Patent Application
20190120069
This invention relates generally to rotor blades for use in turbine engines, and more specifically, but not by way of limitation, rotor wheel assemblies that promote efficient installation while also reducing certain types of wear.
As will be appreciated, turbine engines (for example, combustion or steam turbine engines) include flowpaths defined through turbine sections or turbines through which a pressurized working fluid is expanded during operation. Within such turbine, alternating rows of static nozzles or stator blades and buckets or rotor blades are axially stacked to interact with the flow of working fluid. The stator blades direct the flow of working fluid onto the rotor blades so to induce rotation about a central axis of the turbine. The rotor blades are connected to a rotor wheel that is connected to a shaft so that this rotation drives the rotation of the shaft, which then may be used to do work, for example, turn the coils of a generator.
Such turbines may include several stages or rows of rotor blades, and the size of these rotor blades generally increases as the rows progress in the downstream direction. The rotor blades within the later stages of the turbine engines, thus, typically have considerable length and weight. Along with the highly contoured shapes of these rotor blades, the considerable size creates certain geometrical or spatial restraints during installation, as well as particular structural and retainment issues for the rotor blades during operation.
Turbine rotor blades connect to the rotor wheel via particular types of connectors or connection assemblies. These typically include a particularly shaped root of the rotor blade—for example, a dovetail or “multi-tang” fir tree shape—that engages a correspondingly shaped slot formed through the outer perimeter of the rotor wheel. Such shaped connectors are effective at providing a number of stress-spreading contact surfaces between the root and the slot, and, once these contact surfaces engage, relative movement between the rotor blade and the rotor wheel is substantially restrained. According to certain conventional designs, such rotor blade and rotor wheel connections are often constructed with a certain degree of “wiggle room”, “play” or “excess room” in the radial direction, which allows some freedom of movement relative to the rotor wheel for rotor blades already engaged within the slot.
During high speed operation, it will be appreciated that such excess room in the radial direction does not lead to the rotor blade moving within the connector because the centrifugal forces drive the rotor blade in an outward radial direction and thereby fix it against the contact surfaces within the slot. As will be appreciated, the rotor blade will remain in this position as long as the turbine continues operating at high speed. However, during low speed operation, such as turning gear operation, the excess room allowed in the radial direction results in the rotor blade moving or jostling in this direction as it rotates. This movement is generally undesirable due to the wear it causes to the contact faces of the root and within the slot. However, having the excess room in the connector is nonetheless often necessary to facilitate assembly of the rotor blades. Specifically, some movement or “fanning” of rotor blades is needed during the assembly of the row. One of the reasons for this is that the outer tips of the airfoil of the rotor blade typically have interlocking features. Further, the airfoil portions of the rotor blades may overlap such that the assembly of the last rotor blades in the row is made difficult, if not impossible, unless a certain amount of movement is not maintained within the connectors.
Conventional technology includes the use of springs or, alternatively, overly tight dovetail fits, but each has limitations that are undesirable for use with the longer and heavier rotor blades in the later stages of the turbine. For example, springs may be used, but such springs and forces they needed to provide to radially secure the rotor blades are sizeable, particularly to overcome the 3-o'clock and 9-o'clock moment loading of the rotor blades during slow speed operation. Springs large enough to do this may limit the robustness of the rotor wheel design because the oversized dovetail bottoms required to accomplish this increases the stresses applied to the rotor wheel. Springs also are difficult to install and add to the complexity of the assembly. On the other hand, with overly tight connectors, the relative movement between the rotor blade and rotor wheel that is needed for efficient installation is eliminated.
Given these considerations, novel connection assemblies between rotor blades and rotor wheels, which permit some relative movement during installation but that may be made to restrain such movement once installation is completed, would have considerable economic value.
The present application thus describes a turbine engine that include: rotor blades circumferentially arrayed about a rotor wheel; a connection assembly by which each of the rotor blades connects to the rotor wheel, the connection assembly including: an axially oriented slot formed through a perimeter face of the rotor wheel; a root of the rotor blade installed within the slot, the root being shaped in relation to the slot such that the installation therein forms an axially extending shim cavity between opposing exterior surfaces of the root and the slot; and a shim installed within the shim cavity for restraining movement of the rotor blade relative to the rotor wheel in a radial direction.
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 present application 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. 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 appreciated 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. Thus, 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.
