Acoustic properties of aircraft wake vortices

Abstract

The noise generation by aircraft wake vortices has been studied numerically and experimentally. The numerical study revealed a relation between the circulation Γ, the vortex core size rc and the frequency fa of the peak level in the vortex noise spectra, fa ≈ Γ/(2π rc)2. The experimental data were obtained in measurements at airports applying phased microphone arrays. It has been revealed that sound sources are closely located to the vortex cores. The focused noise spectra of the wake vortices of all measured aircraft types are dominated by two maxima. The second maximum at f = 100 Hz is clearly caused by wake vortices. The origin of the first at 12 Hz has not been identified. Wake vortices were acoustically detected in 80 percent of the flyovers. Lowest detection rates were observed for the newer aircraft types Airbus 319, 320 and Boeing 737-800. A comparison of the wake trajectories obtained by phased microphone arrays and LIDAR revealed that the detection capability of the latter is superior.