scholarly journals Shear instability of an axisymmetric air–water coaxial jet

2018 ◽  
Vol 843 ◽  
pp. 575-600 ◽  
Author(s):  
Jean-Philippe Matas ◽  
Antoine Delon ◽  
Alain Cartellier
Keyword(s):  
Surface Tension ◽  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Convective Instability ◽  
Scaling Laws ◽  
Shear Instability ◽  
Liquid Jet ◽  
Absolute Instability ◽  
Instability Waves

We study the destabilization of a round liquid jet by a fast annular gas stream. We measure the frequency of the shear instability waves for several geometries and air/water velocities. We then carry out a linear stability analysis, and show that there are three competing mechanisms for the destabilization: a convective instability, an absolute instability driven by surface tension and an absolute instability driven by confinement. We compare the predictions of this analysis with experimental results, and propose scaling laws for wave frequency in each regime. We finally introduce criteria to predict the boundaries between these three regimes.

Spiralling Liquid Jets

2002 ◽  
Author(s):  
Andrew King ◽  
Stephen Decent ◽  
Iain Wallwork ◽  
Emilian Parau ◽  
Mark Simmons ◽  
...  
Keyword(s):  
Surface Tension ◽  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Rotation Rate ◽  
Liquid Jets ◽  
Liquid Jet ◽  
Leading Order ◽  
Temporal And Spatial ◽  
Exit Speed

We examine the dynamics of a spiralling slender liquid jet which emerges from a rotating cylindrical drum. Such jets arise in the manufacture of fertiliser and magnesium pellts in the prilling process. Exploiting the slenderness of the jet we determine the steady trajectory of the jet, and find that at leading-order it is a function of the rotation rate of the drum, the surface tension and density of the liquid, the exit speed and exit radius of the jet, the radius of the cylinder, but not of the viscosity of the liquid. We carry out a linear stability analysis of the steady solution, using both inviscid and viscous perturbations, and considering both temporal and spatial stability. We compare our results to experiments, obtaining favourable agreement.

scholarly journals Steep Shelf Stabilization of the Coastal Bransfield Current: Linear Stability Analysis

2014 ◽  
Vol 44 (2) ◽  
pp. 714-732 ◽  
Author(s):  
F. J. Poulin ◽  
A. Stegner ◽  
M. Hernández-Arencibia ◽  
A. Marrero-Díaz ◽  
P. Sangrà
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Baroclinic Instability ◽  
Shear Instability ◽  
Coastal Current ◽  
Horizontal Shear ◽  
Shelf Slope ◽  
Topographic Parameter ◽  
Selection Of

Abstract In situ measurements obtained during the 2010 COUPLING cruise were analyzed in order to fully characterize the velocity structure of the coastal Bransfield Current. An idealized two-layer shallow-water model was used to investigate the various instability processes of the realistic current along the coastal shelf. Particularly studied is how the topographic parameter To (ratio between the shelf slope and the isopycnal slope of the surface current) impacts the growth and the wavelength of the unstable perturbations. For small bottom slopes, when the evolution of the coastal current is controlled by the baroclinic instability, the increase of the topographic parameter To yields a selection of smaller unstable wavelengths. The growth rates increase with small values of To. For larger values of To (To ≳ 10, which is relevant for the coastal Bransfield Current), the baroclinic instability is strongly dampened and the horizontal shear instability becomes the dominant one. In this steep shelf regime, the unstable growth rate and the wavelength selection of the baroclinic coastal current remains almost constant and weakly affected by the amplitude of the bottom velocity or the exact value of the shelf slope. Hence, the linear stability analysis of an idealized Bransfield Current predicts a typical growth time of 7.7 days and an alongshore scale of 47 km all along the South Shetland Island shelf. The fact that these large growth times are identical to the typical transit time of water parcels along the shelf may explain why the current does not exhibit any unstable meanders.

Linear stability analysis of a slightly viscoelastic liquid jet

2013 ◽  
Vol 28 (1) ◽  
pp. 249-256 ◽  
Author(s):  
Li-jun Yang ◽  
Yuan-yuan Qu ◽  
Qing-fei Fu ◽  
Bing-rui Xu ◽  
Wei Zhang ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Viscoelastic Liquid ◽  
Liquid Jet

Pulsatile flow in stenotic geometries: flow behaviour and stability

2009 ◽  
Vol 622 ◽  
pp. 291-320 ◽  
Author(s):  
M. D. GRIFFITH ◽  
T. LEWEKE ◽  
M. C. THOMPSON ◽  
K. HOURIGAN
Keyword(s):  
Stability Analysis ◽  
Shear Layer ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Base Flow ◽  
Arterial Stenosis ◽  
Working Fluid ◽  
Absolute Instability ◽  
Straight Tube ◽  
Instability Modes

Pulsatile inlet flow through a circular tube with an axisymmetric blockage of varying size is studied both numerically and experimentally. The geometry consists of a long, straight tube and a blockage, semicircular in cross-section, serving as a simplified model of an arterial stenosis. The stenosis is characterized by a single parameter, the aim being to highlight fundamental behaviours of constricted pulsatile flows. The Reynolds number is varied between 50 and 700 and the stenosis degree by area between 0.20 and 0.90. Numerically, a spectral element code is used to obtain the axisymmetric base flow fields, while experimentally, results are obtained for a similar set of geometries, using water as the working fluid. For low Reynolds numbers, the flow is characterized by a vortex ring which forms directly downstream of the stenosis, for which the strength and downstream propagation velocity vary with the stenosis degree. Linear stability analysis is performed on the simulated axisymmetric base flows, revealing a range of absolute instability modes. Comparisons are drawn between the numerical linear stability analysis and the observed instability in the experimental flows. The observed flows are less stable than the numerical analysis predicts, with convective shear layer instability present in the experimental flows. Evidence is found of Kelvin–Helmholtz-type shear layer roll-ups; nonetheless, the possibility of the numerically predicted absolute instability modes acting in the experimental flow is left open.

Washing wedges: capillary instability in a gradient of confinement

2016 ◽  
Vol 790 ◽  
pp. 619-633 ◽  
Author(s):  
Ludovic Keiser ◽  
Rémy Herbaut ◽  
José Bico ◽  
Etienne Reyssat
Keyword(s):  
Surface Tension ◽  
Stability Analysis ◽  
Linear Stability ◽  
Viscous Dissipation ◽  
Linear Stability Analysis ◽  
Theoretical Description ◽  
Oil Droplets ◽  
Bulk Viscous ◽  
Open Question ◽  
Wetting Liquid

We present experimental results on the extraction of oil trapped in the confined region of a wedge. Upon addition of a more wetting liquid, we observe that oil fingers develop into this extracting liquid. The fingers eventually pinch off and form droplets that are driven away from the apex of the wedge by surface tension along the gradient of confinement. During an experiment, we observe that the size of the expelled oil droplets decreases as the unstable front recedes towards the wedge. We show how this size can be predicted from a linear stability analysis reminiscent of the classical Saffman–Taylor instability. However, the standard balance of capillary and bulk viscous dissipation does not account for the dynamics found in our experiments, leaving as an open question the detailed theoretical description of the instability.

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