Abstract: A fluid dynamic structure includes a surface and a microstructure mounted on the surface. The microstructure is defined by a plurality of peaks and valleys (i.e., riblets) and includes a transition region in which each peak and valley changes from a first profile to a second profile along a chord length of the structure. The peaks and/or valleys may have a variable dimension along the length of the microstructure. The peaks and valleys can be non-linear along the chord length and have a smooth transition from the first profile to the second profile. The different profiles of the microstructure are optimized to reduce noise generated by turbulent fluid flow across the structure.

Abstract: A method and an apparatus for measuring an air flow at an airfoil surface are provided, wherein at least one pressure sensor adapted to detect an air flow associated with a rotor blade surface and a pressure transducer which converts the detected air flow into an electrical signal indicating the air flow are provided. The pressure sensor is arranged within the boundary layer of the air flow at the airfoil surface such that the boundary layer profile may be determined from the electrical signal. The air flow sensor is adapted for rotor blades of a wind turbine to assist in adjusting a pitch angle of the rotor blades.

Abstract: A fluid dynamic structure includes a surface and a microstructure mounted on the surface. The microstructure is defined by a plurality of peaks and valleys (i.e., riblets) and includes a transition region in which each peak and valley changes from a first profile to a second profile along a chord length of the structure. The peaks and/or valleys may have a variable dimension along the length of the microstructure. The peaks and valleys can be non-linear along the chord length and have a smooth transition from the first profile to the second profile. The different profiles of the microstructure are optimized to reduce noise generated by turbulent fluid flow across the structure.

Abstract: Low-noise wind turbine blades are provided wherein metallic and/or polymeric cellular materials that are capable of bearing directional loads are used in the construction of wind turbine blade parts or entire sections. The use of such materials influences the air flow over them in such a way that the resulting boundary-layer turbulence is damped in a controlled way, thus weakening the noise scattering mechanism at the trailing edge, and the scattered acoustic waves are absorbed and attenuated by the material acting as an acoustic liner.

Abstract: A method and an apparatus for measuring an air flow at an airfoil surface are provided, wherein at least one pressure sensor adapted to detect an air flow associated with a rotor blade surface and a pressure transducer which converts the detected air flow into an electrical signal indicating the air flow are provided. The pressure sensor is arranged within the boundary layer of the air flow at the airfoil surface such that the boundary layer profile may be determined from the electrical signal. The air flow sensor is adapted for rotor blades of a wind turbine to assist in adjusting a pitch angle of the rotor blades.

Abstract: A nozzle for a gas turbine engine is provided with undulations on a core and/or fan exhaust flow nozzle. An annular wall defines a fluid flow passage and includes a base portion and an adjoining exit portion. The base portion is typically generally frustoconical in shape and includes an arcuate contour in an axial direction. The exit portion includes undulations in a generally radial direction that provide lobes and troughs each respectively including trailing edges. One of the lobe and trough trailing edges are recessed from the other of the lobe and trough trailing edges in a generally axial direction. The other of the lobe and trough trailing edges form apexes with the apexes provided on tabs. The troughs extend radially inward in the axial direction towards the trough trailing edges.

Abstract: Low-noise wind turbine blades are provided wherein metallic and/or polymeric cellular materials that are capable of bearing directional loads are used in the construction of wind turbine blade parts or entire sections. The use of such materials influences the air flow over them in such a way that the resulting boundary-layer turbulence is damped in a controlled way, thus weakening the noise scattering mechanism at the trailing edge, and the scattered acoustic waves are absorbed and attenuated by the material acting as an acoustic liner.

Abstract: A nozzle for a gas turbine engine is provided with undulations on a core and/or fan exhaust flow nozzle. An annular wall defines a fluid flow passage and includes a base portion and an adjoining exit portion. The base portion is typically generally frustoconical in shape and includes an arcuate contour in an axial direction. The exit portion includes undulations in a generally radial direction that provide lobes and troughs each respectively including trailing edges. One of the lobe and trough trailing edges are recessed from the other of the lobe and trough trailing edges in a generally axial direction. The other of the lobe and trough trailing edges form apexes with the apexes provided on tabs. The troughs extend radially inward in the axial direction towards the trough trailing edges.

Abstract: A system for reducing jet noise emission from an internally mixed gas turbine engine exhaust, comprising a fan/core flow mixer having a plurality of mixer lobes and a common flow nozzle having an equal number of tabs located along a circumferential edge of an aft end of the nozzle. There is a predetermined clocking relationship between the plurality of mixer lobes and the plurality of nozzle tabs that results in reduced exhaust noise emission, most evident in the lower frequency range. A method for reducing jet noise emission from an internally mixed gas turbine engine exhaust comprises selectively aligning a circumferential distribution of a mixed flow vorticity field produced by a fan/core mixer with a circumferentially distributed exhaust flow vorticity field produced by a modified common flow nozzle at an exit plane of the engine exhaust.

Abstract: A system for reducing jet noise emission from an internally mixed gas turbine engine exhaust, comprising a fan/core flow mixer having a plurality of mixer lobes and a common flow nozzle having an equal number of tabs located along a circumferential edge of an aft end of the nozzle. There is a predetermined clocking relationship between the plurality of mixer lobes and the plurality of nozzle tabs that results in reduced exhaust noise emission, most evident in the lower frequency range. A method for reducing jet noise emission from an internally mixed gas turbine engine exhaust comprises selectively aligning a circumferential distribution of a mixed flow vorticity field produced by a fan/core mixer with a circumferentially distributed exhaust flow vorticity field produced by a modified common flow nozzle at an exit plane of the engine exhaust.