# Patent

## Title
Gas turbine engine compressor arrangement

## Abstract

A gas turbine engine includes a low pressure compressor section and a high pressure compressor section. A low pressure turbine drives the low pressure compressor section. A gear arrangement is driven by the low pressure turbine to in turn drive a fan section. A pressure ratio across the low pressure compressor section is between about 4-8, and a pressure ratio across the high pressure compressor section is between about 8-15. In a separate feature, a compressor case includes a front compressor case portion and a rear compressor case portion, with the rear compressor case portion being axially further from an inlet case than the front compressor case portion. A support member extends between the fan section and the front compressor case portion.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation in-part of U.S. patent application Ser. No. 13/294,492 filed on Nov. 11, 2011, which was a continuation of U.S. patent application Ser. No. 11/858,988 filed on Sep. 21, 2007, now U.S. Pat. No. 8,075,261, and entitled “Gas Turbine Engine Compressor Case Mounting Arrangement.”


BACKGROUND
The present invention relates generally to a compressor assembly in a gas turbine engine.
Gas turbine engines are known, and typically include a compressor for compressing air and delivering it downstream into a combustion section. A fan may move air to the compressor. The compressed air is mixed with fuel and combusted in the combustion section. The products of this combustion are then delivered downstream over turbine rotors, which are driven to rotate and provide power to the engine.
The compressor includes rotors moving within a compressor case to compress air. Maintaining close tolerances between the rotors and the interior of the compressor case facilitates air compression.
Gas turbine engines may include an inlet case for guiding air into a compressor case. The inlet case is mounted adjacent the fan section. Movement of the fan section, such as during in-flight maneuvers, may move the inlet case. Some prior gas turbine engine designs support a front portion of the compressor with the inlet case while an intermediate case structure supports a rear portion of the compressor. In such an arrangement, movement of the fan section may cause at least the front portion of the compressor to move relative to other portions of the compressor.
Disadvantageously, relative movement between portions of the compressor may vary rotor tip and other clearances within the compressor, which can decrease the compression efficiency. Further, supporting the compressor with the inlet case may complicate access to some plumbing connections near the inlet case.
It would be desirable to reduce relative movement between portions of the compressor and to simplify accessing plumbing connection in a gas turbine engine.
Traditionally, a fan and low pressure compressor have been driven in one of two manners. First, one type of known gas turbine engine utilizes three turbine sections, with one driving a high pressure compressor, a second turbine rotor driving the low pressure compressor, and a third turbine rotor driving the a fan. Another typical arrangement utilizes a low pressure turbine section to drive both the low pressure compressor and the fan.
Recently it has been proposed to incorporate a gear reduction to drive the fan such that a low pressure turbine can drive both the low pressure compressor and the fan, but at different speeds.
SUMMARY
In a featured embodiment, a gas turbine engine includes a fan section and a compressor section including both a low pressure compressor section and a high pressure compressor section. A turbine section includes a high pressure turbine driving the high pressure compressor section and a low pressure turbine driving the low pressure compressor section. A gear arrangement is driven by the low pressure turbine to in turn drive the fan section. An overall pressure ratio provided by the combination of the low pressure compressor section and the high pressure compressor section is provided by a pressure ratio across the low pressure compressor section between about 4-8, and a pressure ratio across the high pressure compressor section between about 8-15 to provide the overall pressure ratio.
In another embodiment, the overall pressure ratio is above or equal to about 35.
In another embodiment according to the foregoing embodiment, the overall pressure ratio is above or equal to about 40.
In another embodiment according to the foregoing embodiment, the overall pressure ratio is above or equal to about 50.
In another featured embodiment, a gas turbine engine comprises a fan section having a central axis and a compressor case for housing a compressor. An inlet case guides air to the compressor. The compressor case is positioned axially further from the fan section than the inlet case. A support member extends between the fan section and the compressor case with the support member restricting movement of the compressor case relative to the inlet case. The compressor case includes a front compressor case portion and a rear compressor case portion. The rear compressor case portion is axially further from the inlet case than the front compressor case portion. The support member extends between the fan section and the front compressor case portion, and the inlet case is removable from the gas turbofan engine separately from the compressor case.
In another featured embodiment of the foregoing embodiment, the compressor case includes a low pressure compressor section and a high pressure compressor section. A low pressure turbine drives the low pressure compressor and a gear arrangement is driven by the low pressure turbine such that the gear arrangement drives the fan section. An overall pressure ratio provided by the combination of the low pressure compressor section and the high pressure compressor section is above or equal to about 35.
In a further embodiment according to the foregoing embodiment, the overall pressure ratio is above or equal to about 40.
In a further embodiment according to the foregoing embodiment, the overall pressure ratio is above or equal to about 50.
In another embodiment according to the foregoing embodiment, the pressure ratio across the low pressure compressor section is between about 4-8 and a pressure ratio across the high pressure compressor section is between about 8-15.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of an embodiment. The drawings that accompany the detailed description can be briefly described as follows.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a schematic sectional view of a gas turbine engine.
FIG. 2 illustrates a sectional view of a prior art compressor case mounting arrangement. Notably, some aspects are not prior art.
FIG. 3 illustrates a sectional view of an example compressor case mounting arrangement of the current invention.
FIG. 4 illustrates a close up sectional view of the intersection between an inlet case and a low pressure compressor case.
FIG. 5 graphically shows a split in the compression ratios between the low pressure and high pressure compressor sections.



