Noise Excitation Source

We need to augment the model to explain how the instrument is excited. Flute players blow a jet of air against a sharp edge, which is placed on the boundary of the pipe. The jet is unstable and tends to flow on only one side of the edge. However, since the attached tube tends to resonate only at harmonics of the fundamental frequency of the tube, the tube causes the jet to switch back and forth between flowing on either side of the edge. This switching occurs at approximately the fundamental frequency of the note being played.

The switching of the jet causes the end of the jet to break up into vortices and turbulence. This nonlinear effect causes noise pressure waves to be injected into the tube [2]. This noise excites the tube can be included in the model as shown in Figure 2. The degree of noise excitation is related to how hard the flutist is blowing. Note that this noise is broadband since it contains energy at all of the frequencies in the audible spectrum.

Figure 2: Simplified flute model including a noise excitation source