BACKGROUND OF THE INVENTION

[0001] The invention relates generally to a turbomachine such as a steam turbine, and more particularly, to a last stage blade of a steam turbine including a plurality of indentations at a leading edge.

[0002] During normal operation conditions of a steam turbine, the through flow extends along the entire length of the last stage steam turbine blades. However, at extreme turndown conditions, with low flow and/or high exhaust pressure, the through flow only flows through the tip portion of the last stage steam turbine blades.

[0003] When the through flow only flows through the tip portion of the last stage steam turbine blades, the blade experiences a supersonic entrance condition, and a shock wave will form at the blade row entrance. Across the shock, the pressure decreases suddenly. The resulting aeromechanical forces and shock wave transient effects from the supersonic entrance conditions can negatively affect the reliability of the last stage blade due to potentially damaging vibration. The tip portion of the last stage steam turbine blade, where the through flow flows through, also experiences an increase in temperature, and a pressure rise in the direction of flow.

BRIEF DESCRIPTION OF THE INVENTION

[0004] Aspects of the invention provide for a last stage blade of a steam turbine. In one embodiment, the last stage blade of a steam turbine includes: a blade leading edge for receiving a through flow, the blade leading edge including a plurality of indentations at a top portion of the steam turbine blade; and a blade trailing edge for exhausting the through flow.

[0005] A first aspect of the invention provides a steam turbine blade, comprising: a blade leading edge for receiving a through flow, the blade leading edge including a plurality of indentations at a top portion of the steam turbine blade; and a blade trailing edge for exhausting the through flow.

[0006] A second aspect of the invention provides a rotor assembly, comprising: a rotor body comprising a plurality of slots; a plurality of steam turbine blades within the plurality of slots of the rotor body, wherein at least one of the steam turbine blades includes: a blade leading edge for receiving a through flow, the blade leading edge including a plurality of indentations at a top portion of the steam turbine blade; and a blade trailing edge for exhausting the through flow.

[0007] A third aspect of the invention provides a steam turbine, comprising: a stator; and a plurality of rotor wheels around the stator, each rotor wheel including: a plurality of steam turbine blades, wherein the steam turbine blades of at least one rotor wheel includes: a blade leading edge for receiving a through flow, the blade leading edge including a plurality of indentations at a top portion of the steam turbine blade; and a blade trailing edge for exhausting the through flow.

[0008] These and other aspects, advantages and salient features of the invention will become apparent from the following detailed description, which, when taken in conjunction with the annexed drawings, where like parts are designated by like reference characters throughout the drawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 shows a perspective partial cut-away view of the low pressure section of a steam turbine.

[0010] FIG. 2 shows a perspective view of a steam turbine blade according to embodiments of the invention.

[0011] It is noted that the drawings of the disclosure are not necessarily to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

[0012] As mentioned above, the invention relates generally to a turbomachine such as a steam turbine, and more particularly, to a last stage blade of a steam turbine including a plurality of indentations at a leading edge.

[0013] During normal operation conditions of a steam turbine, the through flow extends along the entire length of the last stage steam turbine blades. However, at extreme turndown conditions, with low flow and/or high exhaust pressure, the through flow only flows through the tip portion of the last stage steam turbine blades.

[0014] When the through flow only flows through the tip portion of the last stage steam turbine blades, the blade experiences a supersonic entrance condition and a shock wave will form at the blade row entrance. Across the shock, the pressure decreases suddenly. The resulting aeromechanical forces and shock wave transient effects from the supersonic entrance conditions can negatively affect the reliability of the last stage blade due to potentially damaging vibration. The resulting

aeromechanical forces and shock wave transient effects from the supersonic entrance conditions can negatively affect the reliability of the last stage blade due to potentially damaging vibration. The tip portion of the last stage steam turbine blade, where the through flow flows through, also experiences an increase in temperature, and a pressure rise in the direction of flow.

[0015] Referring to the drawings, FIG. 1 shows a perspective partial cut-away illustration of a steam turbine 10. The steam turbine 10 includes a rotor 12 that includes a shaft 14 and a plurality of axially spaced rotor wheels 18. In some embodiments, each rotor wheel 18 may be made of metal such as, for example, steel. A plurality of rotating blades 20 are mechanically coupled to each rotor wheel 18. More specifically, blades 20 are arranged in rows that extend circumferentially around each rotor wheel 18. A plurality of stationary vanes 22 extend circumferentially around shaft 14 and are axially positioned between adjacent rows of blades 20.

