Turbine blade platform cooling system

Aspects of the invention relate to a cooling system for a blade platform that can provide cooling to and reduce stress on the platform. Aspects of the invention relate to including one or more channels in the blade platform such that the channels extend from the trailing edge face of the platform toward, but terminate prior to, the leading edge face of the platform. The channels can be generally oval or oblong in conformation. Extending between the hollow shank and the channels can be a plurality of cooling holes. During engine operation, coolant is supplied to the shank of the blade assembly. Because the pressure at the shank is greater than the pressure at the trailing edge of the platform, coolant flow is induced through the cooling holes and into the channels. After flowing through the channels, the coolant can be dumped at the trailing edge.

FIELD OF THE INVENTION

The invention relates in general to turbine engines and, more particularly, to a system for cooling the platform of a turbine blade.

BACKGROUND OF THE INVENTION

Various components in the turbine section of a turbine engine, including the rotating turbine blades, are subjected to extremely high temperatures, which can impart thermal stresses on such components. With respect to turbine blades, thermal stress is a function of temperature gradients as well as the structural stiffness of the blade. Exposure to high temperatures and thermal stresses can result in the turbine blades having low fatigue lives, which commonly manifest as cracks in the blade platform.

SUMMARY OF THE INVENTION

Thus, one object according to aspects of the present invention is to improve the fatigue life of turbines blades by reducing temperature and stress in the platform. Another object according to aspects of the present invention is to configure a blade platform so as to facilitate coolant flow while also reducing the structural stiffness of the platform. One more object according to aspects of the invention is to use impingement cooling to substantially evenly reduce metal temperatures and thermal gradients in the blade platform. An additional object according to the invention is to employ the pressure differentials existing between various portions of the blade so as to induce cooling flow. Still another object according to aspects of the present invention is to provide a blade platform having an integrated cooling system so as to avoid the need for additional parts and/or subsequent assembly steps. A further object according to aspects of the present invention is to provide cooling to the leading and trailing edge sides of the platform. Objects according to aspects of the present invention also relate to a method for cooling a turbine blade platform.

Aspects of the invention relate to a turbine blade assembly. The blade assembly includes a platform, an airfoil portion, and a hollow shank portion. The platform has a leading edge face, a trailing edge face, a first side and a second side. The airfoil portion extends from the platform, and the hollow shank portion is disposed beneath the platform. A cooling channel extends through the platform, beginning in an area near the leading edge face and extending through the trailing edge face of the platform. The cooling channel extends substantially proximate to the first side of the platform. A plurality of cooling holes extend between the hollow shank portion and the cooling channel. The cooling holes are oriented substantially transverse to the cooling channel. The cooling holes can be substantially circular in cross-section.

The cooling channel can be substantially oval shaped or it can be substantially oblong shaped. In one embodiment, the cooling channel can have substantially rounded corners. Further, the cooling channel can include a substantially flat upper wall and a substantially flat lower wall. The upper and lower walls can be substantially parallel.

The blade assembly can further include a second cooling channel that extends through the platform, beginning in an area near the leading edge face and extending through the trailing edge face of the platform. The second channel can extend substantially proximate to the second side of the platform. A plurality of cooling holes can extend between the hollow shank portion and the second cooling channel. In addition, the cooling holes can be oriented substantially transverse to the second cooling channel.

Further, the blade assembly can include a branch channel in fluid communication with the cooling channel. The branch channel can include an edge segment and an exhaust segment. The edge segment can extend substantially proximately along at least a portion of the trailing edge face of the platform. In one embodiment, the exhaust segment can extend upward from the edge segment and through a top surface of the platform.

The cooling channel can be partially restricted by a cover, which can be one of a plate or a plug. In one embodiment, the blade assembly can include an additional channel. The cooling channel and the additional channel can be in fluid communication. The additional channel can disposed between the cooling channel and the first side of the platform. In another embodiment, the blade assembly can include one or more passages extending between the cooling channel and one of the sides of the platform. In still another embodiment, the blade assembly can include one or more passages extending between the cooling channel and the top surface of the platform.

Other aspects of the invention relate to a turbine blade assembly having a platform, an airfoil portion extending from the platform, and a hollow shank portion disposed beneath the platform. The platform has a leading edge face, a trailing edge face, a first side and a second side. A first cooling channel extends through the platform, beginning in an area near the leading edge face and extending through the trailing edge face of the platform. The first cooling channel extends substantially proximate to the first side of the platform. A second cooling channel extends through the platform, beginning in an area near the leading edge face and extending through the trailing edge face of the platform. The second cooling channel extends substantially proximate to the second side of the platform. Each of the cooling channels is defined by a substantially flat top surface and substantially flat bottom surface and two curved side walls connecting between the top and bottom surfaces. The top and bottom surfaces are substantially parallel to each other.

