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

Darreius problems

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

Reply
 
LinkBack Thread Tools Display Modes
Old   March 1, 2007, 15:35
Default Darreius problems
  #1
DGaden
Guest
 
Posts: n/a
Hey folks,

I'm having a bugger of a time with a 2D darreius turbine simulation. The solution looks intuitively "okay", except the torque is backwards, predicting power loss instead of power production. Worse yet, I have real experimental data to compare against, and it's almost exactly opposite torque. I've been banging my head on the wall, and triple checked all my calculations. The forces all add up to a backwards torque! There must be a flipped sign in there somewhere, but I can't find it.

Perhaps I don't understand rotating reference frames. How would you do a 2D darrieus turbine? -I created a circular mesh region around the blades and hub -Set it as a rotating domain in the direction the blades should rotate. (When I move timestep forward in post, the mesh moves the way the blades should.) -Set the interface as "Transient rotor / stator"

Am I doing something wrong? Should I do something with a rotating mesh, but not using a "Rotating Reference Frame"? Or is the CFD just that wrong?

-Dave Gaden
  Reply With Quote

Old   March 1, 2007, 16:19
Default Re: Darreius problems
  #2
opaque
Guest
 
Posts: n/a
Dear DGaden,

The sign of the force on fluid is opposite to the sign of the force on the wall. From which side are you interpreting the results?

Opaque

  Reply With Quote

Old   March 1, 2007, 16:55
Default Re: Darreius problems
  #3
DGaden
Guest
 
Posts: n/a
Thanks for the suggestion, but it's not that. I'm calculating the forces from the wall:

! $Fx=force("BLADE","X")

The forces I get make sense: the upwind blade experiences a large downstream force; cross-stream forces correspond nicely when the blade is tilted 45 degrees, like a kite.

I think the problem is either: -Something with the rotating reference frame... like "it should be a rotating wall instead of a rotating domain", or -CFD is not good at calculating drag / lift forces.
  Reply With Quote

Old   March 2, 2007, 02:27
Default Re: Darreius problems
  #4
Johnny
Guest
 
Posts: n/a
Make sure you have angular velocity signed correctly - CFX uses the right hand rule - thumb in the positive axis of rotation direction, fingers curl in the positive direction.

Sign on your angular velocity will then refer to the direction in which the blades move.
  Reply With Quote

Old   March 2, 2007, 13:59
Default Re: Darreius problems
  #5
DGaden
Guest
 
Posts: n/a
Thanks for the suggestion, Johnny. I have used the RHR, and double checked it with manual calculations of x,y forces and their component distances. Everything adds up right... except it's backwards... darnit.
  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
[ICEM] Problems with coedge curves and surfaces tommymoose ANSYS Meshing & Geometry 0 August 5, 2011 16:02
Needed Benchmark Problems for FSI Mechstud Main CFD Forum 4 July 26, 2011 12:13
Some problems with Star CD Micha CD-adapco 0 August 6, 2003 13:55
Airpak: Problems with heat flow contour conditions Ivan de Miguel Urain FLUENT 1 November 16, 2001 10:36
Using Fluent for Geophysical Problems Hassid Samuel FLUENT 0 February 23, 2001 07:04


All times are GMT -4. The time now is 19:20.