DETAILED DESCRIPTION
FIG. 1 schematically illustrates an example gas turbine engine 10 including (in serial flow communication) a fan section 14, a low pressure compressor 18, a high pressure compressor 22, a combustor 26, a high pressure turbine 30 and a low pressure turbine 34. The gas turbine engine 10 is circumferentially disposed about an engine centerline X. During operation, air is pulled into the gas turbine engine 10 by the fan section 14, pressurized by the compressors 18, 22 mixed with fuel, and burned in the combustor 26. Hot combustion gases generated within the combustor 26 flow through high and low pressure turbines 30, 34, which extract energy from the hot combustion gases.
In a two-spool design, the high pressure turbine 30 utilizes the extracted energy from the hot combustion gases to power the high pressure compressor 22 through a high speed shaft 38, and a low pressure turbine 34 utilizes the energy extracted from the hot combustion gases to power the low pressure compressor 18 and the fan section 14 through a low speed shaft 42. However, the invention is not limited to the two-spool gas turbine architecture described and may be used with other architectures such as a single-spool axial design, a three-spool axial design and other architectures. That is, there are various types of gas turbine engines, many of which could benefit from the examples disclosed herein, which are not limited to the design shown.
The example gas turbine engine 10 is in the form of a high bypass ratio turbine engine mounted within a nacelle or fan casing 46, which surrounds an engine casing 50 housing a core engine 54. A significant amount of air pressurized by the fan section 14 bypasses the core engine 54 for the generation of propulsion thrust. The airflow entering the fan section 14 may bypass the core engine 54 via a fan bypass passage 58 extending between the fan casing 46 and the engine casing 50 for receiving and communicating a discharge airflow F1. The high bypass flow arrangement provides a significant amount of thrust for powering an aircraft.
The gas turbine engine 10 may include a geartrain 62 for controlling the speed of the rotating fan section 14. The geartrain 62 can be any known gear system, such as a planetary gear system with orbiting planet gears, a planetary system with non-orbiting planet gears or other type of gear system. The low speed shaft 42 may drive the geartrain 62. In the disclosed example, the geartrain 62 has a constant gear ratio. It should be understood, however, that the above parameters are only exemplary of a contemplated geared gas turbine engine 10. That is, aspects of the invention are applicable to traditional turbine engines as well as other engine architectures.
The example engine casing 50 generally includes at least an inlet case portion 64, a low pressure compressor case portion 66, and an intermediate case portion 76. The inlet case 64 guides air to the low pressure compressor case 66.
As shown in FIG. 2, the low pressure compressor case 66 in an example prior art gas turbine engine 80 supports a plurality of compressor stator vanes 68. Notably, the low pressure compressor section 18, and the high pressure compressor section 22, and the arrangement of the rotors 70 and 170, respectively, are not part of the prior art. A plurality of rotors 70 rotate about the central axis X, and, with the compressor stator vanes 68, help compress air moving through the low pressure compressor case 66. Downstream of the low pressure compressor the air passes into the low pressure compressor at section 18 the air passes into the high pressure compressor section 22, and is further compressed by its rotors 170. The mounting of the compressor as shown in FIG. 2 is prior art, however, the structure of the low pressure compressor section 18 and high pressure compressor section 22, and the rotors 70 and 170 were not part of the prior art.
A plurality of guide vanes 72 secure the intermediate case 67 to the fan casing 46. Formerly, the guide vanes 72 each included at least a rear attachment 74 and a forward attachment 78. The rear attachment 74 connects to an intermediate case 76 while the forward attachment 78 connects to the inlet case 64. The lower pressure compressor case 66 was thus supported through the intermediate case 76 and the inlet case 64.
In the prior art, a plumbing connection area 82 is positioned between the rear attachment 74 and the forward attachment 78. The plumbing connection area 82 includes connections used for maintenance and repair of the gas turbine engine 80, such as compressed air attachments, oil attachments, etc. The forward attachment 78 extends to the inlet case 64 from at least one of the guide vanes 72 and covers portions of the plumbing connection area 82. A fan stream splitter 86, a type of cover, typically attaches to the forward attachment 78 to shield the plumbing connection area 82.
Referring now to an example of the present invention shown in FIG. 3, in the turbine engine 90, the forward attachment 78 attaches to a front portion of the low pressure compressor case 66. In this example, the forward attachment 78 extends from the guide vane 72 to support the low pressure compressor case 66. Together, the forward attachment 78 and guide vane 72 act as a support member for the low pressure compressor case 66. The plumbing connection area 82 (which includes connections used for maintenance and repair of the gas turbine engine 90, such as compressed air attachments, oil attachments, etc) is positioned upstream of the forward attachment 78 facilitating access to the plumbing connection area 82. In contrast, the plumbing connection area of prior art embodiments was typically positioned between the rear attachment and the forward attachment and the forward attachment typically extended to the inlet case from at least one of the guide vanes, thereby covering portions of the plumbing connection area, which complicated access thereto; this complicated structure was further complicated by a fan stream splitter, a type of cover, that typically was attached to the forward attachment to shield the plumbing connection area.
In the embodiment shown in FIG. 3, an operator may directly access the plumbing connection area 82 after removing the fan stream splitter 86. The plumbing connection area 82 typically provides access to a lubrication system 82a, a compressed air system 82b, or both. The lubrication system 82a and compressed air system 82b are typically in fluid communication with the geartrain 62.
