SYSTEMS AND METHODS FOR STIFFENING CASES ON GAS-TURBINE ENGINES

An engine case may include a first half and a second half. The first half may have a semiannular geometry with a first flange located at a circumferential edge of the first half. The second half may also have a semiannular geometry. The second half may further include a flange located at a circumferential edge of the first half. The second flange may be aligned with the first flange and mechanically coupled to the first flange. The first flange and the second flange may be configured to substantially align with an engine mounting point. The engine case may also have an annular geometry.

FIELD

The disclosure relates generally to gas turbine engines, and more particularly to the engine compressor case structure and maintaining tip clearances.

BACKGROUND

Gas turbine engines include various rotating airfoil sections in which the tip clearance (e.g., the gap) between the blade tips and the case opposite the blade tips impacts engine performance. Variance in tip clearances and larger tip clearances designed to accommodate clearance fluctuation typically reduce engine performance in terms of stall margin, power output, and efficiency, for example.

As a result, compressors in gas turbine engines are dependent on controlling blade tip clearances to maintain compressor efficiency and operability. One aspect of controlling tip clearances is to minimize the out-of-round deflection of the compressor cases.

SUMMARY

According to various embodiments, an engine case to provide structural stiffening is provided. An engine case may include a first half and a second half. The first half may have a semiannular geometry with a first flange located at a circumferential edge of the first half. The second half may also have a semiannular geometry. The second half may further include a flange located at a circumferential edge of the second half. The second flange may be aligned with the first flange and mechanically coupled to the first flange. The first flange and the second flange may be configured to substantially align with an engine mounting point. The engine case may also have an annular geometry. Typical gas turbine construction has the compressor case split flange oriented on a horizontal plane. In an engine where the engine thrust mount is situated vertically above the engine centerline, a split flange oriented on a horizontal plane will be on the neutral bending axis of the engine and will not influence the case bending stiffness nor out of round deflection. This invention preferably orients the split flange in such an engine on the vertical plane, where by virtue of the parallel axis theorem of mechanics the flange will substantively increase the case stiffness for bending and will reduce out of round deflection.

In various embodiments, the engine case may be a high pressure compressor case. The engine case may include a third flange located at a circumferential edge of the first half, and a fourth flange located at a circumferential edge of the second half. The third flange may be aligned with the fourth flange and mechanically coupled to the fourth flange. The engine case may also include a first seam defined by the first flange and the second flange, and a second seam defined by the third flange and the fourth flange. The first seam may be vertically aligned with the second seam. A fastener may mechanically couple the first flange to the second flange. The first flange may extend axially along the first half to define a mating surface. The mating surface may be coplanar with an engine centerline. The third flange may define a second mating surface that is coplanar with the first mating surface.

A gas turbine engine is also provided. The engine may include a compressor section configured rotate about an axis and a combustor aft of the compressor section and in fluid communication with the compressor section. A turbine section may be disposed aft of the combustor and configured to extract energy from combusted gas exiting from the combustor section. An engine mounting point may be located at a top of the gas turbine engine. A case disposed about the compressor section with the case including a first half with a first upper flange and a second half with a second upper flange. The first upper flange may be mechanically coupled to the second upper flange. The first upper flange may be substantially aligned with the engine mounting point.

In various embodiments, the gas turbine engine may also include a first lower flange extending from the first half of the case, and a second lower flange extending from the second half of the case. The first lower flange may be mechanically coupled to the second lower flange. The first upper flange and the first lower flange may be coplanar. The first upper flange may also be diametrically opposite the first lower flange. The first upper flange and the axis may also be coplanar. The case may be at least partially disposed about a high pressure compressor of the compressor section. The first upper flange may extend axially along an edge of the first half of the case. The first upper flange may also define a mating surface.

A compressor section is also provided. The compressor section may include a high pressure compressor configured to rotate about an axis and a case. The case may have an annular geometry and be disposed about the high pressure compressor. The case may include a first half having a first flange extending axially and a second half having a second flange extending axially. The first flange may be mechanically coupled to the second flange. The first flange and the second flange may be configured to substantially align with an engine mounting point.

In various embodiments, the first flange may be coplanar with the axis. The compressor section may also include a third flange extending axially along the first half, and a fourth flange extending axially along the second half. The third flange may be mechanically coupled to the fourth flange. The first flange may also be diametrically opposite the third flange.

