Assessment of Rotorcraft Brownout Severity in Terms of Rotor Design Parameters

Milluzzo, Joseph; Leishman, J. Gordon

doi:10.4050/jahs.55.032009

Cited by 29 publications

(11 citation statements)

References 7 publications

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“…Examining the baseline case (i.e., Figs. 11a-11e), it is apparent that the blade tip vortices, seen as concentrated regions of high velocity in the plane, impinge upon the ground and interact with each other to form a supervortex or ground vortex, as noted in prior research [12,50,51]. The ground vortex begins to form beneath the forward part of the rotor disk (Fig.…”

Section: B Physical Interpretation Of the Resultsmentioning

confidence: 89%

Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

Tritschler

Celi

Leishman

2014

Journal of Guidance, Control, and Dynamics

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A methodology is presented for the selection of approach-to-landing maneuvers that may result in improved brownout characteristics. The methodology is based upon a brownout metric that assesses the relative brownout cloud volume densities in critical regions of the pilot's field of view. The metric becomes the objective function of a procedure in which a typical visual approach profile is parameterized and optimized to minimize brownout in a representative landing maneuver. The optimization is constrained to avoid maneuvers that would be conducive to the onset of vortex ring state or would result in flight within the "avoid" regions of a typical helicopter height-velocity diagram. The analysis uses a free-vortex wake model and simulates the dynamics of the dust particles immersed in the rotor downwash. The results show that the optimal approach trajectories affect the resulting flowfield, particularly the development of a ground vortex ahead of the rotor disk, which influences the rate of development, size, and volume density of the brownout cloud. The results are compared with prior experimental results, and potential operational interpretations of the outcomes are examined. Nomenclature A= rotor disk area, πR 2 , ft 2 BX = objective function, Eq. (12) bX; t = particle count in the "best" region of the pilot's field of view, Eq. (11) C T = rotor thrust coefficient, T∕ρAΩR 2 D = main rotor diameter, ft FX = additional design objective function gX = constraint equation, Eq.(2) H = Hessian matrix h = rotor hub height above ground, ft n ent = number of entrained particles n P = number of particles p app X = series of discrete points describing approach X p HV = series of discrete points describing the "avoid" region boundaries on a height-velocity diagram p VRS = series of discrete points describing flight regime boundaries where VRS may occur R = rotor radius, ft r = longitudinal range from landing point, ft r pd = longitudinal range from landing point at which the peak deceleration occurs, ft S = unit vector T = rotor thrust, lb V = forward velocity, ft∕s or kt V c = climb velocity, ft∕s v h = hover inflow velocity, ft∕s v 0 = initial (asymptotic) velocity, ft∕s or kt X = vector of design variables, γ v 0 r pd T X u = aircraft stability derivative, ∂X∕∂u γ = approach angle, deg ϵ = tolerance value for defining behavior constraints, Eqs. (15) and (16) θ = aircraft pitch angle, deg θ P , ϕ P , ρ P = particle location (azimuth, elevation, distance) in a spherical coordinate systemfluid density, slugs∕ft 3 χ = wake skew angle, deg Ω = rotational frequency, rad∕s Subscripts app = approximation max = maximum allowable value (upper bound) min = minimum allowable value (lower bound) Superscript = value for optimum configuration

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Section: B Physical Interpretation Of the Resultsmentioning

confidence: 89%

Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

Tritschler

Celi

Leishman

2014

Journal of Guidance, Control, and Dynamics

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“…The phenomenon of "brownout" is an operational problem for most types of rotorcraft, especially those operating in dry and arid climates [2][3][4]. The pilot loses all visual references, and this can induce a dangerous sideward or rearward drift during takeoff or touchdown, which most aircraft cannot safely handle [5].…”

Section: Figure 1: Examples Of Dve Conditionsmentioning

confidence: 99%

Performance evaluation of active sub-Terahertz systems in Degraded Visual Environments (DVE)

et al. 2016

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This paper addresses the problem of critical operations in Degraded Visual Environment (DVE). DVE usually refer when the perception of a pilot is degraded by environmental factors, including the presence of obscurants from bad weather (e.g. fog, rain, snow) or accidental events (e.g. brownout, whiteout, smoke). Critical operations in DVE are a growing field of research as it is a cause of numerous fatal accidents for operational forces. Due to the lack of efficient sources and sensors in the Terahertz (THz) region, this domain has remained an unexplored part of the electromagnetic spectrum. Recently, the potential use of sub-Terahertz waves has been proposed to see through dense clouds of obscurants (e.g. sand, smoke) in DVE conditions. In order to conduct a performance evaluation of sub-Terahertz systems, several sub-terahertz systems (e.g. bolometer-array cameras, liquid helium cooled bolometers) were operated in artificial controlled DVE conditions at ONERA facilities. The purpose of this paper is to report field experiments results in controlled DVE conditions: attenuation measurements from 400 GHz to 700 GHz with a performance evaluation of different sub-Terahertz systems are presented.

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“…Despite the overall complexity of brownout, the severity and rate of dust cloud development can be correlated to certain global characteristics of the rotorcraft (Ref. 2), including (but not limited to) disk loading and wake (tip vortex) strength. To better understand the details of brownout formation and to explore the possibilities for mitigating brownout severity, various modeling strategies have been developed (Refs.…”

Section: Introductionmentioning

confidence: 99%

Time-Resolved Measurements of Rotor-Induced Particle Flows Produced by a Hovering Rotor

Sydney¹,

Leishman²

2014

J Am Helicopter Soc

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The flow environment produced by a hovering rotor operated at different heights over a mobile particle bed was studied by using flow visualization (FV), particle image velocimetry (PIV), and particle tracking velocimetry (PTV) techniques. The particle species included three size ranges of well-characterized glass microspheres. Time histories of the rotor wake interactions with the bed were examined, providing a better understanding of the transient processes and mechanisms that lead to the uplift of particles and to the formation of dust clouds around a rotor operating in ground effect over loose sediment. The FV/PIV/PTV measurements confirmed five possible mechanisms of particle uplift and transport: (1) creep, (2) modified saltation and saltation bombardment, (3) vortex-induced trapping, (4) reingestion bombardment, and (5) secondary suspension. High levels of particle entrainment were found to occur near the wake impingement zone on the bed, mainly from the localized effects of the blade tip vortices. Once entrained, the PTV showed that significant numbers of particles were intermittently trapped in the vortex-induced upwash field. The pairing and merging of adjacent turns of the vortex wake was seen to affect particle mobilization and to enhance secondary particle suspension. The bombardment of previously trapped particles back onto the bed by the flow was shown to be a primary mechanism responsible for liberating more particles.

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Assessment of Rotorcraft Brownout Severity in Terms of Rotor Design Parameters

Cited by 29 publications

References 7 publications

Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

Methodology for Rotorcraft Brownout Mitigation Through Flight Path Optimization

Performance evaluation of active sub-Terahertz systems in Degraded Visual Environments (DVE)

Time-Resolved Measurements of Rotor-Induced Particle Flows Produced by a Hovering Rotor

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