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

Don't know where energy lost from my domain

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 27, 2005, 12:11
Default Don't know where energy lost from my domain
  #1
Atit Koonsrisuk
Guest
 
Posts: n/a
I model the flow in solar chimney. The flow gains thermal energy from energy source, afterward the energy is extracted by the model of turbine. I use the actuator disc as the turbine approximation. The actuator disc is very thin such that flow field properties change discontinuously across it. I create the fluid sub-domain, this sub-domain is the actuator disc representation. The ratio of thinkness to diameter of sub-domain is 0.0125, and I use mesh control with 1.2 expansion factor to make the finer grid in sub-domain. I set this sub-domain as the energy source and momentum source simultaneously.

The energy source is (-dW/volume)

and the momentum source is (-dW/(volume x velocity)),

where dW is the power that I want the actuator disc to extract from the flow, and 'volume' is the volume of sub-domain which I input as the number. So only 'velocity that I input as 'v' variable. After CFX converge, I found that the difference of total enthalpy before and after actuator disc doesn't equal 'dW'. For example,

- dW=165; mdot x ( static enthalpy + 0.5x velocity^2)=158

- dW=320; mdot x ( static enthalpy + 0.5x velocity^2)=304

- dW=590; mdot x ( static enthalpy + 0.5x velocity^2)=560 where I get 'mdot x static enthalpy' from the integration of CFX.

I do not understand why they don't equal. I set the wall as the adiabatic free-slip wall. So no other way for energy to be lost, isn't it? Then I specify that when the flow past this sub-domain, the power must be extracted 'dW', the total enthalpy must be lost 'dW'. Do anyone have idea why it doesn't? Thank you very much for your kind consideration.
  Reply With Quote

Old   March 28, 2005, 17:35
Default Re: Don't know where energy lost from my domain
  #2
Glenn Horrocks
Guest
 
Posts: n/a
Hi,

Have you checked the imbalances? Your simulation might not have converged. Converging on imbalances and residuals is often a more reliable convergence measure than residuals alone when you have user sources.

Glenn
  Reply With Quote

Old   March 29, 2005, 05:30
Default Re: Don't know where energy lost from my domain
  #3
Atit Koonsrisuk
Guest
 
Posts: n/a
Dear Glenn, Actually I never check the imbalance, thank you that you introduce me to know about 'imbalance'. After reading your suggestion, I found that the maximum global imbalance occur for H-Energy. It is 0.0036%. So we can be sure that it already converged. What do you think?

Atit
  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
Domain Imbalance HMR CFX 3 March 6, 2011 20:10
Energy Domain Imbalances for Multiphase flow KMJ CFX 4 September 10, 2010 08:06
Material identification between a flow domain and a porous domain Ervideiro CFX 1 June 1, 2010 09:50
Incompressible flow: mechanical energy terms Pinaki Bhattacharya FLUENT 0 January 29, 2009 12:33
turbulent energy spectrum cfd.newbie CD-adapco 1 June 19, 2008 23:48


All times are GMT -4. The time now is 23:53.