# Fluid wall shear stress

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 March 3, 2005, 07:50 I am trying to calculate the w #1 Sinead Kelly (Kelly) Guest   Posts: n/a I am trying to calculate the wall shear stress within a fluid in a cylindrical pipe. I have defined WSS as a volVectorField in a createFields.H file, so that I can look at the wall shear stress in dxFoam. The code I have been using for the wall shear stress is: label patchA = mesh.boundaryMesh().findPatchID("wall"); fixedValueFvPatchVectorField& wallshearstress = refCast(WSS.boundaryField()[patchA]); forAll(wallshearstress, patchFaceA) { volTensorField gradU = fvc::grad(U); volTensorField shear = mu*(gradU + gradU.T()); shear[patchFaceA].component(tensor::XX) = 0; shear[patchFaceA].component(tensor::YY) = 0; shear[patchFaceA].component(tensor::ZZ) = 0; wallshearstress[patchFaceA].component(vector::X) = shear[patchFaceA].component(tensor::XY) + shear[patchFaceA].component(tensor::XZ)); wallshearstress[patchFaceA].component(vector::Y) = shear[patchFaceA].component(tensor::YX) + shear[patchFaceA].component(tensor::YZ) wallshearstress[patchFaceA].component(vector::Z) = shear[patchFaceA].component(tensor::ZX) + shear[patchFaceA].component(tensor::ZY); } So, I have been able to get the stress tensor and set the 3 normal components to zero. I have then added the 2 X components to get the overall X component of the shear stress, added the 2 Y components etc. However, looking at my results in dxFoam, the WSS vectors are not aligned correctly along the wall of the cylinder. Do I have to project my stress vector onto my surface and does anyone have any idea how to do this? Has anyone written a code to calculate the wall shear stress of a fluid already? Thanks, Sinead

 March 3, 2005, 07:56 You might find the applicatio #2 Henry Weller (Henry) Guest   Posts: n/a You might find the application applications/utilities/postProcessing/wall/wallShearStress useful. Simply replace R in the expressions with your shear field and it should do what you want.

 March 30, 2011, 06:41 #3 Senior Member   Join Date: Sep 2010 Posts: 226 Rep Power: 17 hi henry, what do you mean by "R" in the expressions where? thanks