[Bodo1993]

Hi, I am wondering how would I output the total stress tensor (normal + shear) from the openfoam simulation?
I am using openFoam v6 and I work with a multiphase solver, twoLiquidMixingFoam.
Reading through the forum, I got into the custom function object below that should be added to the controlDict file:

    Stress
    {
        libs 				("libutilityFunctionObjects.so");
        type 				coded;
        writeControl            	outputTime;
        writeInterval           	1;
        name            		StressTensor;

        
	codeExecute
        #{
		volTensorField gradU = fvc::grad(U);
		// stress tensor
		volTensorField tau = - mu * (gradU + gradU.T());
        #};
    }

However, I get an error below for "mu"

/opt/openfoam6/src/OpenFOAM/lnInclude/fundamentalConstants.H:73:36: note:   ‘Foam::constant::physicoChemical::mu’
     extern const dimensionedScalar mu;
                                    ^~
/opt/openfoam6/wmake/rules/General/transform:25: recipe for target 'Make/linux64GccDPInt32Opt/functionObjectTemplate.o' failed
make: *** [Make/linux64GccDPInt32Opt/functionObjectTemplate.o] Error 1
[0] 
[0] 
[0] --> FOAM FATAL IO ERROR: 
[0] Failed wmake "dynamicCode/StressTensor/platforms/linux64GccDPInt32Opt/lib/libStressTensor_fa6bcb9352550c3007ffd513d48777a6a88042f2.so"
[0] 
[0] 
[0] file: /home/abdallah/OpenFOAM/abdallah-6/Fall2020/Loc_size/DR25/system/controlDict.functions.Stress from line 152 to line 160.

I am not quite sure if it is recognizing that I want to use the mixture viscosity of the two phases. I am wondering, what is the proper way to call that mixture viscosity in the function object above. Thanks in advance.