Journal ArticleDOI
The formation and evolution of synthetic jets
Barton L. Smith,Ari Glezer +1 more
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In this article, a nominally plane turbulent jet is synthesized by the interactions of a train of counter-rotating vortex pairs that are formed at the edge of an orifice by the time-periodic motion of a flexible diaphragm in a sealed cavity.Abstract:
A nominally plane turbulent jet is synthesized by the interactions of a train of counter-rotating vortex pairs that are formed at the edge of an orifice by the time-periodic motion of a flexible diaphragm in a sealed cavity. Even though the jet is formed without net mass injection, the hydrodynamic impulse of the ejected fluid and thus the momentum of the ensuing jet are nonzero. Successive vortex pairs are not subjected to pairing or other subharmonic interactions. Each vortex of the pair develops a spanwise instability and ultimately undergoes transition to turbulence, slows down, loses its coherence and becomes indistinguishable from the mean jet flow. The trajectories of vortex pairs at a given formation frequency scale with the length of the ejected fluid slug regardless of the magnitude of the formation impulse and, near the jet exit plane, their celerity decreases monotonically with streamwise distance while the local mean velocity of the ensuing jet increases. In the far field, the synthetic jet i...read more
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Journal ArticleDOI
Synthetic Jets in Cross-flow
Ivana Milanovic,Khairul Q. Zaman +1 more
TL;DR: In this paper, an experimental investigation on synthetic jets from round orifices with and without cross-flow is presented, and the threshold of stroke length for synthetic jet formation is found to be Lo /D approximately 0.5.
Journal ArticleDOI
Stability enhancement by boundary control in 2-D channel flow
TL;DR: This paper stabilize the parabolic equilibrium profile in a two-dimensional channel flow using actuators and sensors only at the wall and arrives at a feedback law using tangential actuation and only local measurements of wall shear stress, allowing to embed the feedback in microelectromechanical systems (MEMS) hardware, without need for wiring.
Journal ArticleDOI
Multiple orifice synthetic jet for improvement in impingement heat transfer.
TL;DR: In this article, the authors explored the use of multiple orifice single-cavity synthetic jet employed in direct impingement mode of cooling and found that the maximum heat transfer coefficient with multiple-orifice synthetic jet is approximately 12 times that of the natural heat transfer coefficients and up to 30% more as compared to that obtained with a conventional single orifice jet.
Journal ArticleDOI
Towards the design of synthetic-jet actuators for full-scale flight conditions Part 1: The fluid mechanics of synthetic-jet actuators
TL;DR: In this paper, a 3-year research program aiming at establishing a capability based on a better understanding of the fluid mechanics of synthetic jets and an improved modelling capacity is reported. But the capability that allows the geometry and operating conditions of these devices to be designed and selected for maximum flow-control effectiveness in full-scale flight conditions has yet to be developed.
Journal ArticleDOI
Some aspects of aerodynamic flow control using synthetic-jet actuation.
TL;DR: Aerodynamic flow control effected by interactions of surface-mounted synthetic (zero net mass flux) jet actuators with a local cross flow is reviewed in this paper, where the authors show that when the actuation frequency is sufficiently high to be decoupled from global instabilities of the base flow, changes in the aerodynamic forces are attained by leveraging the generation and regulation of 'trapped' vorticity concentrations near the surface to alter its aerodynamic shape.
References
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Journal ArticleDOI
An Album of Fluid Motion
Milton van Dyke,Frank M. White +1 more
TL;DR: In this paper, the authors present a visualisation de l'ecoulement for tourbillon and dynamique des: fluides, aubes, cylindre, instabilite.
Journal ArticleDOI
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Luis P. Bernal,Anatol Roshko +1 more
TL;DR: In this paper, it is shown that superimposed on the primary, spanwise vortex structure there is a secondary, steam wise vortex structure, and the spatial organization of the secondary structure produces a well-defined spanwise entrainment pattern in which fluid from each stream is preferentially entrained at different spanwise locations.
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The planar turbulent jet
Ephraim Gutmark,Israel Wygnanski +1 more
TL;DR: In this article, hot-wire measurements in a plane incompressible jet are reported, where the flow was found to be self-preserving beyond x/d > 40 and measurements were made up to x/D = 120.
Journal ArticleDOI
The structure of a self-preserving turbulent plane jet
TL;DR: The structure of a self-preserving turbulent plane jet exhausting into a slow-moving parallel airstream is studied in this paper, where results of turbulence measurements and the structure is compared with that of the plane wake.
Journal ArticleDOI
Preferred modes and the spreading rates of jets
Ephraim Gutmark,Chih-Ming Ho +1 more
TL;DR: In this article, it is suggested that extremely low-level spatially coherent disturbances in individual facilities change the initial conditions of a laminar shear layer and result in the discrepancies reported in the literature.