Smoothing question

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Claudia Sanhueza Claudia Sanhueza
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Smoothing question

Hello,

I would like to say that english is not my first lenguaje so I'm really sorry about grammatical mistakes in this text.

I been working with PIVlab analyzing the vortex shedding downstream a cylinder in a flume with water, after processing the vector field I make the vorticity map and I noticed that, when I use the smoothing tool, the vorticity range changes depending on how strong is the smoothing, for example, if I put the smallest smoothing the vorticity is between 15 and -15 (1/s) but with the biggest smoothing the vorticity is between 6 and -6 (1/s).

So I would like some advices about how choose the right amount of smoothing. The bigger, the better??

Thanks a lot,
Claudia Sanhueza.
Stephan C Stephan C
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Re: Smoothing question

I expect this behavior to be very normal, since vorticity is calculated as a derivative quantity. Smoothing is exactly smoothing out any gradients, thus lowering your vorticity.
Therefore my best guess is that no smoothing at all is the best option.
William William
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Re: Smoothing question

In reply to this post by Claudia Sanhueza
Hi,
this is correct, smoothing lowers the gradients. And the question how much smoothing should be applied is not so easy to answer. PIV introduces some noise to the measurement, and ideally you would smooth out only this measurement noise. The noise is very low in many cases (but that depends a lot on the quality of your images). I would recommend the lowest smoothing setting. It will reduce noise in your data (from whatever source it may come...) but it will not affect your results too much...

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Claudia Sanhueza Claudia Sanhueza
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Re: Smoothing question

Hi

I attached some images so you can see. I think my images have some noise so it's better to smooth them

This is the original photo

This is the piv

This is the vorticity field


I realize that the difference if I make a small smooth it's not big, so I think is the best option.