Tip shroud fillets for turbine rotor blades

A turbine rotor blade including an airfoil, tip shroud, and fillet formed therebetween. The fillet defines a fillet profile variable about the intersection for connecting the tip shroud and airfoil and facilitating aerodynamic airflow. The fillet includes a pressure side fillet. The pressure side fillet comprises a pressure side fillet profile per points within a first set of points of X, Y and Z coordinate values in a Cartesian coordinate system, as set forth in Table I, where X, Y and Z are distances in inches from an origin and, when the points are connected by smooth, continuing arcs, the points define the pressure side fillet profile of the pressure side fillet. The first set of points includes points between and including point 1 and point 50 of each reference plane between and including a reference plane H and a reference plane W, as set forth in Table I.

BACKGROUND OF THE INVENTION

The present invention relates generally to fillets used with a turbine rotor blade, and more specifically, to a fillet used between an airfoil and tip shroud of a turbine rotor blade.

At least some known turbine rotor blades include an airfoil, a platform, a shank, a dovetail extending along a radial inner end portion of the shank, and a tip shroud formed at a tip of the airfoil. On at least some known airfoils, integral tip shrouds are included on a radially outer end of the airfoil to define a portion of a passage through which hot combustion gasses must flow. Known tip shrouds and airfoils typically include a fillet having a predetermined size and shape at the intersection of the tip shroud and airfoil.

During operation, the connection formed between such a tip shroud and airfoil of a rotor blade become highly stressed due to rotationally induced centrifugal and mechanical forces. The fillets formed between the tip shroud and the airfoil are shaped to reduce the stress concentrations that occur in this region. However, known fillet shapes still allow the buildup of stress concentrations that reduce the effective life of the component. Further, known fillets may reduce engine efficiency due to drag forces and obstruction produced by the fillets. Consequently, there is a need for improved fillet shapes that further reduce stress concentrations, while also aerodynamically performing so to promote engine efficiency.

BRIEF DESCRIPTION OF THE INVENTION

The present application thus describes a rotor blade for a turbine of a gas turbine that includes an airfoil, a tip shroud, and a fillet formed about an intersection of the airfoil and the tip shroud. The fillet defines a fillet profile variable about the intersection for connecting the tip shroud and the airfoil and facilitating aerodynamic airflow. The fillet includes a pressure side fillet formed between the pressure side of the airfoil and the inner surface of the tip shroud, and a suction side fillet formed between the suction side of the airfoil and the inner surface of the tip shroud. The pressure side fillet includes a pressure side fillet profile substantially in accordance with points within a first set of points of X, Y and Z coordinate values in a Cartesian coordinate system, as set forth in Table I, where X, Y and Z are distances in inches from an origin and, when the points within the first set of points are connected by smooth, continuing arcs, the points within the first set of points define the pressure side fillet profile of the pressure side fillet. The first set of points includes each of the points between and including point 1 and point 50 of each reference plane between and including a reference plane H and a reference plane W, as set forth in Table I.

The present application further describes a rotor blade for a turbine of a gas turbine that includes an airfoil, a tip shroud, and a fillet formed about an intersection of the airfoil and the tip shroud. The fillet defines a fillet profile variable about the intersection for connecting the tip shroud and the airfoil and facilitating aerodynamic airflow. The fillet includes a pressure side fillet formed between the pressure side of the airfoil and the inner surface of the tip shroud, and a suction side fillet formed between the suction side of the airfoil and the inner surface of the tip shroud. The suction side fillet includes a suction side fillet profile substantially in accordance with points within a first set of points of X, Y and Z coordinate values in a Cartesian coordinate system, as set forth in Table II, where X, Y and Z are distances in inches from an origin and, when the points within the first set of points are connected by smooth, continuing arcs, the points within the first set of points define the suction side fillet profile of the suction side fillet. The first set of points includes each of the points between and including point 1 and point 50 of each reference plane between and including a reference plane H and a reference plane W, as set forth in Table I.

DETAILED DESCRIPTION OF THE INVENTION

A tip shroud, including a fillet, may be formed integrally with the turbine rotor blade at the radially outer end of an airfoil. The tip shroud generally provides a surface area that covers a tip of the airfoil. During operation, the tip shroud engages, at opposite ends, the tip shrouds of the circumferentially-adjacent rotor blades such that a generally annular ring or shroud is formed that substantially circumscribes a hot gas path. This annular ring contains the expanding combustion to improve engine efficiency. The fillet joins the tip shroud to the airfoil and, thereby, provides support to the tip shroud to prevent it from dislodging from the airfoil during operation.

