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

Determination of the induced Drag for a rectangular wing

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   April 9, 2015, 14:11
Default Determination of the induced Drag for a rectangular wing
  #1
New Member
 
Join Date: Dec 2014
Posts: 9
Rep Power: 11
matmax-168 is on a distinguished road
Hello,
I am currently working at an Optimization for Wingtip Fences for a rectangular wing in subsonic (incompressible) flows. For my seminar paper one task is to determine the separate drag forces.

To determine the induced drag I watch the losses of momentum in the control volume.

Di = \int\int[(Pressure@IN)-(Pressure@OUT)] dy dz = 0.5*(Density)*\int\int(v^2+w^2) dy dz

Expression in Post: "0.5*Density*areaInt((Velocity v)^2+(Velocity w)^2)@OUT"

where v and w are the induced velocities in a yz-Plane (Trefftz), very far behind the wing.

I have observed, that the viscosity of the used gas (air at 25°C) has no large influence at the so calculated drag. Additional to that, I determined the zeroliftdrag (nearly the parasitic drag) and subtracted it from the general wingdrag to become a guess for the induced drag.

My question: Why are the results for the induced drag so different for the different ways of calculation?

Thank you very much!
matmax-168 is offline   Reply With Quote

Old   April 9, 2015, 18:29
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
This approach appears to be very sensitive to the global imbalances. Try converging to tighter imbalances and see if that improves things.
ghorrocks is online now   Reply With Quote

Old   April 10, 2015, 06:01
Default
  #3
New Member
 
Join Date: Dec 2014
Posts: 9
Rep Power: 11
matmax-168 is on a distinguished road
Hi ghorrocks,
thx for your fast answer! I'm an absolute newcomer in cfd-practice. What do you mean with "converging to tighter imbalances". I have choosen a huge control volume sourrounding the wing (wingdept x 100 x100 x 800) and for first evaluations a rough unstructured grid. For better results I will refine the Mesh with Prism Layers around the wing.

Is the formulation of my expression:

"0.5*Density*areaInt((Velocity v)^2+(Velocity w)^2)@OUT"

equal to the above shown formula?
KV.jpg

Wing.jpg
matmax-168 is offline   Reply With Quote

Old   April 12, 2015, 08:46
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,655
Rep Power: 143
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Quote:
For better results I will refine the Mesh with Prism Layers around the wing.
Your results are going to be very inaccurate without this.

And while you are at it, you transition very quickly from fine mesh on the wing to coarse mesh further away. This will also be a problem, especially if you are trying to pick up small differences in the momentum field. Have a look in the literature at the sort of meshed they use - you will find the transition is much gentler, and they usually have a tail of fine mesh in the wake region (which is where your momentum deficit will exist).
ghorrocks is online now   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
Rectangular wing Induced drag milind543 SU2 Shape Design 2 August 19, 2013 14:18
Calculating Induced drag of a wing from Trefftz plane analysis in FLUENT pratikkr FLUENT 0 May 16, 2013 15:14
Negative Fuselage Drag on a Tandem Wing? mmn1239 STAR-CCM+ 3 April 28, 2012 09:20
Negative Fuselage Drag on a Tandem Wing? mmn1239 Main CFD Forum 1 April 7, 2012 05:52
Isolating wing induced drag component siw CFX 2 June 22, 2010 11:21


All times are GMT -4. The time now is 04:52.