Friday, April 11, 2014

Seeing sound...

Seeing sound...  This NPR video nicely shows how Schlieren flow visualization works.  Here's a company that actually sells these systems.

Many years ago – in the late '60s – I briefly worked for a company that made electric coffee makers for passenger aircraft.  These were quite innovative at the time because they heated water on demand for brewing (today such systems are the standard, but back then it was bleeding-edge stuff).

One of the design challenges was making sure that no heat (in the form of hot air or water vapor) escaped the wrong parts of the coffee brewing machine.  To analyze this, the company I worked for built a fairly large (14" mirrors) home-made Schlieren flow visualization system, and part of my job was to keep it in alignment.  This was quite a tedious task, as the system wasn't very well built and parts kept moving with respect to each other – the slightest accidental touch of any component could throw the entire gadget out of whack.

When the Schlieren flow visualization system was working, though, it was almost magical.  Our system had a viewing screen under a hood, much like a rear projection camera lucida.  It also had an ordinary film camera for making permanent records.  When I was aligning the system, I'd put a cup of hot water in its field of view, and I never tired of watching the resulting patterns – a bit like watching the water flowing in a fast stream...

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