Patent Application
20170175557
The present invention relates generally to combustion gas turbine engines (“gas turbines”), and more specifically to a rim cavity sealing systems and processes for the gas turbine engines.
During operation, because of the extreme temperatures of the hot-gas path, great care is taken to prevent components from reaching temperatures that would damage or degrade their operation or performance. One area that is particularly sensitive to extreme temperatures is the space that is inboard of the hot-gas path. This area, which is often referred to as the rim or wheelspace cavity of the turbine, contains the several turbine wheels or rotors onto which the rotating rotor blades are attached. While the rotor blades are designed to withstand the high temperatures of the hot-gas path, the rotors are not and, thus, it is necessary that the working fluid of the hot-gas path be prevented from flowing into the rim cavity. However, as will be appreciated, axial gaps necessarily exist between the rotating blades and the surrounding stationary parts, and it is through these gaps that the hot gases of the working fluid gains access to the internal regions. In addition, because of the way the engine warms up and differing thermal expansion coefficients, these gaps may widen and shrink depending on the way the engine is being operated. This variability in size makes the proper sealing of these gaps a difficult design challenge.
More specifically, gas turbines includes a turbine section with multiple rows of stator blades and rotor blades in which the stages of rotor blades rotate together around the stationary guide vanes of the stator blades. The stator blades and assemblies related thereto extend into a rim cavity formed between two stages of the rotor blades. Seals are formed between the inner shrouds of the rotor blades and the stator blades, and between the inboard surface of the stator blade diaphragm and the two rotor disk rim extensions. As will be appreciated, the hot gas flow pressure is higher on the forward side of the stator blades than on the aft side, and thus a pressure differential exists within the rim cavity. In the prior art, seals on the inboard surface of the stator diaphragm may be used to control of leakage flow across the row of stator blades. Additionally, knife edge seals may be used on the stator blade cover plate to produce a seal against the hot gas ingestion into the rim cavity. Hot gas ingestion into the rim cavity is prevented as much as possible because the rotor disks are made of relatively low temperature material than the airfoils. The high stresses operating on the rotor disks along with exposure to high temperatures will thermally weaken the rotor disk and shorten the life thereof. Purge cooling air discharge from the stator diaphragm has been used to purge the rim cavity of hot gas flow ingestion.
However, very little progress has been made in the control of rim cavity leakage flow so to reduce the usage of purge air. Difficulties regarding distribution of purge are result in inefficient usage, which, of course, comes at a cost. As will be appreciated, purging systems increase the manufacturing and maintenance cost of the engine, and are often inaccurate in terms of maintaining a desired level of pressure or outflow from the rim cavity. Further, purge flows adversely affect the performance and efficiency of the turbine engine. That is, increased levels of purge air reduce the output and efficiency of the engine. Hence, it is desirable that the usage of purge air be minimized. As a result, there is a continuing need for improved methods, systems and/or apparatus that better seal the gaps, trench cavities, and/or rim cavities from the hot gases of the flow path.
The present application thus describes a gas turbine that includes a trench cavity seal sealing the trench cavity defined between a stator inboard face of a stator blade and a rotor inboard face of a rotor blade. The trench cavity seal may include a stator overhang formed on the stator blade face that extends axially toward the rotor inboard face. The stator overhang may include an overhang topside, which defines an inner boundary of a working fluid flowpath through the turbine, an overhang underside, which opposes the overhang topside, and an overhang face, which is defined between the overhang topside and underside. The trench cavity seal may further include a platform having a platform lip extending axially from the rotor inboard face toward the stator inboard face and circumferentially spaced turbulators extending axially from the rotor inboard face, the turbulators being positioned inboard of the platform lip. An outboard edge and an inboard edge of the stator overhang may each include axially jutting edges such that, therebetween, a recessed pocket on the overhang face is formed. The platform lip may radially overlaps the recessed pocket on the overhang face of the stator overhang and be positioned relative thereto so to form a multiple switch-back flowpath in a mouth section of the trench cavity formed therebetween.
These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.
