Patent Application
20120107135
The present application relates generally to combustion turbine engines, which, as used herein and unless specifically stated otherwise, includes all types of combustion turbine engines, such as those used in power generation and aircraft engines. More specifically, but not by way of limitation, the present application relates to apparatus, systems and/or methods for cooling the platform region of turbine rotor blades.
A gas turbine engine typically includes a compressor, a combustor, and a turbine. The compressor and turbine generally include rows of airfoils or blades that are axially stacked in stages. Each stage typically includes a row of circumferentially spaced stator blades, which are fixed, and a set of circumferentially spaced rotor blades, which rotate about a central axis or shaft. In operation, the rotor blades in the compressor are rotated about the shaft to compress a flow of air. The compressed air is then used within the combustor to combust a supply of fuel. The resulting flow of hot gases from the combustion process is expanded through the turbine, which causes the rotor blades to rotate the shaft to which they are attached. In this manner, energy contained in the fuel is converted into the mechanical energy of the rotating shaft, which then, for example, may be used to rotate the coils of a generator to generate electricity.
Referring to
As illustrated, the platform 110 may be substantially planar. More specifically, the platform 110 may have a planar topside 113, which, as shown in
In general, the platform 110 is employed on turbine rotor blades 100 to form the inner flow path boundary of the hot gas path section of the gas turbine. The platform 110 further provides structural support for the airfoil 102. In operation, the rotational velocity of the turbine induces mechanical loading that creates highly stressed regions along the platform 110 that, when coupled with high temperatures, ultimately cause the formation of operational defects, such as oxidation, creep, low-cycle fatigue cracking, and others. These defects, of course, negatively impact the useful life of the rotor blade 100. It will be appreciated that these harsh operating conditions, i.e., exposure to extreme temperatures of the hot gas path and mechanical loading associated with the rotating blades, create considerable challenges in designing durable, long-lasting rotor blade platforms 110 that both perform well and are cost-effective to manufacture.
One common solution to make the platform region 110 more durable is to cool it with a flow of compressed air or other coolant during operation, and a variety of these type of platform designs are known. However, as one of ordinary skill in the art will appreciate, the platform region 110 presents certain design challenges that make it difficult to cool in this manner. In significant part, this is due to the awkward geometry of this region, in that, as described, the platform 110 is a periphery component that resides away from the central core of the rotor blade and typically is designed to have a structurally sound, but thin radial thickness.
To circulate coolant, rotor blades 100 typically include one or more hollow cooling passages 116 (see
In some cases, the coolant may be directed from the cooling passages 116 into a cavity 119 formed between the shanks 112 and platforms 110 of adjacent rotor blades 100. From there, the coolant may be used to cool the platform region 110 of the blade, a conventional design of which is presented in
It will be appreciated, however, that this type of conventional design has several disadvantages. First, the cooling circuit is not self-contained in one part, as the cooling circuit is only formed after two neighboring rotor blades 100 are assembled. This adds a great degree of difficulty and complexity to installation and pre-installation flow testing. A second disadvantage is that the integrity of the cavity 119 formed between adjacent rotor blades 100 is dependent on how well the perimeter of the cavity 119 is sealed. Inadequate sealing may result in inadequate platform cooling and/or wasted cooling air. A third disadvantage is the inherent risk that hot gas path gases may be ingested into the cavity 119 or the platform itself 110. This may occur if the cavity 119 is not maintained at a sufficiently high pressure during operation. If the pressure of the cavity 119 falls below the pressure within the hot gas path, hot gases will be ingested into the shank cavity 119 or the platform 110 itself, which typically damages these components as they were not designed to endure exposure to the hot gas-path conditions.
It will be appreciated that the conventional designs of
As a result, conventional platform cooling designs are lacking in one or more important areas. There remains a need for improved apparatus, systems, and methods that effectively and efficiently cool the platform region of turbine rotor blades, while also being cost-effective to construct, flexible in application, and durable.
The present application thus describes a platform cooling arrangement in a turbine rotor blade having a platform at an interface between an airfoil and a root, wherein the rotor blade includes an interior cooling passage that extends from the root to at least the approximate radial height of the platform, and wherein, along a side that corresponds with a pressure face of the airfoil, a pressure side of the platform comprises a substantially planar topside that extends circumferentially from the airfoil to a pressure side slashface, and, along a side that corresponds with a suction face of the airfoil, a suction side of the platform comprises a substantially planar topside that extends circumferentially from the airfoil to a suction side slashface. The platform cooling arrangement may include a linear plenum residing just inboard of the planar topside and linearly extending through the platform from either the pressure side slashface or the suction side slashface to a connection with the interior cooling passage, the linear plenum having a longitudinal axis that is approximately parallel to the planar topside; and a plurality of cooling apertures linearly extending from a topside outlet formed on the topside of the platform to a connection with the linear plenum, wherein the cooling apertures are configured such that each forms an acute angle with the topside of the platform.
