CFD Online Discussion Forums - wallShearStress Monitoring

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wallShearStress Monitoring

Hi Guys,
I am simulating a flow over an external body in which calculating wallShearStress is my major effort. I want to be able to monitor this field, therefore I can stop simulations whenever the value of this field gets steady.
Right now i am monitoring U field without any problems using probes function object.
As you know wallShearStress is defined on surfaces, I don't know how to monitor specified points on particular surfaces.
Is there any function object similar to probes that can handle surfaces?

Thank you very much,
Mojtaba

Hi,

Did you find an answer to this? I wrote a utility which writes out the wallShearStress at runtime using function objects and then tried using the patchCloud runtimeObject to extract the values over a set of points (see below) but it didn't work, I end up with no output files. However, if I tell it to probe pressure it works just fine...

If you haven't worked this out yet maybe together we can find a solution..

Best wishes,

Artur

Code:

samplingLine

{

    type            sets;

    functionObjectLibs ("libsampling.so");



    outputControl   outputTime;

    writeInterval   1600;



    setFormat   vtk;

    fields          ( p wallShearStress );



    interpolationScheme cellPoint;



    sets

    (

        plateProbePoints

        {

        type        patchCloud;

        axis        xyz;

        points

        (

            (0 0.01 0.05)

            (0.2 0.01 0.05)

            (0.4 0.01 0.05)

            (0.6 0.01 0.05)

            (0.8 0.01 0.05)

            (1 0.01 0.05)

        );

        maxDistance 0.1;    // maximum distance to search

        patches     (plate);

        }



    );

}

Quote:

Originally Posted by Artur (Post 463591)

Code:

samplingLine

{

    type            sets;

    functionObjectLibs ("libsampling.so");



    outputControl   outputTime;

    writeInterval   1600;



    setFormat   vtk;

    fields          ( p wallShearStress );



    interpolationScheme cellPoint;



    sets

    (

        plateProbePoints

        {

        type        patchCloud;

        axis        xyz;

        points

        (

            (0 0.01 0.05)

            (0.2 0.01 0.05)

            (0.4 0.01 0.05)

            (0.6 0.01 0.05)

            (0.8 0.01 0.05)

            (1 0.01 0.05)

        );

        maxDistance 0.1;    // maximum distance to search

        patches     (plate);

        }



    );

}

Hi,
Unfortunately I haven't found a solution yet. Well this is interesting. How have you been able to monitor a surface? You have monitored surface pressure successfully using this utility?
Can you upload your utility?

Quote:

Originally Posted by Mojtaba.a (Post 463694)

Hi,

The provided snippet, when put in the functions( ); in the controlDict will extract the pressure over a surface. The algorithm will snap the points from the specified locations to the nearest point on the surface and sample there (governed by the max distance). Say if my surface was at y=0 (which it is) it would sample at the x locations given and z=0.05. It won't do the wall shear stress though. Hence I modified the utility that calculates wallShearStess at runtime to dump the values to a file. I only coded it last night and can't spend too much time on it since it's just a side project and so it's not very well written and will dump the values for all cell centres of a specific patch (I need it for a 2D case and so that's good enough for me). If you need it only for monitoring convergence you can just pick a few points from there and look at their time trace and it should work just as well. See the dropbox link for a test case and the utility (I use OF 2.2.2) is attached..

https://www.dropbox.com/s/zuq0k17vhdik6bm/flatPlate.tgz

All the best,

Artur

Do you still have the case files?

Hi Artur,

Do you happen to still have the case files you posted the dropbox link for?

Cheers,

Hi,

This is a bit of a blast from the past. As such, I don't have the test case anymore and don't really have time to make a new one, but from what I can see it was just a flat plate with an extra function object. Have a look here to see how to include it in your simulation (tutorial 9):
https://github.com/UnnamedMoose/Basi...mmingTutorials

Also, I wrote the tool for OpenFOAM 2.2.2. Since then, the post-processing part of the code evolved a lot, so it's quite likely that you don't really need my code, unless, for some reason, you are stuck using the old OpenFOAM. Have a look at this official flat plate tutorial, for instance:
https://github.com/OpenFOAM/OpenFOAM...simpleFoam/T3A

Good luck,

Artur