# Drag forces

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 May 16, 2011, 02:43 Drag forces #1 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 hii.can anybody tell me how to calculate pressure drag and skin friction drag seperately in fluent

 May 16, 2011, 08:47 #2 Senior Member     Amir Join Date: May 2009 Location: Montreal, QC Posts: 739 Blog Entries: 1 Rep Power: 16 Hi, report->forces (set the drag direction ....)

 May 16, 2011, 09:34 #3 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 thanks for reply..but from moniter forces ..we can find the total drag.but i need to calculate the pressure drag and the skin friction drag seperately

 May 16, 2011, 09:44 #4 New Member   Join Date: Mar 2011 Posts: 20 Rep Power: 8 if you want both don't use the drag monitor but Report> forces, be careful to the director vector (give right values for X and Y). This will give you the pressure and viscous forces in the monitor

 May 16, 2011, 09:53 #5 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 can you plz tell me that what will be the value of X any Y for pressure and Viscous Drag

 May 16, 2011, 10:35 #6 New Member   eddy Join Date: Apr 2011 Posts: 8 Rep Power: 8 pressure should be same vector as flow direction

 May 16, 2011, 10:43 #7 New Member   Join Date: Mar 2011 Posts: 20 Rep Power: 8 What is your geometry and flow parameters?

 May 17, 2011, 00:55 #8 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 i have a semi circular cylinder in a rectangular shaped domain . the left BC is velocity inlet , the right is velocity outlet and the top and bottom is symmetric.and its in 2D. plz help me

 May 17, 2011, 09:12 #9 New Member   Join Date: Mar 2011 Posts: 20 Rep Power: 8 You can have a look to this link, it's an example for an airfoil https://confluence.cornell.edu/displ...+Specification you will find how to proceed...

 May 17, 2011, 11:20 #10 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 @saclu ..thanks for the reply..but here in the sample problem they have fount the lift coefficient and drag coefficient ...by changing the force vector.but i need to find the coefficient of pressure drag and coefficient of skin friction drag separately....

 May 18, 2011, 02:57 #11 New Member   Join Date: Mar 2011 Posts: 20 Rep Power: 8 the example was just to show you how to find the right values for the drag direction vector (X et Y). Once you have these values go in Report>force, choose the the wall zone, completed the direction vector with the values you calculated then press print and you will have the pressure and viscuous force separetly on your monitor. CFDstudent123 likes this.

 May 19, 2011, 03:15 #12 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 @saclu...hi your reply was very useful to me ..but now i need to find the time average value of coefficent of pressure drag....and i am solving for an unsteady state problem

 May 20, 2011, 04:44 #13 New Member   Join Date: Mar 2011 Posts: 20 Rep Power: 8 Hi, I wouldn't know how to do without using a UDF (User Defined Function) but it isn't a good idea if your not familiar with it. May be you could have an approximate value by solving a steady problem.

 May 23, 2011, 08:03 #14 New Member   amrit Join Date: May 2011 Posts: 10 Rep Power: 8 @saclu ..can u plz help me in the UDF part ... plz tell me which function is used to get the pressure drag for writing the UDF

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