a1 Laboratoire d'Hydrodynamique, CNRS – École Polytechnique, 91128 Palaiseau, France
a2 D'Alembert Institute, Université Pierre et Marie Curie (Paris 6), Boite 162, 4 place Jussieu, 75252 Paris Cedex 05, France
The acoustic field generated by the synchronized vortex street in self-excited hot subsonic jets is investigated via direct numerical simulation of the compressible equations of motion in an axisymmetric geometry. The simulation simultaneously resolves both the aerodynamic near field and the acoustic far field. Self-sustained near-field oscillations in the present flow configurations have been described as nonlinear global modes in an earlier study. The associated acoustic far field is found to be that of a compact dipole, emanating from the location of vortex roll-up. A far-field solution of the axisymmetric Lighthill equation is derived, on the basis of the source term formulation of Lilley (AGARD-CP, vol. 131, 1974, pp. 13.1–13.12). With the near-field source distributions obtained from the direct numerical simulations, the Lighthill solution is in good agreement with the far-field simulation results. Fluctuations of the enthalpy flux within the jet are identified as the dominant aeroacoustic source. Superdirective effects are found to be negligible.
(Received July 29 2009)
(Revised November 17 2009)
(Accepted November 20 2009)