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Organized motions in a jet in crossflow

Published online by Cambridge University Press:  25 September 2001

A. RIVERO
Affiliation:
Departament d'Enginyeria Mecànica Escola Técnica Superior d'Enginyeria Química (ETSEQ), Universitat Rovira Virgili, Ctra. de Salou s/n, 43006-Tarragona, Catalunya, Spain
J. A. FERRÉ
Affiliation:
Departament d'Enginyeria Mecànica Escola Técnica Superior d'Enginyeria Química (ETSEQ), Universitat Rovira Virgili, Ctra. de Salou s/n, 43006-Tarragona, Catalunya, Spain
FRANCESC GIRALT
Affiliation:
Departament d'Enginyeria Química Escola Técnica Superior d'Enginyeria Química (ETSEQ), Universitat Rovira Virgili, Ctra. de Salou s/n, 43006-Tarragona, Catalunya, Spain
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Abstract

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An experimental study to identify the structures present in a jet in crossflow has been carried out at a jet-to-crossflow velocity ratio U/Ucf = 3.8 and Reynolds number Re = UcfD/v = 6600. The hot-wire velocity data measured with a rake of eight X-wires at x/D = 5 and 15 and flow visualizations using planar laser-induced fluorescence (PLIF) confirm that the well-established pair of counter-rotating vortices is a feature of the mean field and that the upright, tornado-like or Fric's vortices that are shed to the leeward side of the jet are connected to the jet flow at the core. The counter-rotating vortex pair is strongly modulated by a coherent velocity field that, in fact, is as important as the mean velocity field. Three different structures – folded vortex rings, horseshoe vortices and handle-type structures – contribute to this coherent field. The new handle-like structures identified in the current study link the boundary layer vorticity with the counter-rotating vortex pair through the upright tornado-like vortices. They are responsible for the modulation and meandering of the counter-rotating vortex pair observed both in video recordings of visualizations and in the instantaneous velocity field. These results corroborate that the genesis of the dominant counter-rotating vortex pair strongly depends on the high pressure gradients that develop in the region near the jet exit, both inside and outside the nozzle.

Type
Research Article
Copyright
© 2001 Cambridge University Press