Experimental Investigation on the Jet Noise Sources for Chevron Nozzles in Under-expanded Condition

Abstract

Additional noise sources known as Screech and BBSAN are common in jet noise for imperfectly expanded jet flow. They are generated by the interaction between the instability waves that propagate from the lip of the nozzle and the shock-cells shock cell structures. In this study, thorough experimental investigations have been carried out on chevron nozzles to assess the importance of chevron parameters such as the number of chevrons (chevron count) and chevron penetration. Data were acquired in the state-of-the-art aeroacoustic facility at the University of Bristol. Acoustic measurements such as overall sound pressure level, spectra, and directivity along with near-field measurements have been made for jet Mach numbers ranging from M = 1.1-1.4. Fourier-based and Wavelet-based analyses have been used to highlight the different features of the various tested nozzles.