CFD Online Discussion Forums - Surface Sampling

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Surface Sampling

Dear Foamers,

I have an engine case where I need to extract velocities on different cut planes.
To do that I am using sample utility in OpenFoam with a format raw (which gives the coordinates and the velocity components). Later I am plotting the 2D velocity vectors in Matlab. But since the mesh is not an evenly spaced grid , I am having some issues in creating the contours and vectors.

My question is there a way I could get the velocities on a regular grid (like remapping the sampled velocity on an evenly spaced grid)? Or a surface write format which writes the sampled data at regular intervals given a dx , a dy and start and end points? I am aware that line sampling can do that, but I need surface sampling in this case.

Thanks for your time.

Well I had to provide a cloud of points using set sampling to get what I wanted.It works but creating a cloud is not fun, especially if the domain is big and we want to sample at many points.

Thanks !

Another question is that when we provide the coordinates of several points to sample, and say a point A(0.5,0.5,0.5) lies outside our solution domain , then the sample utility does not output any value at that point (I am using "raw" write format).

All I want is that OpenFOAM outputs "NaN" values at all those points which lie outside the domain. Does anyone have an idea about how to accomplish this?

Thanks in advance !

Quote:

Originally Posted by AA29 (Post 504697)

Hi, I am wondering if you were able to make OpenFOAM output NAN for the points which are outside your domain. Thanks.

Sample on array of points

I also needed to sample on set of points on a surface and found a solution.

It's possible to sample on a surface drawn in a CAD program (I use blender), which is exported as stl. If you draw the points where you need to sample and connect them as a surface, it is possible to sample on these points.

You can then add to your controlDict (openfoam.com v2012):

Code:

planesVelocity

{

     type            surfaces;

     libs ("libfieldFunctionObjects.so");

     enabled         true;

     writeControl    runTime;//Writes data every writeInterval seconds of     simulated time. 

     writeInterval 0.001;

     interpolationScheme cellPoint;

     surfaceFormat raw;

     surfaces

     (

         y0

         {

             type            sampledTriSurfaceMesh;

             surface         y0.stl;

             interpolate     true;

             source insideCells;

         }            

     );

     fields

     (   

         U 

         turbulenceProperties:R

     );

}

For the setting source I find:
source=insideCells, interpolate=true Per surface point interpolate cell containing it.
https://cpp.openfoam.org/v4/classFoa...rfaceMesh.html . The stl file is located in constant/triSurface

I didn't check thoroughly, but values outside the domain seem missing. I will write a script (Python) to add the missing coordinates and set them to NaN.