Abstract: An inlet door for an auxiliary power unit includes a door body with opposed interior and exterior surfaces. The interior surface of the inlet door is curved to diffuse sound waves received by the interior surface.

Abstract: An exhaust system for an APU in a gas turbine engine aircraft having a tail cone in which exhaust noise is reduced. An APU exhaust liner is attached to the APU and extending to an oval cutout at the tail cone The liner has a first constant cross section from the APU to a point proximate the tail cone, and a second, increasing cross section from the point proximate the tail cone to the liner cutout. The liner is turned toward the side of the tail. The liner cutout is further enlarged with at least one larger cutout.

Abstract: A retainer for a gas turbine engine includes a center body, a plurality of struts, and a ring. The plurality of struts are connected to and extend outward from the center body. The ring is connected to the plurality of struts and is positioned aft of the center body with respect to a direction of airflow through the gas turbine engine.

Abstract: An exhaust system for an APU in a gas turbine engine aircraft having a tail cone in which exhaust noise is reduced. An APU exhaust liner is attached to the APU and extending to an oval cutout at the tail cone The liner has a first constant cross section from the APU to a point proximate the tail cone, and a second, increasing cross section from the point proximate the tail cone to the liner cutout. The liner is turned toward the side of the tail. The liner cutout is further enlarged with at least one larger cutout.

Abstract: An anti-surge mechanism has a duct for tapping compressed air and delivering that air into an exhaust flow. A selectively open valve allows the tapped air to flow into the exhaust flow through a plurality of holes. The holes are sized to tune a frequency of a sound created by the tapped air to a frequency range outside of normal human hearing. A gas turbine engine is also disclosed.

Abstract: An inlet door for an auxiliary power unit includes a door body with opposed interior and exterior surfaces. The interior surface of the inlet door is curved to diffuse sound waves received by the interior surface.

Abstract: An air inlet assembly comprising an entrance region configured to receive an airflow, an exit region configured to output the airflow, and an attenuation region disposed between the entrance region and the exit region. The attenuation region has a cross section aspect ratio of at least about 5-to-1, and comprises acoustic absorbing material.

Abstract: An exemplary diffuser includes a plurality of air flow channels defined by a corresponding plurality of vanes. The vanes extend from a first side of the diffuser and define a width of the air flow channel between the corresponding plurality of vanes. The first side has at least one tapered surface extending from an inner radial position to an outer radial position. The distance between a tapered surface and a top side of the plurality of the vanes defines a depth of the air flow channel. The width of the air flow channel varies relative to the depth of the air flow channel along the length of the air flow channel.

Abstract: A retainer for a gas turbine engine includes a center body, a plurality of struts, and a ring. The plurality of struts are connected to and extend outward from the center body. The ring is connected to the plurality of struts and is positioned aft of the center body with respect to a direction of airflow through the gas turbine engine.

Abstract: An example auxiliary power unit air inlet assembly includes a noise attenuating component disposed within a conduit. The conduit is configured to communicate a first flow of fluid to an auxiliary power unit. A second flow of fluid is communicated to the noise attenuating component. The second flow of fluid limits formation of ice in the conduit. The first flow of fluid is different than the second flow of fluid.

Abstract: An exhaust silencer assembly includes an exhaust duct and an exhaust silencer. The exhaust silencer is disposed about the exhaust duct and has a plurality of solid baffles and at least one perforated baffle The exhaust silencer assembly is disposed downstream of an auxiliary power unit and at least partially attenuates the downstream noise of the combustion gases that result from operation of the auxiliary power unit. In one embodiment, at least one of the plurality of solid baffles is disposed to extend axially between generally radially extending solid baffles, perforated baffle(s), or partially perforated baffles. The axially extending solid baffle allows for cavity depth variation in the silencer to optimize tuning of particular frequencies from the auxiliary power unit.

Abstract: A method of reducing engine noise for an engine under little or low load conditions includes the steps of: establishing an engine idle speed for the engine when the engine has less than a predetermined minimum level of load; measuring the level of load on the engine; measuring the speed of the engine; and reducing the speed of the engine to the engine idle speed if the measured level of load on the engine is less than the predetermined minimum level of load and the measured speed of the engine is greater than the engine idle speed.

Abstract: An exhaust duct system for a gas turbine engine that mounts within a tail cone of an aircraft, comprises an exhaust exit that exits one side of the tail cone offset from the axial centerline of the tail cone and an exhaust duct that couples the engine to the offset exhaust exit, with a straight section of the exhaust duct extending from the exhaust exit for a length that corresponds to at least one diameter of the exhaust duct.

Abstract: A cooling system for the rear bearing capsule of a turbine in a gas turbine engine supported by an exhaust cone attached to multiple exit guide vanes that extend radially from the exhaust cone to an exhaust housing, comprises: an inlet air flow path through each guide vane between a source of cool ambient air and the rear bearing capsule; and at least one discharge air flow path that receives air from the inlet air flow path through each guide vane and passes the air through the exhaust cone from the rear bearing capsule to a high velocity gas flow path in the exhaust housing.

Abstract: A turbine apparatus comprises a rotor with a hub section defined about a rotational axis and a plurality of blades attached to the hub section. The plurality of blades comprises a first group having a first angular spacing in a first circumferential sector of the rotor, and a second group having a second angular spacing in a second circumferential sector of the rotor. The first angular spacing is different from the second angular spacing, and the rotor blades are asymmetric about the rotational axis.

Abstract: An exhaust silencer assembly includes an exhaust duct and an exhaust silencer. The exhaust silencer is disposed about the exhaust duct and has a plurality of solid baffles and at least one perforated baffle The exhaust silencer assembly is disposed downstream of an auxiliary power unit and at least partially attenuates the downstream noise of the combustion gases that result from operation of the auxiliary power unit. In one embodiment, at least one of the plurality of solid baffles is disposed to extend axially between generally radially extending solid baffles, perforated baffle(s), or partially perforated baffles. The axially extending solid baffle allows for cavity depth variation in the silencer to optimize tuning of particular frequencies from the auxiliary power unit.

Abstract: An example auxiliary power unit air inlet assembly includes a noise attenuating component disposed within a conduit. The conduit is configured to communicate a first flow of fluid to an auxiliary power unit. A second flow of fluid is communicated to the noise attenuating component. The second flow of fluid limits formation of ice in the conduit. The first flow of fluid is different than the second flow of fluid.

Abstract: A system for reducing compressor noise includes a rotor having a plurality of blades. The blades have a nominal geometry characterized by a blade parameter. At least some of the blades are mistuned, such that they differ from the nominal geometry by greater than a manufacturing tolerance in the blade parameter. The blades produce shock waves at a blade passing frequency, and the mistuned blades shift acoustic energy away from the blade passing frequency to multiple lower amplitude tones at other frequencies. The system is configurable to be deployed with an inlet silencer that preferentially absorbs acoustic energy at some of the shifted frequencies.

Abstract: An inlet duct for an auxiliary power unit comprises an inlet end, and extends to an outlet end. At least one splitter is positioned within the duct and between the inlet and the outlet end to sub-divide an interior of the duct into plural flow paths.

Abstract: An exemplary diffuser includes a plurality of air flow channels defined by a corresponding plurality of vanes. The vanes extend from a first side of the diffuser and define a width of the air flow channel between the corresponding plurality of vanes. The first side has at least one tapered surface extending from an inner radial position to an outer radial position. The distance between a tapered surface and a top side of the plurality of the vanes defines a depth of the air flow channel. The width of the air flow channel varies relative to the depth of the air flow channel along the length of the air flow channel.