Wavepackets in the velocity field of turbulent jets
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In this article, the velocity field of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers, is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system.Abstract:
We study the velocity fields of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective of the study is to educe wavepackets in such flows and to explore their relationship with the radiated sound. The velocity field is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system. The field can be decomposed into frequency and azimuthal Fourier modes. The low-angle sound radiation is measured synchronously with a microphone ring array. Consistent with previous observations, the azimuthal wavenumber spectra of the velocity and acoustic pressure fields are distinct. The velocity spectrum of the initial mixing layer exhibits a peak at azimuthal wavenumbers ranging from 4 to 11, and the peak is found to scale with the local momentum thickness of the mixing layer. The acoustic pressure field is, on the other hand, predominantly axisymmetric, suggesting an increased relative acoustic efficiency of the axisymmetric mode of the velocity field, a characteristic that can be shown theoretically to be caused by the radial compactness of the sound source. This is confirmed by significant correlations, as high as 10 %, between the axisymmetric modes of the velocity and acoustic pressure fields, these values being significantly higher than those reported for two-point flow–acoustic correlations in subsonic jets. The axisymmetric and first helical modes of the velocity field are then compared with solutions of linear parabolized stability equations (PSE) to ascertain if these modes correspond to linear wavepackets. For all but the lowest frequencies close agreement is obtained for the spatial amplification, up to the end of the potential core. The radial shapes of the linear PSE solutions also agree with the experimental results over the same region. The results suggests that, despite the broadband character of the turbulence, the evolution of Strouhal numbers 0.3 ≤ St ≤ 0.9 and azimuthal modes 0 and 1 can be modelled as linear wavepackets, and these are associated with the sound radiated to low polar angles.read more
Citations
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Book ChapterDOI
Boundary Layer Theory
TL;DR: The boundary layer equations for plane, incompressible, and steady flow are described in this paper, where the boundary layer equation for plane incompressibility is defined in terms of boundary layers.
Journal ArticleDOI
Wave Packets and Turbulent Jet Noise
Peter Jordan,Tim Colonius +1 more
TL;DR: In this paper, the authors review evidence of the existence, energetics, dynamics, and acoustic efficiency of wave packets and highlight how extensive data available from simulations and modern measurement techniques can be used to distill acoustically relevant turbulent motions.
Journal ArticleDOI
Spectral analysis of jet turbulence
TL;DR: In this paper, the structure of turbulence in jets in the subsonic, transonic and supersonic regimes was examined by large-eddy simulation (LES) data and resolvent analysis of the mean flow.
Journal ArticleDOI
Importance of the nozzle-exit boundary-layer state in subsonic turbulent jets
Guillaume A. Brès,Peter Jordan,Vincent Jaunet,Maxime Le Rallic,André V. G. Cavalieri,Aaron Towne,Sanjiva K. Lele,Tim Colonius,Oliver T. Schmidt +8 more
TL;DR: In this paper, large-eddy simulations of an isothermal Mach 0.9 jet issued from a convergent-straight nozzle are performed at a diameter-based Reynolds number of 1 x 10^6.
Journal ArticleDOI
Wavepacket models for supersonic jet noise
TL;DR: In this paper, Gudmundsson and Colonius extended this model to an isothermal and a moderately heated Mach 1.5 jet for which the mean flow fields were obtained from a high-fidelity large-eddy simulation database, and applied a filter based on proper orthogonal decomposition to the data to extract the most energetic coherent components.
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Boundary layer theory
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Orderly Structure in Jet Turbulence
S. C. Crow,F. H. Champagne +1 more
TL;DR: In this paper, the authors show that a large-scale orderly pattern may exist in the noiseproducing region of a round subsonic jet by observing the evolution of orderly flow with advancing Reynolds number.
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