Patent Application
20150354413
The present disclosure relates generally to gas turbine engines, and more particularly to heat management in a turbine exhaust case of a gas turbine engine.
A turbine exhaust case is a structural frame that supports engine bearing loads while providing a gas path at or near the aft end of a gas turbine engine. Some aeroengines utilize a turbine exhaust case to help mount the gas turbine engine to an aircraft airframe. In industrial applications, a turbine exhaust case is more commonly used to couple gas turbine engines to a power turbine that powers an electrical generator. Industrial turbine exhaust cases may, for instance, be situated between a low pressure engine turbine and a generator power turbine. A turbine exhaust case must bear shaft loads from interior bearings, and must be capable of sustained operation at high temperatures.
Turbine exhaust cases serve two primary purposes: airflow channeling and structural support. Turbine exhaust cases typically comprise structures with inner and outer rings connected by radial struts. The struts and rings often define a core flow path from fore to aft, while simultaneously mechanically supporting shaft bearings situated axially inward of the inner ring. The components of a turbine exhaust case are exposed to very high temperatures along the core flow path. Various approaches and architectures have been employed to handle these high temperatures. Some turbine exhaust case frames utilize high-temperature, high-stress capable materials to both define the core flow path and bear mechanical loads. Other turbine exhaust case architectures separate these two functions, pairing a structural frame for mechanical loads with a high-temperature capable fairing to define the core flow path. Turbine exhaust cases with separate structural frames and flow path fairings pose the technical challenge of installing vane fairings within the structural frame. Fairings are typically constructed as a “ship in a bottle,” built piece-by-piece within a unitary frame. Some fairing embodiments, for instance, comprise suction and pressure side pieces of fairing vanes for each frame strut. These pieces are inserted individually inside the structural frame, and joined together (e.g. by welding) to surround frame struts.
The present disclosure is directed toward a turbine exhaust case comprising a fairing defining an airflow path through the turbine exhaust case, and a multi-piece frame disposed through and around the fairing to support a bearing load. The multi-piece frame comprises an inner ring, an outer ring, and a plurality of strut bosses. The outer ring is disposed concentrically outward of the inner ring, and has open bosses at strut locations. The plurality of radial struts pass through the vane fairing, are secured to the inner ring via radial fasteners, and are secured via non-radial fasteners to the open boss.
Low pressure shaft 32, high pressure shaft 34, and power shaft 36 are situated along rotational axis A. In the depicted embodiment, low pressure shaft 32 and high pressure shaft 34 are arranged concentrically, while power shaft 36 is disposed axially aft of low pressure shaft 32 and high pressure shaft 34. Low pressure shaft 32 defines a low pressure spool including low pressure compressor 16 and low pressure turbine 26. High pressure shaft 34 analogously defines a high pressure spool including high pressure compressor 18 and high pressure compressor 24. As is well known in the art of gas turbines, airflow F is received at inlet 12, then pressurized by low pressure compressor 16 and high pressure compressor 18. Fuel is injected at combustor 20, where the resulting fuel-air mixture is ignited. Expanding combustion gasses rotate high pressure turbine 24 and low pressure turbine 26, thereby driving high and low pressure compressors 18 and 16 through high pressure shaft 34 and low pressure shaft 32, respectively. Although compressor 14 and engine turbine 22 are depicted as two-spool components with high and low sections on separate shafts, single spool or three or more spool embodiments of compressor 14 and engine turbine 22 are also possible. Turbine exhaust case 28 carries airflow from low pressure turbine 26 to power turbine 30, where this airflow drives power shaft 36. Power shaft 36 can, for instance, drive an electrical generator, pump, mechanical gearbox, or other accessory (not shown).
In addition to defining an airflow path from low pressure turbine 26 to power turbine 30, turbine exhaust case 28 can support one or more shaft loads. Turbine exhaust case 28 can, for instance, support low pressure shaft 32 via bearing compartments (not shown) disposed to communicate load from low pressure shaft 32 to a structural frame of turbine exhaust case 28.
As noted above with respect to
Power turbine 30 parallels low pressure turbine 26, but extracts energy from airflow F to drive a generator, pump, mechanical gearbox, or similar device, rather than to power compressor 14. Like low pressure turbine 26, power turbine 30 operates by channeling airflow through alternating stages of airfoil vanes and blades. Power turbine vanes 46 channel airflow F to rotate power turbine rotor blades 48 on power turbine rotor disks 50.
Turbine exhaust case 28 is an intermediate structure connecting low pressure turbine 26 to power turbine 30. Turbine exhaust case 28 may for instance be anchored to low pressure turbine 26 and power turbine 30 via bolts, pins, rivets, or screws. In some embodiments, turbine exhaust case 28 may serve as an attachment point for installation mounting hardware (e.g. trusses, posts) that supports not only turbine exhaust case 28, but also low pressure turbine 26, power turbine 30, and/or other components of gas turbine engine 10.
Turbine exhaust case 28 comprises two primary components: frame 100, which supports structural loads including shaft loads e.g. from low pressure shaft 32, and fairing 116, which defines an aerodynamic flow path from low pressure turbine 26 to power turbine 30. Fairing 116 can be formed in a unitary, monolithic piece, while frame 100 is assembled about fairing 116.
