CFD Online Logo CFD Online URL
Home > Forums > Software User Forums > OpenFOAM > OpenFOAM Post-Processing

Post Processing Drag Coefficient

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

Like Tree2Likes
  • 2 Post By squanto773

LinkBack Thread Tools Search this Thread Display Modes
Old   March 7, 2012, 03:27
Default Post Processing Drag Coefficient
New Member
This Wiederkehr
Join Date: Feb 2012
Posts: 2
Rep Power: 0
squanto773 is on a distinguished road
Hi all

I used OpenFoam (simpleFoam with RAS turbulence model komegaSST) to calculate the drag coefficient of a car.
For calculating the drag coefficient I am using the tool and execut it after the simulation by using:

execFlowFunctionObjects -latestTime
That this works I added

    #include "forceCoeffs"
to system/controlDict


    type        forceCoeffs;
    functionObjectLibs ( "" );
    outputControl timeStep;
    outputInterval 1;

    patches     ( "car" );
    pName       p;
    UName       U;
    rhoName     rhoInf;      // Indicates incompressible
    log         true;
    rhoInf      1;           // Redundant for incompressible
    liftDir     (0 0 1);
    dragDir     (-1 0 0);
    CofR        (0.72 0 0);  // Axle midpoint on ground
    pitchAxis   (1 0 0);
    magUInf     27.8;
    lRef        1.0;        // Wheelbase length
    Aref        0.94293;        // Estimated
To dictionary forceCoeffs.

Since the car is in air I changed rhoInf to 1.188. However this did not have any effect to the drag coefficient. Actually changing rhoInf to any value you'd like does not have any effect on the drag coefficient. However from my point of view this should directly influence the drag coeff.

Is this a bug or did I miss something?

BTW: I am using 2.0.1

mm.abdollahzadeh and amuzeshi like this.
squanto773 is offline   Reply With Quote

Old   March 7, 2012, 10:43
New Member
This Wiederkehr
Join Date: Feb 2012
Posts: 2
Rep Power: 0
squanto773 is on a distinguished road
Ah, I think I got it:
For incompressible calculations the pressure and the viscous forces are already divided by the density because kinetic viscosity is used.
see here

Therefore the density should be set to one because no further normalization is required for the calculation of Cd.
Thus also to display the correct pressure I have to multiply it by the density.. correct?

Could anyone comment on this to ensure that I am on the right track?

Thanks and regards

squanto773 is offline   Reply With Quote


coefficient, drag, openfoam

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
Ansys Post processing ano999 ANSYS 1 May 27, 2011 17:24
NO model vs post processing in coal combustion,CFX sakalido CFX 1 April 15, 2011 15:07
Drag coefficient & Lift coefficient?? mehrdadeng CFX 15 December 9, 2009 22:49
Solidification drag coefficient atulverma FLOW-3D 1 May 14, 2009 10:24
drag coefficient Amir FLUENT 6 November 7, 2008 06:47

All times are GMT -4. The time now is 15:43.