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The destabilisation of shear layers by asymmetric confinement and stratification.

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Bibliographic Details
Title: The destabilisation of shear layers by asymmetric confinement and stratification.
Authors: Turner, Matthew R.1 m.turner@surrey.ac.uk
Source: Journal of Fluid Mechanics. 6/10/2026, Vol. 1036, p1-37. 46p.
Subjects: Shear flow, Flow instability, Fluid dynamics
Abstract: The absolute and convective instability properties of a parallel shear flow in a stratified fluid, confined between two parallel rigid plates is considered. The flow is assumed to be two-dimensional, inviscid and incompressible, and is modelled using both a discontinuous two-layer stratification profile and a continuous stratification profile. Significantly, it is found that asymmetrically confining the flow by the two plates, and asymmetrically positioning the density interface such that it does not occur at the centre of the shear layer, both lead to a destabilisation of the flow for a range of flow parameter values, with an absolute instability occurring for an increased parameter range. We identify parameter regimes for asymmetric confinement where the destabilising effect is strong enough to generate an absolutely unstable co-flow shear layer; this contrasts with the unconfined case for which only absolutely unstable counterflow shear layers exist. In the semi-confined case (i.e. asymmetric confinement by one plate) it is found that the most unstable scenario occurs when the plate is placed in the faster/lighter stream. The robustness of the results found for a discontinuous density interface are confirmed using a continuous density profile. These results give valuable new insight into a class of flows such as coaxial injectors for high-speed fluid atomisation. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:The absolute and convective instability properties of a parallel shear flow in a stratified fluid, confined between two parallel rigid plates is considered. The flow is assumed to be two-dimensional, inviscid and incompressible, and is modelled using both a discontinuous two-layer stratification profile and a continuous stratification profile. Significantly, it is found that asymmetrically confining the flow by the two plates, and asymmetrically positioning the density interface such that it does not occur at the centre of the shear layer, both lead to a destabilisation of the flow for a range of flow parameter values, with an absolute instability occurring for an increased parameter range. We identify parameter regimes for asymmetric confinement where the destabilising effect is strong enough to generate an absolutely unstable co-flow shear layer; this contrasts with the unconfined case for which only absolutely unstable counterflow shear layers exist. In the semi-confined case (i.e. asymmetric confinement by one plate) it is found that the most unstable scenario occurs when the plate is placed in the faster/lighter stream. The robustness of the results found for a discontinuous density interface are confirmed using a continuous density profile. These results give valuable new insight into a class of flows such as coaxial injectors for high-speed fluid atomisation. [ABSTRACT FROM AUTHOR]
ISSN:00221120
DOI:10.1017/jfm.2026.11648