The present application further describes a method of creating a platform cooling arrangement in a turbine rotor blade having a platform at an interface between an airfoil and a root, wherein the rotor blade includes an interior cooling passage that extends from the root to at least the approximate radial height of the platform, and wherein, along a side that corresponds with a pressure face of the airfoil, a pressure side of the platform comprises a planar topside that extends circumferentially from the airfoil to a pressure side slashface, and, along a side that corresponds with a suction face of the airfoil, a suction side of the platform comprises a planar topside that extends circumferentially from the airfoil to a suction side slashface. The method may include the steps of: machining at least one linear plenum, the linear plenum configured to reside just inboard of the planar topside and linearly extend through the platform from a starting point at a position on either the pressure side slashface or the suction side slashface to a connection with the interior cooling passage, the linear plenum having a longitudinal axis that is approximately parallel to the planar topside; and machining a plurality of cooling apertures that linearly extend from a starting point at a position on the topside of the platform to a connection with the linear plenum, wherein the cooling apertures are configured such that each forms an acute angle with the topside of the platform, the acute angle comprising an angle of less than 60°.
These and other features of the present application will become apparent upon review of the following detailed description of the preferred embodiments when taken in conjunction with the drawings and the appended claims.
These and other features of this invention will be more completely understood and appreciated by careful study of the following more detailed description of exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:
It will be appreciated that cooling configurations of conventional turbine rotor blades 100 typically have an interior cooling passage 116 that extends radially from the root 104 of the blade 100 to a location within the airfoil 102. Typically, the interior cooling passage 116 is configured to form a winding, serpentine path that promotes a one-way flow of coolant and the efficient exchange of heat. In operation, a pressurized coolant, which is typically compressed air and bled from the compressor (though other coolants may be used), is supplied to the interior cooling passage 116. The pressure drives the coolant through the interior cooling passage 116, and the coolant convects heat from the surrounding walls. (It will be appreciated that the present invention may be practiced in rotor blades 100 having internal cooling passages of different configurations and is not limited to cooling passages having a serpentine shape. Accordingly, the term “interior cooling passage” or “cooling passage” is meant to include any passage or hollow channel through which coolant may be circulated in the rotor blade).
In general, the various conventional designs of internal cooling passages 116 are effective at providing active cooling to certain regions within the rotor blade 100. However, as one of ordinary skill in the art will appreciate, the platform region proves more challenging. This, at least in part, is due to the awkward geometry of the platform region—i.e., its narrow radial height and the manner in which it juts away from the core or main body of the rotor blade 100. However, given its exposures to the extreme temperatures of hot gas path and high mechanical loading, the cooling requirements of the platform are considerable. As described above, conventional platform cooling designs are ineffective because they fail to address the particular challenges of the region, are inefficient with their usage of coolant, and/or are costly to fabricate.
Referring now to
As illustrated, the linear plenum 132 may be configured such that it resides just inboard of the planar topside 113. The linear plenum 132 may extend in a linear fashion through the platform 110 from either the pressure side slashface 126 or the suction side slashface 122 to a connection with the interior cooling passage 116. The linear plenum 132 may be configured to have a longitudinal axis that is approximately parallel to the planar topside 113. The platform cooling arrangement may have a plurality of linear plenums 132. In some embodiments, as shown in
In a preferred embodiment, each of the linear plenums 132 may extend diagonally across the platform 110 (i.e., in relation to the pressure side slashface 126 and the suction side slashface 122). More specifically, from a position on the pressure side slashface 126, the linear plenum 132 may extend along a diagonal path across at least a significant portion of the platform 110. As illustrated, the diagonal path may include an axial-downstream directional component as well as a circumferential directional component. Accordingly, as shown in
A plurality of cooling apertures 140 may extend in linear fashion from a topside outlet 145 formed through the topside 113 of the platform 110 to a connection made with the linear plenum 132. As shown in
The cooling apertures 140 may be configured to expel coolant in an approximate downstream direction. In some embodiments, the cooling apertures 140 extend diagonally across a portion of the platform 110 from the connection with the linear plenum 132. The diagonal path may include an axial-downstream and a circumferential directional component. As shown in
In some embodiments, the cooling apertures 140 extending from a particular linear plenum 132 may comprise either a short length or long length. In this case, the cooling apertures 140 may have an alternating short/long configuration, where the short length comprises approximately 40%-60% of the long length, as illustrated in
In one exemplary embodiment, at least two linear plenums 132 are provided: a first linear plenum 132 and a second linear plenum 132. The first linear plenum 132 (which, for the sake of this example, may be thought of as being configured similarly to the forward linear plenum 132 of
Each of the first and second linear plenums 132 may include a plurality of cooling apertures 140 that extend therefrom. The second linear plenum 132 may have a plurality of cooling apertures 140 on the pressure side of the platform 110 and a plurality of the cooling apertures 140 on the suction side of the platform 110. In this manner, the second linear plenum 132 may be used to cool either side of the platform 110.
