Air Jet Dynamics in a Flue Instrument

Abstract

In a flue instrument such as the recorder, an air jet undergoes an oscillatory motion with the jet directed alternately to either side of the labium. The dynamics of that oscillation, including the trajectory followed by the jet, depends on the jet speed, a parameter controlled by the blowing pressure. We describe new studies of how the jet oscillations depend on blowing pressure in a recorder. Small Pitot-tube-like pressure sensors are installed in close proximity to the labium tip of a soprano recorder, with two sensors above the tip and two below. The pressures at these four locations give the timeaveraged spatial profile of the air jet. This profile is observed to change as the blowing pressure is increased from low values, where the note C5 is produced, to high pressures where the note an octave higher, C6, is sounded. Additionally, it was found that different spatial profiles are found for C5 and C6 even when they are produced at the same blowing pressure. We have compared the experimentally measured jet profiles with the results of Navier-Stokes-based simulations of the same instrument geometry under the same blowing conditions, and find similar variations in the timeaveraged jet profiles. The simulations also give the timeresolved jet profiles, which provide further insight into this behavior.