The invention relates to a nubomachine with a longitudinal axis, comprising two, respectively upstream (122) and downstream, coaxial outer propellers (122), characterised in that at least some of the blades (148) of the upstream propeller (122) comprise at least one internal air circulation chimney (150) that communicates with air-bleeding openings (152) in tire boundary layers of the blades (148). and communicates with air outflow openings (158) on the radially outer end thereof, the air-bleeding openings (152) leading to opening inlets (152a) on tire passive surfaces (156) of the blades (148). the inlets (152a) of the air-bleeding openings being radially arranged in an area (H1) contained between 10% and 45% of the radial dimension (H2) of the blades (148). measured above turd from the radial height of the blades for which the tangent of the leading edge (138) of the blades is orthogonal to the longitudinal axis, and the inlets (152a) of the air bleeding openings being arranged in an area contained between 0% and 30% of the local chord of the blades (148), measured at the level of said inlets (152a) and from the leading edges (138) of tire blades (148).

An aerial vehicle is provided including rotor units connected to the aerial vehicle, and a control system configured to operate at least one of the rotor units. The rotor unit includes rotor blades, wherein each rotor blade includes a surface area, and wherein an asymmetric parameter is defined, at least in part, by the relationship between the surface areas of the rotor blades. The value of the asymmetric parameter is selected such that the operation of the rotor unit: (i) moves the rotor blades such that each rotor blade produces a respective vortex and (ii) the respective vortices cause the rotor unit to produce a sound output having an energy distribution defined, at least in part, by a set of frequencies, wherein the set of frequencies includes a fundamental frequency, one or more harmonic frequencies, and one or more non-harmonic frequencies having a respective strength greater than a threshold strength.

An aerial vehicle is provided including rotor units connected to the aerial vehicle, and a control system configured to operate at least one of the rotor units. The rotor unit includes rotor blades, wherein each rotor blade includes a surface area, and wherein an asymmetric parameter is defined, at least in part, by the relationship between the surface areas of the rotor blades. The value of the asymmetric parameter is selected such that the operation of the rotor unit: (i) moves the rotor blades such that each rotor blade produces a respective vortex and (ii) the respective vortices cause the rotor unit to produce a sound output having an energy distribution defined, at least in part, by a set of frequencies, wherein the set of frequencies includes a fundamental frequency, one or more harmonic frequencies, and one or more non-harmonic frequencies having a respective strength greater than a threshold strength.

An acoustic cavity tailored synthetic jet employs a body having a cavity with a wall including a taper from a first extent to an aperture. The cavity is configured to produce a matched acoustic resonance. A drive system has a piston engaged to the cavity at the first extent. The drive system and piston are configured for oscillatory motion inducing a synthetic jet at the aperture.

A leading edge high-lift device, that may be deployable from a wing of an aircraft, may include a leading edge and a trailing edge. A lower surface and an upper surface may both extend between the leading edge and the trailing edge. A trailing edge region may be defined by the trailing edge and an adjacent region thereto. A shaping device may be disposed at the trailing edge region and may be movable between a non-activated position and an activated position.

A noise-abatement systems (10) provide noise abatement to a wing assembly (Wp) provided with a forward edge slat (ES) and include an elongated shield element (20) which is unconnected but positionable adjacent to a lower trailing edge (16a) of the edge slat (ES) along a lengthwise extent thereof, and a support tab (24) having a distal end fixed to the shield element (20) and a proximal end capable of fixation to an interior cove surface of the edge slat (ES) adjacent an upper trailing edge (22) thereof. The support tab (24) will therefore allow movement of the shield element (20) towards and away from the lower trailing edge (16a) of the edge slat (ES) between an operative position wherein the shield element (20) is positioned adjacent to the lower trailing edge (16a) of the edge slat (ES) along the lengthwise extent thereof and an inoperative position wherein the shield element (20) is spaced from the lower trailing edge (16a) of the edge slat (ES) and positioned in the cove region (12) thereof, respectively.

[Object] To provide a noise reduction apparatus, an aircraft, and a noise reduction method capable of increasing the amount of noise reduction.

[Solving Means] The noise reduction apparatus 1 includes a porous plate 2 disposed to face a fluid flow, the porous plate 2 including a bend region 5 bent toward an upstream side of the fluid flow. The bend region 5 is provided at the end portion 6 of the porous plate 2, and has a concave R-shape on an upstream side of the fluid flow. Although the direction of the fluid flow is typically deflected toward the outside from the center of the porous plate 2 due to the porous plate 2, the deflected fluid easily passes through the porous plate 2 since the porous plate has the bend region 5. Thus, the shear layer of the fluid flow is weakened, the noise induced by the vortex is reduced, and it is possible to increase the reduction amount of noise.

An aerofoil has a leading edge, a trailing edge, a suction surface and a pressure surface. The leading edge includes apertures extending through the aerofoil from the suction surface to the pressure surface. The apertures define a first row spaced a distance (L.sub.1) of between 2 and 6 cm from the leading edge in a chordal direction (C).

An aerial vehicle is provided including rotor units connected to the aerial vehicle, and a control system configured to operate at least one of the rotor units. The rotor unit includes rotor blades, wherein each rotor blade includes a surface area, and wherein an asymmetric parameter is defined, at least in part, by the relationship between the surface areas of the rotor blades. The value of the asymmetric parameter is selected such that the operation of the rotor unit: (i) moves the rotor blades such that each rotor blade produces a respective vortex and (ii) the respective vortices cause the rotor unit to produce a sound output having an energy distribution defined, at least in part, by a set of frequencies, wherein the set of frequencies includes a fundamental frequency, one or more harmonic frequencies, and one or more non-harmonic frequencies having a respective strength greater than a threshold strength.

An acoustic insert comprises a sleeve and a number of wave-shaped passageways within the sleeve. A contour of the number of wave-shaped passageways is selected to provide a desired level of attenuation for a frequency of sound waves entering the sleeve.