Patent Application
20090035145
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 operating requirements for that particular stage and also be capable of efficient manufacture.
The invention may be embodied in a turbine bucket including a bucket airfoil having an airfoil shape, said 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 to 1 convertible to Z distances in inches by multiplying the Z′ values by airfoil height in inches and adding the radius of the airfoil base, 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 invention may also be embodied in 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 to 1 convertible to Z distances in inches by multiplying the Z′ values by the airfoil height in inches and adding the radius of the airfoil base, 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, Y and Z distances being scalable as a function of the same constant or number to provide a scaled-up or scaled-down airfoil.
The invention may further be embodied in a turbine comprising a turbine wheel having a plurality of buckets, each of said buckets including an airfoil having an airfoil shape, said 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 to 1 convertible to Z distances in inches by multiplying the Z′ values by the airfoil height in inches and adding the radius of the airfoil base, 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.
These and other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred example embodiments of the invention taken in conjunction with the accompanying drawings, in which:
Referring now to the drawings, particularly to
Referring to
The 7FB Integrated Gasification Combined Cycle (IGCC) gas turbine hot gas path requires a third stage airfoil that meets system requirements of aerodynamic and mechanical blade loading and efficiency. To define the airfoil shape of each third 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 are arrived at by iteration between aerodynamic and mechanical loadings enabling the turbine to run in an efficient, safe and smooth manner. These points are unique and specific to the system and are not obvious to those skilled in the art. The loci which defines the bucket airfoil profile of the invention comprises a set of 3,200 points with X, Y and Z′ dimensions relative to the reference origin coordinate system established as shown in
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, at each Z distance along the length of the airfoil can be ascertained. By connecting the X and Y values with smooth continuing arcs, each profile section at each distance Z is fixed. The airfoil profiles of the various surface locations between the distances Z are determined by smoothly connecting the adjacent profile sections to one another to form the airfoil profile.
The Table I values are generated and shown to four decimal places for determining the profile of the airfoil. As the blade heats up in surface, stress and temperature will cause a change in the X, Y and Z's. Accordingly, the values for the profile given in Table I represent ambient, non-operating or non-hot conditions and are for an uncoated airfoil.
There are typical manufacturing tolerances as well as coatings which must be accounted for in the actual profile of the airfoil. Each section is joined smoothly with the other sections to form the complete airfoil shape. 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 ±0.060 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.
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. A scaled version of the coordinates in Table I would be represented by X, Y and Z′ coordinate values of Table I, with X and Y and the non-dimensional Z′ coordinate value converted to inches, multiplied or divided by a constant number.
An important term in this disclosure is profile. The profile is the range of the variation between measured points on an airfoil surface and the ideal position listed in Table I. The actual profile on a manufactured blade will be different then those in Table I and the design is robust to this variation meaning that mechanical and aerodynamic function are not impaired. As noted above, a + or −0.06 inch profile tolerance is used herein.
The disclosed airfoil shape optimizes and is specific to the machine conditions and specifications. It provides a unique profile to achieve 1) interaction between other stages in the high pressure turbine; 2) aerodynamic efficiency; and 3) normalized aerodynamic and mechanical blade loadings. The disclosed loci of points allow the 7FB IGCC gas turbine to run in an efficient, safe and smooth manner. As also noted, any scale of the disclosed airfoil may be adopted as long as 1) interaction between other stages in the high pressure turbine; 2) aerodynamic efficiency; and 3) normalized aerodynamic and mechanical blade loadings are maintained in the scaled turbine.
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.
