No abstract

No abstract

Atmospheric temperature uctuation data collected from a Grumman Gulfstream II aircraft show features in temperature power spectral density functions that do not follow the expected ¡ 5 3 slope for homogeneous isotropic turbulence. Spectral analysis techniques show that these features result from the upstream propagation of a nondispersive acoustical wave. The source of the acoustical wave, which appears only at ight altitudes greater than 28,000 ft (8530 m), is attributed to engine acoustics in the form of jet screech where vortical structures interact with a quasi-periodic shock cell structure, both in the jet exhaust. The nature of the acoustical disturbance is shown to be dependent on velocity, with increased velocity resulting in a decrease in jet-screech peak frequency. These results are found to be consistent with those of other researchers investigating jet screech in jet ows.

No abstract