Axial compressor with arrangement for bleeding air from variable stator vane stages

A compressor includes: a compressor spool rotatable about an axis carrying axially-spaced-apart blade rows of compressor blades; a casing surrounding the compressor blades, the casing carrying a liner assembly defining a boundary of a primary compressor flowpath; and a plurality of axially-spaced-apart stator rows of stator vanes carried by the liner assembly, the stator rows alternating axially with the blade rows. At least some of the stator rows are variable stator rows, the stator vanes of which are mounted on trunnions passing through the casing, and are pivotable relative to the casing. An actuator arm is coupled to each trunnions, outside the casing. At least one first bleed slot passes through the liner structure between axially adjacent first and second ones of the variable stator rows; and a first flow path defined by the casing communicates with the first bleed slot and with the exterior of the casing.

BACKGROUND OF THE INVENTION

This invention relates generally to thermodynamics in gas turbine engines and more particularly to apparatus for extracting bleed air in such engines.

A gas turbine engine includes a turbomachinery core having a high pressure compressor, combustor, and high pressure turbine in serial flow relationship. The core is operable in a known manner to generate a primary flow of propulsive gas. A typical turbofan engine adds a low pressure turbine driven by the core exhaust gases which in turn drives a fan rotor through a shaft to generate a bypass flow of propulsive gas. In the case of a high bypass engine this provides the majority of the total engine thrust.

A typical axial flow high pressure compressor in such an engine includes a number of stages. Each stage has a row of rotating airfoils or blades and row of stationary airfoils or vanes. The vanes serve to turn the airflow exiting an upstream row of blades before it enters the downstream row of blades. It is known to construct one or more rows of vanes so that their angle of incidence can be changed in operation. These are referred to as variable stator vanes or simply “VSVs”. The VSVs enable throttling of flow through the compressor so that it can operate efficiently at different flow rates, without the losses incurred by other mechanisms such as bleed valves. Because of high overall pressure ratios and stage count in many compressors, there will often be many stages of VSVs.

It is known to extract high-pressure compressed air from the high pressure compressor. This referred to as “bleed air” and may be used for purposes such as engine or aircraft anti-icing, boundary layer control devices, aircraft environmental control systems and the like. For optimal engine performance, bleed should occur at the stage that provides the minimum source pressure the user requires. However, in the prior art, sources have been limited to stages aft of the last VSV stage, because of the structural difficulty of extracting air from the VSV stages. Thus, the only conveniently available bleed source is at an undesirably high pressure.

Accordingly, there is a need for a compressor which allows air to be bled from the VSV stages.

BRIEF DESCRIPTION OF THE INVENTION

This need is addressed by the present invention, which provides a compressor bleed apparatus which bleeds air between VSV stages and provides a path for the air to be extracted clear of structure external to the compressor casing.

According to one aspect of the invention a compressor apparatus includes: a compressor spool mounted for rotation about a centerline axis and carrying a plurality of axially-spaced-apart blade rows, each blade row including an annular array of airfoil-shaped compressor blades; a casing surrounding the compressor blades, the casing carrying a liner assembly which defines a boundary of a primary gas flowpath through the compressor; a plurality of axially-spaced-apart stator rows carried by the liner assembly, each stator row including an annular array of airfoil-shaped stator vanes, wherein the stator rows alternate axially with the blade rows, wherein at least some axially adjacent ones of the stator rows are variable stator rows, the stator vanes of which are mounted on trunnions passing through the casing, so as to be pivotable relative to the casing; an actuator arm coupled to each of the trunnions, outside the casing; at least one first bleed slot passing through the liner structure between axially adjacent first and second ones of the variable stator rows; and a first flow path defined by the casing, communicating with the at least one first bleed slot and with the exterior of the casing.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,FIG. 1depicts a portion of a high pressure compressor10, which is part of a gas turbine engine as described above. The compressor10includes an axially-elongated annular spool12mounted for rotation about a centerline axis “A”. The spool12may be built up from several smaller components. In accordance it includes one or more drum portions14and several annular disks16which all rotate together as a unit. The spool12is depicted in half-section but it will be understood that it is a body of revolution. Several blade rows are carried at the outer periphery of the spool12. Each blade row comprises an annular array of airfoil-shaped compressor blades18which extend radially outward from the spool12. An annular liner assembly20closely surrounds the compressor blades18and defines the radially outer boundary of a primary gas flowpath through the compressor10. The liner assembly20is built up from a plurality of smaller components, some of which will be described in more detail below. An annular casing22surrounds the liner assembly20and provides structural support to it. Several stator rows are carried by the liner assembly20. Each stator row comprises an annular array of airfoil-shaped stator vanes24which extend radially inward from the liner assembly20. The stator rows alternate with the blade rows in the axial direction. Each blade row and the axially downstream stator row constitute a “stage” of the compressor10. In operation, the compressor10draws in air (from the left side of the figure) and compresses it as it pumps it axially downstream, towards the right side of the figure. Each stage contributes an incremental pressure rise to the air, with the highest pressure being at the exit of the last stage.

