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Modal and non-modal evolution of perturbations for parallel round jets

Jimenez-Gonzalez, José Ignacio and Brancher, Pierre and Martínez-Bazán, Carlos Modal and non-modal evolution of perturbations for parallel round jets. (2015) In: 68th Annual Meeting of the APS Division of Fluid Dynamics, 22 November 2015 - 24 November 2015 (Boston, United States).

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Abstract

We investigate the local modal and non-modal stability of round jets for varying aspect ratios and Reynolds numbers. The competition between axisymmetric (azimuthal wavenumber m = 0) and helical (m = 1) perturbations depending on the jet aspect ratio, \alpha = R / \theta, where R is the jet radius and \theta the shear layer momentum thickness, is quantified at different time horizons. Optimal excitation and optimal perturbation analyses allow us to characterize the transient dynamics of jets, showing that two mechanisms may cause large energy gains, namely the Orr mechanism at small wavelengths and the “shift-up” mechanism, in the long wavelength limit, which is found to shift the jet as a whole in a way that resembles the classical lift-up effect active in wall shear flows. The “shift-up” mechanism is found to be especially efficient for vanishing perturbations axial wavenumbers. Furthermore, it has been found that adjoint modes drive the transient process at relatively short temporal horizons, in such a way that, for large aspect ratios, an optimal excitation analysis might suffice to properly characterize transient dynamics.

Item Type:Conference or Workshop Item (UNSPECIFIED)
Additional Information:Thanks to APS https://meetings.aps.org/Meeting/DFD15/Session/G5.8
Audience (conference):International conference proceedings
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
Other partners > Universidad de Jaén - UJA (SPAIN)
Laboratory name:
Funders:
Spanish MINECO, Junta de Andaluca and EU Funds under projects DPI2011-28356-C03-03 and P11-TEP7495
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Deposited On:06 Sep 2016 09:47

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