Overview of NATO AVT-282: Unsteady Aerodynamic Response of Rigid Wings in Gust Encounters

Jones, Anya R.; Çeti̇ner, Okşan

doi:10.2514/6.2020-0078

Cited by 6 publications

(2 citation statements)

References 68 publications

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“…As scale increases, increased flexibility in the wing or turbine blade means that studying the unsteady aerodynamic response becomes more important. More pedestrian unmanned aerial vehicles also encounter challenges due to unsteady gusts at low altitude [10,11]. At smaller scales, a better understanding of unsteady aerodynamics eases the design of both oscillating energy harvesting devices [12] and also micro air vehicles that mimic insects using flapping wing technology.…”

Section: Introductionmentioning

confidence: 99%

Applying Frequency-Domain Unsteady Lifting-Line Theory to Time-Domain Problems

Bird

Ramesh

2022

AIAA Journal

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Section: Introductionmentioning

confidence: 99%

Applying Frequency-Domain Unsteady Lifting-Line Theory to Time-Domain Problems

Bird

Ramesh

2022

AIAA Journal

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“…Literature regarding dynamic stall was initially motivated by helicopter rotor aerodynamics and flutter [5,6,7], and received renewed interest due to problems related to gust interactions [8,9]. The main parameter governing flow unsteadiness related to the kinematics of a pitching airfoil is the reduced pitch rate k defined as:…”

Section: Introductionmentioning

confidence: 99%

The dynamics and timescales of static stall

Fouest,

Deparday,

Mulleners

2021

Preprint

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Airfoil stall plays a central role in the design of safe and efficient lifting surfaces. We typically distinguish between static and dynamic stall based on the unsteady rate of change of an airfoil's angle of attack. Despite the somewhat misleading denotation, the force and flow development of an airfoil undergoing static stall are highly unsteady and the boundary with dynamic stall is not clearly defined. We experimentally investigate the forces acting on a two-dimensional airfoil that is subjected to two manoeuvres leading to static stall: a slow continuous increase in angle of attack with a reduced pitch rate of 1.3 × 10 −4 and a step-wise increase in angle of attack from 14.2°to 14.8°within 0.04 convective times. We systematically quantify the stall reaction delay, or the timespan between the moment the blade exceeds its critical static stall angle and the onset of stall, for many repetitions of these two manoeuvres. The onset of flow stall is marked by the distinct drop in the lift coefficient. The reaction delay for the slow continuous ramp-up manoeuvre is not influenced by the blade kinematics and its occurrence histogram is normally distributed around 32 convective times.The static reaction delay is compared with dynamic stall delays for dynamic ramp-up motions with reduced pitch rates ranging from 9 × 10 −4 to 0.14 and for dynamic sinusoidal pitching motions of different airfoils at higher Reynolds numbers up to 1 × 10 6 . The stall delays for all conditions follows the same power law decrease from 32 convective times for the most steady case down to an asymptotic value of 3 convective times for reduced pitch rates above 0.04. Static stall is not phenomenologically different than dynamic stall and is merely a typical case of stall for low pitch rates where the onset of flow separation is not promoted by the blade kinematics. Based on our results, we suggest that conventional measurements of the static stall angle and the static load curves should be conducted using a continuous and uniform ramp-up motion at a reduced frequency around 1 × 10 −4 .

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