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August 25, 2018, 09:44 
location of separation point

#1 
Senior Member
A. Min
Join Date: Mar 2015
Posts: 308
Rep Power: 12 
Hi foamers
I want to find the exact location of separation point in flow around cylinder. According to fluid mechanics books, I should find the point (on the cylinder surface) in which shear stress is zero.(is it correct?) I calculate the xy component of stress tensor as: Code:
List<symmTensor> Tau00; List<scalar> Tau0; Tau00 = (tauS+tauP).boundaryField()[cylinder]; forAll(Tau00,i) { Tau0[i] = Tau00[i].xy(); } While streamlines show that separation is happened in teta=150: Could you please tell me what the problem is? Thanks 

August 26, 2018, 08:07 

#2 
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Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
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Not only shear, but when the pressure gradient along the surface inflects from adverse to positive...


August 26, 2018, 12:30 

#3 
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Michael Alletto
Join Date: Jun 2018
Location: Bremen
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I think tau0.xy gives you the shear stress in the case of a flat plate which is parallel to the xaxis.
To get the shear stress in an arbitrarily defined surface in 3d the steps to perform are the following: 1) Project the shear stress tensor on the surface > this gives you the vector of the force acting on the surface taus 2) Compute the dot product of taus with the vector pointing parallel to the surface > this gives you the shear stress 

August 27, 2018, 06:12 

#4  
Senior Member
A. Min
Join Date: Mar 2015
Posts: 308
Rep Power: 12 
Quote:
Thanks for your reply. I rotated the stress tensor from xy to rteta coordinates. I think this is correct, isn't it? 

August 27, 2018, 10:36 

#5 
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Michael Alletto
Join Date: Jun 2018
Location: Bremen
Posts: 616
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yes this should be correct


Tags 
cylinder, separation, shear stress 
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