Numerical Study of Sound Refraction by a Jet Flow. I. Ray Acoustics

Sound rays are traced numerically from a point source on the axis of a jet flow with realistically chosen velocity profiles. The directivity patterns computed from the ray paths have no cone of absolute silence, in contrast with analytic results for nonspreading jets. A related observation is that the surfaces of constant phase are ultimately spherical. Nevertheless, the computed axial refraction valleys are much deeper than those observed in jet noise studies. The difference is due to diffraction, which tends to offset refraction effects at all but the highest (ray-acoustic) frequencies.