Mass Flow from expression problem

Zigec · May 15, 2019, 15:08

Hello,

I have this one problem. A little background: I have an empirical equation from which the mass flow is calculated. In the equation there are only constants, except for one, which is the pressure in a point, which I know how to read it etc. Nothing hard, except when I first wanted to do this with an UDF, but not even the Ansys Support knows why Fluent freezes in the moment you press Initialization.

They told me there is a option to do this over the Named Expressions, which I did. Basically it works fine, except it doesn't. The problem is Fluent reads the pressure in each iteration and calculates a new mass flow each time, which makes it to diverge. I need Fluent to only calculate the new mass flow each time step and not iteration. Any one knows if this is possible and if, how to do it? I just want to do 200-300 iteration in each time step before changing the inlet condition.

Best regards,
Ziga

acalado · May 23, 2019, 15:14

Can you share the expression you have? Are you taking the average pressure over a surface?

May 15, 2019, 15:08	Mass Flow from expression problem	#1
Zigec New Member Ziga Join Date: Feb 2016 Location: Maribor, Slovenia Posts: 27 Rep Power: 10	Hello, I have this one problem. A little background: I have an empirical equation from which the mass flow is calculated. In the equation there are only constants, except for one, which is the pressure in a point, which I know how to read it etc. Nothing hard, except when I first wanted to do this with an UDF, but not even the Ansys Support knows why Fluent freezes in the moment you press Initialization. They told me there is a option to do this over the Named Expressions, which I did. Basically it works fine, except it doesn't. The problem is Fluent reads the pressure in each iteration and calculates a new mass flow each time, which makes it to diverge. I need Fluent to only calculate the new mass flow each time step and not iteration. Any one knows if this is possible and if, how to do it? I just want to do 200-300 iteration in each time step before changing the inlet condition. Best regards, Ziga

May 23, 2019, 15:14		#2
acalado Senior Member André Join Date: Mar 2016 Posts: 133 Rep Power: 10	Can you share the expression you have? Are you taking the average pressure over a surface? __________________ Sapere aude!

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Outlet boundary condition in interFoam	Andrea_85	OpenFOAM Running, Solving & CFD	51	July 20, 2017 14:31
Exit Corrected Mass Flow Rate Mesh Sensitivity Study	s__s__s	CFX	4	July 20, 2016 12:46
total mass loss/gain--simulating taylor couette flow	nwpukaka	OpenFOAM Programming & Development	0	February 12, 2014 19:57
Problem for Mass flow average in Post...	ST	CFX	2	October 27, 2005 14:35
fluid flow fundas	ram	Main CFD Forum	5	June 17, 2000 22:31