Flow sensing (Doppler) "outside" the pipe - anyone did it before?

[wdmagic]

here is a good link to more info on what your wanting to do, scroll down about halfway, I have only seen stuff done with thermal mass flow meters, and venturi meters. but his page has some formulas and such that may help.

LINK

[flotulopex]

Yup, I googled that one already.

It would be nice to have some "practical" info, schematics or experience from someone.

[LinkMTech]

I read about this sometime ago where the water flow sound was measured using a mic at various flows to get a reasonable flow rate measurement but can't recall the published paper.
I did find this simple project using a piezo transducer and an Arduino. Though written in C, the build directions are spelled out so it can be converted to PBP.