US20140174056A1 - Gas turbine engine with low stage count low pressure turbine - Google Patents

Abstract

A gas turbine engine comprises a gear train defined along an axis. A spool along the axis drives the gear train and includes a low stage count low pressure turbine. A fan i s rotatable at a fan speed about the axis and driven by the low pressure turbine through the gear train. The fan speed is less than a speed of the low pressure turbine. A core is surrounded by a core nacelle defined about the axis. A fan nacelle i s mounted at least partially around the core nacelle to define a fan bypass airflow path for a fan bypass airflow. A bypass ratio defined by the fan bypass passage airflow divided by airflow through the core is greater than about ten (10).

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• The present disclosure is a continuation-in-part of U.S. patent application Ser. No. 13/340,988, filed Dec. 30, 2011, which was a continuation-in-part of U.S. patent application Ser. No. 12/131,876, filed Jun. 2, 2008.
BACKGROUND
• The present invention relates to a gas turbine engine and more particularly to an engine mounting configuration for the mounting of a turbofan gas turbine engine to an aircraft pylon.
• A gas turbine engine may be mounted at various points on an aircraft such as a pylon integrated with an aircraft structure. An engine mounting configuration ensures the transmission of loads between the engine and the aircraft structure. The loads typically include the weight of the engine, thrust, aerodynamic side loads, and rotary torque about the engine axis. The engine mount configuration must also absorb the deformations to which the engine is subjected during different flight phases and the dimensional variations due to thermal expansion and retraction.
• One conventional engine mounting configuration includes a pylon having a forward mount and an aft mount with relatively long thrust links which extend forward from the aft mount to the engine intermediate case structure. Although effective, one disadvantage of this conventional type mounting arrangement is the relatively large “punch loads” into the engine cases from the thrust links which react the thrust from the engine and couple the thrust to the pylon. These loads tend to distort the intermediate case and the low pressure compressor (LPC) cases. The distortion may cause the clearances between the static cases and rotating blade tips to increase which may negatively affect engine performance and increase fuel burn.
SUMMARY
• In a featured embodiment, a gas turbine engine comprises a gear train defined along an axis. A spool along the axis drives the gear train and includes a low stage count low pressure turbine. A fan i s rotatable at a fan speed about the axis and driven by the low pressure turbine through the gear train. The fan speed is less than a speed of the low pressure turbine. A core is surrounded by a core nacelle defined about the axis. A fan nacelle is mounted at least partially around the core nacelle to define a fan bypass airflow path for a fan bypass airflow. A bypass ratio defined by the fan bypass passage airflow divided by airflow through the core is greater than about ten (10).
• In another embodiment according to the previous embodiment, the low stage count includes six or fewer stages.
• In another embodiment according to any of the previous embodiments, the low stage count includes three (3) stages.
• In another embodiment according to any of the previous embodiments, the low stage count includes five (5) stages.
• In another embodiment according to any of the previous embodiments, the low stage count includes six (6) stages.
• In another embodiment according to any of the previous embodiments, the spool is a low spool.
• In another embodiment according to any of the previous embodiments, a fan variable area nozzle is axially movable relative the fan nacelle to vary a fan nozzle exit area and adjust the fan pressure ratio of the fan bypass airflow during engine operation.
• In another embodiment according to any of the previous embodiments, a controller i s operable to control the fan variable area nozzle to vary the fan nozzle exit area and adjust the pressure ratio of the fan bypass airflow.
• In another embodiment according to any of the previous embodiments, the controller is operable to reduce the fan nozzle exit area at a cruise flight condition.
• In another embodiment according to any of the previous embodiments, the controller is operable to control the fan nozzle exit area to reduce a fan instability.
• In another embodiment according to any of the previous embodiments, the fan variable area nozzle defines a trailing edge of the fan nacelle.
• In another embodiment according to any of the previous embodiments, the gear train defines a gear reduction ratio of greater than or equal to about 2.5.
• In another embodiment according to any of the previous embodiments, the gear train defines a gear reduction ratio of greater than or equal to about 2.3.
• In another embodiment according to any of the previous embodiments, the gear train defines a gear reduction ratio of greater than or equal to 2.5.
• In another embodiment according to any of the previous embodiments, the low pressure turbine defines a low pressure turbine pressure ratio that is greater than about five (5).
• In another embodiment according to any of the previous embodiments, the low pressure turbine defines a low pressure turbine pressure ratio that is greater than five (5).
• In another embodiment according to any of the previous embodiments, the low pressure turbine is one of three turbine rotors. The low pressure turbine drives the fan, while the other two of the turbine rotors each drive a compressor section
