Sound Generation by Aircraft Wake Vortices

This report provides an extensive analysis of potential wake vortex noise sourcesthat might be utilized to aid in their tracking. Several possible mechanisms of aircraftvortex sound generation are examined on the basis of discrete vortex dynamic modelsand characteristic acoustic signatures calculated by application of vortex sound theory. Itis shown that the most robust mechanisms result in very low frequency infrasound. Aninstability of the vortex core structure is discussed and shown to be a possible mechanismfor generating higher frequency sound bordering the audible frequency range. However,the frequencies produced are still low and cannot explain the reasonably high-pitchedsound that has occasionally been observed experimentally. Since the robust mechanismsappear to generate only very low frequency sound, infrasonic tracking of the vortices maybe warranted.