An acoustic core may include an array of resonant cells configured as a plurality of resonant cell groups. The resonant cell groups may include a plurality of resonant cells configured as a partitioned resonant cell that include a converging resonant cell and a diverging resonant cell. The converging resonant cell and the diverging resonant cell may be defined by a plurality of cell walls integrally formed with one another and a partition integrally formed with the plurality of cell walls. The partition may at least partially delimit the converging resonant cell from the diverging resonant cell. The converging resonant cell may define an upper resonant space delimited by the partition and a top face of the array of resonant cells. The diverging resonant cell may define a lower resonant space delimited by the partition and a bottom face of the array of resonant cells.

A rotor blade with a leading edge and a trailing edge is provided, wherein the rotor blade is designed and configured for being exposed to a fluid flowing substantially from the leading edge to the trailing edge, the rotor blade includes at least two sensors designed for detecting flow characteristics of the fluid and providing respective sensor signals, and the rotor blade further includes at least two actuators for producing an anti-noise signal based on a sensor signal, the sensors are arranged spanwise and the actuators are arranged chordwise at the surface of the rotor blade, and the actuators are arranged and prepared such that flow-induced edge noise of the rotor blade, which is generated by the fluid, is at least partly cancelled out by the anti-noise signal. Also provided is a method for creating such rotor blade and a related wind turbine.

A noise attenuation panel for a bleed flow is presented that causes a total pressure loss of the bleed flow before it is exhausted. The total pressure loss results from at least two regions in which the flow area contracts and then rapidly expands, with the rapid expansion causing mixing and turbulence rather than full total pressure recovery. This reduced pressure means that when the flow is exhausted into a flow (which may be the bypass flow of a gas turbine engine), its energy, and thus its noise, are reduced.

A blade for a rotating machine, particularly for a gas turbine engine, has a leading edge and a trailing edge joined by pressure and suction surfaces. The trailing edge has a serrated form including a first periodic variation and a second periodic variation of higher frequency and lower amplitude than the first periodic variation.

The present invention relates to airfoils having surface treatments to reduce trailing edge noise. The surface treatment is designed to reduce trailing edge noise by modifying the boundary layer turbulence as it approaches the trailing edge. The surface treatment accomplishes its function by breaking up spanwise-oriented turbulence approaching the trailing edge, thereby reducing the spanwise correlation lengthscales; deflecting the boundary layer turbulence away from the edge; and/or creating spanwise vortices or instability waves to reduce the turbulence-edge interaction.

An arrangement for reducing noise which is generated by a wind turbine blade is provided. The wind turbine blade has a first panel and a second panel. The first and the second panel are arranged at a trailing edge of the wind turbine blade, wherein the first panel is adjacent to the second panel. The first panel includes a first transition zone and the second panel includes a second transition zone. The first transition zone and the second transition zone are engaged in a way that whistle tones produced by a gap of the wind turbine blade, the gap being located between the first panel and the second panel, is reduced or even avoided.

A method of controlling airborne tonal noise which originates from a component of a wind turbine, the wind turbine comprising a vibration control system comprising a plurality of actuators. The method comprising identifying a first operating state of the wind turbine; and selecting a first set of one or more of the actuators on the basis of the identified first operating state. Each actuator of the first set is operated to apply a vibration control oscillation to the component in phase opposition to a vibration of the component, thereby damping the vibration of the component and in turn reducing airborne tonal noise originating from the component. A change of the wind turbine to a second operating state is detected, then a second set of one or more of the actuators is selected on the basis of the identified second operating state. Each actuator of the second set is operated to apply a vibration control oscillation to the component in phase opposition to a vibration of the component, thereby damping the vibration of the component and in turn reducing airborne tonal noise originating from the component.

A wind turbine blade, comprising a sensor device for detecting properties of flow-induced noise produced by the blade and an actuator device for emitting an anti-noise signal for at least partially cancelling out the flow-induced noise, wherein the actuator device comprises an aerodynamically shaped housing attached to an outer surface of the blade. The aerodynamically shaped housing of the actuator device reduces a deterioration the aerodynamic efficiency of the blade. Further, the generation of turbulences at sharp edges of the housing is avoided.