On the Bursting Criterion for Laminar Separation Bubbles

Diwan, Sourabh S.; Chetan, S.; Ramesh, O. N.

doi:10.1007/1-4020-4159-4_57

Cited by 32 publications

(25 citation statements)

References 8 publications

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“…The process through which a short bubble suddenly fails to reattach and becomes a long bubble after a small variation in angle of attack or Reynolds number is referred to as bursting. Its physical causes and the determination of an adequate criterion for predicting its occurrence are still today an active topic of research (Gaster 1967;Pauley, Moin & Reynolds 1990;Diwan, Chetan & Ramesh 2006;Marxen & Henningson 2011).…”

Section: Introductionmentioning

confidence: 99%

The two classes of primary modal instability in laminar separation bubbles

2013

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The self-excited global instability mechanisms existing in flat-plate laminar separation bubbles are studied here, in order to shed light on the causes of unsteadiness and threedimensionality of unforced, nominally two-dimensional separated flows. The presence of two known linear global mechanisms, namely an oscillator behaviour driven by local regions of absolute inflectional instability and a centrifugal instability giving rise to a steady three-dimensionalization of the bubble, is studied in a series of model separation bubbles. These results indicate that absolute instability, and consequently a global oscillator behaviour, does not exist for two-dimensional bubbles with a peak reversed-flow velocity below 12 % of the free-stream velocity. However, the threedimensional instability becomes active for recirculation levels as low as u rev ≈ 7 %. These findings suggest a route to the three-dimensionality and unsteadiness observed in experiments and simulations substantially different from that usually found in the literature of laminar separation bubbles, in which two-dimensional vortex shedding is followed by three-dimensionalization.

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Section: Introductionmentioning

confidence: 99%

The two classes of primary modal instability in laminar separation bubbles

2013

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“…The process in which a short bubble suddenly fails to reattach and becomes a long bubble after a small variation on angle of attack or Reynolds number is referred to as bursting; 4 its physical causes and the determination of an adequate criteria for predicting its occurrence have been since the 60's, and are still today, an active topic of research. [4][5][6][7][8] The usual picture of inviscid instability of the separated shear layer leading to laminar-turbulent transition, and turbulent mixing being ultimately responsible for the reattachment of the separation bubble suggested considering the properties of the boundary-layer at separation as a criterion for bursting. Besides bursting, the prediction of other characteristics of separated flow like the onset of unsteadiness (sometimes associated directly with bursting 6 ) or three-dimensionalization of nominally two-dimensional laminar separation bubbles 9,10 has been attempted through the study of linear instability mechanisms of the flow.…”

Section: Introductionmentioning

confidence: 99%

On the two classes of global primary modal instability in laminar separation bubbles

Rodríguez

Gennaro

Juniper

2013

43rd Fluid Dynamics Conference

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The self-excited global instability mechanisms existing in flat-plate laminar separation bubbles are studied here, in order to shed light on the causes of unsteadiness and threedimensionality of unforced, nominally two-dimensional separated flows. The presence of two known linear global mechanisms, namely an oscillator behavior driven by local regions of absolute inflectional instability and a centrifugal instability giving rise to a steady threedimensionalization of the bubble, is studied in a series of model separation bubbles. Present results indicate that absolute instability, and consequently a global oscillator behavior, does not exist for two-dimensional bubbles with a peak reversed-flow velocity below 12% of the free-stream velocity. However, the three-dimensional instability becomes active for recirculation levels as low as urev ≈ 7%. These findings suggest a route to the three-dimensionality and unsteadiness observed in experiments and simulations substantially different from that usually found in the literature, in which two-dimensional vortex shedding is followed by three-dimensionalization.

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“…This was contradicted by Schmidt & Mueller 19 , who concluded that at low Reynolds number situations the laminar part of the bubble had a very important influence on the flow development. Diwan et al 20 proposed a refined bursting criterion, which takes into account not only the length of the separation bubble but also the maximum height, as it was argued that the transition to turbulence was initiated roughly at a streamwise location corresponding to the maximum height. Their refined non-dimensional pressure gradient parameter is given as…”

Section: Section View Of a Laminar Separation Bubble (From Mayle 31 )mentioning

confidence: 99%

Experimental Investigation of the Structure and Dynamics of Laminar Separation Bubbles at the onset of Bursting

Jagadeesh

Balthazar

Groß

et al. 2013

31st AIAA Applied Aerodynamics Conference

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A two-dimensional laminar separation bubble on a flat plate is studied experimentally using Particle Image Velocimetry (PIV) and flow visualization. The separation bubble was generated on a flat plate by an imposed adverse pressure gradient. The adverse pressure gradient was generated by using an inverted wing with a NACA 643-618 airfoil mounted above the flat plate. A parametric study of the effect of the upstream flow velocity and the induced pressure gradient on the mean flow topology and the unsteady behaviour of the separation bubble was carried out in the low-speed water tunnel of the Hydrodynamics Laboratory at the University of Arizona. The structure and dynamics of the laminar separation bubble were found to depend strongly on the aforementioned parameters. As the flow velocity is reduced, at very low flow velocities the bubble is seen to undergo a drastic change in geometry, resulting in bubble bursting. An attempt is made in this work at understanding the physics of bubble bursting. For certain flow conditions, strong vortex shedding near the reattachment region of the bubble was observed, which is a characteristic behaviour of short bubbles. High-resolution spatio-temporal PIV measurements were made to analyze the formation and breakdown of these flow structures.

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On the Bursting Criterion for Laminar Separation Bubbles

Cited by 32 publications

References 8 publications

The two classes of primary modal instability in laminar separation bubbles

The two classes of primary modal instability in laminar separation bubbles

On the two classes of global primary modal instability in laminar separation bubbles

Experimental Investigation of the Structure and Dynamics of Laminar Separation Bubbles at the onset of Bursting

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