| アブストラクト: |
The topic of excitation of acoustical resonance by air jet has been investigated since quite a time resulting in some controversial conclusions as to importance of volume flow or vortex dissipation. The theory of vortex sound (Powell 1964, Howe 1975) is applied to wind instruments, e. g. the flute. The source terms (vortex sound) of the jet-labium interaction are measured with a new technique, the Particle Image Velocimetry (PIV). It allows a quantitive determination of the velocity fields.The source terms are deduced from the vorticity, the jet speed and the acoustical field. Actually they represent the fluid dynamical counter part of what is known as "Weisskopf units" in nuclear gamma transitions. A far field comparison of the source terms with the acoustical
power radiated by the flute at different jet speeds and frequencies is presented.
As as a side observation the coverage of the embouchure with the jet can explain the conditions necessary to efficiently excite a low tone without overblowing. |
