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How to use ANSYS CFX to get the drag coefficient? 

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September 24, 2005, 10:46 
How to use ANSYS CFX to get the drag coefficient?

#1 
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I used CFX to simulation a bluff body. CFX offers viscous force and pressure force,but it doesn't the coefficient. How can I get the coefficient of the bluff body? Please the masterhands help me! Thanks a lot!


September 24, 2005, 15:09 
Re: How to use ANSYS CFX to get the drag coefficie

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Hi,
In CFXPost you can obtain force_x()@Surface, force_y()@Surface and force_z()@Surface. If the velocity is aligned with the xaxis, you could obtain the drag coefficient as Cd = force_x()@Surface / (0.5*Rho*U^2*A) 

October 7, 2005, 08:13 
Re: How to use ANSYS CFX to get the drag coefficie

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Many thanks for you reply! Can you sent the tutorial of drag coefficient?


June 20, 2010, 07:05 

#4 
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hi
to find drag coefficient, in the above formulae what is A, is A = length * width * 0.8 

June 20, 2010, 07:22 

#5 
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Glenn Horrocks
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A is a representative area. For bluff bodies that is usually the frontal area by for airfoils they frequently use the planform area. Check you use the right area definition.
But this is very basic stuff which is dicussed in most introductory fluid mechanics books. Go to your library and look it up. 

January 23, 2012, 12:04 
error help

#6 
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Tom Walker
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I know this is quite an old post but I don't know where else to turn..
when I try and do force calculations in CFX i get an error message that says "Only geometries with surface data are allowed for calculating force" what does this mean and how do I generate surface data? Thanks Tom Walker 

January 23, 2012, 17:37 

#7 
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Glenn Horrocks
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It means exactly what it says  you can only calculate force on surfaces. You are trying to calculate force on a point, line or volume body and that is not meaningful.


January 23, 2012, 20:50 

#8 
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Tom Walker
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thank you very much, I can't believe I was over thinking it like that!


October 1, 2015, 02:45 

#9  
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N B Khan
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Quote:
Sir, Kindly tell me how to monitor the value of Cd or Cl... In case of Fluent, we can monitor it and later on, we can also plot the graph of Cd vs time or Cl vs time.... but I am unable to monitor the Drag force or lift force on cylinder while using CFX... Please help 

October 1, 2015, 03:44 

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October 1, 2015, 04:58 

#11  
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N B Khan
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Quote:
I tried to make the expression as show in image... In CEL, I couldnt find the exact way to write formula.. In my case Vel=0.034m/s density=1.185kg/m^3 Projected Area=0.02m^2 Drag forces are in x direction ACtually Even in writing formula in EXPRESSION, it is not possible to separate Force in x and y component for Drag and lift coefficient respectively. 

October 1, 2015, 06:12 

#12  
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Quote:
2. You should write values along with their dimensions in square brackets. 3. You may use variables names to access their values. Your CEL for Cd may look like that: Code:
2*force_x()@Cylinder / (Projected Area*massFlowAve(Density)@inlet *(massFlowAve(Velocity)@inlet)^2) 

October 1, 2015, 06:30 

#13  
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N B Khan
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Quote:
I did it... Thank you again... Actually, In post CFD, there is "force_x" term available while write the formula in EXPRESSION...but in CFX pre, there is only term "force ()@region..."...so I was bit confused how to insert "force_x" component... but now i simply write manually "_x" in available term " force ()@region"... 

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