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How to obtain fluid shear stress (not only wall shear stress) in openFOAM 

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July 12, 2020, 15:33 
How to obtain fluid shear stress (not only wall shear stress) in openFOAM

#1 
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Sourav Mandal
Join Date: Jul 2019
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Dear All,
I want to calculate/visualise shear stress inside the fluid domain. I came through wallShearStress utility but as you know, it only calculates the shear stress at the wall. My model is very simple: a long pipe, with a nonNewtonian fluid simulated at a certain pressure difference between the inlet and the outlet, solved using simpleFoam. Surprisingly, I found no relevant documentation, although there is plenty of discussion regarding the shear stress at the wall. I came through this helpful post, which enabled me to calculate shear strain in the fluid domain but finding it hard to adopt the approach to obtain shear stress. Function object for strain rate tensor? I tried with the approach mentioned there, by making files named fluidShearStressSM.C etc. At the wmake stage it throws a lot of errors such as : Code:
g++ std=c++11 m64 Dlinux64 DWM_ARCH_OPTION=64 DWM_DP DWM_LABEL_SIZE=32 Wall Wextra Woldstylecast Wnonvirtualdtor Wnounusedparameter Wnoinvalidoffsetof Wnoattributes O3 DNoRepository ftemplatedepth100 I/opt/openfoam7/src/finiteVolume/lnInclude I/opt/openfoam7/src/meshTools/lnInclude I/opt/openfoam7/src/lagrangian/basic/lnInclude I/opt/openfoam7/src/fileFormats/lnInclude I/opt/openfoam7/src/sampling/lnInclude I/opt/openfoam7/src/surfMesh/lnInclude I/opt/openfoam7/src/thermophysicalModels/basic/lnInclude I/opt/openfoam7/src/thermophysicalModels/solidThermo/lnInclude I/opt/openfoam7/src/transportModels I/opt/openfoam7/src/transportModels/compressible/lnInclude I/opt/openfoam7/src/TurbulenceModels/turbulenceModels/lnInclude I/opt/openfoam7/src/TurbulenceModels/incompressible/lnInclude I/opt/openfoam7/src/TurbulenceModels/compressible/lnInclude IlnInclude I. I/opt/openfoam7/src/OpenFOAM/lnInclude I/opt/openfoam7/src/OSspecific/POSIX/lnInclude fPIC c fluidShearStressSM/fluidShearStressSM.C o /opt/openfoam7/platforms/linux64GccDPInt32Opt/src/functionObjects/field/fluidShearStressSM/fluidShearStressSM.o fluidShearStressSM/fluidShearStressSM.C: In member function ‘virtual bool Foam::functionObjects::fluidShearStressSM::calc()’: fluidShearStressSM/fluidShearStressSM.C:65:13: error: expected primaryexpression before ‘const’ 65  const volTensorField& gradU = fvc::grad(U);  ^~~~~ fluidShearStressSM/fluidShearStressSM.C:68:43: error: ‘mu’ was not declared in this scope 68  const volTensorField& tau =  mu * (gradU + gradU.T());  ^~ fluidShearStressSM/fluidShearStressSM.C:68:49: error: ‘gradU’ was not declared in this scope 68  const volTensorField& tau =  mu * (gradU + gradU.T());  ^~~~~ fluidShearStressSM/fluidShearStressSM.C:69:9: error: expected primaryexpression before ‘)’ token 69  );  ^ fluidShearStressSM/fluidShearStressSM.C:68:35: warning: unused variable ‘tau’ [Wunusedvariable] 68  const volTensorField& tau =  mu * (gradU + gradU.T());  ^~~ fluidShearStressSM/fluidShearStressSM.C: In constructor ‘Foam::functionObjects::fluidShearStressSM::fluidShearStressSM(const Foam::word&, const Foam::Time&, const Foam::dictionary&)’: fluidShearStressSM/fluidShearStressSM.C:90:5: error: type ‘Foam::functionObjects::fvMeshFunctionObject’ is not a direct base of ‘Foam::functionObjects::fluidShearStressSM’ 90  fvMeshFunctionObject(name, runTime, dict),  ^~~~~~~~~~~~~~~~~~~~ fluidShearStressSM/fluidShearStressSM.C:91:5: error: class ‘Foam::functionObjects::fluidShearStressSM’ does not have any field named ‘logFiles’ 91  logFiles(obr_, name),  ^~~~~~~~ fluidShearStressSM/fluidShearStressSM.C:92:5: error: class ‘Foam::functionObjects::fluidShearStressSM’ does not have any field named ‘writeLocalObjects’ 92  writeLocalObjects(obr_, log),  ^~~~~~~~~~~~~~~~~ fluidShearStressSM/fluidShearStressSM.C:93:1: error: expected identifier before ‘{’ token 93  {  ^ fluidShearStressSM/fluidShearStressSM.C:93:1: error: no matching function for call to ‘Foam::functionObjects::fieldExpression::fieldExpression()’ In file included from fluidShearStressSM/fluidShearStressSM.H:42, from fluidShearStressSM/fluidShearStressSM.C:26: lnInclude/fieldExpression.H:88:9: note: candidate: ‘Foam::functionObjects::fieldExpression::fieldExpression(const Foam::word&, const Foam::Time&, const Foam::dictionary&, const Foam::word&, const Foam::word&)’ 88  fieldExpression  ^~~~~~~~~~~~~~~ lnInclude/fieldExpression.H:88:9: note: candidate expects 5 arguments, 0 provided fluidShearStressSM/fluidShearStressSM.C:95:5: error: ‘resetName’ was not declared in this scope; did you mean ‘resultName_’? 95  resetName(typeName);  ^~~~~~~~~  resultName_ fluidShearStressSM/fluidShearStressSM.C:96:5: error: ‘resetLocalObjectName’ was not declared in this scope 96  resetLocalObjectName(typeName);  ^~~~~~~~~~~~~~~~~~~~ make: *** [/opt/openfoam7/wmake/rules/General/transform:26: /opt/openfoam7/platforms/linux64GccDPInt32Opt/src/functionObjects/field/fluidShearStressSM/fluidShearStressSM.o] Error 1 I am new to OpenFOAM & have no prior exposure to OOC++ coding. Any suggestion or pointers in the right direction would help me greatly in my research, with this nice opensource software. 