As described, the linear plenums 132 may include one or two slashface outlets 147. The first linear plenum 132, for example, may have a slashface outlet 147 on the pressure side slashface 126. In a preferred embodiment, the slashface outlet 147 may include a reduced cross-sectional flow area. The second linear plenum 132, for example, may have a slashface outlet 147 on the pressure side slashface 126 and a slashface outlet 147 on the suction side slashface 122. In preferred embodiments, the slashface outlet 147 on the pressure side slashface 126 is axially forward of the slashface outlet 147 on the suction side slashface 122. In a preferred embodiment, both slashface outlets 147 of the second linear plenum 132 may have a reduced cross-sectional flow area. As used herein, a reduced cross-sectional flow area comprises a cross-sectional flow area that is less than the cross-sectional flow area through the linear plenum 132 that the slashface outlet 147 serves.
As discussed in more detail below, reducing the cross-sectional flow area of a slashface outlet 147 may be done for at least a couple of reasons. First, the cross-sectional flow area may be reduced to impinge the coolant exiting through these outlet locations. This, as one of ordinary skill in the art will appreciate, may result in the exiting coolant having a desired coolant impingement characteristic, such as a high coolant exit velocity, which would improve its cooling effect on a target surface. Given the location of the slashface outlets 147, it will be appreciated that the slashface outlets 147 may be configured to exhaust an impinged flow of coolant into a slashface cavity that is formed between adjacent installed rotor blades 100. That is, slashface outlets 147 may direct impinged coolant having a relatively high velocity against the slashface of the neighboring turbine blade 100. It will be appreciated that the slashface cavity and the slashfaces that define them are difficult regions of the platform 110 to cool, and that slashface outlets 147 configured in the manner may provide effective cooling to this area.
Second, the cross-sectional flow area of the slashface outlets 147 may be reduced because of the size of the linear plenum 132 and the need to evenly distribute or meter coolant throughout the interior of the platform 110. That is, the linear plenum 132 is designed to distribute coolant to the several cooling apertures 140 with little pressure loss. To accomplish this, the cross-sectional flow area of the linear plenum 132 typically is significantly larger than the cross-sectional flow area of the cooling apertures 140. It will be appreciated that if the slashface outlets 147 were not reduced in size compared to the size of the linear plenum 132, an inordinate amount of coolant would exit the platform 110 through the slashface outlets 147 and the supply of coolant available to the cooling apertures 140 would be likely insufficient. The slashface outlets 147, thus, also may be sized to have a cross-sectional flow area that corresponds to a desired metering characteristic. A “desired metering characteristic,” as used herein, refers to a flow area through the coolant passageway that corresponds or results in a desired distribution of coolant or expected distribution of coolant through the several coolant passageways and/or the outlets that are formed within the platform 110.
In some embodiments, a plug 149 may be used to reduce the cross-sectional flow area of the slashface outlets 147, as illustrated. The plug 149 may be formed such that, upon installation, it reduces the cross-sectional flow area through the cooling passage in which it resides. In this case, the plug 149 is configured to allow a desired level of flow through the passage and directs the remainder through alternative routes. As used herein, plugs of this type will be referred to “as partial plugs.” Accordingly, the partial plug 149 may be configured to be inserted into the slashface outlet 147 and reduce its cross-sectional flow area by blocking a portion of the flow area through the slashface outlet 147. The partial plug 149 may be designed so that it reduces the flow area to a desired or predetermined flow area. In one preferred embodiment, the partial plug 149 is formed with a central aperture such that it formed an approximate “doughnut” shape. The central aperture is formed to provide the desired flow area through the slashface outlet 147. As stated above, the predetermined cross-sectional flow area may relate to a desired coolant impingement characteristic and/or a desired metering characteristic, as one of ordinary skill in the art will appreciate. The partial plug 149 may be made of conventional materials and installed using conventional methods (i.e., welding, brazing, etc.). Once installed, an outer face of the partial plug 149 may reside flush in relation to the surface of the pressure side slashface 126 or suction side slashface 122. In some embodiments, it may be desirable to block flow through a slashface outlet 147 completely. In this case, a plug 149 that blocks the flow completely (which, as used herein, will be referred to as a “full plug”) may be used.
