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Flow visualization and numerical analysis of a coflowing jet: a three-dimensional approach

Published online by Cambridge University Press:  21 April 2006

Juan C. Agüí
Affiliation:
Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA
Lambertus Hesselink
Affiliation:
Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA

Abstract

The instabilities of an acoustically excited coflowing jet are investigated by using a time series of cross-sections of large-scale structures present in the flow and by a fully three-dimensional numerical simulation via the vortex-element method. These structures are first revealed by a flow-visualization technique based on smoke seeding the inner jet flow and observing the flow cross-sections as the structures are convected past a stationary sheet of laser light. Usage of image-processing techniques along with computer graphics allows the full three-dimensional reconstruction of the structure. The general morphology of the flow is determined from the reconstructed views and shows that the vorticity is mainly concentrated into a single large-scale vortex ring. Hypotheses regarding the nature and origin of the longitudinal instabilities observed in the flow can be drawn from the reconstructed views, and are supported by the numerical simulations. Quantitative values such as the surface-to-volume ratio and the entrainment level are also obtained from the experimental data. The onset of stremwise vorticity and its distribution are derived from the numerical calculations as well. Three-dimensional views and a holographic display of a charactristic eddy are also presented.

Type
Research Article
Copyright
© 1988 Cambridge University Press

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