Optimal velocity and density profiles for the onset of absolute instability in jets
Lutz Lesshafft,Olivier Marquet +1 more
TLDR
In this paper, the absolute/convective character of axisymmetric jets is investigated for a wide range of parallel velocity and density profiles, and an adjoint-based sensitivity analysis is carried out in order to maximize the absolute growth rate of jet profiles with and without density variations.Abstract:
The absolute/convective character of the linear instability of axisymmetric jets is investigated for a wide range of parallel velocity and density profiles. An adjoint-based sensitivity analysis is carried out in order to maximize the absolute growth rate of jet profiles with and without density variations. It is demonstrated that jets without counterflow may display absolute instability at density ratios well above the previously assumed threshold ρ jet /ρ ∞ = 0.72, and even in homogeneous settings. Absolute instability is promoted by a strong velocity gradient in the low-velocity region of the shear layer, as well as by a step-like density variation near the location of maximum shear. A new efficient algorithm for the computation of the absolute instability mode is presented.read more
Citations
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Why Nonuniform Density Suppresses the Precessing Vortex Core
TL;DR: In this article, the authors applied linear stability analysis to a swirl-stabilized combustor flow with the aim of understanding how the flame shape and associated density field affects the manifestation of self-excited flow instabilities.
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Large-eddy simulation of flow over a cylinder with from to : a skin-friction perspective
TL;DR: In this paper, the authors present wall-resolved large-eddy simulations of flow over a smooth-wall circular cylinder up to, where is Reynolds number based on the cylinder diameter and the free-stream speed.
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Global stability of buoyant jets and plumes
TL;DR: In this paper, the effects of buoyancy on the base flow and on the instability dynamics of laminar buoyant jets and plumes were investigated under the low-Mach-number approximation.
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Linear stability analysis of a three-dimensional viscoelastic liquid jet surrounded by a swirling air stream
TL;DR: In this paper, a theoretical model is established to investigate the instability of a viscoelastic liquid jet with axisymmetric and non-axisymetric disturbances, which is moving in a swirling air stream.
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Global instability of low-density jets
TL;DR: In this article, the global stability of axisymmetric low-density jets is investigated in the low Mach number approximation, and the linear modal dynamics is found to be characterised by two features: a stable arc branch of eigenmodes and an isolated eigenmode.
References
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Local and global instabilities in spatially developing flows
TL;DR: In this article, a review of recent developments in the hydro- dynamic stability theory of spatially developing flows pertaining to absolute/convective and local/global instability concepts is presented.
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Self-excited oscillations and mixing in a heated round jet
TL;DR: In this article, an axisymmetric hot-air jet discharging into cold ambient air is investigated experimentally and it is demonstrated by several different experiments that, for sufficiently low Reynolds number and a ratio of jet exit to ambient density below approximately 0.7, global oscillations of the "jet column" become self-excited, a behaviour which is related to local absolute instability in the potential core region.
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Absolute instability in hot jets
Peter A. Monkewitz,Kiho D. Sohn +1 more
TL;DR: In this paper, a linear inviscid stability of heated compressible axisymmetric jets is examined, focusing on the impulse response of the flow, and the results suggest that a self-excited global resonance may dominate the heated jet response in situations of practical interest.
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Mode selection in swirling jet experiments: a linear stability analysis
TL;DR: In this article, the authors identify the selection mechanism responsible for the appearance of a double-helix structure in the pre-breakdown stage of so-called screened swirling jets for which the circulation vanishes away from the jet.
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The effect of base flow variation on flow stability
TL;DR: In this paper, the authors assess the sensitivity of the Orr-Sommerfeld operator's eigenvalues to modifications of the base flow, which need not be infinitesimally small.