Hi Ehsan,

I'm pretty sure this is linked the continuity   of the solution spatial derivatives across elements boundaries, I've always had similar "issues" with derived quantities, like vorticity and Reynolds stresses. 
Please keep in mind that the Reynolds stresses are usually evaluated by taking the spatial derivatives of the continuous velocity field, once you calculate the derivative it's highly likely that you end up with a "less smooth" function and possibly discontinuous across large elements boundaries.

I would rather try to refine a little bit in order to preserve gradients smoothness across the elements boundaries. That is, scaling down the elements size relatively below the sharp gradients length scale.

Or try some post-processing interpolation to smooth out the gradients.

Hope it helps

Regards

Saad


On Thu, Sep 28, 2023, 15:17 Ehsan Asgari <eh.asgari@gmail.com> wrote:

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Dear All

I am doing a quasi 3-d simulation with a periodic direction in Z. When I use the "ReynoldsStresses" filter, I get a smooth time-averaged velocity, but I see the footprints of macro-elements on the Reynolds stress contours.
I wonder why this can happen, as the Reynolds stresses are derived directly from the velocity and as far as I can tell, the representation of velocity contours is fine.

Is there any reason that can explain this?

Kind regards
syavash
 
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