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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Proceedings ArticleDOI
Recent results from NASA's morphing project
Anna-Maria Rivas McGowan,Anthony E. Washburn,Lucas G. Horta,Robert G. Bryant,David E. Cox,Emilie J. Siochi,Sharon L. Padula,Nancy M. Holloway +7 more
TL;DR: The NASA Morphing Project as discussed by the authors seeks to develop and assess advanced technologies and integrated component concepts to enable efficient, multi-point adaptability in air and space vehicles, including smart materials, adaptive structures, micro flow control, biomimetic concepts, optimization and controls.
Journal ArticleDOI
The near wall effect of synthetic jets in a boundary layer
Mark Jabbal,Shan Zhong +1 more
TL;DR: In this article, an experimental investigation to analyse the qualitative near wall effect of synthetic jets in a laminar boundary layer has been undertaken for the purpose of identifying the types of vortical structures likely to have delayed separation on a 2D circular cylinder model described in this paper.
Proceedings ArticleDOI
Periodic Excitation for Jet Vectoring and Enhanced Spreading
G Pack LaTunia,Seifert Avi +1 more
TL;DR: The effects of periodic excitation on the evolution of a turbulent jet were studied experimentally in this article, where a short, wide-angle diffuser was attached to the jet exit and excitation was introduced at the junction between the jet exiting and the diffuser inlet.
Journal ArticleDOI
Transient Separation Control Using Pulse-Combustion Actuation
TL;DR: In this article, the authors investigated the transitory response of the flow over a stalled, two-dimensional (NACA 4415) airfoil to pulsed actuation on time scales that are an order of magnitude shorter than the characteristic convective time scale.
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
Streamwise vortex structure in plane mixing layers
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.
Journal ArticleDOI
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.