# understanding the term: fvm::Sp(fvc::div(phi), h)

 User Name Remember Me Password
 Register Blogs Members List Search Today's Posts Mark Forums Read

 LinkBack Thread Tools Display Modes
 October 6, 2009, 11:34 understanding the term: fvm::Sp(fvc::div(phi), h) #1 New Member   Dominik Christ Join Date: Mar 2009 Posts: 28 Rep Power: 10 Hello everyone, when having a closer look at the energy equation as it is used by solvers for reacting cases, I cannot figure out where the term - fvm::Sp(fvc::div(phi), h) comes from. All I could find out is that it is a source term of some kind but when I try to derive an energy equation for enthalpy I do not get such a source term. Could anybody please enlighten me? :-) Thanks in advance! Regards Dominik

April 28, 2011, 11:37
#2
Senior Member

Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 612
Rep Power: 22
Quote:
 Originally Posted by dominik_christ Hello everyone, when having a closer look at the energy equation as it is used by solvers for reacting cases, I cannot figure out where the term - fvm::Sp(fvc::div(phi), h) comes from. All I could find out is that it is a source term of some kind but when I try to derive an energy equation for enthalpy I do not get such a source term. Could anybody please enlighten me? :-) Thanks in advance! Regards Dominik

Dominik,

I know this is an old thread, but I'm sure others run into it and have the same question. The origin of this term Sp(div(phi),h) comes from the expansion of the div(U,h) term in the transport equation.

div(U,h) = h*div(U) + U&grad(h).

In a completely converged domain the div(U) -> 0.

However, sometimes there is incomplete convergence and there is some generation (or consumption) that will throw off the energy balance. Have a look at

http://www.cfd-online.com/Forums/ope...silon-eqn.html

and

http://www.cfd-online.com/Forums/ope...culations.html

for maybe a little explanation.

Dan

May 7, 2011, 05:53
#3
Member

Kai
Join Date: May 2010
Location: Stockholm
Posts: 45
Blog Entries: 1
Rep Power: 9
Hi Dan, you mentioned that

Quote:
 Originally Posted by chegdan In a completely converged domain the div(U) -> 0.
which I cannot understand. For example, in an incompressible flow we may have div(U) = 0 everywhere. But how could you apply it to all the other cases? And what is the definition of U in you opinion? For example in two phase flow, will it be the velocity of each component or a mixed velocity? Or maybe there's no physics principle for div(U) = 0 at all? Is it a kind of restriction from mathematics? If possible, can you give me some references? Thx

// Kai

 May 7, 2011, 08:14 #4 Member   Kai Join Date: May 2010 Location: Stockholm Posts: 45 Blog Entries: 1 Rep Power: 9 Hi Foamers again... about the div U =0... 'cause it's obviously correct in the simple single-phase incompressible flow. However if it comes to two phase flow, where there is a phase change term on RHS of eq. for instance in alphaEqn.H, it looks like Code: ``` ddt(alpha) + div(phi, alpha) == Gamma/rhoa``` It is a kind of 1st order differential equations. alpha is bounded only if we have div(phi)=0, as the equation required. It seems that we cannot find any proof of div(phi)=0 directly from physics. All we can find come from the mathematical requirement. Any comments? //Kai

 Tags energy equation, source term

 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 zwdi FLUENT 14 June 27, 2017 15:40 SAKTI Siemens 1 August 28, 2008 01:38 Brian FLUENT 1 October 24, 2005 09:15 Atit Koonsrisuk Main CFD Forum 2 January 10, 2002 11:52 Michael Main CFD Forum 1 June 25, 1999 10:20

All times are GMT -4. The time now is 21:52.

 Contact Us - CFD Online - Privacy Statement - Top