Abstract: A turbomachinery stage comprising two axially spaced blade rows, one of which is rotatable, wherein the blades of the upstream row are contoured to present a leaned wake to the downstream row. In the preferred embodiment, the blades of the upstream row extend radially from a central hub and, at a radius above the hub, are physically curved circumferentially from a radial line through the hub. The physical lean locally complements the inherent aerodynamic lean at each radius such that the integrated acoustic power of the stage is essentially at a minimum, thus maximizing the acoustic attenuation. Preferably, the constraint is imposed that the blade physical curvature is essentially smooth, continuous and without an inflection point.

Abstract: A sound-attenuating inlet duct is provided for a gas turbine engine wherein the inlet duct includes a casing defining, in serial flow relationship, a minimum area throat of predetermined axial extent, a diffuser and a cylindrical section. Sound-absorbent acoustic material is disposed upon the inner walls of the duct in the cylindrical section. A first amount of acoustic attenuation is provided by accelerating the motive fluid to high subsonic velocities through the throat. A second amount of acoustic attenuation is provided by locally accelerating the motive fluid in the vicinity of the acoustic material, thereby imparting a velocity component to the acoustic waves which is normal to the acoustic material, thereby enhancing absorption. By sizing the various sections of the inlet duct in a unique predetermined relationship the effects of the two sources of acoustic attenuation may be made additive.