Velocity field of a lifting rotor blade in hover

Komerath, N. M.; Thompson, T.L.; Kwon, Oh Joon; Gray, Robin B.

doi:10.2514/3.45585

Cited by 8 publications

(5 citation statements)

References 7 publications

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“…Each experimental point is the average of the 60 six-degree slot-average velocities. This is preferred over a straight arithmetic mean of all 30,000 data values to avoid "velocity bias", which would overestimate the mean velocity 6 . Agreement is excellent in the inboard region.…”

Section: Resultsmentioning

confidence: 99%

“…Ref. 6 reported detailed measurements of all three components of the velocity field in the near field of a single-bladed stiff rotor blade in hover . The velocity field above and below a stiff rotor/airframe configuration in forward flight 7 and the inflow to a flexible rotor system in forward flight 8 have been measured.…”

Section: Introductionmentioning

confidence: 99%

“…As demonstrated by Refs. [6][7][8], techniques for measuring the inflow to the rotor plane are well-understood, as long as the measurements can be averaged over several revolutions. Typical data rates achievable with a laser Doppler velocimeter in large facilities have usually been limited to around 1000 per second.…”

Section: Introductionmentioning

confidence: 99%

“…Scattered light is collected in the backscatter mode. To achieve the high data rate required for the dynamic tests, two Lauterbach-type seeders 6 are used upstream of the rotor plane. Tests showed that the seeders could fill up the room atmosphere with atomized mineral oil within 5 to 10 minutes and give a transient data rate as high as 6000 per second in backscatter.…”

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confidence: 99%

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Measurement Around a Rotor Blade Excited in Pitch, Part 1: Dynamic Inflow

Liou

Komerath

Lal

1994

j am helicopter soc

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This is the first of two papers describing experiments on a two-bladed rotor in hover, under controlled pitch excitation. Measurements of the inflow to the rotor are described, first under steady conditions, and then under prescribed 4-per-rev pitch excitation. The high data rates, data acquisition techniques and data quality required for this experiment are demonstrated, including 4-per-rev velocity variations due to 1-degree pitch oscillation, extracted over a single period of rotor revolution at 600rpm. The steady case results agree with lifting-line-based analytical predictions except in the tip region, as expected. The excited-blade case shows the 4-per rev velocity perturbation, and the dependence on the phase of the excitation. Spectral analysis of the LDV data shows multiple harmonics of the excitation frequency. The rate of pitch change is seen to be high enough to produce substantial hysteresis effects, whose variation with radial position is measured. The hysteresis is seen to arise from the inboard shed vorticity, and to decay towards the tip.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Measurement Around a Rotor Blade Excited in Pitch, Part 1: Dynamic Inflow

Liou

Komerath

Lal

1994

j am helicopter soc

Self Cite

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“…Applications include the prediction of blade-vortex interaction noise 1,2 , improvement of rotor performance 3,4,5,6,7 , prediction of mutual interaction between wakes, and wake /rotor /airframe interactions involving the main rotor(s), fuselage and tail rotor 8,9 and predicting wake-ground interactions which are important to improve handling qualities and reduce debris hazards in near-ground operation 10 . This paper examines issues related to the formation and the decay of vortices from rotor blades in the light of recent measurements and analyses.…”

Section: Introductionmentioning

confidence: 99%

On the Formation and Decay of Rotor Blade Tip Vortices

Komerath

Wong

Ganesh

2004

34th AIAA Fluid Dynamics Conference and Exhibit

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Models for the rate of decay of rotor tip vortices, based on near-wake data and computations, are in conflict with the observed persistence of rotor tip vortices for many revolutions. A correlation of data from the literature shows that the measured tip vortex strength is only 40% of the strength expected from the peak of the blade bound circulation, for blades with sharply-cut straight-edged tips, over a wide range of tip Mach and Reynolds numbers. Explanations of this drop in the near wake through turbulence models, are seen to be both counter-intuitive and in conflict with measurements of turbulent fluctuations. Using flow visualization and velocimetry in the wake of a 2-bladed rotor in low-speed forward flight, explanations are shown for these mysteries. Shear layer development at the blade tip, and the twist distribution of the blade have a strong influence on the fraction of the blade tip vorticity lost into the inboard counter-rotating wake. The observations of elliptic core shape and of multiple local extrema of axial velocity deficit, are shown to be features of the shear-layer separation and rollup processes. Blade-to-blade differences in vortex evolution from the same rotor are traced to surface texture differences at the blade tip. Results in the literature reporting 90 t0 100% tip circulation recovery for such blades, are seen to be in cases where the induced velocity due to the tip vortex could not be distinguished from that due to the inboard sheet.

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The near wake of a model horizontal-axis wind turbine—I. Experimental arrangements and initial results

Ebert

Wood

1997

Renewable Energy

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Velocity field of a lifting rotor blade in hover

Cited by 8 publications

References 7 publications

Measurement Around a Rotor Blade Excited in Pitch, Part 1: Dynamic Inflow

Measurement Around a Rotor Blade Excited in Pitch, Part 1: Dynamic Inflow

On the Formation and Decay of Rotor Blade Tip Vortices

The near wake of a model horizontal-axis wind turbine—I. Experimental arrangements and initial results

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