Patent Application
20140099193
The present invention generally involves a rotor blade and a method for cooling the rotor blade.
Turbines are widely used in industrial and commercial operations. A typical commercial steam or gas turbine used to generate electrical power includes alternating stages of stationary and rotating airfoils or blades. For example, stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, and rotor blades may be attached to a rotor located along an axial centerline of the turbine. A compressed working fluid, such as but not limited to steam, combustion gases, or air, flows through the turbine, and the stator vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotor blades to impart motion to the rotor blades, thus turning the rotor and performing work.
Compressed working fluid that leaks around or bypasses the rotor blades reduces the efficiency of the turbine. To reduce the amount of compressed working fluid that bypasses the rotor blades, the casing may include stationary shroud segments that surround each stage of rotor blades, and each rotor blade may include a tip cap at an outer radial tip that reduces the clearance between the shroud segments and the rotor blade. Although effective at reducing or preventing leakage around the rotor blades, the interaction between the shroud segments and the tip caps may result in elevated local temperatures that may reduce the low cycle fatigue limits and/or lead to increased creep at the tip caps. As a result, a cooling media may be supplied to flow inside each rotor blade before flowing through cooling passages in the tip cap to provide film cooling over the tip cap of the rotor blade.
In particular designs, each tip cap may include an outer surface or tip plate that is at least partially surrounded by a rim. The rim and the tip plate may at least partially define a tip cavity, also known as a squealer tip cavity, between the rim, the tip plate, and the surrounding shroud segments. In this manner, the cooling media supplied to the squealer tip cavity may remove heat from the tip cap before flowing over the rim and out of the squealer tip cavity. However, excessive cooling media that flows over the suction side of the rotor blade may disrupt the flow of the compressed working fluid over the rotor blades and/or reduce the operating efficiency of the turbine. As a result, an improved rotor blade and a method for cooling the rotor blade would be useful.
Aspects and advantages of the invention are set forth below in the following description, or may be obvious from the description, or may be learned through practice of the invention.
One embodiment of the present invention is a rotor blade that includes an airfoil having a tip plate that extends across an outer radial end. A rim extends radially outward from the tip plate and surrounds at least a portion of the airfoil and includes a concave portion opposed to a convex portion. A plurality of dividers extend between the concave and convex portions to define a plurality of pockets between the concave and convex portions at the outer radial end. A plurality of cooling passages through the tip plate provide fluid communication through the tip plate to the plurality of pockets. A first fluid passage in at least one divider provides fluid communication between adjacent pockets across the at least one divider.
Another embodiment of the present invention is a rotor blade that includes an airfoil having a leading edge, a trailing edge downstream from the leading edge, a concave surface between the leading and trailing edges, a convex surface opposed to the concave surface between the leading and trailing edges, and an outer radial end. A tip plate extends across the outer radial end of the airfoil. A concave portion extends radially outward from the concave surface of the airfoil. A convex portion extends radially outward from the convex surface of the airfoil. A plurality of dividers extend between the concave portion and the convex portion to define a plurality of pockets at the outer radial end. A plurality of cooling passages through the tip plate provide fluid communication through the tip plate to the plurality of pockets. A first fluid passage in at least one divider provides fluid communication between adjacent pockets across the at least one divider.
The present invention may also include a turbine that includes a casing and a plurality of airfoils circumferentially arranged inside the casing. Each airfoil has a leading edge, a trailing edge downstream from the leading edge, a concave surface between the leading and trailing edges, a convex surface opposed to the concave surface between the leading and trailing edges, and an outer radial end. A tip plate extends across the outer radial end of each airfoil. A concave portion extends radially outward from the concave surface of each airfoil. A convex portion extends radially outward from the convex surface of each airfoil. A plurality of dividers extend between the concave portion and the convex portion to define a plurality of pockets at the outer radial end. A plurality of cooling passages extend through the tip plate to provide fluid communication through the tip plate to the plurality of pockets. A second fluid passage is in at least one of the concave or convex portions to provide fluid communication across at least one of the concave or convex portions.
Those of ordinary skill in the art will better appreciate the features and aspects of such embodiments, and others, upon review of the specification.
A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention. As used herein, the terms “first”, “second”, and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. In addition, the terms “upstream” and “downstream” refer to the relative location of components in a fluid pathway. For example, component A is upstream from component B if a fluid flows from component A to component B. Conversely, component B is downstream from component A if component B receives a fluid flow from component A.
Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that modifications and variations can be made in the present invention without departing from the scope or spirit thereof. For instance, features illustrated or described as part of one embodiment may be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.
Various embodiments of the present invention include a rotor blade and a method for cooling the rotor blade. The rotor blade generally includes an airfoil with an outer radial end, and a rim extends radially outward from a tip plate at the outer radial end to at least partially define a squealer tip cavity. A plurality of dividers extend across the tip plate to separate the squealer tip cavity into a plurality of pockets, and a plurality of cooling passages provide fluid communication for a cooling media to flow through the tip plate to the plurality of pockets. In particular embodiments, a fluid passage in one or more dividers may provide fluid communication for the cooling media to flow between adjacent pockets. Alternately or in addition, another fluid passage in the rim may provide fluid communication for the cooling media to flow across the rim and out of the pockets. Although exemplary embodiments of the present invention may be described generally in the context of a rotor blade incorporated into a gas turbine or other turbomachine, one of ordinary skill in the art will readily appreciate from the teachings herein that embodiments of the present invention are not limited to a gas turbine or other turbomachine unless specifically recited in the claims.
Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures,
As shown in
The airfoil 46 generally includes a concave pressure surface 50 and a circumferentially or laterally opposite convex suction surface 52 that extend axially between a leading edge 54 and a trailing edge 56. The pressure and suction surfaces 50, 52 also extend in the radial direction between a radially inner root 58 at the platform 48 and an outer radial end 60, which will be described in more detail in the discussion related to
As further shown in
The pockets 82 may vary in width, depth, length, and/or volume, particularly in the direction of the trailing edge 56; however, the present invention is not limited to any particular shape, size, or orientation of the pockets 82 unless specifically recited in the claims. As seen most clearly in
In particular embodiments, the tip plate 70, rim 72, and/or dividers 80 may be treated with a coating, such as a bond coat or other type of high-temperature coating. The coating may include, for example, a corrosion inhibitor with a high aluminum content, such as an aluminide coating. Aluminide coatings are highly effective against corrosion, but tend to wear quickly. As a result, aluminide coatings are well-suited for the interior of the pockets 82 because this location is relatively sheltered from rubbing against adjacent parts.
The rotor blade 30 may further include a plurality of cooling passages 84 that provide fluid communication through the tip plate 70 to the individual pockets 82. The size and number of cooling passages 84 in each pocket 82 is selected to deliver the desired pressure and flow rate of cooling media from the cavity 62 inside the airfoil 46 and into the pockets 82. As one of ordinary skill in the art will appreciate, the differential pressure across the airfoil 46 tends to sweep the cooling media over the convex portion 76 of the rim 72 and out of the pockets 82. Cooling media lost in this manner not only reduces the cooling provided to the outer radial end 60, but it also negatively impacts the efficiency of the turbine 10. As a result, the rotor blade 30 may further include fluid passages 86 in the dividers 80 and/or fluid passages 88 in the rim 72 to enhance distribution and/or flow of the cooling media between adjacent pockets 82. The cooling media may thus flow through the cooling passages 84 and into the individual pockets 82 to convectively and conductively cool the tip plate 70, rim 72, and dividers 80 while also partially insulating these surfaces from the extreme temperatures associated with the compressed working fluid 26 flowing through the gas path 16. In addition, the cooling media may flow through the fluid passages 86 in the dividers 80 to provide additional cooling to adjacent pockets 82 before flowing out of the pockets 82 through the fluid passages 88 in the rim 72. In this manner, the outer radial end 60 of the rotor blade 30 may be maintained at an acceptable temperature during operation without increasing the flow rate of cooling media through the pockets 82. Further, as one of ordinary skill in the art will appreciate, the resulting decrease in temperatures generally reduces the amount of oxidation that occurs during operation along outer radial end 60 of the rotor blade 30. The reduction in oxidation improves the aerodynamic performance of the airfoil 46 and, ultimately, reduces repair costs. In addition, the cooling media flow over the rim 72 acts as a seal across that portion of the rotor blade 30 to reduce the amount of compressed working fluid 26 that might otherwise bypass the rotor blade 30, further improving turbine 10 performance.
One of ordinary skill in the art will readily appreciate from the teachings herein that the embodiments shown and described with respect to
It is anticipated that the various embodiments shown and described in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
