GAS TURBINE ENGINE EXHAUST DIFFUSER WITH MOVABLE STRUTS

Abstract

An exhaust diffuser for a gas turbine engine gas turbine engine includes a multiple of circumferentially spaced struts that extend between an inner gaspath wall and an outer gaspath wall, at least one of the multiple of circumferentially spaced struts movable about a strut axis.

Description

BACKGROUND

The present disclosure relates generally to a gas turbine engine and, more particularly, to an exhaust diffuser of an auxiliary power unit (APU).

An auxiliary power unit (APU) is commonly installed in aircraft and vehicles to provide mechanical shaft power for electrical and hydraulic equipment such as electrical power generators, alternators and hydraulic pumps. APUs, much like other gas turbine engines, produce a certain amount of noise during operation. Typical noise reduction systems include baffle mufflers and Herschel Quincke tubes, however, noise reduction and pressure recovery may often be a design challenge.

SUMMARY

An exhaust diffuser for a gas turbine engine according to one disclosed non-limiting embodiment of the present disclosure includes an inner gaspath wall, an outer gaspath wall and a multiple of circumferentially spaced struts that extend between said inner gaspath wall and said outer gaspath wall, at least one of said multiple of circumferentially spaced struts movable about a strut axis.

In a further embodiment of the foregoing embodiment, each one of the multiple of circumferentially spaced strut is movable about a respective strut axis.

In a further embodiment of any of the foregoing embodiments, the inner gaspath wall is defined around an engine centerline axis.

In a further embodiment of any of the foregoing embodiments, the outer gaspath wall is defined around an engine centerline axis.

In a further embodiment of any of the foregoing embodiments, the at least one of said multiple of circumferentially spaced struts includes a shroud movable about a pivot tube mounted to said inner gaspath wall and said outer gaspath wall. In the alternative or additionally thereto, in the foregoing embodiment the pivot tube is hollow.

In a further embodiment of any of the foregoing embodiments, the at least one of said multiple of circumferentially spaced struts is movable over an approximate +/−twenty degree range.

A gas turbine engine according to another disclosed non-limiting embodiment of the present disclosure includes an exhaust diffuser that defines a gaspath, a multiple of circumferentially spaced struts that extend across the gaspath, at least one of the multiple of circumferentially spaced struts movable about a strut axis.

In a further embodiment of the foregoing embodiment, each one of said multiple of circumferentially spaced strut is movable about a respective strut axis.

In a further embodiment of any of the foregoing embodiments, the gas path is annular.

In a further embodiment of any of the foregoing embodiments, the exhaust diffuser is downstream of a turbine section.

A method of operating a gas turbine engine according to another disclosed non-limiting embodiment of the present disclosure includes modulating an exhaust diffuser downstream of a turbine section.

In a further embodiment of the foregoing embodiment, the modulating includes moving at least one of a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.

In a further embodiment of any of the foregoing embodiments, the modulating includes pivoting at least one of a multiple of circumferentially spaced struts that extend across a gaspath defined by the exhaust diffuser.

In a further embodiment of any of the foregoing embodiments, the modulating includes moving a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.

In a further embodiment of any of the foregoing embodiments, the modulating includes pivoting a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 is a general schematic view of an exemplary gas turbine engine according to one non-limiting embodiment;

FIG. 2 is an expanded view of an exhaust diffuser of the gas turbine engine;

FIG. 3 is an expanded perspective view of a movable exhaust strut of the exhaust diffuser; and

FIG. 4 is an expanded sectional view of the movable exhaust strut of the exhaust diffuser taken along line 4-4 in FIG. 2 to illustrate an example range of movement.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as an Auxiliary Power Unit (APU), however various gas turbine engines such as turboshaft engines may also benefit herefrom. The gas turbine engine 20 is circumferentially disposed about an engine centerline A. The gas turbine engine 20 generally includes a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. The fan section 22 draws in ambient air through for compression in the compressor section 24. The compressed air is then mixed with fuel and ignited in the combustor section 26 to generate an annular stream of hot combustion gases that is expanded through the turbine section 28 to extract energy and drive the fan section 22 and the compressor section 24.

The gas turbine engine 20 further includes an exhaust diffuser 30 that generally includes an inner gaspath wall 32, an outer gaspath wall 34 and a multiple of circumferentially spaced struts 36 that extends therebetween. The exhaust diffuser 30 defines an annular gaspath 38 for the hot combustion gases downstream of the turbine section 28.

In the disclosed non-limiting embodiment, at least one of the multiple of circumferentially spaced struts 36 is movable about a strut axis P (a moveable strut 36′ of FIG. 2) that is transverse or perpendicular to the engine longitudinal axis A. Although only a single movable strut 36′ will be described in detail, it should be appreciated that all or a subset of the multiple of circumferentially spaced struts 36 may be pivotable and thus generally equivalent to the moveable strut 36′ described in detail herein.

