Airfoil having built-up surface with embedded cooling passage

The present invention relates to turbine engines, and, more particularly, to cooling passages provided in the sidewall of a component, such as the sidewall for an airfoil in a gas turbine engine.

In a turbomachine, such as a gas turbine engine, air is pressurized in a compressor section then mixed with fuel and burned in a combustor section to generate hot combustion gases. The hot combustion gases are expanded within a turbine section of the engine where energy is extracted to power the compressor section and to produce useful work, such as turning a generator to produce electricity. The hot combustion gases travel through a series of turbine stages within the turbine section. A turbine stage may include a row of stationary airfoils, i.e., vanes, followed by a row of rotating airfoils, i.e., turbine blades, where the turbine blades extract energy from the hot combustion gases for powering the compressor section and providing output power. Since the airfoils, i.e., vanes and turbine blades, are directly exposed to the hot combustion gases, they are typically provided with internal cooling channels that feed a cooling fluid, such as compressor bleed air, through the airfoil and through various film cooling holes around the surface thereof.

One type of airfoil extends from a radially inner platform at a root end to a radially outer portion of the airfoil, and includes opposite pressure and suction sidewalls extending axially from leading to trailing edges of the airfoil. The cooling channel extends inside the airfoil between the pressure and suction sidewalls.

After periods of use, it has been found that areas adjacent to locations near the airfoil leading edges where the airfoils intersect with the platform lacks adequate cooling. Therefore, these areas are susceptible to damage, i.e., due to overheating and oxidation, such that repair/replacement procedures are required.

In accordance with a first embodiment of the present invention, a method is provided of servicing an airfoil of a gas turbine engine. A surface is built up adjacent to a leading edge of the airfoil at an intersection between the airfoil and a platform associated with the airfoil by applying a high heat tolerant material to the surface. At least one cooling passage is formed at least partially within the built-up surface at the intersection between the airfoil and the platform. The at least one cooling passage is in fluid communication with a main cooling channel within the airfoil and has an outlet at the platform for providing cooling fluid directly from the main cooling channel to the platform.

In accordance with a second embodiment of the invention, a component is provided in a gas turbine engine. The component includes an airfoil extending radially outwardly from a platform associated with the airfoil. The airfoil includes a pressure sidewall and a suction sidewall opposed from the pressure sidewall. The pressure and suction sidewalls converge at a first location defined at a leading edge of the airfoil and at a second location defined at a trailing edge of the airfoil opposed from the leading edge. The component includes a built-up surface adjacent to the leading edge at an intersection between the pressure sidewall and the platform, and at least one cooling passage at least partially within the built-up surface at the intersection between the pressure sidewall and the platform. The at least one cooling passage is in fluid communication with a main cooling channel within the airfoil and has an outlet at the platform for providing cooling fluid directly from the main cooling channel to the platform.

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

FIG. 1 is a perspective view of a portion of a turbine section of an engine including a plurality of airfoils according to an embodiment of the invention;

FIG. 2 is an enlarged perspective view illustrating a portion of one of the airfoils shown in FIG. 1 ;

FIG. 3 is a cross sectional view of the portion of the airfoil illustrated in FIG. 2 ;

FIG. 4 is an enlarged perspective view illustrating a portion of an airfoil according to another embodiment of the invention;

FIG. 5 is a cross sectional view of a portion of an airfoil according to yet another embodiment of the invention; and

FIG. 6 is a flow chart illustrating steps for servicing an airfoil according to yet another embodiment of the invention.

In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

Referring to FIG. 1 , first and second exemplary airfoils 10 A, 10 B, i.e., stationary vanes, are shown. The airfoils 10 A, 10 B are adjoined in the circumferential direction together and form part of a row of airfoils 12 that extends circumferentially about a turbine rotor (not shown) in a turbine engine. Hot combustion gases H G created in a conventional combustor assembly (not shown) are discharged into a turbine section 13 in which the airfoils 10 A, 10 B are employed. Rows of the stationary vanes, such as the row of airfoils 12 , direct the hot combustion gases H G toward rows of rotating turbine blades (not shown), which blades are caused to rotate and cause corresponding rotation of the turbine rotor.

