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

Modelling unsteady 2D aerofoil drag

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

Reply
 
LinkBack Thread Tools Display Modes
Old   June 24, 2011, 04:42
Default Modelling unsteady 2D aerofoil drag
  #1
New Member
 
Pete Greaves
Join Date: Jan 2011
Posts: 6
Rep Power: 6
xlxc34 is on a distinguished road
Hi, I've posted about this before but only on specific modelling techniques...

I'm working on modelling fatigue testing of wind turbine blades. This video (of my finite element model so far) shows how it's done better than I can explain!



The blade is being excited at it's flapwise, or out of plane, natural frequency and it's edgewise (in plane) natural frequency at the same time. The blue and green arrows are the flapwise and edgewise excitation forces respectively, and the red arrows are the aerodynamic drag force (they are scaled up 10 times compared to the excitation forces so they are easier to see).

At the moment those forces are calculated by resolving the velocity of each node (the blade model uses beam elements, the ends of which are shown by the black lines on the blade in the video) into a flapwise and edgewise component, and then applying a force as below to the node.

F=-1/2*rho*Area around node*node velocity*abs(node velocity)*Cd.

We've done some 2D CFD with a moving mesh which shows that because of a leading edge vortex and the fact that the blade encounters it's own wake the value of Cd can be up to 5.

The way in which I'm modelling drag is not very satisfactory to me at all, so I've been looking into other ways of modelling it to get a proper fluid structure interaction. Those that I've looked at so far include:

-Smoothed particle hydrodynamics (tried to implement this in matlab and failed miserably, and I can't spend too long on the aerodynamics as I need to focus on the structural side of things... also didn't run anywhere near as quickly as it needs to).
-Vortex methods https://dspace.lib.cranfield.ac.uk/b...1/fulltext.pdf . This looked promising, but as I need to run long simulations I can't keep track of all the vortices.
- Morrisions equation - this helps slightly but doesn't do enough to get the 'drag coefficient' as high as it is in CFD.

So instead of asking for help on any of these sub categories, I just want to throw the problem out there and ask if anyone has any ideas for how I could model the drag better? They can be quick and dirty, so long as they are better than what I'm doing at the moment. Any ideas are welcome!
xlxc34 is offline   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
Ideas for modelling effect of roughness on drag? andy2O CFX 13 January 18, 2009 19:30
Unsteady modelling technique? Carlos FLUENT 0 September 26, 2008 11:37
About unsteady flow modelling Cagdas FLUENT 0 July 7, 2007 10:15
Modelling Unsteady Compressible Flow Vince Main CFD Forum 0 March 10, 2004 12:01
Unsteady state modelling Mehul Kinariwala FLUENT 3 September 1, 2000 09:58


All times are GMT -4. The time now is 13:54.