In the illustrated example, only some of the stages of the compressor10are shown. The stages forward and aft of those illustrated are not of consequence to the invention. The stages which are shown are labeled sequentially “S1” through “S7”. These numbers are used solely for the sake of easy reference and do not necessarily correspond to the actual number of the stages in the complete compressor10. The four stages S1 through S4 shown on the left side of the figure (towards an inlet end of the compressor10) incorporate variable stator vanes or simply “VSVs”; the stator vanes24of these stages are constructed so that their angle of incidence can be changed in operation (i.e. these stator vanes24can be pivoted about the radial axes shown in dashed lines). The remaining stages to the right side of the figure (towards an exit end of the compressor) do not incorporate VSVs. It is noted that the principles of the present invention are generally applicable to any axial compressor having two or more axially adjacent stages of VSVs, without regard to the total number of stages, or how many stages include VSVs. The VSVs enable throttling of flow through the compressor10in a known manner, so that it can operate efficiently at both high and low mass flow rates. The stator vane24of each stage S1 through S4 has a corresponding trunnion (generically referred to as “26” and labeled26A through26D, respectively) that extends radially outward through the liner assembly20and the casing22. An actuator arm (generically referred to as “28” and labeled28A through28D, respectively) is attached to the distal end of each trunnion26A-26D. All of the actuator arms28A-28D for an individual stage are coupled together by a ring30(generically referred to as “30” and labeled30A through30D, respectively). Rotation of the rings30A-30D about the engine's longitudinal axis A thus causes all of the actuator arms28coupled to that specific ring30A-30D to move in unison, in turn pivoting all of the trunnions26A-26D with their attached stator vanes24in unison.

In this particular example a rear bleed slot32, which may comprise an annular array of individual slots, penetrates the liner assembly20aft of the stage S6. The rear bleed slot32communicates with a rear plenum36defined between the liner assembly20and the casing22. One or more rear extraction ports38in the casing22provide a location to extract the air from the rear plenum36. In use the rear extraction port38would be coupled to appropriate pipework or ducting external to the casing22(not shown).

A middle bleed slot40, which may comprise an annular array of individual slots, penetrates the liner assembly20aft of the stage S3. The middle bleed slot40communicates with a middle plenum42defined between the liner assembly20and the casing22and isolated from the rear plenum36. One or more middle extraction ports44in the casing22provide a location to extract the air from the middle plenum42. In use this extraction port44would be coupled to appropriate pipework or ducting external to the casing22(not shown).

A forward bleed slot46, which may comprise an annular array of individual slots, penetrates the liner assembly20aft of the stage S1. The forward bleed slot46communicates with a forward plenum48defined between the liner assembly20and the casing22and isolated from the rear and middle plenums36and42. One or more forward extraction ports50in the casing22provide a place to extract the air from the forward plenum48. In use this extraction port50would be coupled to appropriate pipework or ducting external to the casing22(not shown).