Stationary vanes 22 cooperate with blades 20 to form a turbine stage and to define a portion of a steam flow path through turbine 10. [0016] During operation, working fluid 24 enters an inlet 26 of steam turbine 10 and is channeled through stationary vanes 22. Vanes 22 direct fluid 24 downstream against blades 20. Fluid 24 passes through the remaining stages imparting a force on blades 20 causing shaft 14, rigidly connected to rotor 12, to rotate. At least one end of steam turbine 10 may extend axially away from rotor 12 and may be attached to a load or machinery (not shown) such as, but not limited to, a generator, and/or another turbine. Accordingly, a large turbine unit may actually include several turbines that are all co-axially coupled to the same shaft 14. Such a unit may, for example, include a high pressure turbine coupled to an intermediate-pressure turbine, which is in turn coupled to a low pressure turbine.

[0017] As shown in FIG. 1, turbine 10 includes five stages referred to as L0, LI, L2, L3 and L4. Stage L4 is the first stage and is the smallest (in a radial direction) of the five stages. Stage L3 is the second stage and is the next stage in an axial direction. Stage L2 is the third stage and is shown in the middle of the five stages. Stage LI is the fourth and next-to-last stage. Stage L0 is the last stage and is the largest (in a radial direction). It is to be understood that five stages are shown as one example only; some turbine embodiments can have more or less than five stages. As noted, each stage is made up of a rotor wheel 18, the blades 20 coupled to that rotor wheel 18, and the corresponding vane 22.

[0018] Aspects of the invention described herein apply to the last stage L0 of steam turbine 10. In one embodiment, the last stage blade of a steam turbine includes: a blade leading edge for receiving a through flow, the blade leading edge including a plurality of indentations at a top portion of the steam turbine blade; and a blade trailing edge for exhausting the through flow. The plurality of indentations at the top portion of the steam turbine blade will reduce the level to aeromechanical forces due to supersonic entrance conditions and the shock wave transient effect.

[0019] Turning now to FIG. 2, a perspective view of a last stage blade 100 for steam turbine 10 (FIG.l) according to embodiments of the invention is shown. Although only a single last stage blade 100 is shown in FIG. 2, it is understood that the rotor wheel 18 at last stage L0 (FIG. 1) includes a plurality of last stage blades 100 around a circumference of the rotor body 12 (FIG. 1).

[0020] Blade 100 includes a leading edge 110 for receiving the through flow and a trailing edge 120 for exhausting the through flow. As mentioned above, at extreme turndown conditions when there is low through flow and/or high exhaust pressure, which are necessitated by high ambient temperatures and a light load demand, the through flow only flows through a top portion 130 of the blade 110. This causes unwanted aeromechanical forces which can damage the blades.

[0021] To reduce the aeromechanical forces during the extreme turndown conditions, the blade leading edge 110 includes a plurality of indentations 140 at the top portion 130 of the blade 100. The top portion 130 of the blade 100 may be at least approximately ten percent of the blade 100, but no more than approximately twenty percent of the blade 100. However, it is understood that these percentages of the blade 100 are for exemplary purposes only, and that the plurality of indentations 140 may extend along the entire surface of the leading edge 110.

[0022] As illustrated, rotor body 12 includes a plurality of slots 150 for receiving the blade 100 and securing blade 100 to the rotor body 12. Although the dovetail connection between the slots 150 and blade 100 are shown in a pine-tree

configuration, it is understood that blade 100 may connect to rotor body 12 via a t- root style configuration, or any now known or later developed configuration.

[0023] As used herein, the terms "first," "second," and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix "(s)" as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the metal(s) includes one or more metals). Ranges disclosed herein are inclusive and independently combinable (e.g., ranges of "up to about 25 mm, or, more specifically, about 5 mm to about 20 mm," is inclusive of the endpoints and all intermediate values of the ranges of "about 5 mm to about 25 mm," etc.).

[0024] 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 by those skilled in the art, and are within the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.