
[Sponsors] 
September 10, 2019, 18:11 
Changing differential equation in CFX

#1 
New Member
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 5 
Is there a way to change the terms of Differential equation(Especially momentum equation)?
I was hoping that i could 1) Input the values of Coriolis force and Centrifugal force, so as to examine their effect on my system 2) Turnoff the Coriolis force component, and only have centrifugal force Please help 

September 10, 2019, 19:17 

#2 
Senior Member
Join Date: Jun 2009
Posts: 1,609
Rep Power: 29 
May I ask why would you want to do that? The equations would be incorrect; therefore, any conclusions will be polluted.
Perhaps you want to compare the contributions to the momentum equation, i.e. a force balance. You can compute the sources yourself via expressions, and compare the ratio between them. Say Coriolis force/pressure force, Coriolis force/inertial term or the like In fact, you may want to read about the following dimensionless number associated with rotating physics Rossby/Kibel number Taylor number Ekman number 

September 11, 2019, 02:18 

#3  
New Member
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 5 
Quote:
Thanks! 

September 11, 2019, 07:06 

#4 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,231
Rep Power: 135 
You can add the centripetal and coriolis effects as a momentum source terms. That what you can turn them on and off, or double one and halve the other or whatever you like. Have a look in the documentation on the source terms used for the rotating domain model and write your own source terms for them.
Note that compressible flow has additional changes in rotating frames of reference which might be a little harder to reproduce  again, see the CFX documentation for details.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. 

September 12, 2019, 09:37 

#5  
New Member
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 5 
Quote:
I have searched the documentation thoroughly, where I couldn't explicitly any reference to control Coriolis and centrifugal source terms. Additionally I have to solve the problem/equation in stationary domain. Could you kindly provide some reference in documentation/tutorials where these changes can be done? Thanks a lot! 

September 12, 2019, 19:46 

#6 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,231
Rep Power: 135 
You can't control the Coriolis and Centripetal terms. You can only turn them both on and off by activating the rotating frames of reference model.
My post said if you want to control them individually you need to define a momentum source term using the same equations as used in the rotating frame of reference model. As you define this source term, you can define the inputs any way you like.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. 

September 15, 2019, 07:26 

#7 
New Member
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 5 
Thanks for your reply.
How do I change/deactivate the rotating frames of reference model? Also can you please guide me regarding where can I add momentum source terms in CFX? Is it part of buoyancy acceleration in boundary conditions or should I use some programming language? Thanks a lot! 

September 15, 2019, 19:59 

#8 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,231
Rep Power: 135 
Please do the CFX tutorials and read the documentation. All your questions are very basic questions which are explained well in the documentation. The search function works well and you will find details of the source terms soon enough.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. 

Tags 
centrifugal force, cfx solver control, coriolis force, differential equations 
Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
CFX Electric Potential Equation Residual Problem  hsezsz  CFX  2  October 7, 2016 04:35 
Explicit RungeKutta of a Differential Equation  HakikiCanakkaleli  OpenFOAM Programming & Development  1  September 25, 2014 07:18 
Calculation of the Governing Equations  Mihail  CFX  7  September 7, 2014 07:27 
Basic question about writing a differential equation related to finite element  RbBb  Main CFD Forum  1  April 10, 2014 04:50 
CFX Additional Variable Transport Equation  Scott Nordsen  CFX  3  January 30, 2010 06:36 