ASA 125th Meeting Ottawa 1993 May

2pNS3. Jet noise generation mechanism.

Seungbae Lee

William C. Meecham

Dept. of Mech., Aerosp., and Nucl. Eng., Univ. of California, Los Angeles, CA 90024

The breakdown process of the initial large-scale structures into substructures near the end of the potential core is examined and the production of aerosound as a result is discussed. The quadrupole-like directivity pattern of jet noise is numerically obtained by applying the large-eddy simulation (LES) technique for the fluid flow. The Lighthill analogy is used to obtain the acoustic far field. Most of the sound comes from a region near the end of the potential core. A discussion to explain this quasiaxisymmetric directivity pattern is given. The directivity maximum is obtained at about 45(degrees) from the axis of the jet exhaust. This will be explained in terms of turbulent velocities. The convective effect on sources is introduced by ray tracing to calculate retarded times. The result is to obtain more radiation downstream, as is observed. The relation of this correction to the Lighthill theory will be discussed.