Generally, in terms of engine performance, it is desirable to have relatively large tip shrouds that overhang both the pressure side and suction side of the outer radial tip of the airfoil. With regard to aerodynamic performance, however, it is advantageous for tip shroud fillets to remain as small and streamlined as possible. Given these competing interests—i.e., that tip shrouds be large enough to divert the greatest possible amount of working fluid over the airfoils, while the fillets remain small and streamlined to promote aerodynamic efficiency—it should be appreciated that the design of tip shrouds and the fillets that support them is a rigorous and highly specialized undertaking. Successful designs effectively balance the high stresses caused on each side of the airfoil by the overhanging tip shroud mass and, in so doing, may materially extend the life of the component, enable larger tip shrouds, and/or reduce fillet size for improved aerodynamic performance. As will be seen, the present application discloses fillet designs that are specifically adapted for achieving these objectives. That is, the presently disclosed fillets—which also may be referred to herein as the “present invention” or “present fillets”—may be employed to reduce and redistribute mass in the fillet region so that the fillet remains streamlined for aerodynamic performance, while still providing a structural configuration that further reduces stress concentrations and supports larger tip shrouds without sacrificing lifespan.

For background purposes,FIG. 1is a schematic illustration of an exemplary gas turbine engine12that includes a compressor15, a combustor16, and a turbine22extending therethrough from an intake side to an exhaust side, all coupled in a serial flow arrangement. Engine12includes a centerline axis23and a hot gas path is defined from intake side to exhaust side. In operation, air flows into the intake side and is routed to compressor15. Compressed air is channeled from compressor15to combustor16, wherein it is mixed with a fuel and ignited to generate combustion gases. The combustion gases are channeled via the hot gas path from combustor16towards turbine22, where turbine22converts the heat energy into mechanical energy to power compressor15and/or another load, such as a generator (not shown).

FIG. 2is a schematic representation of an exemplary hot gas path20defined in multiple stages of turbine22used in gas turbine engine12. Three stages are illustrated, each of which includes a row of vanes or nozzles24and a row of buckets or rotor blades26. Each of the rows of nozzles24include a plurality of nozzles24circumferentially-spaced one from the other about axis23(shown inFIG. 1). Each of the rows of rotor blades26include a plurality of rotor blades26circumferentially-spaced about a rotor disk27for rotation about axis23. It should be appreciated that the nozzles24and rotor blades26are each positioned in hot gas path20of turbine22. The direction of gas flow through hot gas path20is indicated by an arrow36.

FIG. 3illustrates a perspective view of a rotor blade26in accordance with an exemplary embodiment of the present invention. As shown, rotor blade26may include a platform40, a shank42, a dovetail44, a tip shroud48, and a fillet50. Dovetail44is used to couple rotor blade26to a rotor disk27(as shown inFIG. 2). Rotor blade26also may include an airfoil46that extends radially between platform40and tip shroud48. Airfoil46has a leading edge52, a trailing edge54, a pressure side53, and an opposite suction side55. Pressure side53extends from leading edge52to trailing edge54and forms a concave exterior surface of airfoil46. Suction side55extends from leading edge52to trailing edge54and forms a convex exterior surface of airfoil46. Fillet50is defined and extends between airfoil46and tip shroud48. More specifically, fillet50extends within the intersection formed between an outer radial tip49of airfoil46and tip shroud48and, thereby, structurally supports tip shroud48. Tip shroud48may include seal rails56that extend circumferentially and a cutter tooth57that facilitates sealing with a stationary casing. During operation, hot combustion gases flow over both pressure side53and suction side55of airfoil46to induce rotation of rotor blade26. Specifically, the flow of the hot gases over pressure side53and suction side55of airfoil46induces rotor blades26to rotate on each respective rotor disk27such that the energy of the expanding hot gases is converted into mechanical energy.

