NDLI: Optimally growing boundary layer disturbances in a convergent nozzle preceded by a circular pipe

Content Provider	Springer Nature Link
Author	Uzun, Ali Davis, Timothy B. Alvi, Farrukh S. Hussaini, M. Yousuff
Copyright Year	2017
Abstract	We report the findings from a theoretical analysis of optimally growing disturbances in an initially turbulent boundary layer. The motivation behind this study originates from the desire to generate organized structures in an initially turbulent boundary layer via excitation by disturbances that are tailored to be preferentially amplified. Such optimally growing disturbances are of interest for implementation in an active flow control strategy that is investigated for effective jet noise control. Details of the optimal perturbation theory implemented in this study are discussed. The relevant stability equations are derived using both the standard decomposition and the triple decomposition. The chosen test case geometry contains a convergent nozzle, which generates a Mach 0.9 round jet, preceded by a circular pipe. Optimally growing disturbances are introduced at various stations within the circular pipe section to facilitate disturbance energy amplification upstream of the favorable pressure gradient zone within the convergent nozzle, which has a stabilizing effect on disturbance growth. Effects of temporal frequency, disturbance input and output plane locations as well as separation distance between output and input planes are investigated. The results indicate that optimally growing disturbances appear in the form of longitudinal counter-rotating vortex pairs, whose size can be on the order of several times the input plane mean boundary layer thickness. The azimuthal wavenumber, which represents the number of counter-rotating vortex pairs, is found to generally decrease with increasing separation distance. Compared to the standard decomposition, the triple decomposition analysis generally predicts relatively lower azimuthal wavenumbers and significantly reduced energy amplification ratios for the optimal disturbances.
Starting Page	317
Ending Page	348
Page Count	32
File Format	PDF
ISSN	09354964
Journal	Theoretical and Computational Fluid Dynamics
Volume Number	31
Issue Number	3
e-ISSN	14322250
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2017-03-01
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Boundary layers Turbulence Hydrodynamic stability Parabolized stability equations Engineering Fluid Dynamics Classical and Continuum Physics Computational Science and Engineering
Content Type	Text
Resource Type	Article
Subject	Fluid Flow and Transfer Processes Condensed Matter Physics Computational Mechanics

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