July 13, 2020, 04:13 

#2 
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Join Date: Oct 2011
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Move to $FOAM_SRC/etc/caseDicts/postProcessing/fields
make a copy of vorticity to strainRate, replace every occurance of vorticity with strainRate in the files Move to $FOAM_SRC/functionObjects/field/make. Edit "files", add strainRate/strainRate.C after vorticity copy the folder vorticity in $FOAM_SRC/functionObjects/field to strainRate replace vorticity with strainRate in the copied filenames in strainRate.C replace #fvcCurl.H with #fvcGrad.H, replace function calc() with Code:
bool Foam::functionObjects::strainRate::calc() { if (foundObject<volVectorField>(fieldName_)) { return store ( resultName_, sprt(2.0)*mag(symm(fvc::grad(lookupObject<volVectorField>(fieldName_)))) ); } return false; For nonNewtonian Liquids this formula is generally wrong. I could not find a better approach, yet. 

August 6, 2020, 14:41 

#3  
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Sourav Mandal
Join Date: Jul 2019
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Quote:
BTW, the problem I am facing isn't with implementing strain rate (it works as that link says), rather with the shear stress in the entire fluid domain. Sorry, if I wasn't clear enough... 

August 6, 2020, 14:56 
Using swak4FOAM, but shear stress & wall shear stress do not match

#4 
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Sourav Mandal
Join Date: Jul 2019
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I found a workaround while fiddling with Swak4Foam. He files or commands that I used are as follow:
Code:
FoamFile { version 2.0; format ascii; instance "system"; local ""; class dictionary; object funkySetFieldsDict; } expressions ( setTau { field Tau; create true ; expression "mag(grad(U))*nu"; } );
The simulation is as such that the highest shear stress would be at the wall. So, I compare the maximum values of shear stress and wall shear stress (using the wallShearStress utility), it's hugely different. I am not sure now, which one is correct. Can anybody help me inferring where is the error? 

November 17, 2020, 16:32 

#5 
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Hi Sourav,
I am wondering if you managed to get a way to extract the correct stress tensor from the openFoam simulations. Thanks. 

December 10, 2020, 13:44 
Version 8 of OpenFOAM has natively implemented this

#6  
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Sourav Mandal
Join Date: Jul 2019
Posts: 55
Rep Power: 6 
Hello Bodo1993, if you haven't found it already there are two ways to achieve this.
First, with OpenFOAM version 8, you can just add these lines at the end of your controldict file: Code:
functions { //https://www.openfoam.com/documentation/guides/latest/doc/guidefunctionobjects.html #includeFunc shearStress; } Quote:
Last edited by sourav90; December 10, 2020 at 13:46. Reason: update 

February 13, 2022, 00:10 
Encounter the same problem, find a solution

#7  
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刘旭阳
Join Date: Feb 2022
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I have a similar problem, would you like to ask if it is solved? If solved, can you share the code for calculating fluid shear stress? I would be very grateful and happy to share it. Thanks!
Quote:


June 7, 2023, 07:26 

#8  
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Sourav Mandal
Join Date: Jul 2019
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Quote:
You can find a minimal reproducible example (MRE), for the published paper with this work here: inSilicoE3DBP_model_MRE 

June 27, 2023, 11:03 

#9 
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Shanu
Join Date: Jun 2023
Posts: 3
Rep Power: 2 
Hi Sourav and everyone,
I know this is an ancient post but I hope someone can find me a solution. I have been stuck for a very long time. I am actually doing LES and cannot figure out how to output wall shear stress during the simulation in openfoam. So I was trying to calculate the wall shear stress in Paraview using gradientOfUnstructuresDataSet and then extracting the surface and computing the surface normals and then doing the dot product of this gradient tensor with the surface normal vector and the dynamic viscosity to calculate the wall shear stress. But my gradient vectors are computed all zero on the wall. I don't know how to include the gradient at the cell centroid and not at the face of the wall cell. Any help will be highly appreciated. 

Tags 
fluid shear stress, function objects, post procesing, programming, runtime processing 
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