These and other features of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention. Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical designations to refer to features in the drawings. Like or similar designations in the drawings and description may be used to refer to like or similar parts of embodiments of the invention. As will be appreciated, each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. It is to be understood that the ranges and limits mentioned herein include all sub-ranges located within the prescribed limits, inclusive of the limits themselves unless otherwise stated. Additionally, certain terms have been selected to describe the present invention and its component subsystems and parts. To the extent possible, these terms have been chosen based on the terminology common to the technology field. Still, it will be appreciate that such terms often are subject to differing interpretations. For example, what may be referred to herein as a single component, may be referenced elsewhere as consisting of multiple components, or, what may be referenced herein as including multiple components, may be referred to elsewhere as being a single component. In understanding the scope of the present invention, attention should not only be paid to the particular terminology used, but also to the accompanying description and context, as well as the structure, configuration, function, and/or usage of the component being referenced and described, including the manner in which the term relates to the several figures, as well as, of course, the precise usage of the terminology in the appended claims. Further, while the following examples are presented in relation to a certain type of gas turbine or turbine engine, the technology of the present invention also may be applicable to other types of turbine engines as would the understood by a person of ordinary skill in the relevant technological arts.
Given the nature of gas turbine operation, several descriptive terms may be used throughout this application so to explain the functioning of the engine and/or the several sub-systems or components included therewithin, and it may prove beneficial to define these terms at the onset of this section. Accordingly, these terms and their definitions, unless stated otherwise, are as follows. The terms “forward” and “aft” or “aftward”, without further specificity, refer to directions relative to the orientation of the gas turbine. That is, “forward” refers to the forward or compressor end of the engine, and “aft” or “aftward” refers to the aft or turbine end of the engine. It will be appreciated that each of these terms may be used to indicate movement or relative position within the engine. The terms “downstream” and “upstream” are used to indicate position within a specified conduit relative to the general direction of flow moving through it. (It will be appreciated that these terms reference a direction relative to an expected flow during normal operation, which should be plainly apparent to anyone of ordinary skill in the art.) The term “downstream” refers to the direction in which the fluid is flowing through the specified conduit, while “upstream” refers to the direction opposite that. Thus, for example, the primary flow of working fluid through a gas turbine, which begins as air moving through the compressor and then becomes combustion gases within the combustor and beyond, may be described as beginning at an upstream location toward an upstream or forward end of the compressor and terminating at a downstream location toward a downstream or aft end of the turbine. In regard to describing the direction of flow within a common type of combustor, as discussed in more detail below, it will be appreciated that compressor discharge air typically enters the combustor through impingement ports that are concentrated toward the aft end of the combustor (relative to the combustors longitudinal axis and the aforementioned compressor/turbine positioning defining forward/aft distinctions). Once in the combustor, the compressed air is guided by a flow annulus formed about an interior chamber toward the forward end of the combustor, where the air flow enters the interior chamber and, reversing it direction of flow, travels toward the aft end of the combustor. In yet another context, the flow of coolant through cooling channels or passages may be treated in the same manner.
Additionally, the term “rotor blade”, without further specificity, is a reference to the rotating blades of either the compressor or the turbine, which include both compressor rotor blades and turbine rotor blades. The term “stator blade”, without further specificity, is a reference to the stationary blades of either the compressor or the turbine, which include both compressor stator blades and turbine stator blades. The term “blades” will be used herein to refer to either type of blade. Thus, without further specificity, the term “blades” is inclusive to all type of turbine engine blades, including compressor rotor blades, compressor stator blades, turbine rotor blades, and turbine stator blades.
Finally, given the configuration of compressor and turbine about a central common axis, as well as the cylindrical configuration common to many combustor types, terms describing position relative to an axis may be used herein. In this regard, it will be appreciated that the term “radial” refers to movement or position perpendicular to an axis. Related to this, it may be required to describe relative distance from the central axis. In this case, for example, if a first component resides closer to the central axis than a second component, the first component will be described as being either “radially inward” or “inboard” of the second component. If, on the other hand, the first component resides further from the central axis than the second component, the first component will be described herein as being either “radially outward” or “outboard” of the second component. Additionally, as will be appreciated, the term “axial” refers to movement or position parallel to an axis. Finally, the term “circumferential” refers to movement or position around an axis. As mentioned, while these terms may be applied in relation to the common central axis that extends through the compressor and turbine sections of the engine, these terms also may be used in relation to other components or sub-systems of the engine.
By way of background, referring now to the figures,
In one example of operation, the rotation of compressor rotor blades 14 within the axial compressor 11 may compress a flow of air. In the combustor 13, energy may be released when the compressed air is mixed with a fuel and ignited. The resulting flow of hot gases or working fluid from the combustor 13 is then directed over the turbine rotor blades 16, which induces the rotation of the turbine rotor blades 16 about the shaft. In this way, the energy of the flow of working fluid is transformed into the mechanical energy of the rotating blades and, given the connection between the rotor blades and the shaft, the rotating shaft. The mechanical energy of the shaft may then be used to drive the rotation of the compressor rotor blades 14, such that the necessary supply of compressed air is produced, and also, for example, a generator to produce electricity.
