Stability of the solitary wave boundary layer subject to finite-amplitude disturbances

The stability and transition in the bottom boundary layer under a solitary wave are analysed in the presence of finite-amplitude disturbances. First, the receptivity of the boundary layer is investigated using a linear input-output analysis, in which the environment noise is modelled as distributed...

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Bibliographic Details
Published inJournal of fluid mechanics Vol. 896
Main Authors Önder, Asim, Liu, Philip L.-F.
Format Journal Article
LanguageEnglish
Published Cambridge, UK Cambridge University Press 10.08.2020
Subjects
Amplitude
Amplitudes
Boundary layer stability
Boundary layer transition
Boundary layers
Computational fluid dynamics
Computer simulation
Disturbances
Fluid flow
Fluid mechanics
JFM Papers
Low speed
Mathematical models
Noise
Nonlinear equations
Reynolds number
Shear layers
Solitary waves
Stability
Stability analysis
Stress concentration
Turbulence
Velocity
Vortices
Wave crest
Wave crests
solitary waves
transition to turbulence
boundary-layer stability
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Summary:The stability and transition in the bottom boundary layer under a solitary wave are analysed in the presence of finite-amplitude disturbances. First, the receptivity of the boundary layer is investigated using a linear input-output analysis, in which the environment noise is modelled as distributed body forces. The most ‘dangerous’ perturbations in a time frame until flow reversal are found to be arranged as counter-rotating streamwise-constant vortices. One of these vortex configurations is then selected and deployed to nonlinear equations, and streaks of various amplitudes are generated via the lift-up mechanism. By means of secondary stability analysis and direct numerical simulations, the dual role of streaks in the boundary-layer transition is shown. When the amplitude of streaks remains moderate, these elongated features remain stable until the adverse-pressure-gradient stage and have a dampening effect on the instabilities developing thereafter. In contrast, when the low-speed streaks reach high amplitudes exceeding 15 % of the free stream velocity at the respective phase, they become highly unstable to secondary sinuous modes in the outer shear layers. Consequently, a subcritical transition to turbulence, i.e. bypass transition, can be initiated already in the favourable-pressure-gradient region ahead of the wave crest.
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content type line 14
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2020.351