(interfoam) shear stress at water air interface !
hi guys
I'm using interfoam solver for my 2D multiphase problem (water  air) My goal on my simulation is to calculate the shear stress on the waterair interface Because alpha_1 is not a discreet variable (range from 1 for water to 0 for air) so i can't really define the interface Can any one have experience in this matter tell me how to calculate the shear stress on the interface using some utility in openfoam or even share an effective idea.. thank you very much .. best regards.. 

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yes i know that is very good ,, but do you know a way to automatically calculate shear stress using a utility in openfoam or in paraview i think if i didn't find any of those ,, the standard way is to calculate the velocity gradient in the cells of alpha1=0.5 ,, then i must get the gradient in the direction of the interface ( because the shear force must be tangent to the interface ),, which is a very complicated issue (i must also know the direction of the interface at every cell ) best regards 
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Application interfaceProperties Description Properties to aid interFoam : 1. Correct the gamma boundary condition for dynamic contact angle. 2. Calculate interface curvature. 3. Calculate the shear stress. 
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do you know how can i get the velocity gradient in the output data of my final time like U , p , and alpha1 thank you 
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But from the information at slice 34 I'm not so sure anymore. Otherwise you will have to do it yourself. You can create the explicit gradient from the finite volume calculus class: Code:
fvc::grad(U) 
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if i know that this member functin grad(U) for fvc class is used to get the gradient of the velocity , how can i use it to get the gradient of the last time of the simulation I'mvery sorry cause I'm quite new to C++ programming best regards 
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I suggest you have a look into the code of the foamCalc function which caluclates magGrad or magU. I suppose it will do the same loop. 
Hello,
I know this thread is a little bit old but nevertheless I hope someone could help me: I also want to calculate the interfacial shear stress. Did anyone find a good way to calculate it? Thanks a lot. 
I am working on the same problem and almost done with the equations to be calculated. I got a lot of help from this post. I will suggest anyone working on this problem reads this post first.
http://www.cfdonline.com/Forums/ope...bendpipe.html I understand all the formulations given in that post. I am working with two incompressible immiscible fluids (VOF formulation) with interFoam solver. The only question I have is regarding the stress tensor that should be used for the calculation of traction. Should the viscous stress tensor be used for calculating the Traction vector? This is what I would do if I was doing solids or, The total stress tensor including the pressure term should be used? 
Hello shikamaru,
are you still interested in this topic? I would use the first equation you wrote in the last post for i is not equal to j. Did you calculate the shear stress on the wall or at the interface? See you idefix 
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