All you need to do is solve a user scalar for potential. You can then apply constant voltages (phi = Const) on your electrode walls, or a zero flux condition for insulators (this is the default for walls). There are however, two things that are required:

1) You must turn off convection for the potential field (i.e. current is NOT washed downstream with the fluid). I think Robin specified a means of doing this in CCL some time back.

2) It is handy to set a zero flux condition on inlets and outlets as well. Outlets and openings are no problem, this will happen automatically as long as the flow is "out" and not in. Inlets are another issue. In CFX-4 I used to set the INLET boundary value based on the value obtained "just inside" the domain on the first adjacent node. This, in effect, gave a zero flux condition which worked quite well. I am not sure how to do this in CFX-5.

Re: How to calculate grad Electric Potential?
 

...specify your scalar to be solved as a transport equation. Then, manually edit your CCL and change:

Option = Transport Equation

to

Option = Diffusive Transport Equation

Regards, Robin