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

FLUENT Scaling - Force Coefficients

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 8, 2019, 10:40
Default FLUENT Scaling - Force Coefficients
  #1
New Member
 
Join Date: Dec 2019
Posts: 13
Rep Power: 3
sbro is on a distinguished road
Hi all,

I'm running a 2D thin airfoil simulation in FLUENT which returns force coefficients for lift and drag at 6 degrees AoA with a chord length=1m of CL=0.60 and a Cd=0.018.

I've re-run this case (same AoA) with a scaled model (1/4c) and the same Reynolds number (model scaled by a factor of 1/4, therefore free-stream/inlet velocity has been doubled and the kinematic viscosity halved to maintain consistent Re) expecting to return equivalent values for the force coefficients but this hasn't been the case; solution returned CL~0.15 and a Cd~0.0045 which is a quarter of the original solution.

As the Re is the same and the mesh has been scaled with the airfoil surface (giving same Y+) I don't understand the reasoning for this or if i've simply made a mistake configuring the sim?

Any advisement would be greatly appreciated! Thanks.
sbro is offline   Reply With Quote

Old   December 8, 2019, 13:59
Default
  #2
Senior Member
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 2,731
Rep Power: 38
flotus1 has a spectacular aura aboutflotus1 has a spectacular aura about
Did you adjust the reference length to match your scaled model? From the coefficients you obtained, it seems like you forgot to do that.
flotus1 is offline   Reply With Quote

Old   December 9, 2019, 08:01
Default
  #3
New Member
 
Join Date: Dec 2019
Posts: 13
Rep Power: 3
sbro is on a distinguished road
Quote:
Originally Posted by flotus1 View Post
Did you adjust the reference length to match your scaled model? From the coefficients you obtained, it seems like you forgot to do that.
Thanks for the reply.

You're correct that I forgot to adjust the reference length but, having re-run the simulation now, I'm still obtaining the same result(?)
sbro is offline   Reply With Quote

Old   December 9, 2019, 08:23
Default
  #4
Senior Member
 
flotus1's Avatar
 
Alex
Join Date: Jun 2012
Location: Germany
Posts: 2,731
Rep Power: 38
flotus1 has a spectacular aura aboutflotus1 has a spectacular aura about
I should have been less specific. What I actually meant was "reference values" instead of reference length.
Lift and drag coefficients are calculated using the reference area.
Anyway, that's just post-processing. Changing reference values does not change the solution.
flotus1 is offline   Reply With Quote

Old   December 9, 2019, 08:59
Default
  #5
New Member
 
Join Date: Dec 2019
Posts: 13
Rep Power: 3
sbro is on a distinguished road
Quote:
Originally Posted by flotus1 View Post
I should have been less specific. What I actually meant was "reference values" instead of reference length.
Lift and drag coefficients are calculated using the reference area.
Anyway, that's just post-processing. Changing reference values does not change the solution.
So, by scaling the geometry by a factor of 1/4 (in X & Y), am I correct in thinking the reference area should be amended by (1/4)^2?

For this case where I am keeping Re consistent, am I correct in thinking I should expect the same force coefficients (lift / drag)?

Thanks again for your help!
sbro is offline   Reply With Quote

Reply

Tags
drag coefficient, lift coefficient, reynolds number, scaling

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
Pressure force UDF with Fluent rsarma Fluent UDF and Scheme Programming 2 January 20, 2020 02:19
Problem in using parallel process in fluent 14 Tleja FLUENT 3 September 13, 2013 10:54
problem in using parallel process in fluent 14 aydinkabir88 FLUENT 1 July 10, 2013 02:00
Force Contour Plots in Fluent 14.0 lew FLUENT 0 May 31, 2013 09:29
how does Fluent calculate the pressure and viscous force vector? Ralf Schmidt FLUENT 2 May 17, 2010 15:49


All times are GMT -4. The time now is 14:52.