Torsional oscillation of helicopter blades due to stall.

Ham, Norman D.; Young, M. I.

doi:10.2514/3.43728

Cited by 48 publications

(12 citation statements)

References 2 publications

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“…12) At 31:9 deg, the suction peak has completely disappeared and the lift coefficient has dropped to 0.88. 13 phenomenon is occurring as a result of the creation of a dynamic stall vortex (DSV) and its propagation downstream. While the dynamic stall vortex is on the surface of the wing, it increases significantly the value of the lift coefficient.…”

Section: B Dynamic Stall Mechanismmentioning

confidence: 99%

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Bifurcation Behavior of Airfoil Undergoing Stall Flutter Oscillations in Low-Speed Wind Tunnel

Dimitriadis

2009

AIAA Journal

123

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Stall flutter is a nonlinear aeroelastic phenomenon that can affect several types of aeroelastic systems such as helicopter rotor blades, wind turbine blades, and highly flexible wings. Although the related aerodynamic phenomenon of dynamic stall has been the subject of many experimental studies, stall flutter itself has rarely been investigated. This paper presents a set of experiments conducted on a NACA0012 airfoil undergoing stall flutter oscillations in a low-speed wind tunnel. The aeroelastic responses are analyzed with the objective of characterizing the local bifurcation behavior of the system. It is shown that symmetric stall flutter oscillations are encountered as a result of a subcritical Hopf bifurcation, followed by a fold bifurcation. The cause of these bifurcations is the occurrence of dynamic stall, which allows the transfer of energy from the freestream to the wing. A second bifurcation occurs at the system's static divergence airspeed. As a consequence, the wing starts to undergo asymmetric stall flutter bifurcations at only positive (or only negative) pitch angles. The dynamic stall mechanism itself does not change but the flow only separates on one side of the wing.

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Section: B Dynamic Stall Mechanismmentioning

confidence: 99%

“…In the 1960s, Ham and Young [13] defined stall flutter as an oscillation of a wing (or helicopter blade) during which the timeaveraged damping in pitch is exactly zero over a cycle of the oscillation. Such oscillations are self-excited and self-limiting, that is, limit cycle oscillations.…”

Section: Introductionmentioning

confidence: 99%

Bifurcation Behavior of Airfoil Undergoing Stall Flutter Oscillations in Low-Speed Wind Tunnel

Dimitriadis

2009

AIAA Journal

123

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“…[70][71][72]. They examined pressure measurements from both a hover rotor test and a two-dimensional (2D) airfoil undergoing a ramp increase in angle of attack in the wind tunnel to characterize dynamic stall.…”

Section: Understanding Airloadsmentioning

confidence: 99%

Rotorcraft Airloads Measurements: Extraordinary Costs, Extraordinary Benefits<BR> <I>The 31st Alexander Nikolsky Honorary Lecture</I>

Bousman¹

2014

J Am Helicopter Soc

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office and asked how they had structured their Dryden Lectureship in Research. The AIAA staffer I spoke with was very kind and sent me considerable information on the award. I then called the AHS and asked Kim Smith how we could go about proposing a new honorary award. She explained the process of making a formal proposal and then presenting it to the Board.The chapter and I put together a proposal for an honorary lectureship that would include both a lecture and a subsequent written manuscript to be published in the AHS Journal.

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“…An understanding of the dynamic variation of pitching moment is key to analyzing a range of dynamic problems, including buffeting of long-span suspension bridges (Zhao et al 2016), the phenomenon of stall flutter on helicopters (Ham & Maurice 1966) and wind turbines (Hansen 2007), as well as flapping flight (Krashanitsa et al 2009) particularly when the wings or lifting sections are very flexible in torsion. In these cases which involve either bluff bodies or leading-edge separation, the unsteady effect of the pitching moment can play a very important role in the stability and dynamic response of the body when coupled to the effects of structural compliance or rigid-body dynamics (Ham & Maurice 1966). Therefore, there is a very practical interest in calculating the unsteady pitching moment on a body, especially in separated flows.…”

Section: Introductionmentioning

confidence: 99%