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

High Cd value in FLUENT..

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

Reply
 
LinkBack Thread Tools Display Modes
Old   February 9, 2011, 11:54
Thumbs down High Cd value in FLUENT..
  #1
Member
 
John
Join Date: Jan 2011
Posts: 58
Rep Power: 6
John222 is on a distinguished road
I have done a well mesh in workbench and run the solution but sadly the value of the drag is too high and I guess the problem is with the URF settings, I have uploaded a picture of the solution while converging and a picture of the settings of the URF.

My Cd is supposed to be around 0.4-0.8 not more or less.

In the first I tried the momentum with 0.7 and the solution wasn't stable and got divergence error for momentum then I changed it to 0.2 where I got low coefficient drag force.

Please help me I really need to solve this problem and get a full converged answer, I also uploaded a picture of the mesh for you just in case.


Thanks, John
Attached Images
File Type: jpg solution control.JPG (17.0 KB, 17 views)
File Type: jpg Low Cd.jpg (93.9 KB, 27 views)
File Type: jpg truck mesh.jpg (99.9 KB, 25 views)
John222 is offline   Reply With Quote

Old   February 10, 2011, 02:52
Default
  #2
Super Moderator
 
-mAx-'s Avatar
 
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 2,972
Rep Power: 30
-mAx- will become famous soon enough
did you set well the reference values?
Is your model scaled?
__________________
In memory of my friend Hervé: CFD engineer & freerider
-mAx- is offline   Reply With Quote

Old   February 10, 2011, 10:43
Default
  #3
Member
 
John
Join Date: Jan 2011
Posts: 58
Rep Power: 6
John222 is on a distinguished road
Quote:
Originally Posted by -mAx- View Post
did you set well the reference values?
Is your model scaled?
no max I didn't set the reference values its default, and by scaled you mean meshed or what?
John222 is offline   Reply With Quote

Old   February 10, 2011, 10:55
Default
  #4
Super Moderator
 
-mAx-'s Avatar
 
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 2,972
Rep Power: 30
-mAx- will become famous soon enough
*with scaled, I meant your model has been designed in mm, and your solver is still in m.
I don't think it should be the case in the new release of Fluent-Ansys, but with Gambit-Fluent combination, you had to scaled your mesh within Fluent (Gambit export a dimensionless mesh)

*Coefficients are Forces divided by 0.5*rho*A*v**2 (where rho, A and v are reference values you have to give in Reference Values Panel)
You don't need to recompute your model since your force is the only value computed within iterations. You just have to adjust the 1/(0.5*rho*A*v**2) factor
__________________
In memory of my friend Hervé: CFD engineer & freerider
-mAx- is offline   Reply With Quote

Old   February 11, 2011, 10:17
Default
  #5
Member
 
John
Join Date: Jan 2011
Posts: 58
Rep Power: 6
John222 is on a distinguished road
Quote:
Originally Posted by -mAx- View Post
*with scaled, I meant your model has been designed in mm, and your solver is still in m.
I don't think it should be the case in the new release of Fluent-Ansys, but with Gambit-Fluent combination, you had to scaled your mesh within Fluent (Gambit export a dimensionless mesh)

*Coefficients are Forces divided by 0.5*rho*A*v**2 (where rho, A and v are reference values you have to give in Reference Values Panel)
You don't need to recompute your model since your force is the only value computed within iterations. You just have to adjust the 1/(0.5*rho*A*v**2) factor
Have you got any idea how to change the scale cause I think my scale is wrong.
John222 is offline   Reply With Quote

Old   February 11, 2011, 10:42
Default
  #6
Super Moderator
 
-mAx-'s Avatar
 
Maxime Perelli
Join Date: Mar 2009
Location: Switzerland
Posts: 2,972
Rep Power: 30
-mAx- will become famous soon enough
I was talking about scale because earlier (fluent 6.3) we had to scale the mesh. Now I assume you don't have anymore to scale your model since you can build, mesh and compute your model within the same soft legacy.
Should be confirmed from someone else.
To check I would compute le massflow through your inlet. You can display the velocity contour on inlet, just for having an idea of inlet velocity (average).
Then Q = U. A, and you get the computed inlet area (for a comparison)
__________________
In memory of my friend Hervé: CFD engineer & freerider
-mAx- 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
How to open Icem mesh in Ansys Fluent? emmkell FLUENT 26 June 9, 2015 15:38
Two questions on Fluent UDF Steven Fluent UDF and Scheme Programming 4 September 20, 2013 16:30
Fluent 6.3 32bit vs Fluent 12.0 64bit ibex7 FLUENT 7 April 18, 2011 02:44
Integration of a Custom C++ Model into FLUENT Syed Haider FLUENT 1 February 20, 2006 05:49
Advanced Turbulence Modeling in Fluent, Realizable k-epsilon Model Jonas Larsson FLUENT 5 March 13, 2000 04:27


All times are GMT -4. The time now is 05:07.