# location of separation point

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 August 25, 2018, 08:44 location of separation point #1 Senior Member   A. Min Join Date: Mar 2015 Posts: 281 Rep Power: 9 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 Tau00; List Tau0; Tau00 = (tauS+tauP).boundaryField()[cylinder]; forAll(Tau00,i) { Tau0[i] = Tau00[i].xy(); }``` the tau_xy - teta diagram is: While streamlines show that separation is happened in teta=150: Could you please tell me what the problem is? Thanks

 August 26, 2018, 07:07 #2 Senior Member   Santiago Lopez Castano Join Date: Nov 2012 Posts: 317 Rep Power: 12 Not only shear, but when the pressure gradient along the surface inflects from adverse to positive...

 August 26, 2018, 11:30 #3 Senior Member   Michael Alletto Join Date: Jun 2018 Location: Bremen Posts: 453 Rep Power: 9 I think tau0.xy gives you the shear stress in the case of a flat plate which is parallel to the x-axis. 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, 05:12
#4
Senior Member

A. Min
Join Date: Mar 2015
Posts: 281
Rep Power: 9
Quote:
 Originally Posted by mAlletto I think tau0.xy gives you the shear stress in the case of a flat plate which is parallel to the x-axis. 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
Dear Michael

I rotated the stress tensor from xy to r-teta coordinates. I think this is correct, isn't it?

 August 27, 2018, 09:36 #5 Senior Member   Michael Alletto Join Date: Jun 2018 Location: Bremen Posts: 453 Rep Power: 9 yes this should be correct alimea likes this.

 Tags cylinder, separation, shear stress