At the topside 113 of the platform 110, each of the cooling apertures 140 includes a topside outlet 145. The topside outlet 145 may be configured to have a predetermined cross-sectional flow area. In preferred embodiments, the predetermined cross-sectional flow area corresponds to at least one of a desired metering characteristic or a desired film cooling characteristic for each topside outlet 145. It will be appreciated by those of skill in the art that coolant released from the topside outlets 145 may be useful in that it may provide a layer that protects the platform 110 from the higher temperatures of the working fluid. This type of cooling is typically referred to as “film cooling” and the manner in which coolant is released into the hot gas path may affect the efficiency of this strategy. It will be appreciated that the topside outlets 145 may be configured to improve film cooling performance. In some embodiments, each of the topside outlets 145 of the cooling apertures 140 may include a plug 149. The plug 149 may be configured to create a predetermined or desirable cross-sectional flow area through the topside outlets 145.
In one preferred embodiment, as depicted in
The present invention further includes a novel method of forming interior cooling channels within the platform region of a rotor blade in a cost-effective and efficient manner. Referring to flow diagram 200 of
Once the linear plenum 132 is formed, at a step 204, the cooling apertures 140 may be formed similarly using a conventional line-of-sight machining or drilling process. Again, the machining process may be initiated from an accessible location (i.e., the topside 113 of the platform 110).
Separately, as necessary, partial or full plugs 149 may be fabricated at a step 206. As discussed above, the partial plugs may have several different configurations and function to reduce the flow area of an outlet. The full plug may be formed to completely block the flow area of the outlet. The plugs 149 may be fabricated from conventional materials. Finally, at a step 208, the plugs 149 may be installed in predetermined locations. This may be done using conventional methods, such as welding, brazing, or mechanical attachment.
In operation, it will be appreciated that the linear plenum 132 and the cooling apertures 140 may be configured to direct a supply of coolant from the interior cooling passage 116 to a plurality of outlets 145, 147 formed on the pressure side slashface 126, the suction side slashface, and/or platform topside 113. More particularly, the platform cooling arrangement of the present invention extracts a portion of the coolant from the cooling passages 116, uses the coolant to remove heat from the platform 110, and then expels the coolant into the slashface cavity and across the topside of the platform such that the coolant is used efficiently to cool the interior region of the platform and the slashface cavity formed with the neighboring blade (as well as reducing the ingestion of hot gas path fluids). In addition, the coolant is used to provide film cooling to the surface of the platform 110. The present invention provides a mechanism to actively cool the platform region of a combustion turbine rotor blade by efficiently forming a complex, effective cooling arrangement using a series of cost-effective, conventional techniques. As stated, this region is typically difficult to cool and, given the mechanical loads of the area, is a location that receives high distress, particularly as engine firing temperatures are further increased. Accordingly, this type of active platform cooling is a significant enabling technology as higher firing temperatures, increased output, and greater efficiency are sought. Further, it will be appreciated that the usage of post-cast processes in the formation of the platform cooling channels provides greater flexibility to redesign, reconfigure, or retrofit platform cooling arrangements. Finally, the present invention teaches the simplified/cost-effective formation of platform cooling channels that have complex geometries and effective platform coverage. Whereas before, complex geometries necessarily meant a costly investment casting process or the like, the present application teaches methods by which cooling channels having complex design may be formed through the combination of several uncomplicated machining and/or casting processes.
As one of ordinary skill in the art will appreciate, the many varying features and configurations described above in relation to the several exemplary embodiments may be further selectively applied to form the other possible embodiments of the present invention. For the sake of brevity and taking into account the abilities of one of ordinary skill in the art, all of the possible iterations is not provided or discussed in detail, though all combinations and possible embodiments embraced by the several claims below or otherwise are intended to be part of the instant application. In addition, from the above description of several exemplary embodiments of the invention, those skilled in the art will perceive improvements, changes, and modifications. Such improvements, changes, and modifications within the skill of the art are also intended to be covered by the appended claims. Further, it should be apparent that the foregoing relates only to the described embodiments of the present application and that numerous changes and modifications may be made herein without departing from the spirit and scope of the application as defined by the following claims and the equivalents thereof.