The following examples may be presented in relation to particular types of turbine engines. However, it should be understood that the technology of the present application may be applicable to other categories of turbine engines, without limitation, as would the appreciated by a person of ordinary skill in the relevant technological arts. Accordingly, unless otherwise stated, the usage herein of the term “turbine engine” is intended broadly and without limiting the usage of the claimed invention with various types of turbine engines, including various types of combustion or gas turbine engines as well as steam turbine engines.
Given the nature of how turbine engines operate, several terms prove particularly useful in describing certain aspects of their function. The terms “downstream” and “upstream” are used herein to indicate position within a specified conduit or flowpath relative to the direction of flow (hereinafter “flow direction”) moving through it. Thus, the term “downstream” refers to the direction in which a fluid is flowing through the specified conduit, while “upstream” refers to the direction opposite that. These terms may be construed as referring to the flow direction through the conduit given normal or anticipated operation. Given the configuration of turbine engines, particularly the arrangement of the turbine section about a common shaft or axis, terms describing position relative to an axis may be regularly 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 such cases, 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, the first component will be described as being either “radially outward” or “outboard” of the second component. As used herein, the term “axial” refers to movement or position parallel to an axis, while the term “circumferential” refers to movement or position around an axis. Unless otherwise stated or plainly contextually apparent, these terms should be construed as relating to the central axis of the turbine as defined by the shaft extending therethrough, even when these terms are describing or claiming attributes of non-integral components—such as rotor or stator blades—that function therein. Finally, the term “rotor blade” is a reference to the blades that rotate about the central axis of the turbine engine during operation, while the term “stator blade” is a reference to the blades that remain stationary.
Referring now to the drawings, wherein like characters designate like or corresponding parts throughout the several views, for background purposes,
The airfoil 25 of the rotor blade 16 typically includes a concave pressure face 26 and a circumferentially or laterally opposite convex suction face 27. The pressure face 26 and suction face 27 may extend axially between opposite leading and trailing edges 28, 29, respectively, and, in the radial direction, between an inboard end, which may be defined at the junction with a platform 24, and an outboard tip 31. The airfoil 25 may include a curved or contoured shape that is designed for promoting the desired aerodynamic performance. The platform 24, as shown, generally forms the junction between the root 21 and the airfoil 25, and thus the inboard end of the airfoil 25. As will be appreciated, the platform 24 also may define a section of the inboard boundary of the working fluid flowpath of the turbine.
The rotor blade 16 may be connected to the rotor wheel 19 via a connection assembly formed therebetween. As part of conventional design, the root 21 may be formed as dovetail or “fir tree” shaped connector that engages a correspondingly shaped slot 20 formed in the rotor wheel 19. In such connection assemblies, as shown, the root 21 and the slot 20 each include a number of projections or teeth that register with grooves formed within the other. In this way, a number of contact surfaces are created between the root 21 and the slot 19 so that operational stresses are spread. The slot 20 within the rotor wheel 19 may be axially oriented, or approximately so, so that the root 21 of the rotor blades 16 engages or is installed therewithin via an axially sliding motion. As discussed more below, to prevent axial movement of the rotor blade 16 once it is installed, an axial retainment feature may be provided. As shown in
As used herein, the root 21 is described as having an inlet side or upstream face 38, which corresponds with the leading edge 28 of the airfoil 25, and an exit side or downstream face 39 that corresponds with the trailing edge 29 of the airfoil 25. Additionally, as used herein, the root 21 includes a bottom or inboard most edge or face that is referred to as a bottom face 41 of the root 21. As further indicated in
As stated, the size of the rotor blades within the several stages of a turbine generally increases as the rows of rotor blades progress in the downstream direction. As a result, the rotor blades within these later stages of the turbine have considerable length and weight, which typically creates restrictive spatial considerations that must be taken into account during the installation of the rotor blades within a row. The length and weight of such rotor blades also result in particular structural and retainment issues for the rotor blades during operation, which often necessitate the use of interlocking tip and/or midspan shrouds.
Turbine rotor blades are typically connected to the rotor wheel via particular types of connectors (which may also be referred to herein as “connection assemblies”). As already described, such connectors typically include the root of the rotor blade having a shaped profile, such as a dovetail or “multi-tang” fir tree shape, that engages a correspondingly shaped slot formed through an outer perimeter of the rotor wheel. Such shaped connectors are configured like this to provide a number of stress-spreading contact surfaces between the root of the rotor blade and the slot of the rotor wheel. Once these contact surfaces are engaged, relative movement between the rotor blade and the rotor wheel is substantially restrained. According to conventional designs, however, such connection assemblies between rotor blades and rotor wheels are often made to have a certain degree of “play” or “excess room” in the radial direction, which allows the installed rotor blades at least some movement in this direction relative to the rotor wheel.
