title: On the wavenumber spectra for sound within subsonic jets.
abstract: This paper explores the nature of sound spectra within subsonic jets. Three problems of increasing complexity are presented. First, a point source is placed in a two-dimensional plug flow and the sound field is obtained analytically. Second, a point source is embedded in a diverging axisymmetric jet and the sound field is obtained by solving the linearized Euler equations. Finally, an analysis of the acoustic waves propagating through a turbulent jet obtained by direct numerical simulation is presented. In each problem, the pressure or density field is analyzed in the frequency-wavenumber domain. It is found that acoustic waves can be classified into three main frequency-dependent groups. A physical justification is provided for this classification. The main conclusion is that, at low Strouhal numbers, acoustic waves satisfy the d'Alembertian dispersion relation.
authors.affiliation: Department of Engineering, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Agarwal
authors.affiliation: Faculty of Engineering and the Environment, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom.
authors.forename: S
authors.initials: S
authors.lastname: Sinayoko
authors.affiliation: Faculty of Engineering and the Environment, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom.
authors.forename: R D
authors.initials: RD
authors.lastname: Sandberg