Role of the foot chamber in the sounding mechanism of a flue organ pipe

Abstract

Two-demensional (2D) models of a flue organ pipe are studied with compressible fluid simulation, specifically compressible Large Eddy Simulation, focusing on the influence of the geometry of the flue and the foot on the jet motion and acoustic oscillation in the pipe. When the foot geometry is fixed, the models having a flue with chamfers show good performances in stabilizing the acoustic oscillation in the steady state. Furthermore, we find that the foot chamber works as a Helmholtz resonator. If the frequency of the acoustic oscillation in the pipe is higher than the resonance frequency of the Helmholtz resonator by almost the full-width at half-maximum, anti-phase synchronization between the acoustic oscillation in the pipe and that in the foot chamber occurs. In this case, the acoustic oscillation in the pipe grows rapidly in the attack transient and is stabilized in the steady state.