Each of the airfoils 10 A, 10 B extends radially outwardly from and is integrally joined at a root end 14 A, 14 B thereof to a corresponding radially inner shroud or platform 16 A, 16 B. The platforms 16 A, 16 B are suspended radially outwardly from a casing structure (not shown). While pairs of the airfoils 10 A, 10 B are illustrated herein as sharing a platform 16 A, 16 B, it is noted that additional or fewer airfoils 10 A, 10 B may be associated with each platform 16 A, 16 B. Each of the airfoils 10 A, 10 B is integrally joined at a tip end 18 A, 18 B thereof to a radially outer shroud 19 , which outer shroud 19 may include one or more pieces or sections 19 A, 19 B that each may be associated with one or more of the airfoils 10 A, 10 B.

As shown in FIG. 1 , each airfoil 10 A, 10 B includes a generally concave pressure sidewall 20 A, 20 B and an opposed, generally convex suction sidewall 22 A, 22 B. The pressure and suction sidewalls 20 A, 20 B and 22 A, 22 B of each airfoil 10 A, 10 B converge at a first location defined at a leading edge 24 A, 24 B and at a second location defined at a trailing edge 26 A (the trailing edge of the second airfoil 10 B is not shown) opposed from the leading edge 24 A, 24 B of the respective airfoil 10 A, 10 B. The pressure and suction sidewalls 20 A, 20 B and 22 A, 22 B extend in a chordal direction C, i.e., in a generally axial direction of the engine, between the opposite leading and trailing edges 24 A, 24 B and 26 A of the airfoils 10 A, 10 B. The leading and trailing edges 24 A, 24 B and 26 A extend radially in span from the root ends 14 A, 14 B to the tip ends 18 A, 18 B of the airfoils 10 A, 10 B.

The airfoils 10 A, 10 B are suspended in the circumferential row 12 about the turbine rotor and are spaced circumferentially or laterally apart from one another to define flow passages 30 therebetween for channeling the combustion gases H G through the turbine section 13 during engine operation. Each flow passage 30 is defined and bounded by the pressure sidewall of one airfoil, e.g., the pressure sidewall 20 A of the first airfoil 10 A, and the suction sidewall of an adjacent airfoil, e.g., the suction sidewall 22 B of the second airfoil 10 B. The flow passages 30 are also defined radially between the inner platforms, e.g., the platforms 16 A and 16 B, and the outer shroud 19 .

The hot combustion gases H G flow through the corresponding flow passages 30 during operation of the engine and are diverged by the individual airfoils 10 A, 10 B. For example, the combustion gases H G are diverged in the circumferential direction at the leading edges 24 A, 24 B of the first and second airfoils 10 A, 10 B and form corresponding boundary layers along the opposite pressure and suction sidewalls 20 A, 20 B and 22 A, 22 B of the airfoils 10 A, 10 B. The combustion gases H G also form boundary layers along the individual platforms 16 A, 16 B, as the combustion gases H G are diverged at the airfoil leading edges 24 A, 24 B at their intersections with the platforms 16 A, 16 B, i.e. at the root ends 14 A, 14 B. The diverged combustion gases H G flow along the platforms 16 A, 16 B, which may result in a pair of counter-rotating horseshoe vortices 36 a , 36 b (see FIG. 1 ) that flow axially downstream through the flow passages 30 along the opposite pressure and suction sidewalls 20 A, 20 B and 22 A, 22 B of each airfoil 10 A, 10 B. These horseshoe vortices 36 a , 36 b create turbulence in the boundary layers and migrate radially outwardly toward mid-span regions of the airfoils 10 A, 10 B, which creates pressure losses and reduces turbine efficiency. Additional details in connection with the horseshoe vortices 36 a , 36 b can be found in U.S. Pat. No. 7,134,842, the entire disclosure of which is hereby incorporated by reference herein.

