An experimental study of the flow-induced noise created by a wall-mounted finite length airfoil

AIAA 2014-3290This paper presents the results of an experimental investigation of the sound produced by flow interaction with a wall-mounted finite length airfoil at low-to-moderate Reynolds number. Acoustic measurements have been taken in an anechoic wind tunnel at a range of Reynolds numbers, angles of attack and for a variety of airfoil aspect ratios (airfoil length to chord ratio) with a single microphone and two perpendicular planar microphone arrays. For comparison, measurements have also been taken with a semi-infinite or two- dimensional airfoil and a half-span airfoil with tip flow but no boundary layer impingement. The experimental data is used to examine changes in wall-mounted finite airfoil noise production as a function of Reynolds number, angle of attack and airfoil aspect ratio. Additionally, the data gives insight into the airfoil noise generation mechanisms and the influence of flow at the airfoil tip and wall junction on noise productionDanielle J. Moreau , Zebb Prime and Con J. Doola

On the generation of discrete frequency tones by the flow around an aerofoil

Tonal noise, the self-induced discrete frequency noise generated by aerofoils, is investigated. It is heard from an aerofoil placed in streams at low Mach number flows when inclined at a small angle to the stream. It is a piercing whistle, commonly up to 30 dB above the background noise level. Previous authors have attributed tonal noise to a feedback loop consisting of a coupling between laminar boundary-layer instability waves and sound waves propagating in the free stream. Boundary-layer measurements have shown the presence of tonal noise is closely related to the existence of a region of separated flow close to the trailing edge of the aerofoil. An analysis of the linear stability of the boundary-layer flow over the aerofoil is presented. The amplification of the instability waves is shown to be controlled almost entirely by the region of separated flow close to the trailing edge. In light of these new experimental and theoretical results the suitability of the aero-acoustic feedback model is discussed

Optimum spanwise camber for minimum induced drag

SIGLEAvailable from British Library Document Supply Centre- DSC:6015.42F(N--90-18369)(microfiche) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Low temperature thermal expansions of PEEK, HTA and some of their composites reinforced with carbon fibres

SIGLEAvailable from British Library Document Supply Centre- DSC:7620.858(BU-DAE-R--404) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Angle of Attack and Planform Effects on Flat Plate Vortices at Low Reynolds Numbers

Tip vortices of low aspect ratio wings were studied in a water tunnel at Reynolds numbers of 8,000 and 24,000, with dye injection and digital particle image velocimetry in crossflow planes in the near wake, for rectangular, semi-elliptical and delta-wing planforms. The velocity data were used to calculate lift via circulation, and the results were compared with direct force measurements. The objectives of the study were to assess how low vortex circulation, how well the measurement of lift coefficient from tip-vortex circulation, how well the measurements, fit the slender wing theory lift curve slope, and the extent to which planform shape affects lift coefficient while aspect ratio and area are kept constant. All models were thin flat plates with square edges. For the range of streamwise locations and angles of attack studied, apparent viscous effects on vorticity in the wake were small, resulting in good agreement between lift coefficient values inferred from the measurements, the force balance data, and the classical inviscid formulas