Calculation of Aircraft Wake Velocity Profiles and Comparisonwith Experimental Measurements

Donaldson, Coleman duP.; Snedeker, Richard S.; Sullivan, Roger D.

doi:10.2514/3.60385

Cited by 54 publications

(26 citation statements)

References 10 publications

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“…As will be shown, we have used a number of techniques and all have shown promise in the near wake. The main reason for this is that each approach, passive or active, is rooted in the hypothesis of Betz (1933), as extended ingeniously by Donaldson and his collaborators (Donaldson et al, 1974).…”

Section: Objective and Scopementioning

confidence: 99%

“…Furthermore, decoupling vortex management from the control surfaces and only applying it selectively, ensures relatively small wing-load excursions. The aforementioned assertions were initially made by the first author (Greenblatt, 2005(Greenblatt, , 2007) based on the method of Betz (1933) as extended by Donaldson et al (1974). The principle computation advantage of Betz's method is that it does not explicitly treat the rollup mechanism, but rather employs three conservation relations between the span-loading ) ( y and the rolling-up vortex ) (r .…”

Section: Flap-vortex Control Basicsmentioning

confidence: 99%

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Active Management of Flap-Edge Trailing Vortices

Greenblatt

Yao

Vey

et al. 2008

4th Flow Control Conference

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The vortex hazard produced by large airliners and increasingly larger airliners entering service, combined with projected rapid increases in the demand for air transportation, is expected to act as a major impediment to increased air traffic capacity. Significant reduction in the vortex hazard is possible, however, by employing active vortex alleviation techniques that reduce the wake severity by dynamically modifying its vortex characteristics, providing that the techniques do not degrade performance or compromise safety and ride quality. With this as background, a series of experiments were performed, initially at NASA Langley Research Center and subsequently at the Berlin University of Technology in collaboration with the German Aerospace Center. The investigations demonstrated the basic mechanism for managing trailing vortices using retrofitted devices that are decoupled from conventional control surfaces. The basic premise for managing vortices advanced here is rooted in the erstwhile forgotten hypothesis of Albert Betz, as extended and verified ingeniously by Coleman duPont Donaldson and his collaborators. Using these devices, vortices may be perturbed at arbitrarily long wavelengths down to wavelengths less than a typical airliner wingspan and the oscillatory loads on the wings, and hence the vehicle, are small. Significant flexibility in the specific device has been demonstrated using local passive and active separation control as well as local circulation control via Gurney flaps. The method is now in a position to be tested in a wind tunnel with a longer test section on a scaled airliner configuration. Alternatively, the method can be tested directly in a towing tank, on a model aircraft, a light aircraft or a full-scale airliner. The authors believed that this method will have significant appeal from an industry perspective due to its retrofit potential with little to no impact on cruise (devices tucked away in the cove or retracted); low operating power requirements; small lift oscillations when deployed in a time-dependent manner; and significant flexibility with respect to the specific devices selected. American Institute of Aeronautics and Astronautics= slot width h G = Gurney flap height relative to the chord l G = Gurney flap span relative to the flap span L f = flap length, from slot to trailing-edge q = free-stream dynamic pressure r = distance measured form the vortex center Re = Reynolds number based on chord-length U j = peak jet slot blowing velocity U = free-stream velocity U,V,W = mean velocities in directions x,y,z X = distance from perturbation to wing trailing-edge x,y,z = coordinates measured from model leading-edge and root (left-hand system) = angle of attack s = static stall angle = flap deflection angle = wavelength = phase shift in degrees = vortex sheet strength, d /dy = bound circulation = rolled-up wake vortex strength = sweep-back angle x = streamwise vorticity, W/ y-V/ z * = indicates control

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Section: Objective and Scopementioning

confidence: 99%

Section: Flap-vortex Control Basicsmentioning

confidence: 99%

Active Management of Flap-Edge Trailing Vortices

Greenblatt

Yao

Vey

et al. 2008

4th Flow Control Conference

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“…Despite the relative simplicity of the method, it predicts flap vortex details that are in surprisingly good agreement with aircraft-wake wing tip vortices. 28 Implementation of the method presented a difficulty due to the dearth of theoretical or computational methods capable of accurately predicting the effects of zero-efflux perturbations.…”

Section: A Control Predictions Using Inviscid Rollup Relationsmentioning

confidence: 99%

“…Predicting the effect of separation control on flap vortex characteristics was achieved using the method of Betz,27 in the form developed by Donaldson et al 28 Betz's method does not explicitly treat the rollup mechanism, but rather employs three conservation relations between the span-loading ) ( y Γ and the rolling-up vortex ) (r Γ ′ . Betz employed the conservation of vorticity (see eqn.…”

Section: A Control Predictions Using Inviscid Rollup Relationsmentioning

confidence: 99%

Managing Flap Vortices via Separation Control

Greenblatt

2006

AIAA Journal

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A pilot study was conducted on a flapped semi-span model to investigate the concept and viability of near-wake vortex management by means of boundary layer separation control.Passive control was achieved using a simple fairing and active control was achieved via zero mass-flux blowing slots. Vortex sheet strength, estimated by integrating surface pressures, was used to predict vortex characteristics based on inviscid rollup relations and vortices trailing the flaps were mapped using a seven-hole probe. Separation control was found to have a marked effect on vortex location, strength, tangential velocity, axial velocity and size over a wide range of angles of attack and control conditions. In general, the vortex trends were well predicted by the inviscid rollup relations. Manipulation of the separated flow near the flap edges exerted significant control over either outboard or inboard edge vortices while producing small lift and moment excursions. Unsteady surface pressures indicated that dynamic separation and attachment control can be exploited to perturb vortices at wavelengths shorter than a typical wingspan. In summary, separation control has the potential for application to time-independent or time-dependent wake alleviation schemes, where the latter can be deployed to minimize adverse effects on ride-quality and dynamic structural loading.

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“…Recently this problem has received considerable attention in the study of aircraft wake turbulence, -where attempts have been made to predict the trailing vortex structure in the wake of an arbitrarily loaded aircraft wing. Donaldson [5] has sho%.m that the long forgotten model of Betz [6] can be successfully applied to the problem. Betz assumes that the circulation and moment of vorticity of the.…”

Section: Introduction -mentioning

confidence: 99%

Effect of tip vortex structure on helicopter noise due to blade-vortex interaction

Widnall

Wolf

1980

Journal of Aircraft

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A potential cause of helicopter impulsive noise, commonly called blade slap, is the unsteady lift fluctuation on a rotor blade due to interaction with the vortex trailed from another blade. The relationship between vortex structure and the intensity of the acoustic signal is investigated. The analysis is based on a theoretical model for blade/vortex interaction, due originally to Widnall. Unsteady lift on the blades due to blade/vortex interaction is calculated using linear unsteady aerodynamic theory, and expressions are derived for the directivity, frequency spectrum, and transient signal of the radiated noise. The inviscid rollup model of Betz is used to calculate the velocity profile in the trailing vortex from the spanwise distribution of blade tip loading. A few cases of tip loading are investigated, and numerical results are presented for the unsteady lift and acoustic signal due to blade/vortex interaction. The intensity of the acoustic signal is shown to be quite sensitive to changes in tip vortex structure.

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Calculation of Aircraft Wake Velocity Profiles and Comparisonwith Experimental Measurements

Cited by 54 publications

References 10 publications

Active Management of Flap-Edge Trailing Vortices

Active Management of Flap-Edge Trailing Vortices

Managing Flap Vortices via Separation Control

Effect of tip vortex structure on helicopter noise due to blade-vortex interaction

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