In an attempt to explore the existence of large-scale coherent structures in the nearly self-preserving region of an axisymmetric free air jet, a 2.54 cm air jet at a Reynolds number ReD = 6.8 × 104 has been investigated for x/D≥40 via both long and short time-averaged space-time correlation measurements. Conventional space-time correlation data with probe separations in the stream wise direction by as much as 25 diameters suggest the passage of large-scale organized structures. The radial extent of these structures is about one local jet diameter, and the azimuthal extent is about a quadrant of the cross-section. Recurring quasi-periodic patterns are observed in the time series of short time-averaged correlations between longitudinal velocity fluctuations obtained with two arrays of hot-wires separated in the streamwise direction. These orderly patterns provide direct evidence for the existence of these structures. Quantitative details of these structures are now being investigated.
Search for Large-Scale Coherent Structures in the Nearly Self-Preserving Region of a Turbulent Axisymmetric Jet
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Tso, J., Kovasznay, L. S. G., and Hussain, A. K. M. F. (December 1, 1981). "Search for Large-Scale Coherent Structures in the Nearly Self-Preserving Region of a Turbulent Axisymmetric Jet." ASME. J. Fluids Eng. December 1981; 103(4): 503–508. https://doi.org/10.1115/1.3241759
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