During high speed operation, it will be appreciated that such excess room in the radial direction does not result in the rotor blades moving within the connection assembly due to the centrifugal forces that drive the rotor blade in an outboard direction. However, during low speed operation—such as turning gear operation—the excess room in the radial direction results in the rotor blades moving or jostling in the radial direction as they rotate. While this movement is generally undesirable due to the wear it causes to the contact faces of the root and slot, the excess room is nonetheless necessary for facilitating the assembly of the rotor blades. Specifically, the excess room allows some movement or “fanning” of rotor blades that is needed during the assembly of the row. One of the reasons for this is the interlocking features that are present at the outboard tips or midspan of the airfoils, which are needed for support and to reduce vibrations. Further, the airfoil portions of the rotor blades may overlap such that the assembly of the last rotor blades in the row is made difficult, if not impossible, unless a certain amount of movement is not maintained within the connection assemblies.
Given these considerations, certain novel connection assemblies for connecting a row of rotor blades to a rotor wheel will now be described. With general reference to
In accordance with exemplary embodiments,
In further describing the shim cavity 51, it may be helpful to define the axial faces of the rotor wheel 19. As used herein, these are designated as an upstream face 52 and a downstream face 53, which are so designated relative to the flow direction of the working fluid 50 through the flowpath of the turbine. Alternatively, the upstream face 52 and downstream face 53 of the rotor wheel 19 are defined, respectively, relative to the corresponding upstream face 38 and downstream face 39 of the rotor wheel 19 (which coincide, respectively, with the leading edge 28 and trailing edge 29 of the airfoil 25). According to preferred embodiments, the upstream face 38 of the root 21 may be coplanar with the upstream face 52 of the rotor wheel 19, while the downstream face 39 of the root 21 may be coplanar with the downstream face 53 of the rotor wheel 19. As shown, a longitudinal axis of the shim cavity 51 may extend between the upstream face 52 and the downstream face 53 of the rotor wheel 19, as well as between the upstream face 38 and downstream face 39 of the root 21 of the rotor blade 16. Consistent with these designations, the shim cavity 51 may be further described as extending between upstream and downstream openings 54, 55, with the upstream opening 54 being the one that is generally coplanar with the upstream faces 38, 52 of the root 21 and rotor wheel 19, and the downstream opening 55 being the one that is generally coplanar with the downstream faces 39, 53 of the root 21 and rotor wheel 19.
According to preferred embodiments, the shim cavity 51 is configured with a tapering height that tapers gradually between a first height that is greater than a second height (which also may be referred to herein simply as a “greater height” and “lesser height”). As illustrated, the first or greater height of the shim cavity 51 may occur at the downstream opening 55. The shim cavity 51 may have a maximum height at the downstream opening 55. The second or lesser height of the shim cavity 51 may occur at the upstream opening 54. The shim cavity 51 may have a minimum height at the upstream opening 54. The taper angle of the shim cavity 51 may be gradual or shallow, for example, within a range of 0.4 to 1.0 degrees. As will be appreciated, the taper angle of the shim cavity 51 may be made to correspond to the taper of the shim 49, as discussed more below. As an example, the height of the shim cavity 51 at the downstream opening 55 may be between 0.25 and 0.35 inches, while the height of the shim cavity 51 at the upstream opening 54 may be between 0.05 and 0.15 inches. Though these dimensions may vary substantially based on varying rotor blade to rotor wheel configurations. According to preferred embodiments, the taper of the shim cavity 51 is produced via an angling of the bottom surfaced 41 of the root 21. In such cases, a radial height of the root 21 may be described as decreasing or tapering in accordance with the desired taper within the shim cavity 51 as the root 21 extends between its upstream and downstream faces 38, 39.
With reference now to
In accordance with exemplary embodiments of the present invention,
With continued reference to
As shown in
With references now to
The present invention, as demonstrated in
As shown in
As shown, the shims 49 are installed by inserting the thin end 68 of the shim 49 into the shim cavity 51 via the larger downstream opening 55. If necessary, the shim 49 then may be tapped into place from the downstream faces 39, 53 of the stage (also known as the exit side). (It should be appreciated that entrance side designs are also feasible.) Thus, a force may be asserted against the thick end 69 of the shim 49, such as by tapping, until the shim 49 has attained a fully inserted position within the shim cavity 51.
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 of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise 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.
