Tone production in Irish Flutes?

Question

Since it's about a technical issue, I thought that this question would fit in here the best (as opposed to the music.stackexchange-site): I'd like to know how tone-production in an irish (wooden) flute takes place: Namely, I'd like to know where exactly the stream of air is split and begins oscillating. To illustrate what I mean, I've drawn two little figures (A and B), and I'd like to know which of them is right.

Edit (because the figures seemed to be confusing): In both figures we see a stream of air directed on either of the two edges in the barrel of a flute mouthpiece, and respectively two streams of air flowing away from the edge, one to the insides of the flute, one to the outside. If an edge-tone develops, the air will (in either of the 2 figures) oscillate between the stream going inward the flute, and the stream going outward.

I always thought the air is split by the upper edge (as it is indicated in figure A). This does as well make sense to me because this edge is mutch more capable of splitting the stream of air.

However, a irish flute player I know suggested to me that instead it is the lower edge in the barrel of the flute where the stream of air is split. At first this seemed odd to me (because the edge is mutch less capable of actually splitting the stream of air there, which is required to generate oscillating air movements). However, this would explain why, when playing irish flute, many flute players suggest to blow "down the whole", instead of blowing on the edge.

So the question goes out to the community: Which figure is right, A or B? I'd be happy if you could provide a source of your knowledge, preferably somebody who either has worked with irish flutes a lot, builds them, or did observe the illustrated air-flows inside.

I'd be also happy if the answers stick to wooden (irish) flutes, as there might be a difference to silver-flutes.

Edit: I'm well aware that the phenomenon of tone production of wind being parted at an edge is called "edge-tone", and that this in fact is the source of the sound in irish flutes. The purpose of this question is, however, to find out where exactly this edge-tone is formed.

Answer 1

I think you are misunderstanding how the edge tone actually works. The flow pattern is oscillating between your diagrams A and B at the fundamental frequency of the note being produced (i.e. hundreds of times per second). If you blow in the right general direction so that the flow pattern is affected at all by the hole, the flow is unstable and the oscillations will quickly build up to their full amplitude.

There is an optimum blowing direction to get the most efficient energy transfer from the work done by the player in blowing, into sound produced. The optimum direction is "not" aiming directly at the lip of the hole, but over it, outside the instrument. The tutorial points out the common beginner's mistake of positioning he flute too high relative to the mouth - which is a natural mistake to make, if you wrongly think you have to "blow into the hole" to produce a sound.

This is perhaps more obvious looking at a modern concert flute, which has a plate attached to the outside of the instrument around the blowing hole, but all flutes work the same way.

This video tutorial makes it fairly clear that the player is not blowing "into" the flute: https://youtu.be/goCd1mEWsWs?t=49 In fact the lower lip is performing the same function as the plate on a concert flute, in directing the air flow over the hole not into it.

How practical instrumentalists describe what they do is psychologically useful (e.g. for teaching), but not necessarily physically accurate. For example in the video she talks about blowing "into" the flute, though that is not what she is actually doing!