Maintenance and repair of the geartrain 62 may require removing the geartrain 62 from the engine 90. Positioning the plumbing connection area 82 ahead of the forward attachment 78 simplifies maintenance and removal of the geartrain 62 from other portions of the engine 90. Draining oil from the geartrain 62 prior to removal may take place through the plumbing connection area 82 for example. The plumbing connection area 82 is typically removed with the geartrain 62. Thus, the arrangement may permit removing the geartrain 62 on wing or removing the inlet case 64 from the gas turbine engine 90 separately from the low pressure compressor case 66. This reduces the amount of time needed to prepare an engine for continued revenue service, saving an operator both time and money.
Connecting the forward attachment 78 to the low pressure compressor case 66 helps maintain the position of the rotor 70 relative to the interior of the low pressure compressor case 66 during fan rotation, even if the fan section 14 moves. In this example, the intermediate case 76 supports a rear portion of the low pressure compressor case 66 near a compressed air bleed valve 75.
As shown in FIG. 4, a seal 88, such as a “W” seal, may restrict fluid movement between the inlet case 64 and the low pressure compressor case 66. In this example, the seal 88 forms the general boundary between the inlet case 64 and the low pressure compressor case 66, while still allowing some amount movement between the cases.
FIG. 5 shows a novel worksplit that has been invented to improve the fuel burn efficiency of a geared turbofan architecture with a fan 18 connected to the low compressor 18 through a speed reduction device such as a gearbox 62. Since a gear reduction 62 is incorporated between the fan 14 and the low pressure compressor 18, the speeds of the low pressure compressor can be increased relative to a traditional two spool direct drive arrangement. This provides freedom in splitting the amount of compression between the low pressure section 18 and the high pressure section 22 that can be uniquely exploited to improve fuel burn efficiency on the geared turbofan architecture described in FIGS. 1 and 2. This resulting worksplit is distinctly different from historical two and three spool direct drive architectures as shown in FIG. 5.
Notably, while the gear train 62 is shown axially adjacent to the fan 14, it could be located far downstream, and even aft of the low turbine section 34. As is known, the gear illustrated at 62 in FIGS. 2 and 3 could result in the fan 14 rotating in the same, or the opposite direction of the compressor rotors 70 and 170.
It is known in prior art that an overall pressure ratio (when measured at sea level and at a static, full-rated takeoff power) of at least 35:1 is desirable, and that an overall pressure ratio of greater than about 40:1 and even about 50:1 is more desirable. That is, after accounting for the fan 18 pressure rise in front of the low pressure compressor 18, the pressure of the air entering the low compressor section 18 should be compressed as much or over 35 times by the time it reaches the outlet of the high compressor section 22. This pressure rise through the low and high compressors will be referred to as the gas generator pressure ratio.
FIG. 5 shows the way that this high pressure ratio has been achieved in the two prior art engine types versus the Applicant's engine's configuration.
Area S1 shows the typical operation of three spool arrangements discussed the Background Section. The pressure ratio of the low compressor is above 8, and up to potentially 15. That is, if a pressure of 1 were to enter the low pressure compressor, it would be compressed between 8 to 15 times.
As can be further seen, the high pressure ratio compressor in this arrangement need only compress a very low pressure ratio, and as low as 5 to achieve a combined gas generator pressure ratio of above 35. In addition, the three spool design requires complex arrangements to support the three concentric spools.
Another prior art arrangement is shown at area S2. Area S2 depicts the typical pressure ratio split in a typical two spool design with a direct drive fan. As can be seen, due to the connection of the fan directly to the low pressure compressor, there is little freedom in the speed of the low pressure compressor. Thus, the low pressure compressor can only do a small amount of the overall compression. As shown, it is typically below 4 times. On the other hand, the high pressure compressor must provide an amount of compression typically more than 20 times to reach the pressure ratio of 40 (or 50).
The S2 area results in undesirably high stress on the high pressure compressor, which, in turn, yields challenges in the mounting of the high pressure spool. In other words, the direct drive system that defines the S2 area presents an undesirable amount of stress, and an undesirable amount of engineering required to properly mount the high pressure spool to provide such high pressure ratios.
Applicant's current low compressor/high compressor pressure split is show at area S3. The fan is driven at a speed distinct from the low pressure compressor, and a higher compression ratio can be achieved at the low pressure compressor section than was the case at area S2. Thus, as shown, the pressure ratio across the low pressure turbine may be between 4 and 8. This allows the amount of compression to be performed by the high pressure compressor to only need to be between 8 times and 15 times.
The area S3 is a enabling design feature that allows the geared turbofan architecture shown in FIGS. 1 and 2 to achieve very high gas generator pressure ratio while avoiding the complexities of historical three spool and two spool direct drive architectures. The area S3 is an improvement over both areas S1 and S2. As an example, a 3-4% fuel efficiency is achieved at area S3 compared to area S1. A fuel savings of 4-5% is achieved at area S3, compared to area S2.
In fact, in comparison to a gas turbine engine provided with a gear drive, but operating in the pressure ratios of area S2, there is still a 2% fuel burn savings at the S3 area.
As such, the area S3 reduces fuel burn, and provides engineering simplicity by more favorably distributing work between the hotter high pressure spools and colder low pressure spools.
Stated another way, the present invention provides a combination of a low pressure compressor and a high pressure compressor which together provides an overall pressure ratio of greater than 35 and, in some embodiments, greater than 40, and even 50. This high overall pressure ratio is accomplished by a beneficial combination of a pressure ratio across the low pressure compressor of about 4-8, and a pressure ratio across the high pressure ratio compressor of about 8-15.
Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