• In another embodiment according to any of the previous embodiments, a high pressure turbine is also included, with each of the low pressure turbine and the high pressure turbine driving a compressor rotor.
• In another embodiment according to any of the previous embodiments, the gear train is positioned intermediate a compressor rotor driven by the low pressure turbine and the fan.
• In another embodiment according to any of the previous embodiments, the gear train is positioned intermediate the low pressure turbine and the compressor rotor is driven by the low pressure turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
• The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently disclosed embodiment. The drawings that accompany the detailed description can be briefly described as follows:
• FIG. 1A is a general schematic sectional view through a gas turbine engine along the engine longitudinal axis;
• FIG. 1B is a general sectional view through a gas turbine engine along the engine longitudinal axis illustrating an engine static structure case arrangement on the lower half thereof;
• FIG. 1C is a side view of an mount system illustrating a rear mount attached through an engine thrust case to a mid-turbine frame between a first and second bearing supported thereby;
• FIG. 1D is a forward perspective view of an mount system illustrating a rear mount attached through an engine thrust case to a mid-turbine frame between a first and second bearing supported thereby;
• FIG. 2A is a top view of an engine mount system;
• FIG. 2B is a side view of an engine mount system within a nacelle system;
• FIG. 2C is a forward perspective view of an engine mount system within a nacelle system;
• FIG. 3 is a side view of an engine mount system within another front mount;
• FIG. 4A is an aft perspective view of an aft mount;
• FIG. 4B is an aft view of an aft mount ofFIG. 4A;
• FIG. 4C is a front view of the aft mount ofFIG. 4A;
• FIG. 4D is a side view of the aft mount ofFIG. 4A;
• FIG. 4E is a top view of the aft mount ofFIG. 4A;
• FIG. 5A is a side view of the aft mount ofFIG. 4A in a first slide position;
• and
• FIG. 5B is a side view of the aft mount ofFIG. 4A in a second slide position.
• FIG. 6 shows another embodiment.
• FIG. 7 shows yet another embodiment.
DETAILED DESCRIPTION
• FIG. 1A illustrates a general partial fragmentary schematic view of agas turbofan engine10 suspended from anengine pylon12 within an engine nacelle assembly N as is typical of an aircraft designed for subsonic operation.
• Theturbofan engine10 includes a core engine within a core nacelle C that houses a low spool14 andhigh spool24. The low spool14 includes alow pressure compressor16 andlow pressure turbine18. The low spool14 drives afan section20 connected to the low spool14 either directly or through agear train25.
• Thehigh spool24 includes ahigh pressure compressor26 andhigh pressure turbine28. Acombustor30 is arranged between thehigh pressure compressor26 andhigh pressure turbine28. The low andhigh spools14,24 rotate about an engine axis of rotation A.
• Theengine10 in one non-limiting embodiment is a high-bypass geared architecture aircraft engine. In one disclosed, non-limiting embodiment, theengine10 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), thegear train25 is an epicyclic gear train such as a planetary gear system or other gear system with a gear reduction ratio of greater than about 2.3 and thelow pressure turbine18 has a pressure ratio that is greater than about 5. In one disclosed embodiment, theengine10 bypass ratio is greater than ten (10:1), the turbofan diameter is significantly larger than that of thelow pressure compressor16, and thelow pressure turbine18 has a pressure ratio that is greater than 5:1. Thegear train25 may be an epicycle gear train such as a planetary gear system or other gear system with a gear reduction ratio of greater than about 2.5:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.
• Airflow enters the fan nacelle F which at least partially surrounds the core nacelle C. Thefan section20 communicates airflow into the core nacelle C to thelow pressure compressor16. Core airflow compressed by thelow pressure compressor16 and thehigh pressure compressor26 is mixed with the fuel in thecombustor30 where is ignited, and burned. The resultant high pressure combustor products are expanded through thehigh pressure turbine28 andlow pressure turbine18. Theturbines28,18 are rotationally coupled to thecompressors26,16 respectively to drive thecompressors26,16 in response to the expansion of the combustor product. Thelow pressure turbine18 also drives thefan section20 throughgear train25. A core engine exhaust E exits the core nacelle C through acore nozzle43 defined between the core nacelle C and atail cone33.
• With reference toFIG. 1B, thelow pressure turbine18 includes a low number of stages, which, in the illustrated non-limiting embodiment, includes three turbine stages,18A,18B,18C. The gear train22 operationally effectuates the significantly reduced number of stages within thelow pressure turbine18. The three turbine stages,18A,18B,18C facilitate a lightweight and operationally efficient engine architecture. It should be appreciated that a low number of stages contemplates, for example, three to six (3-6) stages.Low pressure turbine18 pressure ratio is pressure measured prior to inlet oflow pressure turbine18 as related to the pressure at the outlet of thelow pressure turbine18 prior to exhaust nozzle.
