# Calculated Drag Differences Paraview vs OpenFoam Output

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 November 25, 2013, 09:08 Calculated Drag Differences Paraview vs OpenFoam Output #1 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 7 Hi guys, just want to ask for comments: Drag Coefficient Output @ OpenFoam ControlDict -> 2.83 (like literature) Paraview PostProcessing Calculation -> 2.49.... These are my paraviewsteps in short: 1)Extracted Surface 2)Generate Surface Normals 3)Calculated: cp = normals*p; ->Pressure Drag cf=normals*mu*wallGradU_y -> Friction Drag 4) Build Integral Drag=(cp_X+cf_X)*3.14156 (for Aref=1) equals in 2.49 Did I miss something?

 November 26, 2013, 06:12 #2 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 7 Ok, this is just a guess from my side: Could be the differences caused by derivation error while building dUdY of parafoam?

 January 14, 2014, 12:44 #3 Senior Member   Join Date: Dec 2010 Posts: 135 Rep Power: 7 I am still not sure about this topic, has got anyone any idea? Is there something wrong in my workflow? My reference Area Aref is set to 1 in controldict and my density rho to 1.2. Is paraFoam normalizing the data in strange way?

 March 19, 2014, 12:36 #4 Member   Ye Zhang Join Date: Dec 2009 Location: Delft,Netherland Posts: 92 Rep Power: 9 Hi, Did you find the solution? I also have some difference about drag calculations like you. I use the same workflow.... Best regards, Ye

 March 19, 2014, 14:18 #5 Member   Hannes Join Date: Apr 2009 Location: Schleswig, Germany Posts: 38 Rep Power: 9 You might try to evaluate the sensitivity of forces to angle in surface normals. Regards, Hannes __________________ FluidEngineeringSolutions

 September 24, 2016, 16:15 friction drag #6 New Member   Wouter Join Date: Aug 2013 Posts: 19 Rep Power: 5 Hi all, isn't the difference due to the friction drag (which you don't take into account when using only the pressure in paraview)? Regards, Wouter.

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