CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Changing differential equation in CFX

Register Blogs Community New Posts Updated Threads Search

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   September 10, 2019, 18:11
Question Changing differential equation in CFX
  #1
New Member
 
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 7
Absid is on a distinguished road
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
Absid is offline   Reply With Quote

Old   September 10, 2019, 19:17
Default
  #2
Senior Member
 
Join Date: Jun 2009
Posts: 1,873
Rep Power: 33
Opaque will become famous soon enough
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
Opaque is offline   Reply With Quote

Old   September 11, 2019, 02:18
Default
  #3
New Member
 
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 7
Absid is on a distinguished road
Quote:
Originally Posted by Opaque View Post
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
I wanted to examine the effects of coriolis force and centrifugal force on my working fluid. More specifically I wanted to see what effect coriolis force and centrifugal force have independently on the working fluid. Like, how the gas behaves if there is only coriolis force/centrifugal force. So changing/removing the terms in the DE can help me achieve that. Is there a way that we can change DE terms in CFX?

Thanks!
Absid is offline   Reply With Quote

Old   September 11, 2019, 07:06
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
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.
ghorrocks is offline   Reply With Quote

Old   September 12, 2019, 09:37
Default
  #5
New Member
 
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 7
Absid is on a distinguished road
Quote:
Originally Posted by ghorrocks View Post
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.
Thanks for your reply!

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!
Absid is offline   Reply With Quote

Old   September 12, 2019, 19:46
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
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.
ghorrocks is offline   Reply With Quote

Old   September 15, 2019, 07:26
Default
  #7
New Member
 
Sai Abhishek Siddhartha
Join Date: Sep 2019
Posts: 5
Rep Power: 7
Absid is on a distinguished road
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!
Absid is offline   Reply With Quote

Old   September 15, 2019, 19:59
Default
  #8
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,854
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
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.
ghorrocks is offline   Reply With Quote

Reply

Tags
centrifugal force, cfx solver control, coriolis force, differential equations


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
CFX Electric Potential Equation Residual Problem hsezsz CFX 2 October 7, 2016 04:35
Explicit Runge-Kutta 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


All times are GMT -4. The time now is 21:14.