I for one would be VERY curious to see what a flute’s airstream would look like under this apparatus, especially the toneholes.
Somewhere, I think in a masters or PhD thesis linked to on this site, I have seen some. It must have been after this discussion https://forums.chiffandfipple.com/t/understanding-air-column-and-tone/70021/1 or maybe in the now broken link in one of the last few posts there.
Can’t find it now though.
A lot of studies using the Schlieren technique have come out of LAM (Laboratoire d’acoustique musicale, or Lutheries - Acoustique - Musique) in Paris, and other European centres. For example, Simplified models of flue instruments, and Aeroacoustics of the panpipes.
Numerical study on the function of tone holes… uses numerical models rather than Schlieren pictures, but it does have some pretty pictures of toneholes.
Flutopedia has some really cool animated Schlieren pictures of a fipple flute window, from a paper by Avraham Hirschberg in Dutch.