As further illustrated in
It will be appreciated that a trench cavity 47 may be present at each point along the radially inward or inner boundary of the working fluid flowpath where rotating parts border stationary parts. Thus, as illustrated, a trench cavity 47 may be formed between the trailing edge of the rotor blade 16 and the leading edge of the stator blade 17, and between the trailing edge of the stator blade 17 and the leading edge of the rotor blade 16. Typically, in regard to the rotor blade 16, the shank 36 defines one edge of the trench cavity 47, and, in regard to the stator blades 17, the inner sidewall 42 defines the opposing edge of the trench cavity 47. Axial projections 50, which will be discussed in more detail below, may be configured within the trench cavity 47 so to provide a tortuous path or seal that limits ingestion of working fluid. Axial projections 50 may be defined as radially thin extensions that protrude axially from either the inboard structure or faces of the rotor blades 16 or the stator blades 17. The axial projection 50, as will be appreciated, may be included on each of the circumferentially spaced blades 16, 17 within a particular row such that, together, the axial projections 50 extend circumferentially about the central axis of the turbine 12. As shown, according to certain embodiments, the axial projection 50 may be included on the rotor blade 16 and configured as a so called “angel wing” projection that extends from the inboard structure of the rotor blade 16. As illustrated, inboard of the angel wing axial projection 50, the trench cavity 47 may be described as transitioning into a wheelspace cavity 51. Outboard of the angel wing axial projection 50, as indicated, the stator blade 17 may be configured to include an inner sidewall 42 that projects toward the rotor blade 16 such that a stator overhang 52 is formed. As used herein, the stator overhang 52 is a feature that extends from the stator blade 17 and overhangs or is cantilevered over a portion of the trench cavity 47.
As stated, it is desirable to prevent the working fluid of the working fluid flowpath from entering the trench cavity 47 and the wheelspace cavity 51 because the extreme temperatures of the hot gases may damage the components within this area. According to aspects of the present invention, the axial projection 50 and the stator overhang 52, as illustrated, may be configured so to axially overlap, which may limit some of this ingestion. However, because of the varying width of the trench cavity 47 and the limitations of such seals, the trench cavity 47 may still require purging with compressed air bled from the compressor so to insure against working fluid ingestion. As stated, because purge air negatively affects the performance and efficiency of the gas engine, its usage should be minimized.
As illustrated in
As shown, the stator inboard face 53 may include a stator overhang 52 that axially projects toward the rotor inboard face 54. As will be appreciated, the stator overhang 52 may include an overhanging portion of the sidewall 42. As such, the stator overhang 52 may define an axial section of the inner boundary of working fluid flowpath. The outboard surface of the stator overhang 52, as used herein, will be referred to as an overhang topside 59. As indicated, the stator overhang 52 also may include an overhang underside 60 that opposes the overhang topside 59 across the body of the stator overhang 52. An overhang face 58, as used herein, refers to the radially oriented face that connects the overhang topside 59 to the overhang underside 60. The overhang face 58 defines a boundary of the trench cavity 47 and may be oriented so to face the rotor inboard face 54. As illustrated, edges are defined in profile between the overhang topside 59 and the overhang face 58 as well as between the overhang underside 60 and the overhang face 58. The edge defined between the overhang topside 59 and the overhang face 58, as used herein, will be referred to herein as an outboard edge 56, while the edge defined between the overhang underside 60 and the overhang face 58 will be referred to herein as an inboard edge 57. Thus, the stator overhang 52 may be described as including the outboard edge 56 and inboard edge 57 and, defined between those two features, the overhang face 58.
The rotor inboard face 54, as illustrated, may include a platform lip 66 portion of the platform 38 that extends or juts axially toward the stator inboard face 53. As will be appreciated, the platform 38 of the rotor blade 16 defines an axial section of the inner boundary of the working fluid flowpath. The platform lip 66, thus, may generally oppose the stator overhang 52 across an outboard region or mouth section (or “mouth 48”) of the trench cavity 47. The platform lip 66 generally is formed by an axially jutting, cantilevered portion of the platform 38. As indicated, the platform lip 66 may be described as having a topside 69 and underside 71. According to certain configurations, the platform topside 69 may curve smoothly inboard such that the platform lip 66 tapers in radial width as it nears the stator inboard face 53. As indicated, the tapering platform lip 66 may taper to a tip 73, which represents the furthest point of extension for the platform lip 66.
