Broadband shock-cell noise signature identification using a wavelet-based method

Civil and military aircraft manufacturers need to respond to increasingly more restrictive standards about noise emission. In order to fulfil those requirements the mechanisms underlying the noise production need to be understood. The supersonic jets at the exit of aircraft engines are known to contain several sources of noise, namely: screech (military air-crafts), Broadband Shock–cell Associated Noise (BBSAN) and large–scale structures. The current work is focused on the study of BBSAN by means of a wavelet–based technique. The technique was applied to a pressure nearfield line array for the sake of extracting the ’signatures’ related to noise production mechanisms. Each ’signature’ characterized by its shape and time–scale. The signature found up to approximatively x/D = 6D has a ’wave– packet’ like shape. The same shape is obtained at farfield locations for forward angles. The Sound Pressure Level (SPL) was computed using the nearfield signatures and it is in good agreement with the SPL computed using the pressure signals. The ’wave–packet’ like shape ’signature’ is associated to BBSAN as it has the same characteristics: same SPL and forward angles directivity.