Outer platform 118 and inner platform 120 of fairing 116 define the inner and outer boundaries of an annular gas flow path from low pressure turbine 26 to power turbine 30. Fairing vane 122 is an aerodynamic vane surface surrounding strut 106a. Fairing 116 can have any number of fairing vanes 122 at least equal to the number of struts 106a. In one embodiment, fairing 116 has one vane fairing 122 for each strut 106a of frame 100. In other embodiments, fairing 116 may include additional vane fairings 122 through which no strut 106a passes. Fairing 120 can be formed of a high temperature capable material such as Inconel or another nickel-based superalloy.
Frame 100 is a multi-piece frame comprising three distinct types of structural components, plus connecting fasteners. The outer diameter of frame 100 is formed by outer ring 100a, a substantially frustoconical annulus with strut boss 126a, a radially outward-extending hollow boss that carries chordwise expandable diameter fasteners 112 and circumferentially-oriented expandable diameter fasteners 114a for securing strut 106a. Chordwise expandable diameter fasteners 112 and circumferentially-oriented expandable diameter fasteners 114a may, for instance, be expandable diameter bolts, shafts, or pins capable of extending entirely through both strut 106a and strut boss 126a, and expanding to take in corresponding tolerances and account for thermal drift. Chordwise expandable diameter fasteners 112 extend substantially axially through strut boss 126a and strut 106a, while circumferentially-extending expandable diameter fasteners 114a extend circumferentially through strut boss 126a and strut 106a, and are secured on either angular side of strut boss 126a. As depicted in
The inner diameter of frame 100 is defined by inner ring 104, a substantially cylindrical structure with inner radial strut fasteners 108. Inner radial strut fasteners 108 may, for instance, be screws, pins, or bolts extending radially inward through inner ring 104 and into strut 106a to secure strut 106a at its radially inner extent to inner ring 104. In other embodiments, inner radial strut fasteners 108 may be radial posts extending radially inward from inner ring 106a, and mating with corresponding post holes at the inner diameter of strut 106a. Struts 106a are rigid posts extending substantially radially from inner ring 104, through fairing vanes 122, into strut bosses 126a. Struts 106a are anchored in all dimensions by the combination of chordwise expandable diameter fasteners 112 and circumferentially-oriented expandable diameter fasteners 114a. Frame 100 is not directly exposed to core flow F, and therefore can be formed of a material rated to significantly lower temperatures than fairing 120. In some embodiments, frame 100 may be formed of sand-cast steel.
Turbine exhaust case 28 is assembled by axially and circumferentially aligning fairing 120 with inner ring 104 and outer ring 102, and slotting each strut 106 through strut aperture SA and fairing vane 126 from radially outside onto inner radial strut fasteners 108. In some embodiments (e.g. where inner radial strut fasteners are screws or bolts) inner radial strut fasteners 108 can then be secured to the inner diameter of strut 106. Circumferentially-oriented expandable diameter fasteners 114 (and chordwise expandable diameter fasteners 112, in the embodiment of
The following are non-exclusive descriptions of possible embodiments of the present invention.
A turbine exhaust case comprises a turbine exhaust case comprising a fairing defining and airflow path through the turbine exhaust case, and a multi-piece frame disposed through and around the fairing to support a bearing load. The multi-piece frame comprises an inner ring, an outer ring, and a plurality of strut bosses. The outer ring is disposed concentrically outward of the inner ring, and has open bosses at strut locations. The plurality of radial struts pass through the vane fairing, are secured to the inner ring via radial fasteners, and are secured via non-radial fasteners to the open boss.
The turbine exhaust case of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components:
wherein the multi-piece frame is formed of steel.
wherein the multi-piece frame is formed of sand-cast steel.
wherein the fairing is monolithically formed.
wherein the fairing is formed of a material rated for a higher temperature than the multi-piece frame.
wherein the fairing is formed of a nickel-based superalloy.
further comprising airtight sealing plates covering each open boss.
wherein the non-radial fasteners comprise a circumferentially-oriented expandable diameter fastener.
wherein the non-radial fasteners further comprise at least one chordwise-oriented expandable diameter fastener.
wherein the radial fasteners comprise radial bolts extending through the inner ring and into the radial struts.
A turbine exhaust case comprising an inner cylindrical ring; an outer frustoconical ring with a plurality of angularly distributed hollow strut bosses; and a plurality of radial struts secured to the inner cylindrical ring via radial fasteners, and to the angularly distributed hollow strut bosses via non-radial expandable diameter fasteners.
The turbine exhaust case frame of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components:
wherein the radial fasteners are bolts, pins, or screws extending radially through the inner cylindrical ring and into the radial struts.
wherein the inner non-radial expandable diameter fasteners comprise a circumferentially-oriented expandable diameter fastener.
wherein the inner non-radial expandable diameter fasteners comprise a chordwise-oriented expandable diameter fastener.
further comprising a sealing plate providing an air seal over the outer radial extent of the hollow strut bosses.
A method of assembling a turbine exhaust case, the method comprising: aligning fairing vanes of a flow path defining fairing, radial fasteners on an inner frame ring, and strut apertures in a strut boss of an outer frustoconical ring; inserting a radial strut from radially outside the outer frustoconical ring, through the strut aperture and the fairing vane; securing the radial strut to the inner frame ring via the radial fasteners; and securing the radial strut to the strut boss via non-radial expandable diameter fasteners.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations, and/or additional components:
further comprising covering the sealing aperture with an airtight sealing plate.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/076872 | 12/20/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61747817 | Dec 2012 | US |
