Patent Grant
6857855
The present invention relates to an airfoil for a bucket of a stage of a gas turbine and particularly relates to a third 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 third 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 third stage bucket, that enhances the performance of the gas turbine. The bucket airfoil shape hereof is defined by a unique loci of points to achieve the necessary efficiency, and loading requirements. 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 1001 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 define a smooth continuous airfoil cross-section. The Z coordinates are given in non-dimensionalized form from 0.03 (3%) span to 0.95 (95%) span which excludes fillet regions. By multiplying the airfoil height dimension, e.g., in inches, by the non-dimensional Z values of Table I within the specified range, the airfoil profile sections of the bucket airfoil are obtained. Each defined airfoil section in the X, Y plane is joined smoothly with adjacent airfoil sections in the Z direction to form the bucket 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 0.150 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 and the non-dimensional Z coordinates, when converted to 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, and the Z coordinate values when converted to 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 0.03 span to 0.95 span 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 the bucket 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 0.03 span to 0.95 span 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 the bucket 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 0.03 span to 0.95 span 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 the bucket 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 0.03 span to 0.95 span 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 the bucket airfoil shape, the X and Y distances, and the non-dimensional Z coordinate values when converted to 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 24 of the third stage are mounted on a rotor wheel, not shown, forming part of the turbine rotor. Each bucket 24 is provided, as illustrated in
To define the airfoil shape of each first stage bucket airfoil, 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 1001 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 defines the profile section 38 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 0.03 (3%) span to 0.95 (95% span). To convert the Z value to a Z coordinate value, e.g., in inches, the non-dimensional Z value given in Table I is multiplied by the height of the airfoil 36 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 generally 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 bucket airfoil profile section, e.g., profile section 38 of
The Table I values for X and Y are generated and shown to four decimal places for determining the profile of the airfoil. The fourth decimal place, however, 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 airfoil profile 36 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 ±0.150 inches in a direction normal to any surface location along the airfoil profile 36 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 third stage turbine bucket, there are ninety-two (92) bucket airfoils 36. The root 31 of the bucket airfoil at the midpoint of the platform, i.e., at 0% span, in a preferred embodiment of the turbine lies at 29.365 inches along a radius from the turbine centerline, i.e., the rotor axis. The actual height of the airfoil 36 in a preferred embodiment hereof, that is, the actual Z height of the bucket, is 15.566 inches from the root 31 at the midpoint of the platform 36 to tip 33. Thus, the tip 33 of the bucket 16 in a preferred embodiment lies 44.931 inches along a radius from the turbine centerline 39, i.e., at 100% span.
It will also be appreciated that the airfoil disclosed in the above Table may be scaled up or down geometrically for use in other similar turbine designs. Consequently, the coordinate values set forth in Table 1 may be scaled upwardly or downwardly such that the airfoil profile shape remains unchanged. A scaled version of the coordinates in Table I would be represented by X and Y coordinate values of Table I, and the non-dimensional Z coordinate values when converted to inches, multiplied or divided by a constant number.
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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