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June 14, 2011, 12:27 

#61 
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The True
Join Date: Dec 2010
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I have to change the pRef value to calculate the forces.
I am adding this statement to functions forces: pRef 1000; This does not change anything in values, it looks like it is invariant to the pRef value. How can I adapt the pRef value 

June 16, 2011, 08:39 

#62 
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The True
Join Date: Dec 2010
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The flow field looked oke but given Cl value was not oke. So, I decided to calculate the Cl value by sampling pressure values. I get, Cl = 0.166, which looks oke , for airfoil at 0 angle of attack. ( I have not calculated shear stress, don't know how to do it yet. For now I assume it is small, icoFoam)
The OpenFoam gives these value: Cl = 0.00166316; Cd = 0.0000724 Strange, I see it now, it looks like Cl and Cd is missing a multiply with 100 

June 21, 2011, 11:08 

#63 
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The True
Join Date: Dec 2010
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Still I haven't been able to specify the pRef value
I have tried this in the controlDict file, to calculate force coefficients: pref pRefPoint (x y z); but openfoam doesn't see pRefPoint(x y z) as a scalar I get this error: wrong token type  expected Scalar 

September 8, 2011, 16:22 

#64 
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Santiago
Join Date: Dec 2009
Posts: 85
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Hi,
I would like to be able to take a look at the libforces.so file to understand how it calculate the forces and eventually modify the library. Does anyone knows how to do that? Thanks 

September 16, 2011, 17:13 

#65 
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Santiago
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This thread http://www.cfdonline.com/Forums/ope...tml#post324445 is related to force calculations. Does any one know the answer? Thanks


February 3, 2012, 22:37 

#66  
Senior Member
musaddeque hossein
Join Date: Mar 2009
Posts: 309
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Quote:
wallPressure { type surfaces; functionObjectLibs ("libsampling.so"); outputControl outputTime; outputInterval 5; surfaceFormat raw; interpolationScheme cell; fields ( alpha1 p ); surfaces ( leftwalls { type patch; patches (leftWall); interpolate true; triangulate false; } rightwalls { type patch; patches (rightWall); interpolate true; triangulate false; } ); } 

March 20, 2012, 07:00 

#67 
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The True
Join Date: Dec 2010
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Hi,
I have used for mine new simulation the solution of old case. Only the angle of attack ( so velocity and lift and drag coefficients ) is changed. The simulations went oke, however the calculated lift and drag coefficients are wrong. If I sample the pressure coefficients than I get the correct Cl , Cd values however not exact as I want. Because of the many simulations I do not want to run them all again. Is there any solution for this issue ? Is it possible to calculate the aerodynamic coefficients just based on the last time step ? Last edited by Eren10; March 20, 2012 at 08:41. 

May 10, 2012, 09:13 
Wall pressures in InterDyMFoam

#68 
Senior Member
musaddeque hossein
Join Date: Mar 2009
Posts: 309
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Dear all:
I am simulating a small 2D tank with dimensions 8m long, 5m high and 0.01m in depth. I am subjecting the tank to a sinusoidal displacement only and have modified the controlDict to provide wall pressures for the left and right walls at every 0.02 secs. In my opinion, if I am supplying a sinusoidal displacement, the pressures should also be sinusoidal. However when I plot the pressures corresponding to fluid phase in the left and right walls, I get what looks like a very choppy representation, which does not make sense. Any help or advice on how to fix this would be greatly appreciated, Thanks. I have attached the input plot and the pressure plot. My mesh size is 200x200x1 

October 17, 2012, 12:54 
IRef Aref> BI ELEMENT AIRFOIL

#69 
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Fabio
Join Date: Sep 2012
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One question: If I had a bi element airfoil (main&flap), I put in the patches the name of the two walls (main, flap), but for lRef e Aref I need to put 2 different values because the main airfoil and the flap have different chord and so different area. Help me please


November 11, 2013, 12:16 

#70 
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Pengchuan Wang
Join Date: Nov 2012
Location: Michigan USA
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Hi Petter,
I know this is an old thread. But I want to know whether you have found a way to calculate the multiphase torque? Right now I'm using interFoam as well. And I'm stuck with the multiphase torque calculation. If you have any updates, please let me know. Thank you very much. Penghcuan 

November 17, 2013, 10:09 

#71 
Senior Member
musaddeque hossein
Join Date: Mar 2009
Posts: 309
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Is there some way to introduce fluid / wall friction? I am running sloshingtank2d in interdymfoam. The sloshing I get goes on as long as the simulation continues. How can I introduce wall friction so that the sloshing will slowly dissipate once the displacement stops?


July 8, 2014, 10:42 

#72 
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yalong cai
Join Date: Feb 2014
Location: New York
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Hello, Santos,
I have confusions about the value of rhoInf, in this thread, different values appeared, e.g. 1.17, 1.225 and 1000. This difference confuses me. Thanks for your attention. 

September 2, 2015, 16:49 

#73  
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Join Date: Apr 2015
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Quote:
Could you find out if your nu nu ... approach at the top of the transport properties file is a valid workaround for the problem? Just FYI: for the turbulent interFoam, there is no problem in the force calculations, but the problem exists when using laminar interFoam. This problem is "solved" when I take your approach but I am not sure if it is a correct way of tackling this problem. I am using 221 version. Cheers, Hossein 

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