# Symmetry Plane not aligned to 0 along y direction

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February 26, 2022, 06:59
Plane does not snap completely to symmetry plane
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Hi guys,

Although I follow the forum for a long time mainly for OpenFOAM it's the first time I post a new thread as there's something that drivers me literally crazy.

I am conducting an external aero simulation in STAR CCM+ however I am facing one problem and I would like your advice/help.

Here's my setup:

I am provided a geometry of a vehicle which is already cut in half in order to be simulated as a symmetry problem. At y=0 is located the symmetry plane. I set up my case with no problems at all.

When I finish with the meshing, I create a plane and place it at (0,0,0) in order to post process my results. However the generated plane does not intersect with the symmetry plane but only at 1-2 very very small regions (see 1st attachment, I would expect all cells to be "beige" (=derived parts plane) instead of blue(=symmetry plane)). That means that my symmetry plane is not at 0,0,0 but further inside (y>0)

This is confirmed by moving the plane further in. Moving it by -1*10^(-9) the beige color does appear and now my plane snaps the symmetry plane. Now, it is the other way around. Blue turned into beige, beige into blue. (See 2nd attachment)

I wouldn't mind if all cells were blue. That means that my symmetry plane, thus my case is just further inside. What drives me crazy is that a fraction of cells is at y=0 and the remaining at y=-1*10^(-9).

My questions are:

1) First of all, why does this happen? The easiest guess is that my vehicle is not at position y=0. I checked that by trying to create a dummy block part. Then STAR embraced the vehicle's geometry by its 6 points (x_min, x_max, y_min, y_max, z_min, z_max) and y_min was 0. I understand that this is not the best way. Is there any other, more reliable way to check the origin of a geometry in STAR CCM?

2) Does this may lead to "wrong" results?

3) Does the already splitted in half geometry is responsible for generating this problem? Would it be better to insert it as a whole in STAR and then subtract it there from the domain?

Thank you for your time and I am happy to provide more information in case my description is not clear enough.

Best,
Yannis
Attached Images
 plane000.PNG (22.6 KB, 10 views) plane001.PNG (53.4 KB, 7 views)

Last edited by ybeis; February 26, 2022 at 08:38. Reason: Grammar, spelling