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

Drag Coefficient

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 12, 2009, 14:45
Default Drag Coefficient
  #1
New Member
 
Jon
Join Date: Sep 2009
Posts: 2
Rep Power: 0
stay31 is on a distinguished road
Hey all,

I have read many threads about the drag coefficient for a cylinder and have tried all the suggestions to no avail. I am at a loss and really hoping to achieve a relevant answer. I am using gambit 2.4 to mesh the model and FLUENT 12 to do the analysis
Here is what i have done:
I am doing a steady flow, 3-D case with the standard k-epsilon model with standard wall functions. I have tried two flow speeds, one at 4.5 m/s and another at 50 m/s and have tried changing the turbulent kinetic energy ratio and dissipation rate as well as the other values found under Turbulence quantities. I have changed my yplus and ystar from min=50 and max=500 to min=30 and max=300. I have also ran the simulation using realizable k-epsilon model with enhanced wall treatment. I scale the mesh when I import the mesh into FLUENT from gambit because gambit writes everything in mm. With all the above tried, and more, I still obtain a Cd~0.18-0.2 for both of the above stated flows.
Any help and/or solution is greatly appreciated, thank you!

stay
stay31 is offline   Reply With Quote

Old   October 17, 2009, 12:36
Default
  #2
New Member
 
Emre
Join Date: Oct 2009
Location: Ann Arbor, MI
Posts: 12
Rep Power: 16
esozer is on a distinguished road
I suggest you try:

1. Refine near wall grid to about y+=1
2. Use Menter's SST turbulence model
3. Don't use wall functions for this case

Wall functions don't really work well for separated/high curvature flow regions. SST model scales the eddy viscosity near the wall to account for low-Re region. So you can directly integrate to the wall.
__________________
Free CFD developer
www.freecfd.com
esozer is offline   Reply With Quote

Old   October 17, 2009, 17:01
Default
  #3
New Member
 
Jon
Join Date: Sep 2009
Posts: 2
Rep Power: 0
stay31 is on a distinguished road
esozer,

thank you very much for your input. I will try your suggestions and keep my fingers crossed that it works.

regards,
stay
stay31 is offline   Reply With Quote

Reply

Tags
3-d cylinder, drag coefficient, k-epsilon model, turbulent flow

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
Drag Coefficient Convergence Problem John FLUENT 18 June 24, 2023 10:22
Solidification drag coefficient atulverma FLOW-3D 1 May 14, 2009 10:24
Drag coefficient for parcels in dieselFoam sebastian_vogl OpenFOAM Running, Solving & CFD 5 December 31, 2008 13:19
Automotive test case vinz OpenFOAM Running, Solving & CFD 98 October 27, 2008 09:43
drag and lift coefficient Noé Siemens 5 July 13, 2004 11:21


All times are GMT -4. The time now is 06:40.