CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Fluent UDF and Scheme Programming

Questions about the energy equation

Register Blogs Members List Search Today's Posts Mark Forums Read

Reply
 
LinkBack Thread Tools Display Modes
Old   April 2, 2014, 23:00
Default Questions about the energy equation
  #1
Member
 
Peter Aestas
Join Date: Dec 2013
Posts: 64
Rep Power: 5
aestas is on a distinguished road
Dear all, i got two problems
1.in fluent6.3 help manual, i saw the energy equation form like this in the picture,so my question is, does that means i should make the energy equation(take temperature as an argument) into this form(take E as an argument) ,then use UDF to define the source and diffusivity term?
2.A friend of me said, if the energy equation is used in fluent, fluent will take pressure and kinetic energy effect term into consideration automatically,so i don't need to write the pressure and kinetic energy effect term of momentum equation into my udf.Does that true?Where can i find the proof?

Thank you so much~
111.jpg
aestas is offline   Reply With Quote

Old   April 4, 2014, 15:52
Default
  #2
Senior Member
 
François Grégoire
Join Date: Jan 2010
Location: Laval University, Canada
Posts: 389
Rep Power: 10
macfly is on a distinguished road
From Fluent Theory Guide 15.0:


5.2.1.4. Inclusion of Pressure Work and Kinetic Energy Terms

Equation 5.1 (p. 134) includes pressure work and kinetic energy terms, which are often negligible in incompressible flows. For this reason, the pressure-based solver by default does not include the pressure work or kinetic energy when you are solving incompressible flow. If you want to include these terms, use the define/models/energy? text command. When asked to include pressure work in energy equation? and include kinetic energy in energy equation?, respond by entering yes in the console window.

Pressure work and kinetic energy are always accounted for when you are modeling compressible flow or using the density-based solver.
macfly is offline   Reply With Quote

Old   April 5, 2014, 05:24
Default
  #3
Member
 
Peter Aestas
Join Date: Dec 2013
Posts: 64
Rep Power: 5
aestas is on a distinguished road
Quote:
Originally Posted by macfly View Post
From Fluent Theory Guide 15.0:


5.2.1.4. Inclusion of Pressure Work and Kinetic Energy Terms

Equation 5.1 (p. 134) includes pressure work and kinetic energy terms, which are often negligible in incompressible flows. For this reason, the pressure-based solver by default does not include the pressure work or kinetic energy when you are solving incompressible flow. If you want to include these terms, use the define/models/energy? text command. When asked to include pressure work in energy equation? and include kinetic energy in energy equation?, respond by entering yes in the console window.

Pressure work and kinetic energy are always accounted for when you are modeling compressible flow or using the density-based solver.
Thx for your reply.I have read this part in the fluent manual.what i want to know is, when the energy equation is being used, how should we handle the pressure terms in momentum equation(the gradient P term)? should it be programmed in my udf source term?
aestas is offline   Reply With Quote

Old   April 5, 2014, 10:17
Default
  #4
Senior Member
 
François Grégoire
Join Date: Jan 2010
Location: Laval University, Canada
Posts: 389
Rep Power: 10
macfly is on a distinguished road
I'm not sure to understand what you want to do, add a source term to the momentum equation? Then you write whatever source term you want to add to the momentum eqn, you don't have to 'handle' anything. The pressure term in the momentum is there and, in my limited experience in fluid mechanics, I've never heard of a case where this term is not included, it sounds unphysical to me, there has to be a pressure gradient so that the fluid moves.
macfly is offline   Reply With Quote

Old   April 5, 2014, 21:05
Default
  #5
Member
 
Peter Aestas
Join Date: Dec 2013
Posts: 64
Rep Power: 5
aestas is on a distinguished road
Quote:
Originally Posted by macfly View Post
I'm not sure to understand what you want to do, add a source term to the momentum equation? Then you write whatever source term you want to add to the momentum eqn, you don't have to 'handle' anything. The pressure term in the momentum is there and, in my limited experience in fluid mechanics, I've never heard of a case where this term is not included, it sounds unphysical to me, there has to be a pressure gradient so that the fluid moves.
Thx so much for your patience, my dear friend.And i'm so sorry to put two questions in one thread making you confused.
My momentum equation is like this below,the argument u and Ti are velocity and temperature for ions, and Te are temperature for electrons(i defined plasma as single fluid of ions.So Te is defined as UDS).
the right side of this equation is the source term of momentum, and according to P=nkT,the first -▽(nikTi) is the -grad P.
Someone told me, if the energy equation is used in fluent. Fluent will take -grad P term of momentum equation into consideration, so i only need to put the last two terms -▽(nekTe)+jx(Bself+Bad) into DEFINE_SOURCE marco.
I don't know whether this is ture or not.
2222.jpg
aestas is offline   Reply With Quote

Old   April 6, 2014, 11:28
Default
  #6
Senior Member
 
François Grégoire
Join Date: Jan 2010
Location: Laval University, Canada
Posts: 389
Rep Power: 10
macfly is on a distinguished road
Sorry, I know next to nothing in electrons/ions transport, I can't help. Good luck.
macfly is offline   Reply With Quote

Reply

Thread Tools
Display Modes

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 On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Solving the total energy equation dohnie OpenFOAM 21 June 13, 2014 00:44
energy equation for porousSimpleFoam m5m5kh OpenFOAM Running, Solving & CFD 1 September 4, 2013 10:46
energy equation in rhoCentralFoam nakul OpenFOAM 0 October 10, 2010 15:07
How to discretize of energy equation ?? Asghari FLUENT 0 October 12, 2006 08:09
How to discretize of energy equation ?? Asghari FLUENT 0 October 12, 2006 08:06


All times are GMT -4. The time now is 22:35.