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-   -   Using Probe for part of a patch (http://www.cfd-online.com/Forums/openfoam-solving/67661-using-probe-part-patch.html)

ndr August 22, 2009 06:58

Using Probe for part of a patch
 
Hi everybody,

I'm using a slightly modified rhoTurbFoam solver with an additional field to calculate the temperature gradient for each timestep at a wall with constant temperature (based on the wallGradU tool). The field for wallGradT is zero for the internal field and only takes values at boundaries. The output of wallGradT within each timestep looks ok.

To monitor the temperature Gradient over time I tried to use the probe utility with two points which are part of the wall. But the probe only returns zero for those points and all timesteps. The code inside the ControlDict looks like this:

Code:

functions
(
    probes
    {
        type probes;
        name probes;
        functionObjectLibs ("libsampling.so");
        probeLocations
      (
        (0.025627 0 -0.00023237)
        (0.0518278 0 -0.000461021)
        );
        fields
        (
        wallGradT
        );
    }

Using the sample utility for the complete patch I get the correct values of wallGradT at exactly the coordinates used for the probe but sample is writing a new directory for each time step and I would like to get one single file with all data for the two points.
The same problem occurs if I try to monitor the temperature which is constant at the wall by definition. While sample returns the constant value, using probe at the same points results in a non-constant temperature.

Any ideas why? Is there any chance to get the probe utility to work for points that are part of a patch?

Thanks a lot

Nils

ndr August 27, 2009 06:45

Nobody got any ideas how to fix this?

sven November 5, 2009 23:59

Hey Nils,

how exactly do you use the wallGradT? I only know it to use it as a post-processing tool. How can I use it in such a way, that I can probe the walltemperature Gradient with time?

ndr November 6, 2009 06:29

Hi Sven,

I did not succeed to use the probe utility, so post-processing really seems to be the only way to use wallGradT right now, writing the results into the time directories.
As far as I know to create data over time you will need to extract the wallGradT sets out of each time directory. Another possibility would be to use Paraview, which should be able to plot a variable over time for a specific point of your grid, but as I do not use Paraview most of the time I don't know the details.

sven November 7, 2009 21:51

Hey Nils,

I found another way to deal with the wallGradT. You can let it write out by your solver, see http://www.cfd-online.com/Forums/ope...tml#post235428. Then the solver writes out GradT for every timestep in the according folder. Then it is also possible to probe the GradT. However, so far I dont know how to probe at a patch in order to get wallGradT. I ll let you know if I find out!

PS: Are you studying Aerospacce engineering in Stuttgart? If so, I know you!

Cheers Sven

ndr November 8, 2009 04:47

Hey Sven,

yes I am and I know you too.

Regarding the solver modification: It is a possibility, especially for the wallGradT field. But to get the Nusselt number and still have a solver applicable to several cases you will have to define the reference temperatures within a properties file and let the solver read them from there. Otherways you will have to change the solver every time you calculate another case.

Thanks for thinking about the probing problem. Personally I think I will use some kind of script to extract the values I need out of the several time directories and write them into a new data file. It seems easier than getting OpenFOAM to probe at walls...


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