Patent Application
20100284800
The present invention relates generally to turbines, and more particularly to a means to cool particular regions of a nozzle segment.
In a typical gas turbine, the turbine section is mounted at the exit of the combustor and is therefore exposed to extremely high temperature combustion gases. To protect turbine components from the hot combustion gases, they are often cooled with a cooling medium. One common approach to cooling turbine airfoil components (e.g., rotor blades and nozzle vanes) is to bleed a portion of the compressed air from the compressor and to direct this bleed air to internal passages in the components. The air circulates through the internal passages to remove heat from the component structure. The air can exit through small film cooling holes formed in the airfoil so as to produce a thin film layer of cooling air on the surface. Film cooling can also be used for the inner and outer bands. In this case, a band includes film cooling holes extending radially therethrough and cooling air passes through the film cooling holes to form a cooling air film on the hot side of the band.
With a known turbine nozzle construction, each of a plurality of cast nozzle segments includes inner and outer band portions and one or more nozzle vanes. The mating surfaces of the band portions include seal slots, which accommodate seals that extend between band portions of adjacent nozzle segments. The nozzle vanes may be cooled by passing a cooling medium through a plenum in the outer band portion of each nozzle segment, through one or more cavities in the nozzle vanes to cool the nozzles, and into a plenum in a corresponding inner band portion. In some nozzle segments, the cooling medium then flows through the inner band portion and again through the one or more nozzle vanes prior to being discharged. In other nozzle segments, the cooling medium flows only once through each nozzle segment.
It is generally recognized that cooling of certain regions of a nozzle segment are not adequate, and that such regions are prone to higher thermal stresses and fatigue. Efforts are being made to improve cooling in these areas. For example, U.S. Pat. No. 7,029,228 describes a configuration wherein a cooling channel extends axially through at least one of the outer and inner bands generally parallel to the mating face of the nozzle segment to cool the mating faces between the seal slots and the hot gas path.
A particularly problematic region for cooling in a nozzle segment is the area in the band portions that extends from the mating face and generally underlies a rail member, which may include an impingement plate, on the back side of the band portion. This area coincides with the trailing edge of the vane on the opposite side of the band portion. Cooled band portions often consist of more than one flow circuit, wherein compressor bleed air is passed through an impingement plate in each circuit to cool the back side of the band portion before exiting through film holes or slots into the gas path. These circuits are divided by the rail member, which is typically located on the back side of the band portions opposite from the trailing edge of the vane. A series of holes is typically drilled through this rail to allow cooling air to pass from the high pressure circuit to the low pressure circuit. However, the presence of the rail at the back side of the band portion prevents impingement and film cooling of the inner face of the band portions around the trailing edge of the vane. A need exists in the art to address the inadequate cooling of this region.
The present invention provides a solution to improved cooling of the band portions of a nozzle segment transverse to the mating side face at the nozzle vane trailing edge. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
In accordance with aspects of the invention, a turbine nozzle segment is provided that includes an outer band portion, an inner band portion, and at least one nozzle vane extending between the inner and outer band portions. The nozzle vane has a leading edge and a trailing edge. Each of the inner and outer band portions include axially extending (relative to the axis of the turbine) mating faces, a combustion gas side, and an opposite back side. A first cooling chamber and a second cooling chamber are defined at the back side of the band portions and, in one particular embodiment, may be separated at least partially by a transversely extending rail member. A cooling plenum is defined in the mating face of at least one of the inner band portion and the outer band portion and extends transversely at least partially through the respective band portion. The cooling plenum may extend so as to run essentially under the rail member in one embodiment, or under the trailing edge of the nozzle vane in another embodiment. At least one first cooling air passage is defined in the band portion from the first cooling chamber into the cooling plenum, and at least one second cooling air passage is defined from the second cooling chamber into the cooling plenum. A plurality of these first and second cooling air passages may be provided along the longitudinal length of the cooling plenum. The passages serve to move air from one cooling chamber to another via the cooling plenum. For example, the first cooling chamber may be a high pressure impingement cooling chamber supplied with compressor bleed-off air, and the second cooling chamber may be a low pressure chamber, whereby the cooling air moves from the high pressure chamber into the cooling plenum via the first cooling air passage, and into the low pressure chamber from the cooling plenum via the second cooling air passage. Cooling air introduced into the cooling plenum thus cools the region of the band portion under and alongside of the plenum and adjacent to the cooling air passages, such as the area under the rail member or the trailing edge of the nozzle vane.
It should be appreciated that the present invention also encompasses a gas turbine having a plurality of nozzle stages, with each of the nozzle stages further including a plurality of nozzle segments as embodied herein.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:
Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. 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 various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used with 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.
The nozzle segment 10 includes at least one nozzle vane 30 extending between the combustion gas sides of the band portions 12, 20, with the nozzle vane having a leading edge 32 and a trailing edge 34. The nozzle segment 10 may include a plurality of vanes 30 in a single segment. The nozzle vane 30 intersects with the combustion gas side 22 of the lower band portion 20 at a root 56. A fillet 58 having a concave radius of curvature is generally formed along the root 56. The interface of the nozzle vane 30 with the combustion gas side 14 of the outer band portion is formed in the same way.
