[ArathoN]

Hello,
I'm a beginner user of OpenFoam, and after days of research i decided to ask your help dear community.

I need to calculate the velocity gradient and the wall shear stress at every output time, and i don't know how I can do it. I tried to modify the solver but my knowledge of C code isn't enough to make me understand what i have to do.

Another question is how can i output afterwards these data? I thought about using the sampledict but what should i choose between surface, sets and all other options?

Finally i saw some output file from the sample function and i didn't understand the meaning of the column, what they represent if i choose for example the variable velocity U and i want to sample in the "x" direction starting from point P1 and ending on point P2?

I thought on making something similar to the post-processing (it is written in the controldict and not in a separate file sampledict) present in the case "pitzDaily" where it outputs the fiels "P U K" every output time, but I don't know how I can do it.

I hope some kind soul could help me and sorry for my bad English (not my native language).

[ArathoN]

I'm using this function in the control dict to calculate wallshearstress at every output time, but it gives me only the min and max value of the variable:

wallShearStress1
    {
        type        wallShearStress;
        functionObjectLibs ("libutilityFunctionObjects.so");
        outputControl   outputTime;
        setFormat       gnuplot;

        patches     ("lowerWall");
    }

what should i add to give me the valu of the stress in the lowerwall and the distance too?

[ArathoN]

I tried to use also the sample function like this:

interpolationScheme cellPoint;
fields
(
    "wallShearStress"
);
sets
(    
lineX1
    {
        type        uniform;
        axis        distance;

        start       (0 0 0);
        end         (2.5 0 0);
        nPoints     10;
    }
);

where the lowerwall in which i'm interested to evaluate the wallshearstress begins from (0 0 0) and ends at (2.5 0 0).

But it will give me a null wallstressshear for every position. can you please tell me what am i doing wrong?

[ArathoN]

finally now i coult sample the wallshearstress. I want now to use the "libutilityfunctionobjects.so" with wallShearStress1 function in controldict. The only problem is that it will give me only the min and max value for every timeset, how can i specify that it should give me all the values on the lowerwall, i need to evaluate the separation point of the flow in a backward facing step.

wallShearStress1
    {
        type        wallShearStress;
        functionObjectLibs ("libutilityFunctionObjects.so");
        outputControl   outputTime;
        setFormat       gnuplot;

        patches     ("lowerWall");
    }

Please Can someone help me??I reached a dead end here and searched all the forum and the source documentation e found nothing.

[ArathoN]

I created the sample file so i can have the values of the wall shear stress with this code:

setFormat gnuplot;

surfaceFormat raw;

interpolationScheme cellPoint;
fields
(
    "wallShearStress"
);

sets
(
    
lineX1
    {
        type        face;
        axis        x;

        start       (0 -0.1 0);
        end         (2.5 -0.1 0);
        nPoints     400;
    }

);

surfaces
(
    
 walls_interpolated
    {
        type            patch;
        patches         ( "lowerWall" );
        interpolate     true;
    }

);

i sampled the same patch in two different modes, wanted to try the capability of the sample function.

I saw that i can add the libsampling.so to the controldict file and by this i can sample too while running the solver i tried modifying the file but with no success, any of you have a hint?

[canopus]

Is it possible now to calculate wallGradU & wallShearStress every output time by using the controldict?

[canopus]

I found its possible to write in runtime with

wallShearStress1
    {
        type        wallShearStress;
        functionObjectLibs ("libutilityFunctionObjects.so");
        patches     ("wallbot");
//        outputControl   timeStep;
        outputControl   runTime;
        writeInterval   0.005;
    }

But problem is

This function object evaluates and outputs the shear stress at wall patches. The result is written as a volVectorField to time folders as field 'wallShearStress'.

How can I make it write in postProcessing directory as the results of probe appear?

[srv537]

Hi
i used

pimpleFoam -postProcess -func wallShearStress

to calculate wallShearStress but it gives me only for saved data file but my case is unsteady so after some time i have to take average of all and to do this i want to calculate wallShearStress at each time step and its temporal average.
how to do it, please tell me. is there any method or code available in controlDict file to do this?

Thank you

[randolph]

Originally Posted by canopus

I found its possible to write in runtime with

wallShearStress1
    {
        type        wallShearStress;
        functionObjectLibs ("libutilityFunctionObjects.so");
        patches     ("wallbot");
//        outputControl   timeStep;
        outputControl   runTime;
        writeInterval   0.005;
    }

But problem is
How can I make it write in postProcessing directory as the results of probe appear?

I do not see how this will work. How will the solver pass the turbulence model information to the function object?