The turbulence structure of a circular air Jet is studied by correlating both full- and narrow-band signals from locally displaced microphone probes. A high degree of statistical interdependence is found for the pressure in planes normal to the axis, in particular, for frequency components at St = 0.5, where the bulk of the fluctuating near-field energy is con¬centrated. The axisymruetric content of the turbulence travels downstream in an almost deterministic wave-like manner. With the turbulence being everything but isotropic, some of the assumptions common in jet-noise theory are re-examined and an alternative model suggested. The continuing work was stimulated. by and may contribute to the controversy about the degree of order in jet turbulence as disputed on the Aerodynamic Noise Symposium at the Loughborough University in 1970 [24] .
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