I have designed and made a few PIV test apparatus in the past. I have also developed an open-source PIV code that is currently available on GitHub.
Many people have used the code and it has even appeared in a couple of publications so far. It's also the first Google suggestion for thePIV code keyword.
Sample Images and Video:
Results:
> Velocity Vectors
> Streamlines
> Correlation Coefficient
My PIV code is freely available on GitHub:
Please use the Python version if possible. The Matlab version has not been maintained for a long time.