Patent Application
20160319672
The present invention generally relates to a rotor blade for a turbine. More particularly, this invention involves a rotor blade having a flared tip configured for cooling a trailing edge portion of the rotor blade.
In an air-ingesting turbo machine (e.g., a gas turbine), air is pressurized by a compressor and then mixed with fuel and ignited within an annular array of combustors to generate combustion gases. The hot gases are routed through a liner and into a hot gas path defined within a turbine section of the turbo machine. Kinetic energy is extracted from the combustion gases via one or more rows of turbine rotor blades that are connected to a rotor shaft. The extracted kinetic energy causes the rotor shaft to rotate, thus producing work.
The turbine rotor blades or blades generally operate in extremely high temperature environments. In order to achieve adequate service life, the blades typically include various internal cooling passages or cavities. During operation of the gas turbine, a cooling medium such as compressed air is routed through the internal cooling passages. A portion of the cooling medium may be routed out of the internal cooling passages through various cooling holes defined along the blade surface, thereby reducing high surface temperatures. An area that is generally challenging to cool effectively via the cooling medium is a blade tip portion of the turbine rotor blade, more particularly a trailing edge region of the blade tip.
The blade tip is generally defined at a radial extremity of the turbine rotor blade and is positioned radially inward from a turbine shroud that circumscribes the row of blades. The turbine shroud defines a radially outward boundary of the hot gas path. The proximity of the blade tip to the turbine shroud makes the blade tip difficult to cool. The contiguity of the shroud and the blade tip minimizes the leakage of hot operating fluid past the tip which correspondingly improves turbine efficiency.
In particular blade designs, a tip cavity formed by a recessed tip cap and a pressure side wall and a suction side wall provides a means for achieving minimal tip clearance while at the same time assuring adequate blade tip cooling. The pressure side wall and the suction side wall extend radially outwardly from the tip cap. At least a portion of at least one of the suction side wall and the pressure side wall is flared or inclined outward with respect to a radial centerline of the blade. The pressure side wall intersects with the suction side wall at a leading edge portion of the blade. However, the pressure side wall does not intersect with the suction side wall at the trailing edge, thus forming an opening therebetween. This configuration is generally due to the lack of an appropriate wall thickness of the blade along the trialing edge.
In operation, the cooling medium is exhausted from the internal passages through holes in the tip cap into the tip cavity, thus effectively cooling the pressure and suction side walls as well as the tip cap surface. However, it may also be desirable to effectively cool the leading and trailing edges of the airfoil. Therefore there is a need for a blade tip design having improved blade tip trailing edge cooling.
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. The rotor blade includes an airfoil having a pressure side wall and a suction side wall that are connected at leading and trailing edges of the airfoil. A blade tip defines a radially outer surface of the airfoil. The rotor blade also includes an internal cavity for receiving a cooling medium. A tip cavity that is in fluid communication with the internal cavity is at least partially defined by a tip cap. The tip cavity is recessed radially inwardly from the radially outer surface and surrounded by the pressure and suction side walls. A portion of at least one of the suction side wall or the pressure side wall that defines the tip cavity extends obliquely outwardly from the tip cavity. A plurality of slots is defined in at least one of the suction side wall or the pressure side wall along the radially outer surface proximate to the trailing edge of the airfoil.
Another embodiment of the present invention is a gas turbine. The gas turbine includes, in serial flow order, a compressor section, a combustion section and a turbine section. The turbine section includes a rotor shaft and a plurality of rotor blades that are coupled to the rotor blade. Each rotor blade includes an airfoil having a pressure side wall and a suction side wall that are connected at leading and trailing edges of the airfoil. A blade tip defines a radially outer surface of the airfoil. The rotor blade also includes an internal cavity for receiving a cooling medium. A tip cavity that is in fluid communication with the internal cavity is at least partially defined by a tip cap. The tip cavity is recessed radially inwardly from the radially outer surface and surrounded by the pressure and suction side walls. A portion of at least one of the suction side wall or the pressure side wall that defines the tip cavity extends obliquely outwardly from the tip cavity. A plurality of slots is defined in at least one of the suction side wall or the pressure side wall along the radially outer surface proximate to the trailing edge of the airfoil.
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. The terms “upstream” and “downstream” refer to the relative direction with respect to fluid flow in a fluid pathway. For example, “upstream” refers to the direction from which the fluid flows, and “downstream” refers to the direction to which the fluid flows. The term “radially” refers to the relative direction that is substantially perpendicular to an axial centerline of a particular component and/or substantially perpendicular to an axial centerline of the turbomachine, and the term “axially” refers to the relative direction that is substantially parallel and/or coaxially aligned to an axial centerline of a particular component and/or to an axial centerline of the turbomachine.
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. Although an industrial or land based gas turbine is shown and described herein, the present invention as shown and described herein is not limited to a land based and/or industrial gas turbine unless otherwise specified in the claims. For example, the invention as described herein may be used in any type of turbine including but not limited to a steam turbine or marine gas turbine.
