Centrifugal/elliptic instabilities in slowly varying channel flows

The instability of the flow in a two-dimensional meandering channel of slowly varying depth is considered. The flow is characterised by $\delta$ the typical slope of the channel walls and the modified Reynolds number $R_m$ which is the usual Reynolds number multiplied by $\delta$. The modified Reyno...

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Bibliographic Details
Published in:Journal of fluid mechanics 2020-11, Vol.903, Article A27
Main Authors: Gajjar, Jitesh S. B., Hall, Philip
Format: Article
Language:English
Subjects:
Amplitudes
Channel flow
Control stability
Direction
Flow stability
Fluid dynamics
Fluid flow
Geometry
Instability
JFM Papers
Meandering
Numerical analysis
Parameter modification
Reynolds number
Two dimensional flow
Vortices
Wavelengths
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Summary:The instability of the flow in a two-dimensional meandering channel of slowly varying depth is considered. The flow is characterised by $\delta$ the typical slope of the channel walls and the modified Reynolds number $R_m$ which is the usual Reynolds number multiplied by $\delta$. The modified Reynolds number is shown to be the appropriate parameter controlling the instability of the flow to streamwise vortices periodic in the spanwise direction. In particular, channels periodic in the streamwise direction are considered and it is found that the most unstable mode can correspond to either a subharmonic or synchronous disturbance. The instability problem at finite $R_m$ is discussed first and then the inviscid and large wavenumber regimes are discussed in detail. The instability is shown to be a hybrid form of centrifugal instability having properties of both Görtler vortices and a parametric resonance usually referred to as an elliptic instability. The limiting case of small wall modulation amplitudes is investigated and the results suggest that at small amplitudes the subharmonic mode is always dominant.
ISSN:0022-1120
1469-7645
DOI:10.1017/jfm.2020.641