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Linear and nonlinear aspects of interactive boundary layer transition

Savin, Deborah Jane; (1996) Linear and nonlinear aspects of interactive boundary layer transition. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Linear and nonlinear investigations into the early stages of transition to turbulence within interactive boundary layer flows are described. The behaviour of linear disturbances downstream of the point of breakaway separation of a high Reynolds number boundary layer away from a smooth wall is investigated first, emphasis being placed on the structure and scales at each stage of the investigation. Neutral eigensolutions of the Rayleigh equation are considered and the wavenumber obtained to leading order. A critical distance downstream of separation is found at which the disturbance characteristics alter rapidly. Moving upstream, next, Rayleigh instability which can occur within locally separating two- and three-dimensional triple-deck boundary layer flows is considered, demonstrating that the existence, locally, of a point of inflection is not a sufficient condition for such instability to occur. Finally, nonlinear vortex/Rayleigh-wave interactions are studied for small wavenumbers and a new wave-pressure amplitude (integro-differential) equation is obtained which further generalizes the application of vortex/wave interactions in interactive boundary layer flows. The inclusion of temporal effects at the onset of inflectional instability leads to a new initial-value problem for weakly nonlinear input holding there. To conclude, nonlinear forced vortex/wave interaction solution properties are discussed and numerical solutions of the corresponding receptivity problem are presented.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Linear and nonlinear aspects of interactive boundary layer transition
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Interactive boundary; Layer transition; Linear; Nonlinear
URI: https://discovery.ucl.ac.uk/id/eprint/10102131
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