Schlieren imaging of loud sounds and weak shock waves in air near the limit of visibility |
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Authors: | Michael John Hargather Gary S Settles Matthew J Madalis |
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Institution: | (1) Experimental Aerodynamics Division, National Aerospace Laboratories, Council of Scientific and Industrial Research, Bangalore, India |
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Abstract: | A large schlieren system with exceptional sensitivity and a high-speed digital camera are used to visualize loud sounds and
a variety of common phenomena that produce weak shock waves in the atmosphere. Frame rates varied from 10,000 to 30,000 frames/s
with microsecond frame exposures. Sound waves become visible to this instrumentation at frequencies above 10 kHz and sound
pressure levels in the 110 dB (6.3 Pa) range and above. The density gradient produced by a weak shock wave is examined and
found to depend upon the profile and thickness of the shock as well as the density difference across it. Schlieren visualizations
of weak shock waves from common phenomena include loud trumpet notes, various impact phenomena that compress a bubble of air,
bursting a toy balloon, popping a champagne cork, snapping a wooden stick, and snapping a wet towel. The balloon burst, snapping
a ruler on a table, and snapping the towel and a leather belt all produced readily visible shock-wave phenomena. In contrast,
clapping the hands, snapping the stick, and the champagne cork all produced wave trains that were near the weak limit of visibility.
Overall, with sensitive optics and a modern high-speed camera, many nonlinear acoustic phenomena in the air can be observed
and studied. |
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Keywords: | |
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