FIG. 2illustrates in more detail the structure used to bleed air between the stages S1 and S2. An annular shroud52surrounds the compressor blade18as described above. The shroud52may be made up of a plurality of segments arranged in a ring to form a complete 360 degree assembly. The shroud segments may include forward and aft rails54and56to mount them in slots in the adjacent portions of the liner assembly20. The forward bleed slots46described above are formed in the shroud52and communicate with the forward plenum48. In this particular example the forward bleed slots46are disposed between the forward rail54and the generally tapered-cylindrical central portion58of the shroud52. A typical construction would have the liner assembly20comprised of a ring of segments and the casing22formed in two sections bolted together at a split line flange60. To avoid leakage at the joints between these components, a duct62may be positioned in the third plenum48. As an example, it may have a forward wall64and an aft wall66which define a flowpath between the shroud52and the extraction port50. The duct62may be made from two or more arcuate segments assembled into a complete annular shape.

The forward plenum48lies axially between two stages having VSVs. In order to provide adequate space to bleed air from the stage S1 and extract that air from the forward plenum48, the operating hardware of the VSVs is positioned differently than in prior art practice. Specifically, the actuator arms28B of the stage S1 extend axially forward, while the actuator arms28C of the stage S2 extend axially rearward. As used herein, the term “axially” refers to directions parallel to the longitudinal axis A shown inFIG. 1. This creates an open void “V” outboard of the casing22, denoted by dashed lines inFIG. 2, not present in prior art configurations. The open void V permits the connection of external pipes or ductwork (not shown) to the extraction port50.

In operation, air can be bled from the stages S1, S3, and S6, providing air flows at three discrete pressures. As much of the bleed air as possible would be extracted at the lowest possible pressure (i.e. the most forward stage possible) in order to minimize the impact on efficiency and specific fuel consumption (“SFC”). In contrast with prior art bleed arrangements, air may be extracted at a desired pressure despite the fact that such pressure is found at the location of the VSV stages.

A similar air bleed configuration may be implemented in a compressor110in which the casing and liner are integrated into a single wall. For example,FIG. 3illustrates a portion of a compressor having a spool112, compressor blades118, and stator vanes124. An annular casing122surrounds the compressor blades118and serves both as a mount for the stator vanes124and as a shroud for the compressor blades118. In effect, it comprises a casing and a liner assembly as described above, in one integral unit. Some of the stator vanes124are variable-angle (or “VSVs”) and include trunnions126A-126D coupled to actuator arms128A-128D and rings130A-130D, respectively. For illustrative purposes the stator vanes124of two axially-adjacent stages will be described. One stage labeled S1′ includes a trunnion126A, an actuator arm128A, and a ring130A. The stage S2′ immediately downstream of the stage S1′ includes a trunnion126B, an actuator arm128B, and a ring130B. The actuator arm128A extends axially forward and the actuator arm128B extends axially rearward, creating a void “V′” shown by dashed lines. A bleed slot146is formed through the casing122and communicates with a plenum148. Because of the presence of the void V′, the plenum148can in turn be coupled to appropriate piping or ductwork (not shown).

FIG. 4illustrates an alternative configuration for bleeding air from a compressor. The figures shows a portion of a high pressure compressor210, which is part of a gas turbine engine as described above and is similar in overall construction to the compressor10and components which are identical to the compressor10will be described in abbreviated fashion. The compressor210includes an annular spool212with blade rows of compressor blades218. An annular liner assembly220closely surrounds the compressor blades218and defines the radially outer boundary of a primary gas flowpath through the compressor210. The liner assembly220is built up from a plurality of smaller components, some of which will be described in more detail below. An annular casing222surrounds the liner assembly220and has several stator rows of stator vanes224.

In the illustrated example, only some of the stages of the compressor210, labeled “S1″” through “S6″” are shown. As noted above, these numbers are used solely for the sake of easy reference and do not necessarily correspond to the actual number of the stages in the complete compressor210. The first three stages shown (i.e. S1″-S3″) incorporate variable stator vanes as described above. The vane224of each stage S1″ through S3″ has a corresponding trunnion that extends radially outward through the liner assembly220and the casing222. The trunnions of stages S2″ and S3″ are labeled226B and226C, respectively. The trunnions of stage S1″ are not shown. The actuating hardware for the trunnions is not shown.

