The mechanism of flow control on a cylinder with the unsteady bleed technique

Williams, David R.; Acharya, Mukund; Bernhardt, J. E.; Yang, Pan-Mei

doi:10.2514/6.1991-39

Cited by 36 publications

(11 citation statements)

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“…The effect of excitation was initially demonstrated using sound waves, emanating from the wind tunnel walls, as a means of controlling boundary layer separation (e.g. Peterka and Richardson [21]), but was later demonstrated by Williams et al [31] to be related to fluidic and not acoustic excitation. Later studies focused on hydrodynamic excitation, for example from a slot (e.g.…”

Section: Active Control Of Cylinder Flowsmentioning

confidence: 98%

“…Later studies focused on hydrodynamic excitation, for example from a slot (e.g. Hsiao et al [11]; Williams et al [31]; Schewe [25]; Pal and Sinha [18]; Heine et al [10]; Amitay et al [2]; Liu and Brodie [14]; Béra et al [4]), producing profound effects on transition and separation, with consequences for lift, drag and vortex shedding. For example, Hsiao et al [11] showed that a suction peak could be generated on one side resulting in C l =0.6 with the excitation location at 100°when F þ f e D=U 1 % 1; similar observations were made by Amitay et al [2] for F + =1.5 who also showed that the separation point could be moved by approximately 60°, resulting in a 25% reduction in form-drag.…”

Section: Active Control Of Cylinder Flowsmentioning

confidence: 99%

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Active Control of a Circular Cylinder Flow at Transitional Reynolds Numbers

Naim

Greenblatt²,

Seifert

et al. 2007

Flow Turbulence Combust

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Active and passive control of flow around a circular cylinder, at transitional Reynolds numbers was investigated experimentally by measuring cylinder surface pressures and wake velocity profiles. Two-and three-dimensional passive boundary layer tripping was considered and periodic active control using piezo-fluidic actuators was introduced from a two-dimensional slot that was nearly tangential to the cylinder surface. The slot location was varied circumferentially by rotating the cylinder and this facilitated either upstream-or downstream-directed actuation using sinusoidal or modulated waveforms. Separation was controlled by two distinct methods, namely: by forcing laminarturbulent transition when applied at relatively small angles (30-60°) from the forward stagnation point; and by directly forcing the separated shear-layer at larger angles. In the latter case, actuation produced the largest load changes when it was introduced at approximately 90°from the forward stagnation point. When the forcing frequency was close to the natural vortex-shedding frequency, the two frequencies "locked-in" creating clear and persistent structures. These were examined and categorized. The "lock-in" effect lowered the base pressure and increased the form-drag whereas delaying separation from the cylinder did the opposite. Nomenclature bslot width C d drag coefficient, d=q 1 D C dp form drag coefficient, dp=q 1 D Flow Turbulence Combust (2007) 78:

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Section: Active Control Of Cylinder Flowsmentioning

confidence: 98%

Section: Active Control Of Cylinder Flowsmentioning

confidence: 99%

Active Control of a Circular Cylinder Flow at Transitional Reynolds Numbers

Naim

Greenblatt²,

Seifert

et al. 2007

Flow Turbulence Combust

View full text Add to dashboard Cite

show abstract

“…It has been shown that the separating shear layer over stalled 2-and 3-D aerodynamic surfaces is typically dominated by a strong coupling to the instability of the near wake (e.g., Wu et al 1998). Traditional separation control strategy uses actuation coupling to the narrow-band receptivity of the separating flow at the unstable Strouhal numbers of the near wake (e.g., St D ~ O(1), Hsiao et al 1990, Neuberger and Wygnanski 1987, Williams et al 1991, Chang et al 1992, Seifert et al 1993). An alternative approach uses actuation at substantially higher frequencies to decouple the global flow instabilities from fluidic modification of the "apparent" aerodynamic shape of the body (e.g., St D » O(1), Erk 1997, Smith et al 1998, Amitay et al 2001, Honohan et al 2000, Glezer et al 2005.…”

Section: Technical Backgroundmentioning

confidence: 99%

Unsteady Aerodynamic Flow Control of Moving Platforms

Glezer¹

2014

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“…In the past 10 years or so, unsteady forcing techniques have been increasingly employed in flow-control applications, albeit under different names: oscillatory control, 13 internal acoustic excitation, 14 unsteady bleed technique, 15,16 and synthetic jets 17−24 as they are referred to here. The use of synthetic jets as flow control or flow reattachment devices is increasingly studied for medium-to high-Reynolds-number flows.…”

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confidence: 99%

Interaction of Synthetic Jet Propulsion with Airfoil Aerodynamics at Low Reynolds Numbers

Whitehead

Gursul

2006

AIAA Journal

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The use of synthetic (zero net mass flux) jets for the propulsion of fixed-wing small unmanned air vehicles was investigated. The formation of a time-averaged jet resulting from periodic excitation of a cavity and its interaction with separated flow over the airfoil were studied. As a thick trailing edge does not have an adverse effect on lift generation at low Reynolds numbers, a synthetic jet was placed at the trailing edge of the airfoil. It was shown that when the synthetic jet is activated the separated shear layer reattaches near the trailing edge of a cambered airfoil for momentum coefficients larger than a critical value, resulting in enhanced lift. For momentum coefficients larger than a critical value, the jet produces positive thrust, which strongly depends on excitation frequency. An optimum frequency range was identified, which produces maximum thrust. Aerodynamic efficiency was investigated as a function of the main parameters. Nomenclature= velocity magnitude x = streamwise distance y = cross-stream distance α = angle of attack ξ = vorticity ρ = density

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The mechanism of flow control on a cylinder with the unsteady bleed technique

Cited by 36 publications

References 0 publications

Active Control of a Circular Cylinder Flow at Transitional Reynolds Numbers

Active Control of a Circular Cylinder Flow at Transitional Reynolds Numbers

Unsteady Aerodynamic Flow Control of Moving Platforms

Interaction of Synthetic Jet Propulsion with Airfoil Aerodynamics at Low Reynolds Numbers

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