As indicated inFIG. 3, airfoil46may be further defined: via an airfoil height61, which represents the overall height of airfoil46(i.e., the distance between platform40and tip shroud48); and an airfoil width62, which represents the overall width of airfoil46(i.e., the distance between leading edge52and trailing edge54). As explained below, one method of defining present fillet50is to define widthwise sections or ranges within airfoil width62and, for each of those, define a height of fillet50(or a range of heights within which the height of fillet50is maintained). As used herein, the height of fillet50represents the radially distance that fillet50extends from the outer most tip of airfoil46toward platform40. For descriptive purposes herein, the outer most tip of airfoil46is considered to be coplanar with a radially inner surface60of tip shroud48. (As shown inFIGS. 4 and 5, inner surface60of the tip shroud48is opposite of outer surface64.) Further, for descriptive purposes, the height of fillet50may be expressed herein relative to the overall height of airfoil46, for example, as a percentage of airfoil height61.

Turning now toFIGS. 4 through 6, more detailed illustrations of present fillet50are provided. (Note thatFIGS. 4 through 9are not drawn to scale and are provided solely to demonstrate a methodology for locating particular points, with the actual locations of those points being provided with specificity in Tables I and II. Accordingly, if there are discrepancies between apparent point locations as depicted in the figures and actual locations described within Tables I and II, it should be understood that, in all cases, the locations of the points as provide in Tables I and II is controlling and determinative, particularly with respect to references to points made within the appended claims.)FIG. 4shows a perspective view of fillet50on pressure side53of airfoil46. Fillet50on pressure side53may be more specifically referred to herein as a “pressure side fillet63”.FIG. 5illustrates a perspective view of fillet50on suction side55of airfoil46. Fillet50on suction side55may be more specifically referred to herein as a “suction side fillet65”. An outer edge of fillet50is formed at an intersection between fillet50and airfoil46on both pressure side53and suction side55, which is depicted by an intersection line58. An outer edge of fillet50is also formed at an intersection between fillet50and tip shroud48, which is depicted by an intersection line59. Intersection line59is shown most clearly inFIG. 6, which provides a cross-sectional view of a portion of airfoil46and fillet50taken along line6-6ofFIG. 3. Additional several reference lines71—as well as particularly located points on those reference lines71that will be used to define profiles of the present fillet50—are also shown inFIGS. 4-6. As will be discussed further with regard toFIGS. 7 through 9, the reference lines71each represents the intersection of a reference plane (for example, reference plane A through Z) with the surface of pressure and suction side fillets63,65.

According to the present invention, as will be seen, fillet50is configured to extend over much of inner surface60of tip shroud48, as shown by intersection line59. Fillet50is configured also to enclose and cover tip49of airfoil46, as shown by intersection line58. Further, between intersection line58and intersection line59, fillet50of the present invention has a thickness that is varied so to form specific surface contours, configurations, or profiles that enhance aerodynamic and structural performance. As should be understood, the precise configuration of present fillet50is based on an optimization in which several competing design criterium—and the complex relationships existing between those criterium—are taken into account and balanced to produce a result that optimizes performance. Fillet50of the present invention has shown in repeated tests to be superior to other known fillet configurations, particularly when combined with a tip shroud having a particular profile. For example, the configuration of present fillet50is streamlined for aerodynamic performance, while also structurally supporting tip shroud48so to optimally spread and balance operational stresses in a manner that materially extends the usable lifespan of the rotor blade.

Referring now toFIGS. 7 through 9, an X, Y and Z coordinate system is illustrated, which, as provided below, will be used to define the specific configurations of present fillet50. That is, fillet50of the present invention will be described by defining one or more of its surfaces or profiles, where those profiles will be described by defining a number of discrete points that occur on them via the X, Y and Z coordinate system depicted inFIGS. 7 through 9. As will be appreciated, inFIG. 7, the general orientation of the X, Y and Z coordinate system is shown with respect to rotor blade26. As indicated, the Z-axis is oriented along a chord of airfoil46of rotor blade26. Thus, the Z-axis extends horizontally between an intersection with leading edge52and trailing edge54of airfoil46. In regard to the Y-axis, it extends vertically in the lengthwise direction of airfoil46. Finally, the X-axis extends perpendicular to both the X-axis and Y-axis, as shown. The X, Y, and Z axes intersect at an origin72.

