Volume fraction time derivative Cel expression
 

Hi

I'm using a CEL expression for to add an expression for the Drag coefficient. The expression is :

Cd1= coef*air.vf.Time Derivative.

coef is a constant factor.
I tried to define my expression as described or with an if condition :

if( Time>Time Step Size, coef*air.vf.Time Derivative, 0)

In both time I get this error :
Error in subroutine GET_VAREL :
Locale BELG3 with entity ICENTRE is illegal for time derivatives
GETVAR originally called by subroutine cal_CAB_MOM

I didn't find documentation on the use of the time derivative so If anyone can help me figure out how can I make it work.

Problem Solved

and the solution was ?

I add an additional variable oldeps term with :
Update Loop = TRANS_LOOP

than the time derivative is (air.vf-oldeps)/time step size


I found the solution in this old post :
https://www.cfd-online.com/Forums/cf...pressions.html

But I still don't know how to use the time derivative function on the CEL expression