Effect of pressure rise time on starting transients of flue pipes

Abstract

A special wind supply provides adjustable rise time Tr. Adjustable closed and open pipes having frequencies 198 to 256 Hz are studied. The steady‐state supply pressure is 530 Pa. The precursor, at several times the fundamental frequency, and a subsequent burst dominated by the next mode above the fundamental are strongest for Tr between 1 and 10 fundamental periods, but may vanish for larger or smaller Tr. For nearly harmonic pipe resonances, the fundamental and higher components can grow simultaneously, and the burst may exceed the steady‐state amplitude. For more inharmonic modes (e.g., a wider pipe) the fundamental quenches the burst when the overall amplitude is well below steady state. External sound at the fundamental frequency suppresses both the precursor and the subsequent burst. Important features of the experimental results occur in a computer model that involves time‐delayed nonlinear feedback and uses simple oscillators to represent resonator modes [N.H. Fletcher, Acustica 34, 224–233 (1976)]. With numerical rather than analytical solutions it is possible to treat the realistic case of the fully switched jet.