With reference to FIG. 2, the movable strut 36′ generally includes a pivot tube 40 and a shroud 42. The pivot tube 40 extends between the inner gaspath wall 32, and the outer gaspath wall 34 to provide a required stiffness to support a rear bearing housing (not shown) and the exhaust diffuser 30. The pivot tube 40 may be hollow to provide a services path across the gaspath for wires, conduits, fluids, scavenging, etc. In one disclosed non-limiting embodiment, the axis P defined by the pivot tube 40 may be located at approximately on-third chord the shroud 42.

The shroud 42 is a generally airfoil-shaped member that surrounds the pivot tube 40 and rotates therearound. The shroud 42 is defined by an outer airfoil wall surface 44 of FIG. 3 between a leading edge 46 and a trailing edge 48. The outer airfoil wall surface 44 defines a generally concave shaped portion to form a pressure side 50 and a generally convex shaped portion to four a suction side 52 (FIG. 3).The outer airfoil wall surface 68 is typically shaped to generally axially straighten the combustion gases discharged from the turbine section 28.

Hot combustion gases discharged from the turbine section 28 into the exhaust diffuser 30 have a residual velocity component in the tangential direction with respect to the engine axis A. The tangential velocity component of the hot combustion gases may detract from the momentum increase that produces a forward axial thrust in the gas turbine engine. The tangential velocity component of the flow is redirected axially by the multiple of circumferentially spaced struts 36. That is, the shroud 42 defines an airfoil profile that axially straightens the combustion gases flow.

In the exhaust diffuser 30 aft of the turbine section 28, the multiple of circumferentially spaced struts 36 axially straightens residual swirl. The amount of swirl may vary from one engine operating condition to another such that in some conditions, the flow may be subject to flow separation. Flow separation may effect efficiency and noise levels as the hot combustion gases discharged from the turbine section 28 into the exhaust diffuser 30 the swirl angle may vary by as much as approximately +/−20 degrees at different conditions.

With reference to FIG. 4, the shroud 42 of each of the movable strut 36′ is freely movable about the pivot tube 40. The shroud 42, in one non-limiting embodiment, may be mechanically limited in pitch to, for example, an approximate +/−twenty degree range. The movable struts 36′ thereby passively adjust to the variable swirl angle of the hot combustion gases discharged from the turbine section 28. In other words, movement of the movable struts 36′ freely changes an angle of attack in response to the aerodynamic forces applied to the shroud 42 to modulate the exhaust diffuser 30 and thereby minimize or eliminate the otherwise possible flow separation that may result from the variance of swirl angle. The reduction or elimination of flow separation increases efficiency and reduces noise levels over a significantly greater range of conditions as compared to conventional fixed strut architectures.

It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the engine but should not be considered otherwise limiting.

Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments.

It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Although the different non-limiting embodiments have specific illustrated components, the embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments.

Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present disclosure.

The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the disclosure may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.

Claims

1. An exhaust diffuser for a gas turbine engine comprising:

an inner gaspath wall;

an outer gaspath wall; and

a multiple of circumferentially spaced struts that extend between said inner gaspath wall and said outer gaspath wall, at least one of said multiple of circumferentially spaced struts movable about a strut axis.

2. The exhaust diffuser as recited in claim 1, wherein each one of said multiple of circumferentially spaced strut is movable about a respective strut axis.

3. The exhaust diffuser as recited in claim 1, wherein said inner gaspath wall is defined around an engine centerline axis.

4. The exhaust diffuser as recited in claim 1, wherein said outer gaspath wall is defined around an engine centerline axis.

5. The exhaust diffuser as recited in claim 1, wherein said at least one of said multiple of circumferentially spaced struts includes a shroud movable about a pivot tube mounted to said inner gaspath wall and said outer gaspath wall.

6. The exhaust diffuser as recited in claim 5, wherein said pivot tube is hollow.

7. The exhaust diffuser as recited in claim 1, wherein said at least one of said multiple of circumferentially spaced struts is movable over an approximate +/−twenty degree range.

8. A gas turbine engine comprising:

an exhaust diffuser that defines a gaspath, a multiple of circumferentially spaced struts that extend across said gaspath, at least one of said multiple of circumferentially spaced struts movable about a strut axis.

9. The gas turbine engine as recited in claim 8, wherein each one of said multiple of circumferentially spaced strut is movable about a respective strut axis.

10. The gas turbine engine as recited in claim 8, wherein said gas path is annular.

11. The gas turbine engine as recited in claim 8, wherein said exhaust diffuser is downstream of a turbine section.

12. A method of operating a gas turbine engine comprising:

modulating an exhaust diffuser downstream of a turbine section.

13. The method as recited in claim 12, wherein said modulating includes moving at least one of a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.

14. The method as recited in claim 12, wherein said modulating includes pivoting at least one of a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.

15. The method as recited in claim 12, wherein said modulating includes moving a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.

16. The method as recited in claim 12, wherein said modulating includes pivoting a multiple of circumferentially spaced struts that extend across a gaspath defined by said exhaust diffuser.