Noise generated by a thin wing in a turbulent jet.

Linearized equations of motion describing a compressible, unsteady, viscous gas under the influence of an externally applied fluctuating force field are examined. The response of the medium is split into a near-field viscous wake mode and a far-field acoustic wave mode. The resulting modal equations are then used to predict both the undulating viscous wake and the far-field acoustic wave emitted by a thin wing (modeled by a dipole force field) in a cylindrical slug jet. The directivity pattern of the acoustic wave which propagates into the quiescent region beyond the jet is compared with available experiments. The peak frequency of the broad-band noise generated by upstream turbulence is also calculated and compared to published data.