Effect of deceleration on jet instability

Shtern, V. N.; Hussain, Fazle

doi:10.1017/s0022112002003646

Cited by 25 publications

(18 citation statements)

References 36 publications

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“…The shear layer instability seems to peak during the flow deceleration stage and this suggests that flow deceleration might be an important factor in these jets. It should be noted that Stern and Hussain (2003), who conducted a study of the flow instability of a conical jet, showed that jet instability is greatly enhanced by the flow deceleration. Once the jet is destabilized, the asymmetric vortices interact with each other and with the wall.…”

Section: B Vortex Dynamics Of Symmetry Breaking and Agjdmentioning

confidence: 99%

“…Second, during stages in the cycle when the jet velocity is low (early opening or late closing stages), even small velocity fluctuations in the surrounding flow can potentially produce large perturbation in the jet. Third, decelerating shear layers are inherently unstable (Stern and Hussain, 2003) and these can cause or enhance asymmetries in the glottal jet. Despite this, many studies, especially the earlier ones (Berg et al, 1957;Guo and Scherer, 1994;Scherer et al, 2001;Fulcher et al, 2006), did not include jet pulsatility in their models.…”

Section: Introductionmentioning

confidence: 99%

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A computational study of asymmetric glottal jet deflection during phonation

Zheng

Mittal

Bielamowicz

2011

The Journal of the Acoustical Society of America

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Two-dimensional numerical simulations are used to explore the mechanism for asymmetric deflection of the glottal jet during phonation. The model employs the full Navier-Stokes equations for the flow but a simple laryngeal geometry and vocal-fold motion. The study focuses on the effect of Reynolds number and glottal opening angle with a particular emphasis on examining the importance of the so-called "Coanda effect" in jet deflection. The study indicates that the glottal opening angle has no substantial effect on glottal jet deflection. Deflection in the glottal jet is always preceded by large-scale asymmetry in the downstream portion of the glottal jet. A detailed analysis of the velocity and vorticity fields shows that these downstream asymmetric vortex structures induce a flow at the glottal exit which is the primary driver for glottal jet deflection.

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Section: B Vortex Dynamics Of Symmetry Breaking and Agjdmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A computational study of asymmetric glottal jet deflection during phonation

Zheng

Mittal

Bielamowicz

2011

The Journal of the Acoustical Society of America

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“…It is worth mentioning that Shtern & Hussain (2003) found similar instabilities for conical jets. They showed via a non-parallel analysis that flow deceleration plays a major role for swirl-free jets, triggering non-axisymmetric instabilities.…”

Section: Symmetry-breaking Bifurcation In the Symmetric Expansionmentioning

confidence: 53%

Global stability of multiple solutions in plane sudden-expansion flow

Lanzerstorfer

Kuhlmann

2012

J. Fluid Mech.

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The two-dimensional, incompressible flow in a plane sudden expansion is investigated numerically for a systematic variation of the geometry, covering expansion ratios (steps-to-outlet heights) from 0.25 to 0.95. By means of a three-dimensional linear stability analysis global temporal modes are scrutinized. In a symmetric expansion the primary bifurcation is stationary and two-dimensional, breaking the mirror symmetry with respect to the mid-plane. The secondary asymmetric flow experiences a secondary instability to different three-dimensional modes, depending on the expansion ratio. For a moderately asymmetric expansion only one of the two secondary flows (the connected branch) is realized at low Reynolds numbers. Since the perturbed secondary flow does not deviate much from the symmetric secondary flow, both secondary stability boundaries are very close to each other. For very small and very large expansion ratios an asymptotic behaviour is found for suitably scaled critical Reynolds numbers and wavenumbers. Representative instabilities are analysed in detail using an a posteriori energy transfer analysis to reveal the physical nature of the instabilities. Depending on the geometry, pure centrifugal and elliptical amplification processes are identified. We also find that the basic flow can become unstable due to the effects of flow deceleration, streamline convergence and high shear stresses, respectively.

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“…For more details concerning the stability problem and the numerical technique, see Ref. 7. Figures 2 and 3 show the summarized results of our stability studies for the flows in conical regions Ͻ cone .…”

mentioning

confidence: 99%

“…These characteristics as well as the entire neutral curves for both mϭ0 and mϭ1 are close to those for the Squire jet. 7 For example, Re a ϭ48.4, ϭ16.2, ␣ i ϭ0.323 at mϭ0 in the Squire jet.…”

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confidence: 99%

Instability versus collapse in a flow driven by the radial electric current

Shtern

2004

Physics of Fluids

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A flow of an electrically conducting fluid induced by a spherically symmetric current ͑discharging from a point source located on the fluid free surface͒ has a striking feature. As increasing total current J reaches a threshold, a jet propagating from the source along the axis of symmetry collapses, i.e., velocity becomes unbounded on the axis. It is shown here that the flow becomes unstable at J smaller than the threshold. For a flow in a conical region, Ͻ cone ͑ is the polar angle from the axis of symmetry͒, the instability leads to either a time-oscillating or steady-swirling flow depending on cone . In a half-space, cone ϭ90°, the instability is oscillatory. The steady swirl first develops as J increases in a cone with cone Ͻ85°.An electric current discharging in a liquid metal can drive a high-speed flow observed, e.g., in electric arcs and electro-slag welding. 1 Similarity modeling helps analyze, understand, and predict the flow features. A mathematically elegant model of electro-slag welding is a radial current discharging from a point electrode on the free surface of a conducting fluid. Zhigulev 2 noticed that the electromagnetic force induced by this spherically symmetric current is vortical and therefore drives a flow. The flow is conically similar; it converges to the electrode along the surface and forms an outflow near the axis of symmetry ͑Fig. 1͒.The practical importance and theoretical simplicity of this flow has stimulated much work including analytical solutions for a weak current, generalizations for conical flow regions, and experimental findings of striking features. A detailed review of early studies and the report on the authors' original research are in the book by Bojarevics et al. 1 Sozou 3 found a curious effect: as current J increases, a strong nearaxis jet forms and the jet velocity becomes unbounded at a finite value of J, i.e., the jet collapses into a singularity line coinciding with the axis of symmetry ͑z in Fig. 1͒.Collapse occurs also in models of tornadoes, 4 thermocapillary convection, 5 and a number of other flows. 6 Collapse mimics a practically important physical process-strong accumulation of both the axial and angular momentum near the axis of symmetry-typical of many natural and technological flows. However, this mathematical feature seems paradoxical for a viscous flow where a singularity is expected to develop in the limiting case as a characteristic Reynolds number Re→ϱ rather than at a finite Re. A question arises whether instability occurs and a secondary flow develops before the primary flow collapses as increasing Re reaches Re co .It is shown here that this scenario indeed occurs in the Sozou flow. Before increasing J reaches its collapse value, the flow becomes unstable with respect to axisymmetric either time-oscillatory meridional-flow or steady swirl disturbances depending on angle cone of a conical flow region. The instability of the primary flow and the development of a secondary flow permit bypassing the collapse. Below we describe the primary flow, the ...

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Effect of deceleration on jet instability

Cited by 25 publications

References 36 publications

A computational study of asymmetric glottal jet deflection during phonation

A computational study of asymmetric glottal jet deflection during phonation

Global stability of multiple solutions in plane sudden-expansion flow

Instability versus collapse in a flow driven by the radial electric current

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