Surface Pressure Measurements at the Tip of a Model Helicopter Rotor in Hover

Shivananda, T.; McMahon, Howard M.; Gray, Robin B.

doi:10.2514/3.58391

Cited by 20 publications

(2 citation statements)

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“…An excess axial velocity in the secondary vortex has been inferred from (mean) suction pressure peaks measured where the axis of the secondary vortex crosses the upper wing surface. 7 ' 8 Turbulence convection velocities in excess of the freestream, measured in this study, provide further supporting evidence of excess axial velocities in the secondary tip vortex.…”

mentioning

confidence: 53%

Pressure fluctuations in the tip region of a blunt-tipped airfoil

1990

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The characteristics of turbulence generated in the tip region of a blunt-tipped airfoil were studied using surface pressure measurements. Pressure transducers were located at five chordwise positions on the upper tip-edge, the lower tip-edge, and on the flat tip. The model was an NACA 0012, 0.76-m chord, aspect ratio 2.7, semispan wing section. Tests were performed at flow speeds of 75, 55, and 35 m/s and angles of attack of 6,12, and 16 deg. Reynolds numbers based on the wing chord were 1.9, 3.0, and 4.1 xlO 6 . Pressure fluctuations measured near the primary tip-vortex on the upper, low pressure side of the wing tip were uncorrelated with those on the blunt tip. Fluctuations on the high pressure side of the wing were strongly correlated with those on the flat tip, but 10-20 dB less intense. Spectra measured on the flat tip displayed pronounced peaks at dimensionless frequencies /f/U 0 = 0.8 to 1.3. Cross correlations between some of the flat-tip pressures displayed two echolike groupings. A model is proposed that explains these correlations. Nomenclature AR -wing aspect ratio (wing span divided by wing chord) C L = wing lift coefficient C d = wing drag coefficient D = diameter of the secondary tip-vortex core E(f) =pressure power spectral density in (N/m 2 ) 2 /Hz / = frequency in Hz f p -frequency, in Hz, of peak energy in spectrum or correlation A/ = bandwidth, in Hz, of energy in a cross correlation <7 0 =freestream head (pC/ 0 2 /2) in. N/m 2 St = Strouhal number, dimensionless frequency, ft/U 0 t = wing thickness in m t d = turbulence convection time U m = mean streamwise velocity in secondary tip-vortex U 0 = freestream velocity in m/s a = wing angle of attack in rad T -correlation delay time

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mentioning

confidence: 53%

Pressure fluctuations in the tip region of a blunt-tipped airfoil

1990

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“…Drag reduction may also be achieved through attention to wing tip design. The sheared tip 12 -" has been studied as a tip configuration which may reduce drag in a manner analogous to a crescent wing. i.e.…”

Section: Introductionmentioning

confidence: 99%

Effects of delta planform tip sails on the performance of a blunt edged rectangular wing

Traub

1997

Aeronaut. j.

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A windtunnel study was undertaken to determine the effects of delta planform tip sails (DPTS) on the aerodynamic characteristics of a planar blunt edged wing. In the investigation, the sail incidence and chordwise attachment position were varied. The results indicate that significant performance improvements can be obtained with DPTS. For all DPTS variations, increases of lift curve slope, maximum lift coefficient and Oswald efficiency factor were recorded and compared to the basic wing.

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A note on the tip noise of rotating blades

Farassat

Martin²

1983

Journal of Sound and Vibration

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Surface Pressure Measurements at the Tip of a Model Helicopter Rotor in Hover

Cited by 20 publications

References 1 publication

Pressure fluctuations in the tip region of a blunt-tipped airfoil

Pressure fluctuations in the tip region of a blunt-tipped airfoil

Effects of delta planform tip sails on the performance of a blunt edged rectangular wing

A note on the tip noise of rotating blades

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