TURBINE AIRFOIL-SIDEWALL INTEGRATION
An arrangement for turbine bucket or nozzle airfoils that accounts for the radial variation of inlet flow angle with the boundary layer of flow adjacent to the inner and outer sidewalls. Local chambering of the airfoil sections in the region of the sidewalls provides an airfoil and fillet with an optimum shape for accommodating the radial distribution of the inlet flow angle for the working fluid in the sidewall region.
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The invention relates generally to turbine blades and to a turbine incorporating the blade. While the invention is primarily concerned with steam and gas turbines, it is also applicable to other turbines and compressors. The term “turbine” is used to include machines of this kind having airfoil blades. The invention is more specifically related to the interface of turbine airfoils with sidewalls for improving aerodynamic performance of the blade.
Turbine efficiency is of great importance, particularly in large installations where a fractional increase in efficiency can produce very large cost savings. Considerable resources are continually expended into research on blade design as this is a critical component with respect to overall performance of the turbine.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Turbine stages extract energy from the combustion gases to power the compressor, while also powering an upstream fan in a turbofan aircraft engine application, or powering an external drive shaft for marine and industrial applications. In a steam turbine, steam is utilized to power the turbine stages.
A turbine may include one or more stages of rotor blades and corresponding turbine nozzles. Each turbine nozzle includes a row of stator vanes having radially outer and inner sidewalls in the form of arcuate bands that support the vanes. Correspondingly, the turbine rotor blades include airfoils integrally joined to radially inner sidewalls or platforms supported in turn by corresponding dovetails which mount the individual blades in dovetail slots formed in the perimeter of the supporting rotor disk. An annular shroud surrounds the radially outer tips of the rotor airfoils in each turbine stage. The stator vanes and rotor blades have corresponding airfoils including generally concave pressure sides and generally convex suction sides extending axially in chord between opposite leading and trailing edges. Adjacent vanes and adjacent blades form corresponding flow passages therebetween bound by the radially inner and outer sidewalls.
During operation, the working fluid flows axially downstream through the respective flow passages defined between the stator vanes and rotor blades. The aerodynamic contours of the vanes and blades, and corresponding flow passages therebetween, are precisely configured for maximizing energy extraction from the combustion gases which in turn rotate the rotor from which the blades extend.
The complex three-dimensional (3D) configuration of the vane and blade airfoils is tailored for maximizing efficiency of operation, and varies radially in span along the airfoils as well as axially along the chords of the airfoils between the leading and trailing edges. Accordingly, the velocity and pressure distributions of the working fluid over the airfoil surfaces, as well as within the corresponding flow passages, also vary.
Undesirable pressure losses in the working fluid flowpaths therefore correspond with undesirable reduction in overall turbine efficiency. For example, the working fluid enters the corresponding rows of vanes and blades in the flow passages therebetween and is necessarily split at the respective leading edges of the airfoils.
The locus of stagnation points of the incident working fluid extends along the leading edge of each airfoil, and corresponding boundary layers are formed along the pressure and suction sides of each airfoil, as well as along each radially outer and inner sidewall, which collectively, bound the four sides of each flow passage. In the boundary layers, the local velocity of the working fluid varies from zero along the sidewalls and airfoil surfaces to the unrestrained velocity in the working fluid where the boundary layers terminate.
While the main span of the airfoils for the nozzles and rotating blades utilize the complex 3D configurations described above and consequently promote efficiency, the regions of the airfoil adjacent to the sidewalls are less adapted to local aerodynamic conditions and incur significantly greater losses compared to the main spans. Accordingly, there is a need to configure the regions of airfoils adjacent to the sidewalls to promote greater airfoil performance.
BRIEF DESCRIPTION OF THE INVENTIONThe present invention relates to a design for turbine bucket or nozzle airfoils that accounts for the radial variation of inlet flow angle with the boundary layer of flow adjacent to the inner and outer sidewalls.
According to a first aspect of the present invention, a turbine stage is provided. The turbine stage includes a row of airfoils integrally joined to corresponding sidewalls and spaced laterally apart to define respective flow passages therebetween for channeling a working fluid. Each of the airfoils includes a concave pressure side and a laterally opposite convex suction side. The airfoils extend in chord between opposite leading and trailing edges. Each of the airfoils blends with the sidewalls in an arcuate fillet. A region of the airfoils in proximity to the corresponding sidewall and the associated arcuate fillet form a surface optimized according to a radial variation in inlet flow angle of the working fluid in proximity to the region.
According to a second aspect of the present invention, a turbine including a turbine casing; a rotor; a stator; and a row of airfoils is provided. Each airfoil is integrally joined to corresponding sidewalls and spaced laterally apart to define respective flow passages therebetween for channeling a working fluid. Each airfoil may include a concave pressure side and a laterally opposite convex suction side, extending in chord between opposite leading and trailing edges. Each airfoil blends with the sidewalls in an arcuate fillet. A region of the airfoils, in proximity to the corresponding sidewall and the associated arcuate fillet, forms a surface adapted to optimize airfoil performance according to a radial variation in inlet flow angle of the working fluid in proximity to the region.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The following embodiments of the present invention have many advantages, including improvement of aerodynamic performance of the airfoil region for turbine nozzles and blades in proximity to the sidewalls, resulting in improvement in the turbine performance.