A plurality of the nozzle segments 10 are arranged circumferentially about the axis of a turbine (not shown) and are secured to the turbine shell to form a nozzle stage. Typically, the turbine includes a plurality of these nozzle stages.
A flow path for hot combustion gases is defined through the nozzle segment 10 by the nozzle vane 30 and the combustion gas surfaces 14, 22, of the outer band portion 12 and inner band portion 20, respectively. The hot gases flow tlirough the segments and around the vanes 30 and engage downstream rotor buckets (not shown) of the turbine to rotate the turbine rotor, as commonly understood in the art.
The mating surfaces 18, 26 include the seals 52 in seal slots 50 (
Referring to
A cooling circuit is defined by the various cavities and structural members of the nozzle segment 10. It should be appreciated that the present invention is not limited by any particular configuration of a cooling circuit. In the illustrated embodiment, cooling air introduced into the first cooling chamber 38 provides impingement and/or convection cooling of structural components of the nozzle segment 10 in this region. The cooling air is introduced into the second or lower pressure cooling chamber 40 (or cavities 36 or other areas in communication with the cooling chamber 40) through the impingement plate 44. A portion of the cooling air may diffuse through film holes 54 through the band portion 12 and into the combustion gas flow. This limited amount of cooling air provides a film cooling to the combustion gas side surfaces of the respective band portions 12, 20. Any array and location of these film holes 54 may be utilized, as variously illustrated in the figures.
The nozzle vane 30 is generally hollow and includes one or more cavities 36. The cooling air moves through the cavities 36 to cool the nozzle vane 30. The cavities 36 may also be in communication with the suction side and pressure side of the nozzle vane 30 through fluid holes 54 defined through the vane 30. In this manner, the outside surface of the nozzle vane 30 is cooled by a cooling air film induced on the surface. The cooling air moves through the vane 30 into the cavities of the inner band portion 20, and may diffuse through the film holes 54 in the band 20. Depending on the configuration of the nozzle segments 10, the cooling air may be re-circulated through other portions of the nozzle segment 10 before being exhausted from the cooling circuit.
Referring to the various figures, the rail member 42 extending between the mating side faces 18 of the outer band portion 12, and the mating side faces 26 of the lower band portion 20, creates a problematic area with respect to cooling. The presence of the structural rail inhibits impingement cooling, particularly in the region of the trailing edge of the nozzle vane 30.
Referring to the various figures and in accordance with aspects of the invention, a cooling plenum 46 is defined in one of the mating faces 18, 26 of at least one of the outer band portion 12 or inner band portion 20. It should be appreciated that this cooling plenum 46 may be included in both of the outer and inner band portions 12, 20, and in both mating faces of each respective band portion. For purposes of discussion, the cooling plenum 46 is described further herein by reference to mating side face 18 of the upper band portion 12.
The cooling plenum 46 is defined in the mating face at any desired location so as to extend transversely into the band portion to cool a particular region of the band portion. In the illustrated embodiments, the cooling plenum 46 is defined at a location adjacent to the rail member 42. For example, referring to
The cooling plenum 46 may be provided with cooling air through various means. In the illustrated embodiments, a plurality of air passages are used to move or transport cooling air into, along, and out of the cooling plenum 46. For example, referring to
It should be appreciated that the plenum 46 is not limited to any particular cross-sectional profile or other configuration. For example, in the embodiment illustrated in
Still referring to
It should be appreciated that the present invention also encompasses embodiments wherein a cooling air plenum 46 is defined in the mating face surface 18 so as to extend transversely into the band portion 12 adjacent to the trailing edge 34 of the nozzle vane 30 regardless of the length of any rail member on the back side 16 of the band portion 12. For example, the back side 16 of the band portion 12 may include a structural member of any design that inhibits impingement cooling of certain regions of the band portion. In this situation, a cooling plenum 46 may be defined in the mating side face surface 18 so as to extend into the band portion 12 generally coincident with this structural member, particularly in the trailing edge region of the nozzle vane 30. Cooling air moving through the plenum 46 will cool the region of the band portion 12 around the trailing edge of the nozzle vane 30. Cooling passages 48, 49 may be defined in the band portion to place the cooling plenum 46 in fluid air communication with a first location and a second location, wherein the cooling air plenum also serves to move air from one location to the other while providing a beneficial impingement cooling to a problematic region of the band portion 12. This concept is illustrated generally in
While the present subject matter has been described in detail with respect to specific exemplary embodiments and methods thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing may readily produce alterations to, variations of, and equivalents to such embodiments. Accordingly, the scope of the present disclosure is by way of example rather than by way of limitation, and the subject disclosure does not preclude inclusion of such modifications, variations and/or additions to the present subject matter as would be readily apparent to one of ordinary skill in the art.