• Thrust is a function of density, velocity, and area. One or more of these parameters can be manipulated to vary the amount and direction of thrust provided by the bypass flow B. The Variable Area Fan Nozzle (“VAFN”)42 operates to effectively vary the area of the fannozzle exit area44 to selectively adjust the pressure ratio of the bypass flow B in response to a controller C. Low pressure ratio turbofans are desirable for their high propulsive efficiency. However, low pressure ratio fans may be inherently susceptible to fan stability/flutter problems at low power and low flight speeds. The VAFN42 allows the engine to change to a more favorable fan operating line at low power, avoiding the instability region, and still provide the relatively smaller nozzle area necessary to obtain a high-efficiency fan operating line at cruise.
• A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. Thefan section20 of theengine10 is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (‘TSFCT’)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. “Low fan pressure ratio” is the pressure ratio across the fan blade alone, without the Fan Exit Guide Vane (“FEGV”) system36. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about 1.45. “Low corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tambient deg R)/518.7)̂0.5]. The “Low corrected fan tip speed” as disclosed herein according to one non-limiting embodiment is less than about 1150 ft/second.
• As the fan blades within thefan section20 are efficiently designed at a particular fixed stagger angle for an efficient cruise condition, the VAFN42 is operated to effectively vary the fannozzle exit area44 to adjust fan bypass air flow such that the angle of attack or incidence on the fan blades is maintained close to the design incidence for efficient engine operation at other flight conditions, such as landing and takeoff to thus provide optimized engine operation over a range of flight conditions with respect to performance and other operational parameters such as noise levels.
• The enginestatic structure44 generally has sub-structures including a case structure often referred to as the engine backbone. The enginestatic structure44 generally includes afan case46, an intermediate case (IMC)48, a highpressure compressor case50, acombustor case52A, a highpressure turbine case52B, athrust case52C, a lowpressure turbine case54, and a turbine exhaust case56 (FIG. 1B). Alternatively, thecombustor case52A, the highpressure turbine case52B and thethrust case52C may be combined into a single case. It should be understood that this is an exemplary configuration and any number of cases may be utilized.
• Thefan section20 includes afan rotor32 with a plurality of circumferentially spaced radially outwardly extendingfan blades34. Thefan blades34 are surrounded by thefan case46. The core engine case structure is secured to thefan case46 at theIMC48 which includes a multiple of circumferentially spaced radially extendingstruts40 which radially span the core engine case structure and thefan case20.
• The enginestatic structure44 further supports a bearing system upon which theturbines28,18,compressors26,16 andfan rotor32 rotate. A #1 fandual bearing60 which rotationally supports thefan rotor32 is axially located generally within thefan case46. The #1 fandual bearing60 is preloaded to react fan thrust forward and aft (in case of surge). A #2 LPC bearing62 which rotationally supports the low spool14 is axially located generally within the intermediate case (IMC)48. The #2LPC bearing62 reacts thrust. A #3 fandual bearing64 which rotationally supports thehigh spool24 and also reacts thrust. The #3 fan bearing64 is also axially located generally within theIMC48 just forward of the highpressure compressor case50. A #4bearing66 which rotationally supports a rear segment of the low spool14 reacts only radial loads. The #4bearing66 is axially located generally within thethrust case52C in an aft section thereof. A #5bearing68 rotationally supports the rear segment of the low spool14 and reacts only radial loads. The #5bearing68 is axially located generally within thethrust case52C just aft of the #4bearing66. It should be understood that this is an exemplary configuration and any number of bearings may be utilized.
• The #4bearing66 and the #5bearing68 are supported within a mid-turbine frame (MTF)70 to straddle radially extendingstructural struts72 which are preloaded in tension (FIGS. 1C-1D). TheMTF70 provides aft structural support within thethrust case52C for the #4bearing66 and the #5bearing68 which rotatably support thespools14,24.
• A dual rotor engine such as that disclosed in the illustrated embodiment typically includes a forward frame and a rear frame that support the main rotor bearings. The intermediate case (IMC)48 also includes theradially extending struts40 which are generally radially aligned with the #2 LPC bearing62 (FIG. 1B). It should be understood that various engines with various case and frame structures will benefit from the present invention.
• The turbofangas turbine engine10 is mounted to aircraft structure such as an aircraft wing through a mount system80 attachable by thepylon12. The mount system80 includes aforward mount82 and an aft mount84 (FIG. 2A). Theforward mount82 is secured to theIMC48 and theaft mount84 is secured to theMTF70 at thethrust case52C. Theforward mount82 and theaft mount84 are arranged in a plane containing the axis A of theturbofan gas turbine10. This eliminates the thrust links from the intermediate case, which frees up valuable space beneath the core nacelle and minimizesIMC48 distortion.
• Referring toFIGS. 2A-2C, the mount system80 reacts the engine thrust at the aft end of theengine10. The term “reacts” as utilized in this disclosure is defined as absorbing a load and dissipating the load to another location of thegas turbine engine10.
