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Linear and nonlinear growth of secondary instabilities of crossflow vortices studied by PSE

Hein, Stefan (2014) Linear and nonlinear growth of secondary instabilities of crossflow vortices studied by PSE. Seminar on Math. Dept., Imperial College London, 12. Dec. 2014, London, United Kingdom.

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Official URL: http://www3.imperial.ac.uk/newsandeventspggrp/imperialcollege/naturalsciences/mathematics/ammpfluiddynamics/eventssummary/event_10-11-2014-15-11-27

Abstract

Laminar-turbulent transition in (quasi-) three-dimensional boundary layers dominated by crossflow vortices is studied for the setup of the DLR swept-flat plate experiment. The linear and subsequent nonlinear stages of both the crossflow vortices and their high-frequency secondary instabilities are modelled by nonlinear parabolized stability equations (PSE). In the first part of the talk it is shown that those high-frequency secondary instabilities may develop from the interaction of stationary and low-frequency travelling crossflow vortices, a transition scenario usually more relevant in wind-tunnel experiments. In low-turbulence-level environments like free flight with stationary crossflow vortices being dominant in amplitude the high-frequency secondary instabilities presumably are triggered directly from environmental disturbances via a receptivity mechanism, however. Therefore, in the second part results from a different approach developed recently based on a bi-directional coupling between a secondary instability code and a PSE code are presented. Thereby, the nonlinear development of secondary instabilities including the generation of higher harmonics could be studied up to the stages where the feedback of the finite-amplitude secondary instability modes on the stationary crossflow vortices is no longer negligible and the skin-friction coefficient starts to deviate from that due to the mean flow distortion caused by the stationary crossflow modes alone. The latter could be used as a criterion for imminent laminar-turbulent transition within the saturation region of the stationary crossflow modes which was lacking in a nonlinear PSE analysis of crossflow-dominated transition until now.

Item URL in elib:https://elib.dlr.de/93725/
Document Type:Conference or Workshop Item (Speech)
Title:Linear and nonlinear growth of secondary instabilities of crossflow vortices studied by PSE
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Hein, Stefanstefan.hein (at) dlr.deUNSPECIFIED
Date:2014
Refereed publication:No
Open Access:No
In DOAJ:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:laminar-turbulent transition, nonlinear PSE, crossflow vortices, secondary instability
Event Title:Seminar on Math. Dept., Imperial College London
Event Location:London, United Kingdom
Event Type:Other
Event Dates:12. Dec. 2014
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:fixed-wing aircraft
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Military Technologies
Location: Göttingen
Institutes and Institutions:Institute of Aerodynamics and Flow Technology > High Speed Configurations
Deposited By: Micknaus, Ilka
Deposited On:17 Dec 2014 14:58
Last Modified:19 Dec 2014 12:50

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