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Lift-up, Kelvin–Helmholtz and Orr mechanisms in turbulent jets

Published online by Cambridge University Press:  26 May 2020

Ethan Pickering Open the ORCID record for Ethan Pickering [Opens in a new window] ,
Georgios Rigas Open the ORCID record for Georgios Rigas [Opens in a new window] ,
Petrônio A. S. Nogueira Open the ORCID record for Petrônio A. S. Nogueira [Opens in a new window] ,
André V. G. Cavalieri Open the ORCID record for André V. G. Cavalieri [Opens in a new window] ,
Oliver T. Schmidt Open the ORCID record for Oliver T. Schmidt [Opens in a new window]  and
Tim Colonius Open the ORCID record for Tim Colonius [Opens in a new window]
Ethan Pickering*
Affiliation:
Mechanical Engineering, California Institute of Technology, Pasadena, CA91125, USA
Georgios Rigas
Affiliation:
Mechanical Engineering, California Institute of Technology, Pasadena, CA91125, USA
Petrônio A. S. Nogueira
Affiliation:
Instituto Tecnológico de Aeronáutica, São José dos Campos, SP12228-900, Brazil
André V. G. Cavalieri
Affiliation:
Instituto Tecnológico de Aeronáutica, São José dos Campos, SP12228-900, Brazil
Oliver T. Schmidt
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA92093, USA
Tim Colonius
Affiliation:
Mechanical Engineering, California Institute of Technology, Pasadena, CA91125, USA
*
†Email address for correspondence: pickering@caltech.edu
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Abstract

Three amplification mechanisms present in turbulent jets, namely lift-up, Kelvin–Helmholtz and Orr, are characterized via global resolvent analysis and spectral proper orthogonal decomposition (SPOD) over a range of Mach numbers. The lift-up mechanism was recently identified in turbulent jets via local analysis by Nogueira et al. (J. Fluid Mech., vol. 873, 2019, pp. 211–237) at low Strouhal number ($St$) and non-zero azimuthal wavenumbers ($m$). In these limits, a global SPOD analysis of data from high-fidelity simulations reveals streamwise vortices and streaks similar to those found in turbulent wall-bounded flows. These structures are in qualitative agreement with the global resolvent analysis, which shows that they are a response to upstream forcing of streamwise vorticity near the nozzle exit. Analysis of mode shapes, component-wise amplitudes and sensitivity analysis distinguishes the three mechanisms and the regions of frequency–wavenumber space where each dominates, finding lift-up to be dominant as $St/m\rightarrow 0$. Finally, SPOD and resolvent analyses of localized regions show that the lift-up mechanism is present throughout the jet, with a dominant azimuthal wavenumber inversely proportional to streamwise distance from the nozzle, with streaks of azimuthal wavenumber exceeding five near the nozzle, and wavenumbers one and two most energetic far downstream of the potential core.

JFM classification

Wakes/Jets: Jets Turbulent Flows: Compressible turbulence Aerodynamics: High-speed flow
Type
JFM Papers
Information
Journal of Fluid Mechanics , Volume 896 , 10 August 2020 , A2
Copyright
© The Author(s), 2020. Published by Cambridge University Press

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