Experimental investigation of the role of instability waves in noise radiation by supersonic jets

Existing ideas of instability waves as the main dynamic noise sources in supersonic jets are tested for conformity with the data of acoustic measurements of this noise. Methodologically, the problem consists in the verification of the main principles of Tam’s theory of noise radiation by supersonic jets based on the ideology of instability waves in the shear layer of the jet and their key role in noise generation. Technologically, the study is based on a new technique for measuring the noise, namely, the azimuthal decomposition method developed by the authors. It is shown that on the Strouhal number range from 0.03 to 0.35 the theory satisfactorily describes the radiation pattern of the individual harmonics, while the initial amplitudes of the instability waves are in qualitative agreement with the assumption of their uniform distribution near the nozzle edge.