A first set of cooling holes extend between the hollow shank portion and the bottom surface of the first cooling channel so as to be oriented substantially transverse to the first cooling channel; a second set of cooling holes extend between the hollow shank portion and the bottom surface of the second cooling channel so as to be oriented substantially transverse to the second cooling channel.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Aspects of the present invention improve upon prior systems for cooling the platform of a turbine blade. Aspects of the present invention relate to a turbine blade assembly having a platform configured to improve fatigue life of the turbine blade by cooling the platform while also reducing thermal stresses on the platform.

Embodiments of the invention will be explained in the context of one possible turbine blade assembly, but the detailed description is intended only as exemplary. Embodiments of the invention are shown inFIGS. 1-9, but the present invention is not limited to the illustrated structure or application.

One example of a turbine blade assembly10is shown in FIG.1. The turbine blade assembly10can include an airfoil portion12extending radially away from a platform portion14. The platform portion can be generally planar, cylindrical or otherwise curved. The airfoil portion12can have a leading edge16and a trailing edge18. The leading edge16is the edge of the airfoil12that generally faces the oncoming combustion gases. Similarly, the platform portion14has a leading edge face20and a trailing edge face22. Again, the leading edge face20of the platform14generally faces the oncoming combustion gases. The blade assembly10further includes a root portion24that can engage with a groove formed in a disc on a turbine rotor (not shown) so as to secure the blade assembly10. Beneath the platform14but above the root24is a generally hollow cavity26, referred to as a shank.

As shown inFIG. 2, aspects of the invention relate to one or more cooling channels30provided in the platform14. The channels30can extend from the trailing edge face22of the platform14and into the platform14toward the leading edge face20of the platform14. However, the channels30do not extend through to the leading edge face20of the platform14, that is, the channels30terminate prior to the leading edge face20.

The channels30can have a variety of cross-sectional conformations such as oval or oblong. Preferably, the channels30have rounded corners so as to avoid stress concentrations. In one embodiment, each of the channels30can be defined by at least a substantially flat top surface and substantially flat bottom surface30a,30b. The top and bottom surfaces30a,30bcan be substantially parallel to each other. Each of the channels30can further be defined by two side walls30c,30dconnecting between the top and bottom surfaces30a,30b. Preferably, the side walls30c,30dare curved, such as being outwardly bowed, so that the channel30has a cross-section that is substantially oval shaped with flattened top and bottom sides. It should be noted that terms like top and bottom used in connection with the surfaces of the channel30, as well as other relative terms used throughout this disclosure, are merely for facilitating discussion and are not intended to limit the scope of the invention.

In one embodiment, the channels30can be slightly tapered such that the channels30are relatively narrow in width near the leading edge face20of the platform14compared to the width of the channels30near or at the trailing edge face22of the platform14. In other words, the channels30can gradually flare outward as the channel30approaches the trailing edge face22of the platform14. Such a configuration can help to reduce cross-flow or choke flow conditions at the exit of the channel30. The taper can occur along one or both of the top and bottom surfaces30a,30bor along one or both of the two side walls30c,30dor along any combination of thereof.

When two or more channels30are provided, the channels30can be substantially identical to each other in terms of size and shape. Alternatively, the two or more channels30can be different. Further, the channels30can have any of a variety of relationships with respect to each other. For instance, the two channels30can be substantially parallel to each other or they may not be substantially parallel.

Preferably, the channels extend substantially proximate to the sides of the platform40,42. Thus, the channels30can provide cooling to at least those portions of the platform that overhang the shank26. While the channels30can cool portions of the platform14, cooling the edge portions of the platform14, especially on the leading and trailing edge faces20,22, can be challenging. Thus, in one embodiment, aspects according to the present invention can be configured to provide cooling to the trailing edge face22of the platform14. For example, as shown inFIG. 5, the channel30can include one or more branch channels32. Preferably, the branch channel32is located near the trailing edge face22of the platform14not only to provide cooling to the trailing edge face22of the platform14, but also to reduce any pressure buildup near the exit of the channel30at the trailing edge face22. To that end, the branch channel32can act as a relief.

The branch channel32can include an edge segment33and an exhaust segment34. The edge segment33of the branch channel32can extend substantially proximate to at least a portion of the trailing edge face22of the platform14as shown in FIG.4. The edge segment33of the branch channel32can be located as close to the trailing edge face22as possible so as to provide cooling to the trailing edge face22of the platform14. From there, the exhaust segment34of the branch channel32can extend upwardly. In one embodiment, the exhaust segment34can extend upward at substantially 90 degrees relative to edge segment33; alternatively, the exhaust segment34can extend gradually upward from the edge segment33. These are merely two examples of the path that the exhaust passage can have. Regardless of the specific path of the branch channel32, the branch channel32exits through the top surface15of the platform14near the trailing edge side22.

