The effects of forced oscillations on the performance of airfoils

Seifert, Avi; Daraby, Bayaz; Nishri, B.; Wygnanski, I.

doi:10.2514/6.1993-3264

Cited by 21 publications

(4 citation statements)

References 2 publications

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“…Experiments performed at low Renolds and Mach numbers (Refs. [1][2][3][4] have shown that cyclic vertical oscillations introduced into a separation boundary layer slightly upstream of the average separation location can effectively delay boundarylayer separation. The improved ability of the boundary layer to overcome an adverse pressure gradient is attributed to enhanced mixing between the low-momentum fluid near the wall and the external high-momentum flow.…”

Section: Introductionmentioning

confidence: 99%

Oscillatory Blowing Control Numerical Simulation of Airfoil Flutter By High Accuracy Method

Jin

Yuan

2004

Journal of Aircraft

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It is known that oscillatory blowing can be used to delay flow separation and stall. The oscillatory blowing technique is applied to control of the airfoil's flutter. A high accuracy fluid-structure coupling numerical method is used. The numerical results show that the steady blowing will weaken the flutter. However, the excess blowing will decrease the lift coefficient. The best blowing velocity can be found by the present numerical method. The influence of the frequency of the oscillatory blowing on the airfoil's vibration is also studied. The numerical results show that the oscillatory blowing is more efficient than steady blowing.

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Section: Introductionmentioning

confidence: 99%

Oscillatory Blowing Control Numerical Simulation of Airfoil Flutter By High Accuracy Method

Jin

Yuan

2004

Journal of Aircraft

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“…Forexample, experiments (ref. 7) showthatthetime-periodic injection of fluid intotheturbulentboundary layermayincrease its resistance to adverse pressure gradients withoutseparation. This impliesanessential improvement of airfoilperformance, upto 60percent forhigh(poststall)angles of attack, accordingto reference 7.…”

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confidence: 98%

“…We must emphasize that while talking about the oscillatory time behavior we mean that some alternating (time-periodic) influence is exerted on the flow (e.g., see experimental work by Seifert, et al in ref. 7) and expect that those frequencies that are connected to this influence will dominate in the solution. We expect that this circumstance will enable us to construct the ABC's without taking into account any other time-dependent effects.…”

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confidence: 99%

Artificial Boundary Conditions for Computation of Oscillating External Flows

Tsynkov¹

1997

SIAM J. Sci. Comput.

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“…It has been hypothesized that unsteady separation control is similar to active boundary layer tripping because both methods take advantage of an instability mechanism. In order to test this hypothesis, transition strips were located at the LE region of airfoils and generic flap configurations 3 . It was shown that neither forced transition, thickened turbulent boundary layers nor elevated Reynolds numbers (up to 3.3xl0 6 tested previously 9 ) had an adverse effect on the efficiency of the method.…”

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confidence: 99%

Oscillatory control of separation and high Reynolds numbers

Seifert

Pack

1998

36th AIAA Aerospace Sciences Meeting and Exhibit

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A recent 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 31x10*. Oscillatory blowing at reduced frequencies in the range 0.5 to 1 is effective over the entire Re range, in accordance with previous low Re tests. Similar gains in airfoil performance require steady blowing with a momentum coefficient that is two orders of magnitude greater. Stall is delayed and post stall characteristics are improved when oscillatory blowing is applied from the leading edge region of the airfoil, while flap effectiveness is increased when control is applied at the flap shoulder. A detailed experimental investigation (accompanied by theory) was undertaken in order to estimate the oscillatory blowing momentum coefficient used in the cryogenic wind tunnel experiment. Based on the findings of the present investigation, the application of active separation control to a commercial jet-liner at take-off is within reach. Nomenclature aspeed of sound c^ steady blowing momentum coefficient, = Jlcq oscillatory blowing momentum coefficient, = < J> Icq Cu combined blowing momentum coefficient,

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The effects of forced oscillations on the performance of airfoils

Cited by 21 publications

References 2 publications

Oscillatory Blowing Control Numerical Simulation of Airfoil Flutter By High Accuracy Method

Oscillatory Blowing Control Numerical Simulation of Airfoil Flutter By High Accuracy Method

Artificial Boundary Conditions for Computation of Oscillating External Flows

Oscillatory control of separation and high Reynolds numbers

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