Influence of coherent structures on the evolution of an axisymmetric turbulent jet
File(s)
Author(s)
Breda, M
Buxton, O
Type
Journal Article
Abstract
The role of initial conditions in affecting the evolution toward self-similarity of an axisymmetric turbulent jet is examined. The jet’s near-field coherence was manipulated by non-circular exit geometries of identical open area, D2e, including a square and a fractal exit, for comparison with a classical round orifice jet. Hot-wire anemometry and 2D-planar particle image velocimetry experiments were performed between the exit and a location 26De downstream, where the Reynolds stress profiles are self-similar. This study shows that a fractal geometry significantly changes the near-field structure of the jet, breaking up the large-scale coherent structures, thereby affecting the entrainment rate of the background fluid into the jet stream. It is found that many of the jet’s turbulent characteristics scale with the number of eddy turnover times rather than simply the streamwise coordinate, with the entrainment rate (amongst others) found to be comparable across the different jets after approximately 3-4 eddies have been overturned. The study is concluded by investigating the jet’s evolution toward a self-similar state. No differences are found for the large-scale spreading rate of the jets in the weakly self-similar region, so defined as the region for which some, but not all of the terms of the mean turbulent kinetic energy equation are self-similar. However, the dissipation rate of the turbulent kinetic energy was found to vary more gradually in x than predicted according to the classical equilibrium theories of Kolmogorov. Instead, the dissipation was found to vary in a non-equilibrium fashion for all three jets tested.
Date Issued
2018-03-29
Date Acceptance
2018-03-02
Citation
Physics of Fluids, 2018, 30 (3), pp.035109-1-035109-24
ISSN
1070-6631
Publisher
AIP Publishing
Start Page
035109-1
End Page
035109-24
Journal / Book Title
Physics of Fluids
Volume
30
Issue
3
Copyright Statement
© 2018 The Author(s). Published by AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Physics of Fluids and may be found at https://aip.scitation.org/doi/10.1063/1.5019668
Sponsor
Engineering & Physical Science Research Council (EPSRC)
Grant Number
EP/L023520/1
Subjects
Science & Technology
Technology
Physical Sciences
Mechanics
Physics, Fluids & Plasmas
Physics
ENERGY-DISSIPATION RATE
VELOCITY-MEASUREMENTS
ENTRAINMENT
MOMENTUM
RESOLUTION
EQUATION
01 Mathematical Sciences
02 Physical Sciences
09 Engineering
Fluids & Plasmas
Publication Status
Published
Article Number
ARTN 035109
Date Publish Online
2018-03-29