In this paper time-resolved, two-dimensional digital particle image velocimetry measurements are presented, which document the flowfield over a 75-deg sweep delta wing at 40 deg angle of attack. The data were taken at a sampling frequency of 500 Hz, which is two orders of magnitude greater than any reported in literature to date. This allows to examine the temporal evolution of vortex breakdown in form of instantaneous sectional streamlines and vorticity contours and to provide for the first time non-invasive spectral information in the breakdown region. It is thus possible to trace accurately the source of the oscillating signals and the corresponding frequencies and connect them to the temporally evolving flow patterns. The oscillations and corresponding frequencies are shown to be caused by a specific motion of the vortex core. The core forms a helix, which spirals in the opposite sense than vorticity lines upstream of breakdown and with in the sense of the vorticity upstream of breakdown. At the same time, the helix is stretching in the downstream direction. New evidence also indicates that the spiraling vortex core entrains fluid as indicated by the stable character of the streamlines in the center of the vortex. However, the axial flow velocity is significantly reduced after breakdown, and reversed flow is observed in some place, but there is no consistent volume containing uniformly reversed flow.
High-speed digital-particle-image-velocimetry study of vortex breakdown
Untersuchung des Wirbelzerfalls über einem Deltaflügel mit digitaler Hochgeschwindigkeits-Teilchenbildgeschwindigkeitsmessung
AIAA Journal ; 43 , 3 ; 642-650
2005
9 Seiten, 8 Bilder, 31 Quellen
Aufsatz (Zeitschrift)
Englisch
FLUID DYNAMICS - High-Speed Digital-Particle-Image-Velocimetry Study of Vortex Breakdown
Online Contents | 2005
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