# how does Fluent calculate the pressure and viscous force ?

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 February 24, 2011, 10:32 how does Fluent calculate the pressure and viscous force ? #1 New Member   esi nikki Join Date: Feb 2011 Posts: 2 Rep Power: 0 can someone explain me, how does Fluent calculate the pressure and viscous force ? In the handbook in section "29.3.1 Computing Forces, Moments, and the Center of Pressure" it is only described, that the total force component is computed using the pressure and viscous force vector. But, hoe are they calculated?? I didn't found anything about that in the manual... Thank you! ESI

 February 25, 2011, 03:23 #2 Member   lalupp Join Date: Jul 2010 Location: India Posts: 44 Rep Power: 15 I think pressure drag = Fx = ∑pA.nx and summation is done over the number of wall faces For estimating viscous drag stress tensor is needed which is a function of strain tensor obtained by appropriate viscous assumption

 March 7, 2011, 20:44 #3 Member   J.-H. Wang Join Date: Oct 2010 Posts: 72 Rep Power: 15 @lalupp: Since you've mentioned, I'm wondering if there are direct ways to output the force and moment during the transient calculation. Let's say per time step for example. It seems to me that we could only use thoses options in "monitor" panel and yet it is restricted to Cl, Cd and Mx only. If you have any thoughts for that please help me out...

 April 9, 2011, 13:23 @ JH, Wang #4 Senior Member   Ugly Kid Joe Join Date: Aug 2010 Posts: 193 Rep Power: 15 Did you find out a direct way to output the forces on a body wrt time ???????? All I can do using FLUENT is to get Cl and Cd using Reference values. Also if the reference values have length & depth then why is there area mentioned. In calculating the Cl or Cd what does FLUENT take into account, length and depth or the ARea ????? Thank you.

April 10, 2011, 21:23
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Vieri Abolaffio
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Quote:
 Originally Posted by vmlxb6 Did you find out a direct way to output the forces on a body wrt time ???????? All I can do using FLUENT is to get Cl and Cd using Reference values. Also if the reference values have length & depth then why is there area mentioned. In calculating the Cl or Cd what does FLUENT take into account, length and depth or the ARea ????? Thank you.
to have the forces, you have to go to results-->reports---> forces.

from there you can set that you are displayed on the console or grouped in a file. they will come splitted between viscous and pressure. you can avarage them in time, fft'em, everything.

 April 10, 2011, 22:07 #6 Senior Member   Ugly Kid Joe Join Date: Aug 2010 Posts: 193 Rep Power: 15 Reporting the forces displays the force (viscous+pr.) at a particular time. How do I get a plot of the forces vs time. Like how we have it for Cl vs time or Cd vs time. Thank you.

 April 11, 2011, 11:00 #7 Member   J.-H. Wang Join Date: Oct 2010 Posts: 72 Rep Power: 15 Dear, Please search my post in this forum. I have answered myself in a series of discussion. JH Wang

 June 27, 2011, 21:31 #8 Member   Tobino Join Date: Jan 2011 Location: Osaka,Japan Posts: 33 Rep Power: 15 Hi, I am not clearly about Pressure Resistance, Viscous resistance and total resistance reporting by Fluent. So, In Fluent Total resistance = Viscous R + Pressure R but flowing theory of resistance Viscous R = Pressure R + Frictional R. What is mean Viscous R and Total resistance in Fluent ? Thanks,

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