The rotor inboard face 54 may further include an axial projection 50 that resides inboard of the platform lip 66. The axial projection 50 may be a radially thin feature that extends axially toward the stator inboard face 53, and, as discussed more below, may include an upturned tip or “angel wing” configuration. The rotor inboard face 54 may further include a pocket 68. The pocket 68, as indicated, is the region overhung by the platform lip 66. The pocket 68 may be radially defined between the underside 60 of the platform lip 66 and the axial projection 50.
According to certain embodiments of the trench cavity seal 55, the inboard edge 57 of the stator overhang 52, as illustrated, may be configured to have an axially jutting configuration. As shown, the inboard edge 57 having the axially jutting configuration may be configured so to radially overlap with the radial height of the pocket 68, which, as stated, is defined between the underside 71 of the platform lip 66 and the axil projection 50. According to other embodiments, the inboard edge 57 having the axially jutting configuration may be made to radially coincide with the approximate radial midpoint of the radial height of the pocket 68.
According to other embodiments of the trench cavity seal 55, the outboard edge 56 of the stator overhang 52 also may be configured to have an axially jutting configuration. As indicated, when both the outboard edge 56 and inboard edge 57 of the stator overhang 52 have axially jutting configurations, a recessed pocket 72 is formed on the overhang face 58. According to certain embodiments, the trench cavity seal 55 includes the outboard boundary of the pocket 68 being positioned so to radially overlap the recessed pocket 72 formed on the overhang face 58. According to other embodiments, the outboard boundary of the pocket 68 may be positioned so to radially coincide with the approximate radial midpoint of the recessed pocket 72 formed on the overhang face 58. According to other exemplary embodiments, the tip 73 of the platform lip 66 is radially aligned within the radial height of the recessed pocket 72, which is a range defined between the inboard and outboard edges 56, 57 of the stator overhang 52. According to certain embodiments, the platform lip 66 is wholly contained within the radial height of the recessed pocket 72.
According to alternative embodiments of the present invention, the axial projection 50 is positioned inboard relative to the stator overhang 52 and is configured to axially overlap therewith. As illustrated, the stator overhang 52 and the axial projection 50 may be configured such that the stator overhang 52 axially overlaps a significant portion of the axial projection 50. The stator overhang 52, thus, overhangs at least a tip 67 of the axial projection 50. As stated, the axial projection 50 may have an angel wing configuration. As illustrated, this type of configuration may include an upturned, concave lip at the tip 67.
As illustrated in
As described, the axial projection 50 is a feature that may be positioned inboard relative to the stator overhang 52 and, extending from the rotor inboard face 54 toward the stator inboard face 53, may be configured such that the tip 67 of the axial projection 50 axially overlaps the stator overhang 52. As depicted, according to exemplary embodiments, the axial projection 50 may be configured to have an upturned tip 67. For example, this upturned tip 67 may be part of the already described “angel wing” configuration in which a concave lip curls in the outboard direction. Specifically, the upturned tip 67 may curl or extend toward the overhang underside 60 of the stator overhang 52. As illustrated, according to preferred embodiments, this upturned tip 67 of the axial projection 50 may be configured so to axially coincide with a range defined between the inboard jutting inner and outer protuberances 80, 81. As such, the upturned tip 67 may axial coincide with the axial width of the underside recessed pocket 83 as defined between the protuberances 80, 81. According to certain preferred embodiments, the upturned tip 67 of the axial projection 50 is configured so to axially coincide with the approximate axial midpoint of the underside recessed pocket 83. In this manner, the trench cavity seal 55 of the present invention may include further corresponding structures that cooperate in order to induce a flowpath through the trench cavity 47 having multiple switch-backs that limits hot gas ingestion.
In this manner, as will be appreciated, the several components of the trench cavity seal 55, as provided above with reference to
For example,
As will be appreciated, in operation, the turbulators 90 may draw in purge air and increase its swirl velocity. While this may result in a small loss of torque, a net gain in efficiency of approximately 0.5% at the turbine stage may be achieved. This gain is a consequence of both the increased purge air swirl velocity, which produces a curtaining effect, described further below, as well as a change in swirl angle of the purge air. This change in swirl angle results in the purge air being better aligned with the hot gas flow, resulting in significantly reduced mixing losses when purge air escapes from trench cavity to join the flow of working fluid.
As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, each possible iteration is not herein discussed in detail, though all combinations and possible embodiments embraced by the several claims below are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.
