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Natural instability of free shear layersUnder controlled small-amplitude excitation, an initially laminar free shear layer experiences maximum growth rate at a Strouhal number St(theta) of 0.017 (consistent with theory) and maximum growth at St(theta) = 0.011, while the natural instability frequency St(theta-n) (of an unexcited shear layer) is found to have an intermediate value. Investigations in both axisymmetric and plane shear layers in a number of independent facilities reveal that the St(theta-n) value falls in the range 0.0125-0.0155, depending on the exit boundary-layer fluctuation level and the spanwise radius of curvature. The St(theta-n) value decreases with increasing jet diameter or exit boundary-layer fluctuation level, but is not a direct function of the exit momentum thickness Reynolds number. For a given facility, the instability details are found to be independent of whether the entrainment at the lip is parallel to the stream or orthogonal (due to the addition of an end plate). The steamwise evolutions of the amplitudes at the fundamental frequency and its harmonics and subharmonics are unique functions of the downstream distance nondimensionalized by the exit momentum thickness, but their details remain functions of the flow geometry (i.e., axisymmetric or plane).
Document ID
19840027345
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Husain, Z. D.
(Houston Univ. TX, United States)
Hussain, A. K. M. F.
(Houston, University Houston, TX, United States)
Date Acquired
August 12, 2013
Publication Date
November 1, 1983
Publication Information
Publication: AIAA Journal
Volume: 21
ISSN: 0001-1452
Subject Category
Fluid Mechanics And Heat Transfer
Accession Number
84A10132
Funding Number(s)
CONTRACT_GRANT: NSF MEA-81-1676
CONTRACT_GRANT: NSG-2337
Distribution Limits
Public
Copyright
Other

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