Referring now to the drawings,
The turbine section 18 may generally include a rotor shaft 24 having a plurality of rotor disks 26 (one of which is shown) and a plurality of rotor blades 28 extending radially outwardly from and being interconnected to the rotor disk 26. Each rotor disk 26 in turn, may be coupled to a portion of the rotor shaft 24 that extends through the turbine section 18. The turbine section 18 further includes an outer casing 30 that circumferentially surrounds the rotor shaft 24 and the rotor blades 28, thereby at least partially defining a hot gas path 32 through the turbine section 18.
During operation, a working fluid such as air flows through the inlet section 12 and into the compressor section 14 where the air is progressively compressed, thus providing pressurized air to the combustors of the combustion section 16. The pressurized air is mixed with fuel and burned within each combustor to produce combustion gases 34. The combustion gases 34 flow through the hot gas path 32 from the combustor section 16 into the turbine section 18, wherein energy (kinetic and/or thermal) is transferred from the combustion gases 34 to the rotor blades 28, thus causing the rotor shaft 24 to rotate. The mechanical rotational energy may then be used to power the compressor section 14 and/or to generate electricity. The combustion gases 34 exiting the turbine section 18 may then be exhausted from the gas turbine 10 via the exhaust section 20.
The airfoil 106 includes an outer surface 112 that surrounds the airfoil 106. The outer surface 112 is at least partially defined by a pressure side wall 114 and an opposing suction side wall 116. The pressure side wall 114 and the suction side wall 116 extend substantially radially outwardly from the platform 110 in span from a root 118 of the airfoil 106 to a blade tip or tip 120 of the airfoil 106. The root 118 of the airfoil 106 may be defined at an intersection between the airfoil 106 and the platform 110. The blade tip 120 is disposed radially opposite the root 118. As such, a radially outer surface 122 of the blade the tip 120 may generally define the radially outermost portion of the rotor blade 100.
The pressure side wall 114 and the suction side wall 116 are joined together or interconnected at a leading edge 124 of the airfoil 106 which is oriented into the flow of combustion gases 34. The pressure side wall 114 and the suction side wall 116 are also joined together or interconnected at a trailing edge 126 of the airfoil 106 which is spaced downstream from the leading edge 124. The pressure side wall 114 and the suction side wall 116 are continuous about the trailing edge 126. The pressure side wall 114 is generally concave and the suction side wall 116 is generally convex. The chord of the airfoil 106 is the length of a straight line connecting the leading edge 114 and the trailing edge 116 and the direction from the leading edge 114 to the trailing edge 116 is typically described as the chordwise direction. A chordwise line bisecting the pressure side wall 114 and the suction side wall 116 is typically referred to as the mean-line or camber-line 128 of the airfoil 106.
Internal cooling of turbine rotor blades is well known and typically utilizes a cooling medium, as indicated by solid and dashed arrows 130, such as a relatively cool compressed air bled from the compressor section 14 (
The internal cavity 132 may take any conventional form and is typically in the form of a serpentine passage. The cooling medium 130 enters the internal cavity 132 from the mounting or shank portion 102 and passes through the internal cavity 132 for suitably cooling the airfoil 106 from the heating effect of the combustion gases 34 flowing over the outer surface 112 thereof. Film cooling holes (not shown) may be disposed on the pressure side wall 114 and/or the suction side wall 116 for conventionally film cooling the outer surface 112 of the airfoil 106.
In various embodiments, a tip cavity or plenum 134 is formed at or within the blade tip 120. The tip cavity 134 is at least partially formed by a tip cap 136. As shown in
The tip cap 136 is connected to and/or forms a seal against an inner surface or side 138 of the pressure side wall 114 and an inner surface or side 140 of the suction side wall 116 along a periphery 142 of the tip cap 136 between the leading and trailing edges 124, 126 of the airfoil 106. The tip cap 136 further includes a plurality of holes or apertures 144 that extend through a top surface or side 146 of the tip cap 136 and that provide for fluid communication between the internal cavity 132 and the tip cavity 134.
In particular embodiments, as shown in
In particular embodiment, as shown in
A portion of the inner surface or side 140 of the suction side wall 116 that defines the tip cavity 134 may extend obliquely outwardly from the tip cavity 134 with respect to radial direction 108, thus increasing an overall volume of the tip cavity 134. In addition or in the alternative, as shown in
In various embodiments, as shown collectively in
For example, in one embodiment, the plurality of slots 148 occurs only along the suction side wall 116. In another embodiment, the plurality of slots 148 occurs only along the pressure side wall 114. In one embodiment, as shown in
In various embodiments, as shown in
In various embodiments, one or more of the slots 148 of the plurality of slots 148 may be tapered and/or non-linear to enable flow of the cooling medium from the tip cavity 134 adjacent to the trailing edge 126. For example, as shown in
As shown in
In particular embodiments, as shown 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 and 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.
