Journal ArticleDOI
Oscillatory Control of Separation at High Reynolds Numbers
Avi Seifert,LaTunia G. Pack +1 more
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TLDR
In this paper, an experiment conducted in a pressurized, cryogenic wind tunnel demonstrates that unsteady flow control using oscillatory blowing (with essentially zero mass flux) can effectively delay flow separation and reattach separated flow on an airfoil at chord Reynolds numbers as high as 38 × 10 6.Abstract:
An experiment conducted in a pressurized, cryogenic wind tunnel demonstrates that unsteady flow control using oscillatory blowing (with essentially zero mass flux) can effectively delay flow separation and reattach separated flow on an airfoil at chord Reynolds numbers as high as 38 × 10 6 . Oscillatory blowing at frequencies that generate one to three vortices over the controlled region at all times are effective over the entire Reynolds number range, in accordance with previous low-Reynolds-number tests. Stall is delayed and poststall characteristics are improved when oscillatory blowing is applied from the leading-edge region of the airfoil, whereas flap effectiveness is increased when control is applied at the flap shoulder. Similar gains in airfoil performance require steady blowing with a momentum coefficient that is two orders of magnitude greater. A detailed experimental and theoretical investigation was undertaken to characterize the oscillatory blowing disturbance, in the absence of external flow, and to estimate the oscillatory blowing momentum coefficient used in the cryogenic wind tunnel experiment. Possible approaches toward closed-loop active separation control are also presentedread more
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Journal ArticleDOI
On Dynamic Mode Decomposition: Theory and Applications
TL;DR: A theoretical framework in which dynamic mode decomposition is defined as the eigendecomposition of an approximating linear operator, which generalizes DMD to a larger class of datasets, including nonsequential time series, and shows that under certain conditions, DMD is equivalent to LIM.
Journal ArticleDOI
The control of flow separation by periodic excitation
TL;DR: In this article, a review of the control of flow separation from solid surfaces by periodic excitation is presented, with an emphasis on experimentation relating to hydrodynamic excitation, although acoustic methods as well as traditional boundary layer control, such as steady blowing and suction are discussed in order to provide an appropriate historical context for recent developments.
Journal ArticleDOI
Aerodynamic Flow Control over an Unconventional Airfoil Using Synthetic Jet Actuators
TL;DR: In this article, the effect of the actuation frequency, actuator location, and momentum coefficient on flow separation on a symmetric airfoil with synthetic jet actuators is investigated.
Journal ArticleDOI
Formation Criterion for Synthetic Jets
TL;DR: In this article, the Strouhal number is defined as the appearance of a time-averaged outward velocity along the jet axis and corresponds to the generation and subsequent convection or escape of a vortex ring.
Journal ArticleDOI
Issues in active flow control: theory, control, simulation, and experiment
TL;DR: In this article, the authors provide a perspective on the current status and future directions for active flow control technology with particular emphasis on oscillatory control, and make recommendations relevant to numerical complications on the route to design oscillatory flow-control systems.
References
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Journal ArticleDOI
Delay of Airfoil Stall by Periodic Excitation
TL;DR: In this article, it was demonstrated that oscillatory blowing can delay separation from a symmetrical airfoil much more effectively than the steady blowing used traditionally for this purpose than the traditional slow blowing.
Journal ArticleDOI
Oscillatory Blowing: A Tool to Delay Boundary-Layer Separation
TL;DR: In this article, the effects of oscillatory blowing as a means of delaying separation are discussed, and experiments were carried out on a follow, flapped NACA 01115 airfoil equipped with a two-dimensional slot over the hinge of the flap.
Journal ArticleDOI
Separation control - Review
TL;DR: The status and outlook of separation control for both steady and unsteady flows are reviewed and both passive and active techniques to prevent or to provoke flow detachment are considered.
Journal ArticleDOI
Separation of flow
TL;DR: Flow separation is perhaps the most important unsolved phenomenon of fluid mechanics which causes energy loss and deviation of stream lines as mentioned in this paper, and a summary of flow separation is presented in order to understand the basic problem, the present state of knowledge and to indicate future development.
Journal ArticleDOI
Effects of Periodic Excitation on Turbulent Flow Separation from a Flap
B. Nishri,Israel Wygnanski +1 more
TL;DR: The effects of periodic perturbations on delaying separation or promoting reattachment of initially separated flow were experimentally investigated in this paper, where the leading parameters affecting the flow are the flap deflection, the input momentum, and its reduced frequency.