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

Error in drag

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 31, 2006, 09:37
Default Error in drag
  #1
Ivanov
Guest
 
Posts: n/a
When I calculate invicid subsonic flow field around airfoil I got 35 counts (Cd=0.035). It result was achieved on different smooth meshes. Node numbers was increased 2X, 4X and result was change to 30 counts (achieved minimum). Who can comment this effect?
  Reply With Quote

Old   January 31, 2006, 13:51
Default Re: Error in drag
  #2
Razvan
Guest
 
Posts: n/a
First, you say that you calculated INVISCID flow around the airfoil. This means that you actually calculated "form" drag, am I right? For the complete "drag" you need to activate viscosity. The interesting phenomena is that although both form and viscous coefficients are sometimes wrong, their sum is quite close to the experimental results! So try, you might obtain surprising results.

Secondly, using a dense mesh around the foil (viscous type mesh) in inviscid flow, is very wrong, because Euler formulation tends to increase numerical error in those regions with mesh clustered to the wall. So, increasing mesh density near the wall of the airfoil is actually worsening the numerical solution!!! This is of course not true with Navier-Stokes formulation (if y+ is appropriate to wall treatment used).

Be careful, Razvan
  Reply With Quote

Old   January 31, 2006, 14:00
Default Re: Error in drag
  #3
Luca
Guest
 
Posts: n/a
Hi Razvan! could you add some details to what you said about grid-density and Euler formulation? I'm very interested to this topic...Luca
  Reply With Quote

Old   February 1, 2006, 05:01
Default Re: Error in drag
  #4
Ivanov
Guest
 
Posts: n/a
Excuse me! I made mistake i. e. 35 counts = Cd = 0.0035
  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
anyone has got this paper? Al Main CFD Forum 3 October 8, 2007 02:04
Pressure drag, friction drag and total drag? Cheng CFX 4 December 2, 2006 23:19
Drag formulation REMY FLUENT 0 March 10, 2002 15:05
Drag formulation remy Main CFD Forum 0 March 10, 2002 14:05
Inviscid Drag at subsonic, subcritical Mach # Axel Rohde Main CFD Forum 1 November 19, 2001 13:19


All times are GMT -4. The time now is 23:43.