The platform14can further include one or more cooling holes36extending between the at least one channel30to the shank portion26of the blade assembly10. The cooling holes36can be extend from the at least one channel30at almost any angle relative to the at least one channel30, but, it is preferred if the cooling holes36are oriented substantially transverse to the at least one channel30. The cooling holes36can be provided along the entire length of the at least one channel30. Ideally, the cooling holes36are arranged and situated so as to minimize cross flow of coolant out of the channel30. Therefore, in one embodiment, the cooling holes36can are provided along less than the entire length of the at least one channel30. For example, the cooling holes36may only provided along a portion of the channel30closer to the leading edge face20of the platform14, as shown inFIGS. 4-5.

The cooling holes30can be arranged according to a pattern or to no particular pattern. In addition, any number of cooling holes36can be provided. Further, the size, spacing and quantity of cooling holes can be optimized to direct coolant where necessary and to meet shank pressure requirements. Also, the size and spacing of the cooling holes36need not be substantially identical among all the cooling holes36provided. The cooling holes36can have any of a number of cross-sectional geometries. Preferably, the cooling holes36are substantially circular, but the cooling holes36can also be, for example, oval, oblong, triangular, polygonal, rectangular, or trapezoidal. In the case of two or more cooling channels30, the pattern, size, spacing, and geometry of the cooling holes36can but need not be identical from one channel30with respect to another channel30.

Another embodiment according to aspects of the invention is shown in FIG.6. Here, an additional channel can be provided that runs substantially adjacent to the channel30and the side42of the platform14. The additional channel106is connected to the channel30by passage104. A cover100can be provided placed over, inside or otherwise proximate the trailing edge side exit of the channel30. The cover100can be a plate or a plug including one or more passages102to allow at least a portion of the flow to exit the channel30. The cover100can be any device that meters, obstructs or restricts the flow out of the channel30. As a result, pressure builds in the channel30and a portion of the flow can be diverted into passage104, through the additional channel106, and ultimately exiting at the trailing edge side22of the platform14. Such a cooling system can reduce cross-flow effects in the channel30. The additional channel106can have any of a number of cross-sectional conformations.

Yet another embodiment, shown inFIG. 7, also relates to at least partially blocking the exit of the channel30at the trailing edge side22using a cover100having one or more openings102so as to build pressure in the channel30. In this case, one or more passages110are provided that extend between the channel30and the side wall42of the platform14. Again, the cover100restrict flow out of the channel30, thereby forcing at least a portion of the flow to exit through passages110. Preferably, the passages110exhaust out of one of the side walls40,42of the platform14in a low pressure area of the platform14so as to avoid the possibility of flow reversal through the passages110. In instances where more than one channel30is provided, one or both of the channels30can include the passages110according to aspects of the invention.

The passages110can be oriented at almost any angle relative to the channel30or the side walls40,42of the platform14. For example, the passages110can be oriented at substantially right angles to the side wall42. However, it is preferred if the passages110are not oriented at substantially right angles with respect to the side wall so as to gain the additional advantage of film cooling. In one instance, the passages are located at about 60 degrees relative to the channel30in the platform.

Instead of discharging through the side walls40,42of the platform14, openings124can be provided so that coolant discharges through other portions of the platform14. For example, as shown inFIG. 8, coolant can be discharged through the top surface15of the platform14. Thus, one or more passages124can be provided in the platform14that extend between at least one of the channels30and the top surface15of the platform14. Because of the flow restriction imposed by the cover120, a portion of the coolant flow will be diverted through the passages124.

The passages124can be oriented at almost any angle relative to the channel30or the top surface15of the platform14. For example, the passages124can be oriented at substantially right angles to the channel30or the top surface15of the platform14. However, it is preferred if the passages124are not oriented at substantially right angles with respect to the channel30or the top surface15of the platform14so as to gain the additional advantage of film cooling. In one instance, the passages124are located at about 60 degrees relative to the channel30or the top surface15of the platform14.

The addition of the one or more channels30and the cooling holes36to the platform14allows for impingement cooling of the platform14. The channels provide convection cooling to the platform14. Moreover, the channels30can create localized regions of reduced thickness so as to reduce the stiffness of the platform14, which in turn can reduce thermal stress. Because of the enhanced cooling and reduction in thermal stress, a turbine blade platform14according to aspects of the invention can have improved fatigue life.

Having described the individual components and features according to aspects of the present invention, one illustrative manner in which aspects of the invention can be provided in a turbine blade will now be described. The following description merely provides examples of processes that can be used to create a blade platform according to aspects of the invention.

