Patent Grant
6881038
The present invention relates to an airfoil for a bucket of a stage of a gas turbine and particularly relates to a second stage turbine bucket airfoil profile.
Many system requirements must be met for each stage of the hot gas path section of a gas turbine in order to meet design goals including overall improved efficiency and airfoil loading. Particularly, the buckets of the second stage of the turbine section must meet the thermal and mechanical operating requirements for that particular stage.
In accordance with the preferred embodiment of the present invention there is provided a unique airfoil shape for a bucket of a gas turbine, preferably the second stage bucket, that enhances the performance of the gas turbine. The airfoil shape hereof also improves the interaction between various stages of the turbine and affords improved aerodynamic efficiency while simultaneously reducing second stage airfoil thermal and mechanical stresses.
The bucket airfoil profile is defined by a unique loci of points to achieve the necessary efficiency and loading requirements whereby improved turbine performance is obtained. These unique loci of points define the nominal airfoil profile and are identified by the X, Y and Z Cartesian coordinates of Table I which follows. The 1100 points for the coordinate values shown in Table I are relative to the turbine centerline and for a cold, i.e., room temperature bucket at various cross-sections of the bucket airfoil along its length. The positive X, Y and Z directions are axial toward the exhaust end of the turbine, tangential in the direction of engine rotation and radially outwardly toward the bucket tip, respectively. The X and Y coordinates are given in distance dimensions, e.g., units of inches, and are joined smoothly at each Z location to form a smooth continuous airfoil cross-section. The Z coordinates are given in non-dimensionalized form from 5% span to 95% span and therefore exclude fillet regions at the platform and tip shroud. By multiplying the airfoil height dimension, e.g., in inches, by the non-dimensional Z value of Table I, the airfoil shape, i.e., the profile, of the bucket airfoil is obtained. Each defined airfoil section in the X, Y plane is joined smoothly with adjacent airfoil sections in the z direction to form the complete airfoil shape.
It will be appreciated that as each bucket airfoil heats up in use, the profile will change as a result of mechanical loading and temperature. Thus, the cold or room temperature profile is given by the X, Y and z coordinates for manufacturing purposes. Because a manufactured bucket airfoil profile may be different from the nominal airfoil profile given by the following table, a distance of plus or minus 0.160 inches from the nominal profile in a direction normal to any surface location along the nominal profile and which includes any coating, defines a profile envelope for this bucket airfoil. The airfoil shape is robust to this variation without impairment of the mechanical and aerodynamic functions of the bucket.
It will also be appreciated that the airfoil can be scaled up or scaled down geometrically for introduction into similar turbine designs. Consequently, the X and Y coordinates in inches of the nominal airfoil profile given below may be a function of the same constant, or number. That is, the X and Y coordinate values in inches may be multiplied or divided by the same constant or number to provide a scaled up or scaled down version of the bucket airfoil-profile while retaining the airfoil section shape.
In a preferred embodiment according to the present invention, there is provided a turbine bucket including a bucket airfoil having an airfoil shape, the airfoil having a nominal profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0.05 to 0.95 convertible to Z distances in inches by multiplying the Z values by a height of the airfoil in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define airfoil profile sections at each distance Z, the profile sections at the Z distances being joined smoothly with one another to form a complete airfoil shape.
In a further preferred embodiment according to the present invention, there is provided a turbine bucket including a bucket airfoil having an uncoated nominal airfoil profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0.05 to 0.95 convertible to Z distances in inches by multiplying the Z values by a height of the airfoil in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define airfoil profile sections at each Z distance, the profile sections at the Z distances being joined smoothly with one another to form a complete airfoil shape, the X and Y distances being scalable as a function of the same constant or number to provide a scaled-up or scaled-down airfoil.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine wheel having a plurality of buckets, each of the buckets including an airfoil having an airfoil shape, the airfoil having a nominal profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0.05 to 0.95 convertible to Z distances in inches by multiplying the Z values by a height of the airfoil in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define the airfoil profile sections at each distance Z, the profile sections at the Z distances being joined smoothly with one another to form a complete airfoil shape.
