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

flow in pipe with momentum and energy source

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   March 27, 2005, 13:43
Default flow in pipe with momentum and energy source
  #1
Atit Koonsrisuk
Guest
 
Posts: n/a
I try to model the thing so-called actuator disc. It is the approximation of turbine. The actuator disc is very thin such that flow field properties change discontinuously across it. Then I test the concept by model the flow of water in circular pipe. I set the boundary condition at pipe inlet as 'inlet' with velocity specified, and at pipe exit as 'outlet' with zero relative static pressure. In addition, I create the fluid sub-domain within the pipe, this sub-domain is the actuator disc. 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 energy 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. The result seems reasonable. The difference between velocity before actuator disc and velocity after actuator disc is only 0.04%. In addition, the difference of total enthalpy before and after actuator disc is about 'dW'. So I'm pretty sure that I understand how to model actuator disc in CFX. However one thing that I do not understand from the result is that the change of velocity inside the sub-domain. The velocity inside the actuator disc is fluctuated, and the maximum value is 163% of the velocity before actuator disc, whereas the pressure is not fluctuated. Do anyone have idea why the velocity inside sub-domain is fluctuated with a large value? I think it might be about the finer grid, however I do not know how to mitigate this problem. Thank you very much for your kind consideration.
  Reply With Quote

Old   March 28, 2005, 14:06
Default Re: flow in pipe with momentum and energy source
  #2
Phil
Guest
 
Posts: n/a
Try setting the CCL parameter 'Redistribute in Rhie Chow=t' under the GENERAL MOMENTUM SOURCE object. (You'll have to do this by changing the CCL rather; it is not currently in the GUI.) This changes some numerics details of momentum sources and often gives better results when the momentum source balances a pressure rise.
  Reply With Quote

Old   March 29, 2005, 07:16
Default Re: flow in pipe with momentum and energy source
  #3
Atit Koonsrisuk
Guest
 
Posts: n/a
Dear Phil, Thank you very much for your kind suggestion. However I am not familiar with 'CCL', could you please say it in more details?

Atit
  Reply With Quote

Old   March 29, 2005, 17:58
Default Re: flow in pipe with momentum and energy source
  #4
Phil
Guest
 
Posts: n/a
In Pre, right-click on your subdomain option and choose 'Edit in Command Editor'. Then type in the line 'Redistribute in Rhie Chow = t' inside the GENERAL MOMENTUM SOURCE object and hit 'Process'. Pre will give a red error message saying that this is an unrecognized option (because it is an expert option); just ignore the error and run in the solver.
  Reply With Quote

Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
no enthalpy change across the momentum source Atit Koonsrisuk CFX 2 December 19, 2005 03:33
Energy Source Help! Andrew Clark FLUENT 1 October 24, 2005 15:39
UDF Scalar Code: HT 1 Greg Perkins FLUENT 8 October 20, 2000 13:40
UDFs for Scalar Eqn - Fluid/Solid HT Greg Perkins FLUENT 0 October 14, 2000 00:03
UDFs for Scalar Eqn - Fluid/Solid HT Greg Perkins FLUENT 0 October 11, 2000 04:43


All times are GMT -4. The time now is 03:41.