# Questions about the energy equation

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

 April 2, 2014, 23:00 Questions about the energy equation #1 Member   Peter Aestas Join Date: Dec 2013 Posts: 64 Rep Power: 5 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

 April 4, 2014, 15:52 #2 Senior Member   François Grégoire Join Date: Jan 2010 Location: Laval University, Canada Posts: 389 Rep Power: 10 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.

April 5, 2014, 05:24
#3
Member

Peter Aestas
Join Date: Dec 2013
Posts: 64
Rep Power: 5
Quote:
 Originally Posted by macfly 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?

 April 5, 2014, 10:17 #4 Senior Member   François Grégoire Join Date: Jan 2010 Location: Laval University, Canada Posts: 389 Rep Power: 10 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.

April 5, 2014, 21:05
#5
Member

Peter Aestas
Join Date: Dec 2013
Posts: 64
Rep Power: 5
Quote:
 Originally Posted by macfly 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

 April 6, 2014, 11:28 #6 Senior Member   François Grégoire Join Date: Jan 2010 Location: Laval University, Canada Posts: 389 Rep Power: 10 Sorry, I know next to nothing in electrons/ions transport, I can't help. Good luck.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post dohnie OpenFOAM 21 June 13, 2014 00:44 m5m5kh OpenFOAM Running, Solving & CFD 1 September 4, 2013 10:46 nakul OpenFOAM 0 October 10, 2010 15:07 Asghari FLUENT 0 October 12, 2006 08:09 Asghari FLUENT 0 October 12, 2006 08:06

All times are GMT -4. The time now is 10:24.