In a further preferred embodiment according to the present invention, there is provided a turbine comprising a turbine wheel having a plurality of buckets, each of the buckets including an airfoil having an uncoated nominal airfoil profile substantially in accordance with Cartesian coordinate values of X, Y and Z set forth in Table I wherein the Z values are non-dimensional values from 0.05 to 0.95 convertible to Z distances in inches by multiplying the Z values by a height of the airfoil in inches, and wherein X and Y are distances in inches which, when connected by smooth continuing arcs, define airfoil profile sections at each distance Z, the profile sections at the Z distances being joined smoothly with one another to form a complete airfoil shape, the X and Y distances being scalable as a function, of the same constant or number to provide a scaled-up or scaled-down bucket airfoil.
Referring now to the drawings, particularly to
It will be appreciated that the buckets, for example, the buckets 20 of the second stage are mounted on a rotor wheel 21 forming part of rotor 17. Each bucket 20 is provided with a platform 30, a shank 32 and a substantially axial entry dovetail 34 for connection with a complementary-shaped mating dovetail, not shown, on the rotor wheel 21. It will also be appreciated that each bucket 20 has a bucket airfoil 36 as illustrated in
To define the airfoil shape of each second stage bucket airfoil 36, there is a unique set or loci of points in space that meet the stage requirements and can be manufactured. This unique loci of points meets the requirements for stage efficiency and reduced thermal and mechanical stresses. The loci of points are arrived at by iteration between aerodynamic and mechanical loadings enabling the turbine to run in an efficient, safe and smooth manner. The loci which defines the bucket-airfoil profile comprises a set of 1100 points relative to the axis of rotation of the turbine. A Cartesian coordinate system of X, Y and Z values given in Table I below define the profile of the bucket airfoil at various locations along its length. The coordinate values for the X and Y coordinates are set forth in inches in Table I although other units of dimensions may be used when the values are appropriately converted. The Z values are set forth in Table I in non-dimensional form from 5% span to 95% span. These values exclude the fillet regions of the platform and the tip shroud. To convert the Z value to, a Z coordinate value, e.g., in inches, the non-dimensional Z value given in the table is multiplied by the height of airfoil in inches. The Cartesian coordinate system has orthogonally-related X, Y and Z axes and the X axis lies parallel to the turbine rotor centerline, i.e., the rotary axis and a positive X coordinate value is axial toward the aft, i.e., exhaust end of the turbine. The positive Y coordinate value looking aft extends tangentially in the direction of rotation of the rotor and the positive Z coordinate value is radially outwardly toward the bucket tip.
By defining X and Y coordinate values at selected locations in a Z direction normal to the X, Y plane, the profile section of the bucket airfoil, e.g., the profile section 38 illustrated in
The Table I values are generated and shown to four decimal places for determining the profile of the airfoil. However, the fourth decimal place is not significant and may., be rounded up-or down. There are typical manufacturing tolerances as well as coatings which must be accounted for in the actual profile of the airfoil. Accordingly, the values for the profile given in Table I are for a nominal airfoil. It will therefore be appreciated that ±typical manufacturing tolerances, i.e., ±values, including any coating thicknesses, are additive to the X and Y values given in Table I below. Accordingly, a distance of ±0.160 inches in a direction normal to any surface location along the airfoil profile defines an airfoil profile envelope for this particular bucket airfoil design and turbine, i.e., a range of variation between measured points on the actual airfoil surface at nominal cold or room temperature and the ideal position of those points as given in the Table below at the same temperature. The bucket airfoil design is robust to this range of variation without impairment of mechanical and aerodynamic functions.
The coordinate values given in Table I below provide the preferred nominal profile envelope.
In this preferred embodiment of a second stage turbine bucket, there are ninety-two (92) bucket airfoils which are air-cooled. In the preferred embodiment of the second stage bucket hereof, the bucket radial height is 14.290 inches between 0% span and 100% span. The airfoil radial height at 0% span from the engine centerline is 46.828 inches and 61.118 inches at 100% span. The airfoil sections in Table I start at Z=5% span and end at Z=95% span and this eliminates fillet regions. While not forming part of the present invention, each second stage bucket airfoil 36 includes a plurality of internal air-cooling passages, not shown, which exhaust cooling air into the hot gas path adjacent the tip shroud 42.
It will also be appreciated that the airfoil disclosed in the above Table I may be scaled up or down geometrically for use in other similar turbine designs. Consequently, the coordinate values set forth in Table I may be scaled upwardly or downwardly such that the airfoil profile shape remains unchanged. The X and Y coordinate values of Table I multiplied or divided by a constant number would represent a scaled version.
To scale the bucket airfoil in the Z direction, the constant may also be applied to the 5% and 95% radial spans given in Table I.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
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