DETAILED DESCRIPTION

In various embodiments and with reference toFIG. 1, a gas-turbine engine20is provided. Gas-turbine engine20may be a two-spool turbofan that generally incorporates a fan section22, a compressor section24, a combustor section26and a turbine section28. Alternative engines may include, for example, an augmentor section among other systems or features. In operation, fan section22can drive the working fluid along a bypass flow-path B while compressor section24can drive the working fluid along a core flow-path C for compression and communication into combustor section26then expansion through turbine section28. Although depicted as a two-spool turbofan gas-turbine engine20herein, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures.

Gas-turbine engine20may generally comprise a low speed spool30and a high speed spool32mounted for rotation about an engine central longitudinal axis A-A′ relative to an engine static structure36via several bearing systems38,38-1, and38-2. Engine central longitudinal axis A-A′ is oriented in the z direction on the provided xyz axis. It should be understood that various bearing systems38at various locations may alternatively or additionally be provided, including for example, bearing system38, bearing system38-1, and bearing system38-2. In various embodiments, bearing system38, bearing system38-1, and bearing system38-2may be contained within a bearing housing and/or integrated into an oil delivery system, as described in further detail below.

Low speed spool30may generally comprise an inner shaft40that interconnects a fan42, a low pressure (or first) compressor section44and a low pressure (or first) turbine section46. Inner shaft40may be connected to fan42through a geared architecture48that can drive fan42at a lower speed than low speed spool30. Geared architecture48may comprise a gear assembly60enclosed within a gear housing62. Gear assembly60couples inner shaft40to a rotating fan structure. High speed spool32may comprise an outer shaft50that interconnects a high pressure (or second) compressor52and high pressure (or second) turbine54. A combustor56may be located between high pressure compressor52and high pressure turbine54.

A mid-turbine frame57of engine static structure36may be located generally between high pressure turbine54and low pressure turbine46. Mid-turbine frame57may support one or more bearing systems38in turbine section28. Inner shaft40and outer shaft50may be concentric and rotate via bearing systems38about the engine central longitudinal axis A-A′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine.

The core airflow C may be compressed by fan section42then low pressure compressor section44then high pressure compressor52, mixed and burned with fuel in combustor56, then expanded over high pressure turbine54and low pressure turbine46. Turbines46,54rotationally drive the respective low speed spool30, fan42, and high speed spool32in response to the expansion.

In various embodiments, engine static structure36may include a compressor case58(i.e., a split case disposed about high pressor compressor52) disposed about a portion of compressor section24. A portion of compressor case58is cutaway inFIG. 1to illustrate components compressor section24retained within compressor case58, however, compressor case58may circumferentially enclose at least a portion of compressor section24and provide structural support. Compressor case58may, for example, enclose high pressure compressor52. Compressor case58may include one or more axial splits substantially parallel to axis A-A′ (and the z axis as illustrated). The axial splits may be selectively oriented circumferentially to provide stiffening in a preferred plane. In typical top mounted engines (e.g., engines where the mounting point59is above axis A-A′ in the y direction, as illustrated), the split may be oriented vertically (e.g., with seams aligned in the y direction) to provide case stiffness. In such cases, engine mounting point59may be a thrust mount located forward of high pressure compressor52. The thrust mount (at mounting point59) may be located at the top of the gas turbine engine. The top of the engine may be described as the side of the engine furthest from the ground while the aircraft is on the ground. In that regard, as explained in greater detail below, the seams and flanges of compressor case58may be substantially aligned with mounting point59at the top of the engine.

Although aircraft and top-mounted engines are described in detail herein, various embodiments may include non-aircraft installations with varied mounting points. The split flanges on engine cases may be oriented relative to a moment applied to the engine to reduce out-of-round deflections. In traditional top-mounted aircraft installations the split flanges will typically thus be oriented in a vertical plane; however, non-vertical orientations may be appropriate in engines with varied mounting structures.

With reference toFIG. 2, an exploded view of an engine case200from forward looking aft is shown, in accordance with various embodiments. Engine case200may be, for example, a high-pressure-compressor case, a low-pressure-compressor case, a high-pressure-turbine case, or a low-pressure turbine case. Engine case200may be an annular shaped structure having two or more portions. Engine case200) may be configured to retain rotating turbomachinery. The circular profile of engine case200may encase or surround the rotational path of a rotating compressor or turbine blade about an engine centerline such as the axis A-A′ inFIG. 1, for example. In that regard, engine case200may be substantially centered about the engine centerline.