A rear bleed slot232, which may comprise an annular array of individual slots, penetrates the liner assembly220aft of the stage S5″. The rear bleed slot232communicates with a rear plenum236defined between the liner assembly220and the casing222. One or more rear extraction ports238in the casing222provide a location to extract the air from the rear plenum236. In use the rear extraction port238would be coupled to appropriate pipework or ducting external to the casing222(not shown).

A middle bleed slot240, which may comprise an annular array of individual slots, penetrates the liner assembly220aft of the stage S2″. The middle bleed slot240communicates with a middle plenum242defined between the liner assembly220and the casing222and isolated from the rear plenum236. One or more middle extraction ports244in the casing222provide a location to extract the air from the middle plenum242. In use the middle extraction port244would be coupled to appropriate pipework or ducting external to the casing222(not shown).

A forward bleed slot246, which may comprise an annular array of individual slots, penetrates the liner assembly220aft of the stage S1″. The forward bleed slot246communicates with a forward plenum248defined between the liner assembly220and the casing222and isolated from the rear and middle plenums236and242. One or more forward extraction ports250in the casing222provide a place to extract the air from the forward plenum248. In use this forward extraction port250would be coupled to appropriate pipework or ducting external to the casing222(not shown).

FIG. 5illustrates in more detail the structure used to bleed air from the stage S1. An annular shroud252surrounds the compressor blades218as described above. The shroud252may be made up of a plurality of segments arranged in a ring to form a complete 360-degree assembly. The shroud segments may include forward and aft rails254and256to mount them in slots in the surrounding portions of the liner assembly220. The forward bleed slots246described above are formed in the shroud252and communicate with the forward plenum248. In this particular example the forward bleed slots246are disposed between the forward rail254and the generally tapered-cylindrical central portion258of the shroud252.

The bushings260which receive the trunnions226C pass through an annular wall-like boss262which is part of the casing222. In order to pass bleed air across the stage S2, the boss262is penetrated at several locations around its periphery by apertures264. The apertures264with the trunnions extending across them can be seen inFIG. 6. Optionally, the trunnions226C may have an axially-elongated noncircular shape which is smaller is a circumferential direction than an axial direction, as seen inFIG. 7, in order to increase the lateral space between adjacent trunnions226and thereby permit more flow through the apertures264. Optionally, to prevent leakage of bleed air between the trunnions226and the casing222, hollow sleeves265may be positioned surrounding the trunnions226, extending radially across the apertures264.

Various means may be used to avoid leakage through the forward plenum248. As noted above, a typical construction would have the liner assembly220comprised of a ring of segments and the casing222formed in two sections bolted together at a split line flange259. To avoid leakage at the joints between these components, annular front and rear ducts266and268may be positioned in the front plenum248. The front duct266comprises an arcuate outer wall270and an inner wall272with an L-shaped cross-section. Together the inner and outer walls270and272define a flowpath between the shroud252and the front face274of the boss262. The rear duct268comprises an outer wall276with a generally U-shaped cross-section and an inner wall278with a generally linear cross-section extending aft and radially outward at an angle. Together the inner and outer walls278and276define a flowpath between the aft face280of the boss262and the inner surface282of the casing222. Both the front and rear ducts266and268may be made from two or more arcuate segments assembled into a complete annular shape.

The bleed configurations described above can be combined and/or adapted as need for any desired bleed location. A particular compressor may have one or multiple bleed locations within either the VSV stages or the non-VSV stages. While locating the bleed port aft of the variable stages maintains compressor length and minimizes VSV complexity, bleeding directly out of the cavity reduces bleed system/leakage losses. In contrast with prior art bleed arrangements, air may be extracted at a desired pressure without regards to the axial location within the compressor. Analysis indicates that the bleed arrangements described here can result in a significant reduction in engine SFC.

The foregoing has described a bleed arrangement for a gas turbine engine compressor. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation.