CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Main CFD Forum

energy eqn + constant fluid properties

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 6, 2013, 06:01
Default energy eqn + constant fluid properties
  #1
New Member
 
Bob
Join Date: Mar 2013
Posts: 1
Rep Power: 0
cfx_user is on a distinguished road
Hello to all,
I'm bit confused about the impact of energy equation on the obtained results, namely: I have launched 2 analyses, one with total energy equation and second one without energy equation.
In both cases I'm simulating the flow of incompressible fluid (water) with constant fluid properties (viscosity/conductivity, density).
Finally i'm obtaining two different pressure drops.
My question is why? Since the fluid properties in both cases are the same (are not temperature depended) I would expect the same results...
Or it does impact on the turbulence ?
Thanks in advance for your suggestions.
Cheers, bob
cfx_user is offline   Reply With Quote

Old   March 6, 2013, 08:13
Default
  #2
Senior Member
 
andy
Join Date: May 2009
Posts: 129
Rep Power: 8
andy_ is on a distinguished road
Quote:
Originally Posted by cfx_user View Post
Hello to all,
I'm bit confused about the impact of energy equation on the obtained results, namely: I have launched 2 analyses, one with total energy equation and second one without energy equation.
In both cases I'm simulating the flow of incompressible fluid (water) with constant fluid properties (viscosity/conductivity, density).
Finally i'm obtaining two different pressure drops.
My question is why? Since the fluid properties in both cases are the same (are not temperature depended) I would expect the same results...
Or it does impact on the turbulence ?
Thanks in advance for your suggestions.
Cheers, bob
Discounting the trivial case, if you solve an energy related equation then the density would normally change. For example, incompressible combustion problems will have a strongly varying density.

If the code lets you hold the density constant then the "thermodynamic pressure" would have to change but I am not sure the physical meaning would be sensible. An incompressible flow usually has a constant "thermodynamic pressure" throughout the solution region and then the "pressure" variations simply follow the mechanical acceleration/deceleration of the fluid. This knocks out sound waves which is usually the main objective. The constant background thermodynamic pressure may change through time (e.g. a piston chamber) but remains constant in space. Varying this background thermodynamic component while hold density constant seems odd but there may be some physical cases where the assumption is reasonable. Anyone?
andy_ is offline   Reply With Quote

Reply

Tags
constant fluid properties, energy equation

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
Chemical properties that are used in Fluent kimej FLUENT 4 August 19, 2011 11:29
Constant flow rate through a small area inside the fluid domain. robingilbert OpenFOAM 7 October 4, 2010 16:19
My Revised "Time Vs Energy" Article For Review Abhi Main CFD Forum 2 July 9, 2002 09:08
Terrible Mistake In Fluid Dynamics History Abhi Main CFD Forum 12 July 8, 2002 09:11
Why FVM for high-Re flows? Zhong Lei Main CFD Forum 23 May 14, 1999 13:22


All times are GMT -4. The time now is 21:32.