The basic turbine blade assembly10can be a cast part. Therefore, in one embodiment, the one or more channels30can be cast into the platform14as well. Casting can be accomplished by creating a ceramic core that in placed in a wax tool. Once the wax mold is created, it can be dipped in ceramic to form a shell. The shell can be used to hold the platform channel core in place during casting. Support pins can be inserted through the platform, as needed, to stabilize the ends of the channel core.

Further, the channels30can be machined in the platform14by any of a number of processes. For example, the channels30can be machined by either electro-discharge machining (EDM) or electro-chemical machining (ECM). Alternatively, the channels30can be formed using conventional machining operations such as milling, drilling or waterjet cut. Regardless of the specific method used, material can be removed from the platform14beginning at the trailing edge face22and extending to the desired depth in the platform14.

Another method for making the channels30is to machine the channels30from the trailing edge face22of the platform14through the leading edge face20of the platform14. In a subsequent step, the opening at the leading edge face20can be substantially sealed by welding a plug inside of the opening or by securing a plate outside of the opening. While possible, such a method is not preferred because it increases the number of parts to the assembly, requires secondary assembly operations, and any welding may introduce undesirable distortions to the material or deposits to the channels30. Alternatively, each channel30can be machined from the adjacent side wall40,42of the platform14. A plate (not shown) can then be inserted and secured to the platform, such as by welding, so as to form one side of the channel30.

Like the channels30, the cooling holes36can be machined in the platform by any of the above described processes. For example, the cooling holes36can be added to the platform14using ECM or EDM operations.

The passages110(FIG. 7) and the passages124(FIG. 8) can be machined or cast into the platform14. Similarly, the cover100(FIGS. 6-7) and the cover120(FIG. 8) can be formed by machining or casting. The cover100,120can be attached to the platform14by any suitable method such as welded, brazed, adhered, fasteners, or interference fit.

In the embodiment shown inFIG. 6, the additional channel106can be added by any of the methods discussed above in connection with the channel30. Further, the passage104can be cast or drilled from the side wall of the platform14so as to connect channel30to channel106. In a subsequent step, the opening of the passage104at the side42of the platform14can be substantially sealed by welding a plug108inside of the opening or by securing a plate outside of the opening.

Having described the cooling system according to aspects of the invention and various manners in which such aspects can be formed in a turbine blade platform, an example of the operation of a turbine blade configured according to aspects of the invention will be described below. Naturally, aspects of the present invention can be employed with respect to myriad blade designs as one skilled in the art would appreciate.

The cooling system according to aspects of the invention takes advantage of pressure differentials acting on the blade assembly10. Specifically, the pressure in the shank portion26of the blade assembly10can be greater than the pressure at the trailing edge face22of the blade platform14.

The relatively high pressure in the shank portion26is as result of supplying a coolant to the shank portion26of the blade assembly10. Because turbine blades operate in the high temperature environment of the turbine, coolant must be supplied to the turbine blade assembly10as well as other components of the turbine section. In one cooling scheme, as shown inFIG. 9, involves supplying cooling air50to the rotor52. A portion54of the rotor cooling air50can be routed to the shank portion26of the blade assembly10. This is just one manner in which a coolant, such as air, can be supplied to the shank portion26of the blade assembly10. Regardless of the source, the supply of coolant to the hollow cavity of the shank26raises the pressure in the shank26that exceeds the low pressure zones experienced at the trailing edge face22of the blade platform14.

A cooling path according to aspects of the invention is shown inFIG. 3. Acoolant55enters the shank portion26of the blade assembly10area. The above described pressure differentials induce coolant flow through the cooling holes36and into the channel30. As it enters the channels30, the coolant will first impinge on the top surface30aof the channels30so as to provide impingement cooling. After that, the coolant can flow toward the low pressure zone at the trailing edge face22of the platform14. Coolant exiting the channel30joins the rest of the gas flowing through the turbine.

As noted earlier, one cooling system according to aspects of the invention can include one or more branch channels32(FIG. 5) off of the channel30so as to cool other portions of the platform14such as, for example, the trailing edge face22. In such case, a portion of the coolant flowing through channel30will be diverted into the branch channel32. The branch channel32can further serve as a relief for any pressure buildup in the channel30. Again, coolant can be dumped through the top15of the platform14near the trailing edge22. Still other cooling systems are possible such as those shown inFIGS. 6-8in which a plate100(FIGS. 6-7) or a plug (FIG. 8) can be used to restrict flow out of the channel30. The resulting pressure buildup can be used to direct the coolant through other additional channels provided in the platform, as discussed earlier.

Aspects of the present invention are especially suited for upstream turbine blades, such as the first or second row or stage of blades, because of the relatively large pressure differentials between the shank portion and the trailing edge face of the platform for those blades. However, aspects of the invention can be applied to any row of blades. Aspects of the present invention can be employed with respect to myriad turbine blade designs as one skilled in the art would appreciate. Thus, it will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention as defined in the following claims.