Exemplary points occurring on the surfaces or profiles of present fillet50—including points on both the pressure side fillet63and suction side fillet65—are defined by X, Y, and Z coordinates as set forth in Tables I and II below. It should be understood that exemplary embodiments of fillet50may include: the substantial entirety of the fillet profile of the illustrated fillet50, as may be described by all of the point included in Tables I and II; or particular surface areas or profiles defined within the illustrated fillet50on either or both the pressure and suction side of the fillet50, as may be defined by a set of points that represents a subset of the points included within Tables I and II. The points listed in Tables I and II are arranged according to several cross-sectional reference planes, reference planes A through Z, which, as shown most clearly inFIG. 8, intersect fillet50on both the pressure side and suction side. Table I includes points occurring on the pressure side of fillet50, and Table II includes points occurring on the suction side of fillet50, with each table arranging points in relation to the reference planes. The reference planes A through Z are defined at predetermined intervals along the Z-axis between leading edge52and trailing edge54of the airfoil46. The reference planes A through Z are each parallel and oriented normal to the Z-axis. Further, Tables I and II include one-hundred (100) points at each of the reference planes, with fifty (50) of those points occurring on the pressure side fillet63and fifty (50) occurring on the suction side fillet65.

Thus, as shown most clearly inFIG. 9, at each location on the Z-axis of one of the reference planes A through Z, the profile of the fillet of the present invention is defined on both the pressure side and suction side in Tables I and II, respectively, by points defined by X-axis and Y-axis dimensions. Thus, as should be understood, each point represents discreet locations at which one of the reference planes intersects the surfaces of either the pressure side fillet63or suction side fillet65. As will be appreciated, given this arrangement, the Z-values given in Tables I and II represent the location of the reference plane on the Z-axis. The X-values given in Tables I and II represent the distance within the applicable reference plane that a given point resides from the X-axis. And, the Y-values given in Tables I and II represent the distance within the applicable reference plane that a given point resides from the Y-axis.

The various points defined by the values of Tables I and II, in whole or in part, may be connected, such as by smooth curves, to define exemplary surface configurations or contours of fillets in accordance with embodiments of the present invention. Such surface configurations or contours of the present fillet may be referred to herein as “fillet profiles”. Further, it should also be understood that the values for determining the fillet profiles of fillet50given in Tables I and II are for a nominal fillet. Thus, +/− typical manufacturing tolerances, including any coating thicknesses, are additive to the fillet surface as determined from the Tables I and II. Accordingly, pursuant to exemplary embodiments, a distance of +/−0.05 inches in a direction normal to any surface location described in Tables I and II defines a fillet profile envelope in accordance with present fillet50, i.e., a range of variation between an ideal configuration of present fillet50, as given by the Tables I and II above, and a range of variation in fillet50configuration at nominal cold or room temperature. Moreover, while Tables I and II defines a surface profile for fillet50using a particular number of points, it should be understood that any number of X, Y, and Z locations may be used to define this profile. Thus, the fillet profiles defined by the values of Tables I and II embrace fillet profiles intermediate to the given X, Y, and Z locations, as well as those defined using fewer X, Y, and Z locations than those included in Tables I and II. Further, it will be appreciated that present fillet50defined in Tables I and II may be proportionally scaled up or down for similar use with tip shrouded airfoils of varying sizes, and that such alternative embodiments are within the scope of the present invention.

In addition, the present invention includes alternative embodiments of fillet50that are defined in a different manner, i.e., in a way other than using the points of Tables I and II. For example, present fillet50may be described in accordance with the path or shape of intersection line58as it extends between leading edge52and trailing edge54. As will be seen, the shape of this path can be described with reference to a characteristic that will be referred to herein as “fillet height”. As used herein, fillet height is the distance that fillet50extends from the outer radial tip of airfoil46toward platform40. More particularly, fillet height is the distance occurring between intersection line58and the outer radial tip of airfoil46.

