Patent Application
20100111674
The subject matter disclosed herein relates generally to thermo-mechanical turbines, and more particularly to a system and method for reducing bucket tip losses.
Performance and efficiency of thermo-mechanical turbines, such as gas or steam turbines, is desirably improved by reducing losses in the thermal to mechanical energy conversion that occurs when high pressure gases (and/or fluids) are applied to turbine blades or “buckets” to cause mechanical rotation and energy output. Such losses often occur due to leakage past the buckets through clearances between the bucket tips and surrounding stationary components (such as shrouds, housings, etc.), which results in undesired pressure mixing and vortex flow generation. Reducing these “over-tip” and “tip-vortex” losses is particularly challenging for unshrouded bucket tip configurations, which are often used in one or more stages of turbines.
According to one aspect of the invention, a system for reducing bucket tip losses includes an airfoil portion of an unshrouded turbine bucket. The airfoil portion includes a pressure-side surface and a suction-side surface each extending from a root surface to a tip surface and joined at a leading edge and a trailing edge. The pressure-side surface has a generally concave shape and the suction-side surface has a generally convex shape. The airfoil portion has an increasing stagger angle in a span-wise direction from the root surface to the tip surface and an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the leading edge. The airfoil portion also has a resultant lean in a direction of the suction-side surface as the leading edge approaches the tip surface. Furthermore, the pressure-side surface and the suction-side surface each have a locally reduced or reversed curvature in a direction of the pressure-side surface at their intersection with the tip surface.
According to another aspect of the invention, a method for reducing bucket tip losses includes providing an airfoil portion of an unshrouded turbine bucket. The airfoil portion includes a pressure-side surface and a suction-side surface each extending from a root surface to a tip surface and joined at a leading edge and a trailing edge. The pressure-side surface has a generally concave shape and the suction-side surface has a generally convex shape. The airfoil portion has an increasing stagger angle in a span-wise direction from the root surface to the tip surface and an increasingly loaded suction-side surface as the suction-side surface approaches the tip surface and the tip surface approaches the leading edge. The airfoil portion also has a resultant lean in a direction of the suction-side surface as the leading edge approaches the tip surface. Furthermore, the pressure-side surface and the suction-side surface each have a locally reduced or reversed curvature in a direction of the pressure-side surface at their intersection with the tip surface.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of various embodiments. However, the embodiments may be practiced without these specific details. In other instances, well known methods, procedures, and components have not been described in detail.
Further, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, or that they are even order dependent. Moreover, repeated usage of the phrase “in an embodiment” does not necessarily refer to the same embodiment, although it may. Lastly, the terms “comprising,” “including,” “having,” and the like, as used in the present application, are intended to be synonymous unless otherwise indicated.
Exemplary embodiments of the invention provide a system and method for reducing bucket tip losses, e.g., in a thermo-mechanical turbine. In accordance with such exemplary embodiments, over-tip and tip-vortex losses are reduced, e.g., in unshrouded bucket configurations. Row inlet flow near the bucket tip is redirected inboard, through body-forces, due to a suction-side down stacking arrangement in combination with a decreased over-tip flow coefficient due to a locally decreasing degree or reversed direction of curvature in the near-tip region.
The airfoil portion 100 may have various additional characteristics, such as according to the following exemplary embodiments. The airfoil portion 100 may comprise a chord-wise loaded, stacked distribution of sections (as further depicted, e.g., in
Exemplary embodiments of the invention also include a method or process for reducing bucket tip losses (not depicted), which includes providing an airfoil portion 100, 200 as described above for
Thus, the technical effect of exemplary embodiments of the invention is a system and method for reducing bucket tip losses, e.g., in a thermo-mechanical turbine. In accordance with such exemplary embodiments, over-tip and tip-vortex losses are reduced, e.g., in unshrouded bucket configurations. Row inlet flow near the bucket tip is redirected inboard, through body-forces, due to a suction-side down stacking arrangement in combination with a decreased over-tip flow coefficient due to a locally decreasing degree or reversed direction of curvature in the near-tip region.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