In various embodiments, engine case200may include a first case202and a second case206. The left half may include an upper flange204and a lower flange205. The upper flange204and lower flange205may be located approximately 180° from one another. Stated another way, the upper flange204and lower flange205may be diametrically opposite one another. Upper and lower flanges may be upper and lower relative to the ground when a plane is on the runway. In that regard, an upper flange may be near the point of the engine furthest from the ground (e.g., near the top of the engine relative to the ground). A lower flange may be near the point of the engine closest to the ground while a plane is on the runway (e.g., near the bottom of the engine).

In various embodiments, upper flange204and lower flange205may be oriented such that the engine mounting points (represented by mounting support location212) are located axially from the upper flange204and diametrically opposite lower flange205. Stated another way, upper flange204may be closer to engine mounting points in a circumferential direction than lower flange205. In a typical engine installation, with engine mounting points at or near the top of the engine (e.g., the portion of the engine furthest from the ground) in the y direction, upper flange204and lower flange205may be aligned in the vertical plane (i.e., the y-z plane). The flanges may thus be oriented at top-dead center and bottom-dead center of an engine case as viewed from the ground while a plane is on the runway.

In various embodiments, engine case200may also include second half206. Second half206may have upper flange208and lower flange209. Upper flange208may be similar to upper flange204. Lower flange209may also be similar to lower flange205. Lower flange209may be pressed against lower flange205and upper flange204may be pressed against upper flange208. Fasteners210may be passed through the upper flanges and the lower flanges to mechanically couple the first half202to the second half206. The seam between the upper flanges may be vertically aligned (e.g., in the y direction) with the seam between the lower flanges. Fasteners210may include rivets, bolts, or other suitable fasteners to couple the first half202and second half206along the flanges. In response to the flanges being mechanically coupled, engine case200may form an annulus.

With reference toFIG. 3, a perspective view of first half202of engine case200is shown, in accordance with various embodiments. Although first half202is illustrated, second half206shares the same characteristics of first half202described herein. First half202of engine case200may include a semi-circular edge302in the x-v plane. A body of first half202of engine case200may extend aft from semi-circular edge302(e.g., in the z direction). Upper flange204and lower flange205may extend in the z direction at the circumferential edges of semi-circular edge302.

In various embodiments, upper flange204and lower flange205may be substantially rectangular and comprise mating surfaces304in the y-z plane. The flat mating surfaces may extend the length of first half202in the z direction. The flat mating surfaces may also be limited in length and partially extend the length of first half202in the z direction. Mating surface304of first half202may be configured to mate with corresponding mating surfaces of second half206. Mating surface304may define openings306configured to receive fasteners210fromFIG. 2. Openings306in mating surface304may align with corresponding openings defined by the mating surface of second half206. Referring briefly toFIG. 2, first half202and second half206may thus be pressed together in the x direction with the mating surface304of second half202aligned with the corresponding mating surface of first half206.

Referring now toFIG. 4, a perspective view of engine case200substantially centered about engine centerline CL with the potential for out-of-round deflection or other deflection resultant from engine operation. Body300of first half202and body400of second half206from the inner surface of the annular geometry with seam402between lower flange205and lower flange209substantially aligned in the y direction with the seam between upper flange204and upper flange208. The engine mounting points may be substantially aligned with the same vertical plane as the flange seams (i.e., the y-z plane). Substantially aligned, as used to describe circumferential alignment between engine mounting points and the flanges of engine case200such that the engine mounting points are within 15° of circumferential arc from upper flange204, upper flange208, lower flange205, and/or lower flange209, as measured from the engine centerline. Although substantially aligned circumferentially, as described above, in various embodiments the engine mounting points may be offset from engine case200in an axial direction.

The axially oriented upper flanges and lower flanges of engine case200may serve as a pair of axial stiffening ribs on, for example, a high pressure compressor case. By orienting the flanges in the vertical plane, for example, on engines with top located mounting points, the flanges serve as stiffening ribs in the plane in which the thrust/thrust mount couple (i.e., mounting point59ofFIG. 1) is applying a moment to the engine case200. Flanges oriented thusly may increase the case moment of inertia and reduce both case bending and out-of-round deflection. As a result, tip clearance may be more stringently maintained, thereby improving engine performance. The vertically oriented flanges may further provide ease of access during maintenance and reduce the effort required to retrieve fallen items that might be retained in a horizontally split case.