## Claims

1. A gas turbine engine comprising:
a fan section;
a compressor section, including both a low pressure compressor section and a high pressure compressor section;
a turbine section, including a high pressure turbine driving said high pressure compressor section, and a low pressure turbine driving said low pressure compressor section, and a gear arrangement driven by said low pressure turbine to in turn drive the fan section; and
an overall pressure ratio provided by the combination of said low pressure compressor section and said high pressure compressor section, with said overall pressure ratio being provided by a pressure ratio across said low pressure compressor section between about 4-8, and a pressure ratio across said high pressure compressor section between about 8-15 to provide said overall pressure ratio.

2. The gas turbine engine as set forth in claim 1, wherein said overall pressure ratio is above or equal to about 35.

3. The gas turbine engine as set forth in claim 2, wherein said overall pressure ratio is above or equal to about 40.

4. The gas turbine engine as set forth in claim 3, wherein said overall pressure ratio is above or equal to about 50.

5. An arrangement for a gas turbine engine comprising:
a fan section having a central axis;
a compressor case for housing a compressor;
a gear arrangement driving said fan section through said compressor;
an inlet case for guiding air to said compressor, said compressor case positioned axially further from said fan section than said inlet case;
a support member extending between said fan section and said compressor case wherein said support member restricts movement of said compressor case relative to said inlet case; and
said compressor case includes a front compressor case portion and a rear compressor case portion, said rear compressor case portion being axially further from said inlet case than said front compressor case portion, wherein said support member extends between said fan section and said front compressor case portion, and said inlet case is removable from said gas turbofan engine separately from said compressor case.

6. The arrangement as set forth in claim 5, wherein said compressor case includes a low pressure compressor section and a high pressure compressor section, and wherein a low pressure turbine drives said low pressure compressor, and said gear arrangement is driven by said low pressure turbine such that said gear arrangement drives said fan section, and an overall pressure ratio provided the combination of said low pressure compressor section and said high pressure compressor section being above or equal to about 35.

7. The arrangement as set forth in claim 6, wherein the overall pressure ratio is above or equal to about 40.

8. The arrangement as set forth in claim 7, wherein the overall pressure ratio is above or equal to about 50.

9. The arrangement as set forth in claim 6, wherein a pressure ratio across said low pressure compressor section is between about 4-8, and a pressure ratio across the high pressure compressor section is between about 8-15.