Self-Sustained Oscillation in a Circular Jet with a Coaxial Pipe. Influence of the Initial Conditions on the Characteristic of Self Excited Tone.

Abstract

Using a quiet jet facility the relationship between self-excited oscillation of the round jet impinging upon a pipe's leading edge and its radiation field was studied experimentally in Reynolds number based on momentum thickness range 144≤Reθ≤502. A pipe's leading edge intercepts a laminar free shear, the shear layer can be into oscillation, depending on the convectional speed and the regular interval of discreat vorticies. The oscillation can produced resonance of air column in a pipe as the oscillation mode become characteristic frequency of pipe length with increase impingiment length. The principal results are as follows : self-excited oscillation were observed in non-dimensionalized dominant components and impingiment length range 0.0028≤βθ/u≤0.21, 18≤l/θ≤380, they are associated with the nonlinear saturation of the unstable wave amplitudes of the shear layer occuring at the vortex-vortex interaction ; the locations and acousitic power of the resonance can estimated from emprilcal curve in figure 4 and emprical equation (2) ; resonance tone are completely disappeared when the free shear layer become to turbulent by enhancement of the tripping wires.