• Theforward mount82 supports vertical loads and side loads. Theforward mount82 in one non-limiting embodiment includes a shackle arrangement which mounts to theIMC48 at two points86A,86B. Theforward mount82 is generally a plate-like member which is oriented transverse to the plane which contains engine axis A. Fasteners are oriented through theforward mount82 to engage the intermediate case (IMC)48 generally parallel to the engine axis A. In this illustrated non-limiting embodiment, theforward mount82 is secured to theIMC40. In another non-limiting embodiment, theforward mount82 is secured to a portion of the core engine, such as the high-pressure compressor case50 of the gas turbine engine10 (seeFIG. 3). One of ordinary skill in the art having the benefit of this disclosure would be able to select an appropriate mounting location for theforward mount82.
• Referring toFIG. 4A, theaft mount84 generally includes afirst A-arm88A, asecond A-arm88B, arear mount platform90, awhiffle tree assembly92 and adrag link94. Therear mount platform90 is attached directly to aircraft structure such as thepylon12. Thefirst A-arm88A and thesecond A-arm88B mount between thethrust case52C atcase bosses96 which interact with the MTF70 (FIGS. 4B-4C), therear mount platform90 and thewhiffle tree assembly92. It should be understood that thefirst A-arm88A and thesecond A-arm88B may alternatively mount to other areas of theengine10 such as the high pressure turbine case or other cases. It should also be understood that other frame arrangements may alternatively be used with any engine case arrangement.
• Referring toFIG. 4D, thefirst A-arm88A and thesecond A-arm88B are rigid generally triangular arrangements, each having afirst link arm89a, asecond link arm89band athird link arm89c. Thefirst link arm89ais between thecase boss96 and therear mount platform90. Thesecond link arm89bis between thecase bosses96 and thewhiffle tree assembly92. Thethird link arm89cis between thewhiffle tree assembly92rear mount platform90. Thefirst A-arm88A and thesecond A-arm88B primarily support the vertical weight load of theengine10 and transmit thrust loads from the engine to therear mount platform90.
• Thefirst A-arm88A and the second A-arm88B of theaft mount84 force the resultant thrust vector at the engine casing to be reacted along the engine axis A which minimizes tip clearance losses due to engine loading at theaft mount84. This minimizes blade tip clearance requirements and thereby improves engine performance.
• Thewhiffle tree assembly92 includes a whiffle link98 which supports a central ball joint100, a first sliding ball joint102A and a second sliding ball joint102B (FIG. 4E). It should be understood that various bushings, vibration isolators and such like may additionally be utilized herewith. The central ball joint100 is attached directly to aircraft structure such as thepylon12. The first sliding ball joint102A is attached to thefirst A-arm88A and the second sliding ball joint102B is mounted to thefirst A-arm88A. The first and second sliding ball joint102A,102B permit sliding movement of the first andsecond A-arm88A,88B (illustrated by arrow S inFIGS. 5A and 5B) to assure that only a vertical load is reacted by thewhiffle tree assembly92. That is, thewhiffle tree assembly92 allows all engine thrust loads to be equalized transmitted to theengine pylon12 through therear mount platform90 by the sliding movement and equalize the thrust load that results from the dual thrust link configuration. The whiffle link98 operates as an equalizing link for vertical loads due to the first sliding ball joint102A and the second sliding ball joint102B. As the whiffle link98 rotates about the central ball joint100 thrust forces are equalized in the axial direction. Thewhiffle tree assembly92 experiences loading only due to vertical loads, and is thus less susceptible to failure than conventional thrust-loaded designs.
• Thedrag link94 includes a ball joint104A mounted to thethrust case52C and ball joint104B mounted to the rear mount platform90 (FIGS. 4B-4C). Thedrag link94 operates to react torque.
• The aft mount84 transmits engine loads directly to thethrust case52C and theMTF70. Thrust, vertical, side, and torque loads are transmitted directly from theMTF70 which reduces the number of structural members as compared to current in-practice designs.
• The mount system80 is compact, and occupies space within the core nacelle volume as compared to turbine exhaust case-mounted configurations, which occupy space outside of the core nacelle which may require additional or relatively larger aerodynamic fairings and increase aerodynamic drag and fuel consumption. The mount system80 eliminates the heretofore required thrust links from the IMC, which frees up valuable space adjacent theIMC48 and the highpressure compressor case50 within the core nacelle C.
• It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.
• FIG. 6 shows anembodiment200, wherein there is afan drive turbine208 driving a shaft206 to in turn drive afan rotor202. Agear reduction204 may be positioned between thefan drive turbine208 and thefan rotor202. Thisgear reduction204 may be structured and operate like the gear reduction disclosed above. Acompressor rotor210 is driven by anintermediate pressure turbine212, and a second stage compressor rotor214 is driven by a turbine rotor216. A combustion section218 is positioned intermediate the compressor rotor214 and the turbine section216.
• FIG. 7 shows yet anotherembodiment300 wherein afan rotor302 and afirst stage compressor304 rotate at a common speed. The gear reduction306 (which may be structured as disclosed above) is intermediate thecompressor rotor304 and ashaft308 which is driven by a low pressure turbine section.
• The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The disclosed embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.

