Multi-pass and interrogation area size selection

[Rainy shi]

Hello,

Does a too large window (maximum displacement of only 1/25) affect the accuracy of the results (low particle concentration, guaranteed 10 particles in the window). Is it necessary to use multiple passses? what is the meaning of multiple channels, and is it feasible to use only a single channel to ensure displacement and particle concentration?

I am going to publish a paper, recommend one of your papers for me to cite!

Best Regards

Thank you!

[William Thielicke]

Hi, what do you mean by 1/25 ? You should aim for a displacement around 2 to 8 pixels or so. Large interrogation areas are good and will only limit your resolution.

Multiple passes are always better and have less noise and bias. What do you mean by multiple channels?

Thus is my latest paper on PIVlab:

Thielicke, W., Sonntag, R. (2021) Particle Image Velocimetry for MATLAB: Accuracy and enhanced algorithms in PIVlab. Journal of Open Research Software, 9: 12. DOI: https://doi.org/10.5334/jors.334

[Rainy shi]

Thank you for your reply, the maxiumum displacement is 4 pixels while the  interrogation area size is 100*100 pixels . And the particle diameter = 2 pixels, the article density = 10，the diameter of the pixel point is 0.085mm.Is the interrogation area size reasonable?  How large will be the error of a single pass compared to multiple pass (ensure 1/4 rule and   Particle density).  Besides, ' multiple channels'  should be  multiple passes .

[William Thielicke]

The error is always very difficult to assess with piv. But your settings sound fine this will give good results. Please check my phd Thesis for more information

https://research.rug.nl/en/publications/the-flapping-flight-of-birds-analysis-and-application

[Rainy shi]

Thank you！ That's help me a lot.