Patent Application
20130209258
The subject matter disclosed herein relates to turbine systems, and more particularly to tip shrouds.
Gas turbine buckets or blades are airfoil-shaped components designed to convert thermal and kinetic energy of flow gases into mechanical rotation of the rotor. Turbine performance may be enhanced by providing a seal at the tip of the airfoil to block the flow of air over the tip of the airfoil which would otherwise bypass the airfoil and thus not perform any work on the rotor. Thus, such tip seals reduce the gap between the bucket and the surrounding stationary casing.
Typically a tip shroud is provided to the tip of the airfoil and adjacent turbine buckets are aligned in a cold assembly condition. However, during hot operating conditions, the tip shrouds tend to have some degree of misalignment. Radial misalignment between two adjacent shrouds will cause obstruction in a main flow path, leading to inefficiency and possibly disengagement. Tangential misalignment will lead to a leakage area for air that therefore does not perform work on the rotor.
According to one aspect of the invention, a tip shrouded blade includes an airfoil rotatable about an axial centerline. Also included is a tip shroud connected at a radially outer tip of the airfoil, wherein the tip shroud includes at least one portion angled about a tangential axis defined by the radially outer tip of the airfoil.
According to another aspect of the invention, a tip shrouded blade includes an airfoil extending away from and rotatable about an axial centerline. Also included is a tip shroud provided at a tip of the airfoil, wherein the tip shroud is tilted about a tangential axis and twisted about a radial axis.
According to yet another aspect of the invention, a turbine system having at least one row of circumferentially aligned tip shrouded blades includes a first turbine bucket having a first airfoil. Also included is a first tip shroud provided at an outer tip of the first airfoil, wherein the first tip shroud is angled about a tangential axis defined by the outer tip of the first airfoil. Further included is a second turbine bucket having a second airfoil disposed adjacent to the first airfoil. Yet further included is a second tip shroud provided at an outer tip of the second airfoil, wherein the second tip shroud is angled to correspond to the first tip shroud during a steady state operation of the turbine system.
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.
Referring to
The turbine system includes a plurality of rows of circumferentially aligned turbine buckets 10. The seal rail 18 extends circumferentially around at least one of the plurality of rows, beyond the airfoil 12 sufficiently to relatively match up with seal rails 18 provided at the outer tip 14 of adjacent airfoils 12, thereby blocking flow from bypassing the row so that airflow must be directed to the length of the airfoil 12, ensuring more efficient rotation of the rotor.
The airfoil 12 rotates in a direction 20 about an axial centerline 22 of the turbine system. A tangential axis 24 and an axial axis 26 at the outer tip 14 of the airfoil 12 are formed relative to the direction 20 of rotation of the outer tip 14. The axial axis 26 extends in the axial direction of the turbine system and is parallel to the axial centerline 22. Additionally, a radial axis 27 extends in a longitudinal direction of the airfoil 12, and specifically an axis extending radially outward from the axial centerline 22 toward the tip shroud 16.
During operation of the turbine system, such as steady-state operation, the turbine buckets 10 and the tip shrouds 16 are subjected to significant forces and thermal stresses that result in asymmetric deflections of the tip shrouds 16. Such asymmetric deflections of the tip shrouds 16 cause misalignment between adjacent tip shrouds 16, resulting in inefficiency and/or stress imbalance which can lead to material creep.
Referring now to
Referring to
The tip shroud 16 may take on various configurations and features, including a recess 40 proximate the rear region 30 of the tip shroud 16 that is configured to allow a protrusion 42 from the front region 28 of an adjacent tip shroud 16 to optionally be disposed therein. Such an arrangement permits the rotational movement of the tip shrouds 16 relative to one another during operation of the turbine bucket 10.
As described above, it is advantageous to pre-tilt or pre-twist the tip shroud 16 to account for deformations that occur during operation of the turbine bucket 10, particularly about multiple axes, such as the axial axis 26, the radial axis 27 and the tangential axis 24. Alternatively, it is contemplated that only one pre-tilting or pre-twisting may be imposed and is determined by the application of use, and additionally more than two axes may be rotated about. The tip shroud 16 merely need be rotated about some axis that is offset in any direction from that of the axial centerline 22. This refers to axes of rotation that are shifted radially, tangentially, or axially from the axial centerline 22. The tip shroud 16 is configured such that it may deflect into a relatively planar member during steady-state operation and oriented within a plane tangential to the outer tip 14 of the airfoil 12.
Irrespective of the precise tip shroud 16 configuration, it should be appreciated that several advantages are attained by such an assembly. Steady-state alignment of the seal rails 18 occurs when the tip shroud 16 is an operating position upon rotation of the airfoil at a predetermined speed. Alignment of the seal rails 18 leads to lower overall flow path leakage, such as through a honeycomb-shaped casing surface located radially outward of the seal rail 18. Additionally, stress states in the tip section of the airfoil 12 are balanced and the potential for disengagement is reduced. These and other advantages are achieved by the tip shroud 16 disclosed herein.
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.
