Please use this identifier to cite or link to this item: https://hdl.handle.net/2440/83303
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Type: Journal article
Title: An axisymmetric 'fluidic' nozzle to generate jet precession
Author: Nathan, G.
Hill, S.
Luxton, R.
Citation: Journal of Fluid Mechanics, 1998; 370:347-380
Publisher: Cambridge University Press
Issue Date: 1998
ISSN: 1469-7645
1469-7645
Statement of
Responsibility: 
G. J. Nathan, S. J. Hill and R. E. Luxton
Abstract: A continuously unstable precessing flow within a short cylindrical chamber following a large sudden expansion is described. The investigation relates to a nozzle designed to produce a jet which achieves large-scale mixing in the downstream field. The inlet flow in the plane of the sudden expansion is well defined and free from asymmetry. Qualitative flow visualization in water and semi-quantitative surface flow visualization in air are reported which identify this precession within the chamber. Quantitative simultaneous measurements from fast-response pressure transducers at four tapping points on the internal walls of the nozzle chamber confirm the presence of the precessing field. The investigation focuses on the flow within the nozzle chamber rather than that in the emerging jet, although the emerging flow is also visualized. Two flow modes are identified: a ‘precessing jet’ mode which is instantaneously highly asymmetric, and a quasi-symmetric ‘axial jet’ mode. The precessing jet mode, on which the investigation concentrates, predominates in the geometric configuration investigated here. A topologically consistent flow field, derived from the visualization and from the fluctuating pressure data, which describes a three-dimensional and time-dependent precessing motion of the jet within the chamber is proposed. The surface flow visualization quantifies the axial distances to lines of positive and negative bifurcation allowing comparison with related flows involving large-scale precession or flapping reported by others. The Strouhal numbers (dimensionless frequencies) of these flows are shown to be two orders of magnitude lower than that measured in the shear layer of the jet entering the chamber. The phenomenon is demonstrated to be unrelated to acoustic coupling.
Rights: © 1998 Cambridge University Press
DOI: 10.1017/S002211209800202X
Published version: http://dx.doi.org/10.1017/s002211209800202x
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Mechanical Engineering publications

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