CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Post-Processing

deriving drag coefficient

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 7, 2022, 09:29
Default deriving drag coefficient
  #1
New Member
 
chen yu Huang
Join Date: Nov 2019
Posts: 18
Rep Power: 5
chenu is on a distinguished road
Hello,
Does anyone know how force function object works?
In my case, I use openFOAM only for mesh generation and post-process. Flow field is solved by my own flow solver, which is compiled to object and imported in OpenFOAM.
If I solve flow field by my own flow solver and set end time 15 seconds, I will have drag coeff. 1.5. However, if I run flow solver again from 15s(either my flow solver or OpenFOAM solver), the drag force is 6.8. I have tried to create a new OF solver, which reads fluid properties from 15 seconds and output force, the drag coefficient is also 6.8, no 1.5

I will appreciate for any suggestion or pointing out any procedure that I missed, thank you.
chenu is offline   Reply With Quote

Old   June 23, 2022, 03:36
Default
  #2
Senior Member
 
Join Date: Dec 2019
Location: Cologne, Germany
Posts: 306
Rep Power: 6
geth03 is on a distinguished road
every force at a patch is calculated by integrating pressure and viscous shear stress.
geth03 is offline   Reply With Quote

Old   June 23, 2022, 08:59
Default
  #3
New Member
 
chen yu Huang
Join Date: Nov 2019
Posts: 18
Rep Power: 5
chenu is on a distinguished road
Hello geth03,
I know that force is calculated by integrating pressure and viscous force on the surface. My question is, I have created a solver in OpenFOAM, the flow field is solved by calling my own function instead of OpenFOAM such as UEqn.solve() and Peqn.solver(). The flow field is consistent with the result from icoFOAM, but the force is always wrong. Once I restart my solver and set the last time step data as initial condition, the force matches icoFoam.
Thank you for your reply.
chenu is offline   Reply With Quote

Old   August 11, 2022, 12:07
Default
  #4
New Member
 
Saddam Hijazi
Join Date: May 2016
Posts: 17
Rep Power: 8
SaddamH is on a distinguished road
Hello, I think something might be wrong in the computations that you are carrying out.


Are you sure that you are normalizing the forces with the correct coefficients ?, also it could be simply that you set the normalizing coefficients in a wrong way in OF making its results not correct.



By the way is the problem steady or unsteady, 2D or 3D ?


if the problem is unsteady you should be able to see if the forces coefficients values at different times are just multiplied by a factor with respect to the one of OF.
SaddamH is offline   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
Drag Force Ratio for Flat Plate Rob Wilk Main CFD Forum 40 May 10, 2020 05:47
Finding Drag Force from Skin Friction Rob Wilk Main CFD Forum 0 May 8, 2020 07:04
Default Need help with Drag Coefficient using ANSYS Fluent welskein ANSYS 0 March 30, 2020 04:56
problem with saving drag coefficient colopolo FLUENT 5 April 12, 2013 11:59
Calculation of Drag Coefficient, Help Please teek22 CFX 1 April 26, 2012 19:41


All times are GMT -4. The time now is 16:47.