The flow around a model helicopter main rotor in ground effect

Nathan, N. D.; Green, R. B.

doi:10.1007/s00348-011-1212-1

Cited by 30 publications

(13 citation statements)

References 13 publications

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Section: Discussionmentioning

confidence: 99%

“…For a rotorcraft hovering in ground effect, the wake first descends axially, impacts the ground surface and then subsequently undergoes lateral expansion [36]. Smoke visualizations of rotors hovering in ground effect also reveal a region of stagnant fluid in the centre of the wake [36,37]. We observed a similar effect in hummingbirds, except that the wings shed pairs of vortices (figure 5a), rather than the single helical wake of rotors or the hypothesized single vortex previously described for hovering hummingbirds [38].…”

Section: Discussionmentioning

confidence: 99%

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Hovering performance of Anna's hummingbirds ( Calypte anna ) in ground effect

Kim

Wolf

Ortega-Jimenez

et al. 2014

J. R. Soc. Interface.

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Aerodynamic performance and energetic savings for flight in ground effect are theoretically maximized during hovering, but have never been directly measured for flying animals. We evaluated flight kinematics, metabolic rates and induced flow velocities for Anna's hummingbirds hovering at heights (relative to wing length R ¼ 5.5 cm) of 0.7R, 0.9R, 1.1R, 1.7R, 2.2R and 8R above a solid surface. Flight at heights less than or equal to 1.1R resulted in significant reductions in the body angle, tail angle, anatomical stroke plane angle, wake-induced velocity, and mechanical and metabolic power expenditures when compared with flight at the control height of 8R. By contrast, stroke plane angle relative to horizontal, wingbeat amplitude and wingbeat frequency were unexpectedly independent of height from ground. Qualitative smoke visualizations suggest that each wing generates a vortex ring during both down-and upstroke. These rings expand upon reaching the ground and present a complex turbulent interaction below the bird's body. Nonetheless, hovering near surfaces results in substantial energetic benefits for hummingbirds, and by inference for all volant taxa that either feed at flowers or otherwise fly close to plant or other surfaces.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Hovering performance of Anna's hummingbirds ( Calypte anna ) in ground effect

Kim

Wolf

Ortega-Jimenez

et al. 2014

J. R. Soc. Interface.

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“…Theoretical examinations have been presented by Betz [Bet37], Heyson [Hey60], and Fradenburgh [Fra59], which introduced models to reproduce the effect of ground on a helicopter. Based on this, several experimental correlations and empirical models have been introduced and validated [Zbr47, SGHK03, LLR08, NG12]. With increasing computational power and effectiveness of computational methods the impact of the ground on the aerodynamics of the helicopter could be analyzed in a purely numerical setup.…”

Section: Related Workmentioning

confidence: 99%

Mass‐Dependent Integral Curves in Unsteady Vector Fields

Günther¹,

Kühn

Kutz

et al. 2013

Computer Graphics Forum

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Recent research in flow visualization is focusing on the analysis of time-dependent, but mass-less particles. However, in many application scenarios, the mass of particles -and their resulting inertia -is essential in understanding fluid mechanics. This includes critical processes, such as dust particles interacting with aircraft (e.g., brownor white-out effects) and particle separation based on density variation. In this paper, we contribute a generalized description of mass-dependent particle trajectories and apply existing unsteady flow visualization methods to the mass-dependent case. This comprises the extension of common concepts, i.e., path lines, streak lines, and time lines. Furthermore, we introduce a new class of integral curves, called mass lines that effectively visualizes mass separation and captures mass-related features in unsteady flow fields that are inaccessible using traditional methods. We demonstrate the applicability of our method, using a number of real-world and artificial data sets, in which mass is a crucial parameter. In particular, we focus on the analysis of brown-out conditions, introduced by a helicopter in forward flight close to the ground.

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“…This effect was shown to have a significant influence on the take-off, landing and low-altitude hovering of helicopters and quadcopters because it can increase the lift force at the same power level. Researchers have investigated the ground effect using different methods, such as theoretical aerodynamic modelling (Xin et al, 1999, Griffiths, 2002, Nathan and Green, 2012, control strategies (Nobahari and Sharifi, 2014, Bernard et al, 2017, Shi et al, 2018 and experiments (Nathan and Green, 2008). Hosseini et al (2011) employed numerical calculations and a novel dipole model to investigate the ground effect on a ducted fan aircraft.…”

Section: Introductionmentioning

confidence: 99%

A Moore-Greitzer Model for Ducted Fans in Ground Effect

Jin¹,

Fu²,

Qian³

et al. 2020

JAFM

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Ducted fans are widely used in unmanned aerial vehicles due to their high propulsive efficiency and safety. The aerodynamics are complex within the vicinity of the ground, including takeoff , landing and hovering. In the present study, the aerodynamic stability of the ducted fan was studied with a modified Moore-Greitzer model to estimate and analyse the stability in ground effect. The model was validated and compared with threedimensional unsteady simulations. The results indicated that the rotating stall occurred for the ducted fan in ground effect. The model results can be used to guide the design and control of the vehicles, to ensure the stability and safety of both the ducted fan and vehicles.

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The flow around a model helicopter main rotor in ground effect

Cited by 30 publications

References 13 publications

Hovering performance of Anna's hummingbirds ( Calypte anna ) in ground effect

Hovering performance of Anna's hummingbirds ( Calypte anna ) in ground effect

Mass‐Dependent Integral Curves in Unsteady Vector Fields

A Moore-Greitzer Model for Ducted Fans in Ground Effect

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