update initial conditions every 10 iterations

lindner · November 28, 2011, 07:45

Hi all,
I'm testing the whole operation curve of a hydraulic turbine, but the net head is highly dependent of the mass flow.
I want to update the Total Pressure inlet condition every 10 timesteps, to match the new losses.
The inlet condition would be something like this:
Ptotal,in = 115000[Pa] - k*Q^2
where k is a constant for losses and Q the massflow.

is it possible to do with cel expressions to update the boundary every 10 or more iterations?

Thank you in advance,
lindner

Cluain · November 28, 2011, 10:06

Yes, you can. However, you will have to do an expression for the current P rather than the total.
Just set the input to an expression and define the expression for current pressure.
CEL is quite easy to learn and there are quite a few specific examples in the tutorials provided with CFX, just watch the units.
Hope this helps.

lindner · November 28, 2011, 11:41

Hi Martin,
Thanks for the quick answer! The cel expression is ok now, the only problem is to force the cfx to execute this expression every x timesteps (without fortran).
Im reading about user functions and user subroutine to find something about it.

Cluain · November 28, 2011, 12:25

Great, a simple iterative function should sort that. A bit of imagination and you will have it.

November 28, 2011, 07:45	update initial conditions every 10 iterations	#1
lindner Member Join Date: Mar 2010 Posts: 42 Rep Power: 16	Hi all, I'm testing the whole operation curve of a hydraulic turbine, but the net head is highly dependent of the mass flow. I want to update the Total Pressure inlet condition every 10 timesteps, to match the new losses. The inlet condition would be something like this: Ptotal,in = 115000[Pa] - k*Q^2 where k is a constant for losses and Q the massflow. is it possible to do with cel expressions to update the boundary every 10 or more iterations? Thank you in advance, lindner

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November 28, 2011, 10:06		#2
Cluain Member Join Date: Oct 2011 Posts: 32 Rep Power: 15	Yes, you can. However, you will have to do an expression for the current P rather than the total. Just set the input to an expression and define the expression for current pressure. CEL is quite easy to learn and there are quite a few specific examples in the tutorials provided with CFX, just watch the units. Hope this helps.

November 28, 2011, 11:41		#3
lindner Member Join Date: Mar 2010 Posts: 42 Rep Power: 16	Hi Martin, Thanks for the quick answer! The cel expression is ok now, the only problem is to force the cfx to execute this expression every x timesteps (without fortran). Im reading about user functions and user subroutine to find something about it.

November 28, 2011, 12:25		#4
Cluain Member Join Date: Oct 2011 Posts: 32 Rep Power: 15	Great, a simple iterative function should sort that. A bit of imagination and you will have it.