Claims (20)

1. A gas turbine engine comprising:

a gear train defined along an axis;

a spool along said axis which drives said gear train, said spool includes a low stage count low pressure turbine;

a fan rotatable at a fan speed about the axis and driven by the low pressure turbine through the gear train, wherein the fan speed is less than a speed of the low pressure turbine;

a core surrounded by a core nacelle defined about the axis; and

a fan nacelle mounted at least partially around said core nacelle to define a fan bypass airflow path for a fan bypass airflow, wherein a bypass ratio defined by the fan bypass passage airflow divided by airflow through the core is greater than about ten (10).

2. The engine as recited inclaim 1, wherein said low stage count includes six or fewer stages.

3. The engine as recited inclaim 1, wherein said low stage count includes three (3) stages.

4. The engine as recited inclaim 1, wherein said low stage count includes five (5) stages.

5. The engine as recited inclaim 1, wherein said low stage count includes six (6) stages.

6. The engine as recited inclaim 1, wherein said spool is a low spool.

7. The engine as recited inclaim 1, further comprising:

a fan variable area nozzle axially movable relative said fan nacelle to vary a fan nozzle exit area and adjust the fan pressure ratio of the fan bypass airflow during engine operation.

8. The engine as recited inclaim 7, further comprising:

a controller operable to control said fan variable area nozzle to vary the fan nozzle exit area and adjust the pressure ratio of the fan bypass airflow.

9. The engine as recited inclaim 8, wherein said controller is operable to reduce said fan nozzle exit area at a cruise flight condition.

10. The engine as recited inclaim 8, wherein said controller is operable to control said fan nozzle exit area to reduce a fan instability.

11. The engine as recited inclaim 8, wherein said fan variable area nozzle defines a trailing edge of said fan nacelle.

12. The engine as recited inclaim 11, wherein said gear train defines a gear reduction ratio of greater than or equal to about 2.5.

13. The engine as recited inclaim 1, wherein said gear train defines a gear reduction ratio of greater than or equal to about 2.3.

14. The engine as recited inclaim 13, wherein said gear train defines a gear reduction ratio of greater than or equal to 2.5.

15. The engine as recited inclaim 14, wherein said low pressure turbine defines a low pressure turbine pressure ratio that is greater than about five (5).

16. The engine as recited inclaim 1, wherein said low pressure turbine defines a low pressure turbine pressure ratio that is greater than five (5).

17. The engine as recited inclaim 1, wherein said low pressure turbine is one of three turbine rotors, and said low pressure turbine driving said fan, while the other two of said turbine rotors each driving a compressor section

18. The engine as recited inclaim 1, wherein also including a high pressure turbine, with each of said low pressure turbine and said high pressure turbine driving a compressor rotor.

19. The engine as recited inclaim 18, wherein said gear train is positioned intermediate a compressor rotor driven by said low pressure turbine and said fan.

20. The engine as recited inclaim 18, wherein said gear train is positioned intermediate said low pressure turbine and said compressor rotor driven by said low pressure turbine.

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