For example, on pressure side53of airfoil46, with specific reference again toFIG. 4, it will be appreciated that the height of fillet50varies considerably between leading edge52and trailing edge54. According to exemplary embodiments, the particular manner in which the height of fillet50is varied across width62of airfoil46may be described with reference to particular height characteristics occurring within five reference sections or ranges that are defined widthwise across airfoil46for this purpose. (As introduced above, the width62of airfoil46is the distance across a chord of the airfoil46or, put another way, the distance between leading and trailing edges52,54of airfoil46.) As should be appreciated, these reference ranges are defined inFIG. 4via reference dashed lines, boundary planes, or “boundaries80”. Specifically, the five reference ranges divide width62of airfoil46into adjacent, non-overlapping parallel sections, which, for the purposes of description, will be referred to herein as: a leading range81; a leading transition range82; a middle range83; a trailing transition range84; and a trailing range85. As shown inFIG. 4, leading range81is the reference section defined adjacent to leading edge52of airfoil46. Middle range83is the reference section occurring in the approximate central portion of airfoil46. Leading transition range82is the reference section that is positioned between leading range81and middle range83. In the case of trailing range85, it is the reference section defined adjacent to trailing edge54of airfoil46, while trailing transition range84is the reference section that is positioned between middle range83and trailing range85.

The above-referenced reference ranges81,82,83,84,85may be particularly located on airfoil46by defining the locations of boundaries80, while the location of boundaries80can be defined in relation to the Z-axis. Specifically, boundaries80will be defined in relation to the position on the Z-axis where a plane normal to the Z-axis would intersects airfoil46at the location of the boundary80. For purposes herein, these locations on the Z-axis will be expressed relative to overall cord length (i.e., the length of the Z-axis between leading edge52and trailing edge54), and, thus, given in terms of a percentage of cord length. Specifically, a position at leading edge52is given a value of 0% of chord length, while a position at the trailing edge54is given a value of 100% of cord length. With this in mind, according to preferred embodiments, the boundary80that divides leading range81and leading transition range82is disposed between 13% and 23% of cord length. The boundary80that divides leading transition range82and middle range83is disposed between 27% and 37% of cord length. The boundary80that divides middle range83and trailing transition range84is disposed between 67% and 77% of cord length. And, finally, the boundary80that divides trailing transition range84and trailing range85is disposed between 87% and 97% of cord length.

In accordance with preferred embodiments of the present invention, fillet height will now be provided for pressure side fillet63within the reference ranges81,82,83,84,85, as those reference ranges are defined above. Further, as stated, fillet height will be expressed in relation to the overall size of the airfoil, for example, in relation to height61of airfoil46. (As already stated, height61of airfoil46is the distance between inner surface60of tip shroud48and surface of platform40, which, because of the slant of the tip shroud, may be different on each side of airfoil46.) More particularly, fillet height will be expressed in terms of a percentage of airfoil height61, where a position at the level of inner surface60of tip shroud48is deemed to have a height of 0% of airfoil height61, while a position at the level of platform40is deemed to have a height of 100% of airfoil height61. According to exemplary embodiments of the present invention, the fillet height within leading range81is maintained between 3% and 13% of airfoil height61. The fillet height within middle range83is maintained within 17% and 27% of airfoil height61. The fillet height within trailing range is maintained within 3% and 13% of airfoil height61. In regard to transitional ranges82,84, leading transition ranges82has a fillet height that smoothly transitions between the fillet height of leading range81and that of middle range83, while trailing transition ranges84has a fillet height that smoothly transitions between the fillet height of middle range83and that of trailing range85.

A tip shroud fillet in accordance with any of the embodiments described herein provides improved support to the tip shroud, thereby extending component life, while also facilitating aerodynamic flow of hot combustion gases through the turbine. As described above, in terms of engine performance, it is desirable to have relatively large tip shrouds that extend over substantially the entire radial outer end of the airfoil. However, it is also desirable that the fillet remain small and streamlined for the sake of aerodynamic efficiency. The fillet according to the present disclosure effectively balances these and other competing objectives such that one or more important performance objectives are improved or optimized. That is, the fillet shape of the present disclosure provides a profile that effectively guides hot gas flow through the turbine while supporting a tip shroud that is large enough to adequately prevent leakage. In addition, when compared to conventional fillets shapes supporting a similarly sized tip shroud, the fillet of the present invention reduces mechanical stresses and evenly spreads load between pressure and suction sides, thereby significantly extending the useful life of the part. The effectiveness of the present fillet shape has been verified by computational fluid dynamics analysis, traditional fluid dynamics analysis, Euler and Navier-Stokes equations, flow testing, other conventional tests, and/or combinations thereof.

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.