Studies on tapered resonance tubes

This paper studies the effect of spacing on the acoustic spectra and directivity of a tapered resonance cavity kept axi-symmetrically in the flow field of a supersonic jet. A parametric study is conducted for various spacings and nozzle pressure ratios. Fundamental frequencies of the tapered cavities for the range of parameters considered are about 500Hz above the fundamental frequency of corresponding case of the cylindrical cavity. The preliminary results indicate that the spacing influences the spectra, and for certain spacings, the fundamental frequency (f1) of the tapered cavity is higher by around 3 times than that of the cylindrical cavity, as manifested in the spectra. The formation of intermediate frequency component between the fundamental frequency and the first harmonic and the disappearance of the intermediate frequency with a slight change of spacing is clearly depicted in the spectra. The periodic variation of fundamental frequency and its occurrence at common positions are discussed.