Sidewall viscous flow effects result in blade row inlet flow angles substantially different those found radially outward from the working fluid path inner diameter or inward from the outer diameter. This causes the flow to likewise deviate from the design flow angles, which are generally selected without regard to wall boundary layer behavior. Deviations in flow angle are associated with energy losses and reduced turbine performance. The invention modifies the design of turbine stationary or moving airfoils near the sidewalls of the gas or steam path to optimize the airfoil geometry with respect to the variation in inlet flow angle immediately adjacent to the walls. This modification results in near wall airfoil sections that provide a varying optimum entrance angle to match the predicted flow angle. The airfoil sections are integrated with the fillet radii at the wall-airfoil intersection, but may extend radially beyond the fillet. The resulting airfoil integral sidewall component will have a distinctive appearance.
In airfoil design, the profile of the turbine blade is carried out to optimize stage performance based in part on the inlet angle of the working fluid with respect to the blade. While the inlet angle of the working fluid with respect to the blade is relatively constant, it has been determined that significant variation of inlet angle for the working fluid is encountered in the region of the blade in proximity to the sidewalls.
The shaping of the profiles at the different near-wall radial distances is generally most critical for airfoil efficiency in the area of the leading edge 650. For purposes of machining time and cost, therefore, it may be desirable to merge the radial distance-dependent profiles into a single optimized radius fillet 655, 656 for a downstream section 660, 670 of the airfoil.
The invention as described above includes a design for turbine bucket or nozzle airfoils that accounts for the radial variation of inlet flow angle with the boundary layer of flow adjacent to the inner and outer sidewalls. This requires local chambering of the airfoil sections in the above regions with the primary objective of providing a continuous airfoil optimum entrance angle radial distribution. The prior art process for accomplishing this ignores the large deviation of inlet flow angle adjacent to the sidewalls, leading to the potential for higher energy losses in this already high loss region.
The invention has been described with respect to working fluid for a turbine stage, however it should be understood that it is equally applicable to steam turbine and gas turbine airfoils and includes compressor airfoils and turbine airfoils, as well as both nozzle airfoils and rotating blade airfoils. While various embodiments are described herein, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention.
Claims
1. A turbine stage comprising:
- a row of airfoils integrally joined to corresponding sidewalls and spaced laterally apart to define respective flow passages therebetween for channeling a working fluid; each of said airfoils including a concave pressure side and a laterally opposite convex suction side, and extending in chord between opposite leading and trailing edges; each of said airfoils blending with said sidewalls in an arcuate fillet, a region of said airfoils in proximity to the corresponding sidewall and the associated arcuate fillet forming a surface adapted to optimize a radial variation in inlet flow angle of the working fluid in proximity to the region.
2. The turbine stage according to claim 1, wherein said region of said airfoils in proximity to the corresponding sidewall comprises a radial location of about 5% airfoil length from the corresponding sidewall.
3. The turbine stage according to claim 1, wherein said region of said airfoils in proximity to the corresponding sidewall comprises a radial location of about 10% airfoil length from the corresponding sidewall.
4. The turbine stage according to claim 3, wherein said blending includes the leading edge of the airfoil on at least one of the suction side and on the pressure side.
5. The turbine stage according to claim 4 wherein said blending is provided from the leading edge of the airfoil to about 50% chord length on at least one of the suction side and on the pressure side of the airfoil.
6. The turbine stage according to claim 4, wherein said turbine stage comprises fixed nozzles.
7. The turbine stage according to claim 4, wherein said turbine stage comprises rotating blades.
8. The turbine stage according to claim 4, wherein said turbine stage comprises a stage of a gas turbine.
9. The turbine stage according to claim 4 wherein said turbine stage comprises a stage of a steam turbine.
10. The turbine stage according to claim 4, wherein said turbine stage comprises a stage of a compressor.
11. A turbine comprising:
- a turbine casing;
- a rotor;
- a stator; and
- a row of airfoils integrally joined to corresponding sidewalls and spaced laterally apart to define respective flow passages therebetween for channeling a working fluid; each of said airfoils including a concave pressure side and a laterally opposite convex suction side, and extending in chord between opposite leading and trailing edges; each of said airfoils blending with said sidewalls in an arcuate fillet, a region of said airfoils in proximity to the corresponding sidewall and the associated arcuate fillet forming a surface adapted to optimize a radial variation in inlet flow angle of the working fluid in proximity to the region.
12. A turbine stage according to claim 11, wherein said region of said airfoils in proximity to the corresponding sidewall comprises a radial location of about 5% airfoil length from the corresponding sidewall.
13. A turbine stage according to claim 11, wherein said region of said airfoils in proximity to the corresponding sidewall comprises a radial location of about 10% airfoil length from the corresponding sidewall.
14. A turbine stage according to claim 12 wherein said blending includes the leading edge of the airfoil on at least one of the suction side and on the pressure side.
15. A turbine stage according to claim 12 wherein said blending is provided from the leading edge of the airfoil to about 50% chord length on at least one of the suction side and on the pressure side of the airfoil.
16. A turbine stage according to claim 12 wherein said turbine airfoils comprise fixed nozzles.
17. A turbine stage according to claim 12 wherein said turbine airfoils comprise rotating blades.
18. A turbine stage according to claim 12 wherein said turbine comprises a gas turbine.
19. A turbine stage according to claim 12 wherein said turbine comprises a steam turbine.
20. A turbine stage according to claim 12 wherein said turbine stage comprises a stage of a compressor.
Type: Application
Filed: Oct 28, 2009
Publication Date: Apr 28, 2011
Applicant:
Inventor: Alan D. Maddaus (Rexford, NY)
Application Number: 12/607,371
International Classification: F01D 9/04 (20060101); F01D 5/14 (20060101);