I have a theory involving aerodynamics and sound

[Jason Summer]

I was pondering to myself one day "how does a flute work?". It bothered me because I knew that our voices and reed instruments work by vibrating quickly, which pushes the air, creating a pressure wave. This couldn't be the case with flutes because the mouthpiece does not move.

All I could find was preschool explanations. I wanted the college professors explanation.

So lacking any support from the internet, I devised a theory on how the sound is produced when a flute is blown. I am looking for opinions and constructive analysis. 

When a flautist blows over the hole just right, the hole disrupts the stream causing oscillating eddies. 

These eddies are the pressure wave. They bounce around against the walls, causing the air inside to vibrate at the frequency of these eddies. When a hole is opened, like when the flautist releases their finger, the resonant property of the air is reduced, raising the frequency. 

So how far off the mark do you suppose I am?

I am no master in fluid dynamics, I just thought it would be fun to do some science: observe, collect data, use data to form a theory to explain a phenomenon.

Edited April 29, 2018 by Jason Summer

[MigL]

I could be wrong, but I would think that the flute, with its holes, is a variable length resonating cavity, much like the differing lengths of pipe on a pipe organ, the blocking/unblocking of holes alters the tube length, and so the resonant frequency, corresponding to the various musical notes.

This would mean that the initiating vibration has to occur in the mouthpiece.
Unfortunately I have no idea what composes the mouthpiece on a flute, as the only exposure I've ever had to flutes was from an episode of Star Trek TNG called 'The Inner Light' ( one of my favorites ).

[Jason Summer]

Yes, I think so. My main concern was figuring out how organs, whistles, and flutes make their sound, since they don't have any moving membranes like other instruments.

[Strange]

Isn't this an example of the Bernoulli effect? The air flowing over the opening reduces the pressure and draws some air out. The low pressure wave flows down the tube and is reflected back from the end causing an oscillation at the resonant frequency of the tube.

Anyway, I have always assumed that is how it works. Not sure how the holes in the tube tune the frequency though ... does the wave get reflected back from the place where a hole is? But I don't see why that would happen...

Edit: I just found this, which suggests that you were closer then me: http://www.lewpaxtonprice.us/fltphys.htm

But it is complicated; especially when it comes the function of the holes!

Edited April 30, 2018 by Strange
link

[Jason Summer]

So the holes being opened actually causes less resistance of movement within the chamber, which speeds up the cycle. Nice!

[studiot]

Flutes and recorders act as open pipes.

Reeded instruments like the clarinet act as closed pipes.

A pipe has a node at a closed end and an antinode at an open one.

https://www.google.co.uk/search?source=hp&ei=GinnWoSGNYakwAL816mgCg&q=is+a+flute+open+or+closed+at+the+end&oq=is+a+flute+open+or+closed+at+the+end&gs_l=psy-ab.3..33i22i29i30k1l5.1682.8680.0.9153.36.35.0.1.1.0.124.3295.24j11.35.0....0...1c.1.64.psy-ab..0.34.3130...0j46j0i131k1j0i46k1j0i131i46k1j46i131k1j0i3k1j0i10k1j0i22i30k1.0.Hg4WwcekEgc

Edited April 30, 2018 by studiot

[Enthalpy]

The tone holes act on the height by changing the length of the vibrating air column hence the resonant frequencies. Pretty much any book gives a decent first-approach explanation to this. Building instruments would need more than a first approach.

The embouchure of a wind instrument must provide air when the pressure is high in the tube, or pressure when air enters the tube. Many attempted explanations would like to see the other way, which would dampen the oscillation instead of keeping it. Good first filter among the explanation attempts. For instance lewpaxtonprice.us fails: it explains why there is no vibration, regrettably.

Bernouilli: then you must still explain why the suction is stronger when the vibrating air exits the tube.

My proposal: when air already enters the tube, it draws the blown jet inside, especially near the first edge of the blow hole. The second edge then directs more blow air inside. When the vibration lets air exit the tube, more blow air is directed outside. This provides power to the oscillation.

Most authors want to inject turbulence and eddies in the explanation, but here I don't need any.

Edited May 1, 2018 by Enthalpy