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Computer simulation of the air flow
past a harmonica reed.
View of the reed is from the front, with the
plate on top and comb below.
The flow is traveling from top to bottom. Accordingly, this reed
is operating in its “closing” mode. (Simulations of
opening reeds are available through
info@turboharp.com)
The red region represents high velocity, and blue represents slow
flow. An increase of pressure above the reed causes it to close. In
the process, flow separation is observed on both lateral edges.
Due to the high velocity, there are some unsteady vortices formed
downstream.
When the reed is nearly shut, there is a very strong aerodynamic
instability observed. In some cases (e.g. certain brands of
harmonicas which will not be mentioned), this instability will lead
to torsional flutter of the reed, known to most players as that
annoying “dog whistle” sound.
Simulation courtesy of Dr. Greg Burgreen
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