Referring additionally to FIG. 3 , each airfoil 10 A, 10 B is hollow and includes a main internal cooling channel 38 A, 38 B, which is located radially outwardly from the respective platforms 16 A, 16 B between the opposite pressure and suction sidewalls 20 A, 20 B and 22 A, 22 B. The airfoils 10 A, 10 B include cooling air inlets 40 A, 40 B (see FIG. 1 ) extending through their tip ends 18 A, 18 B and through the outer shroud 19 . Cooling air, e.g., compressor bleed air, enters the cooling channels 38 A, 38 B of the airfoils 10 A, 10 B via the cooling air inlets 40 A, 40 B.

Portions of the cooling air are discharged from each airfoil 10 A, 10 B through several rows of film cooling holes 42 A, 42 B (see FIG. 1 ) located in desired areas on the pressure and suction sidewalls 20 A, 20 B and 22 A, 22 B of the respective airfoils 10 A, 10 B. The film cooling holes 42 A, 42 B may be concentrated near the leading edges 24 A, 24 B of the airfoils 10 A, 10 B, although each airfoil 10 A, 10 B may also include one or more rows of trailing edge cooling holes (not shown) proximate to the trailing edges 26 A thereof, and/or one or more rows of cooling holes (not shown) in the pressure and/or suction sidewalls 20 A, 20 B and 22 A, 22 B between the leading and trailing edges 24 A, 24 B and 26 A.

Referring to FIGS. 2 and 3 , a portion of the cooling air in the main cooling channel 38 A of the first airfoil 10 A is discharged directly from the main cooling channel 38 A of the first airfoil 10 A through a plurality of primary cooling passages 46 , illustrated herein as first through fourth primary cooling passages 46 a - 46 d , proximate to the leading edge 24 A of the airfoil 10 A. The primary cooling passages 46 a - 46 d are formed in the pressure sidewall 20 A of the first airfoil 10 A and through a built-up surface 54 , which built-up surface 54 will be discussed in detail herein. The primary cooling passages 46 a - 46 d discharge cooling air directly from the main cooling channel 38 A to the platform 16 A to provide cooling to the platform 16 A. It is noted that additional or fewer primary cooling passages 46 a - 46 d may be provided and that only a single primary cooling passage 46 may be utilized to practice this aspect of the invention. It is also noted that the second airfoil 10 B may also include one or more primary cooling passages (not shown) formed therein, if desired.

As shown in FIG. 3 , the primary cooling passages 46 a - 46 d extend radially inwardly in the circumferential direction toward a gap G between the platforms 16 A and 16 B from the main cooling channel 38 A through the built-up surface 54 formed on the first airfoil 10 A. The built-up surface 54 is formed adjacent to the airfoil leading edge 24 A at an intersection 56 between the airfoil pressure sidewall 20 A and the platform 16 A, which intersection 56 is defined at the root end 14 A of the airfoil 10 A, see FIG. 2 . Additional details in connection with the built-up surface 54 will be discussed below.

The primary cooling passages 46 a - 46 d each include an inlet 50 a - 50 d in fluid communication with the main cooling channel 38 A in the first airfoil 10 A and an outlet 52 a - 52 d at the platform 16 A proximate to the gap G. It is noted that the outlets 52 a - 52 d may be formed in the built-up surface 54 adjacent to a location where the built-up surface 54 comes together with a radially outer surface 55 A of the platform 16 A, as shown in FIGS. 2 and 3 . The inlets 50 a - 50 d of the primary cooling passages 46 a - 46 d are each located adjacent to the airfoil leading edge 24 A, and the cooling passages 46 a - 46 d fan out such that the outlets 52 a - 52 d thereof provide cooling fluid to spaced apart locations at the platform 16 A.

It is noted that the outlet 52 a - 52 d of at least one of the primary cooling passages 46 a - 46 d may be angled away from the direction of flow of hot combustion gases H G passing through the gas turbine engine during operation thereof, so as to avoid or reduce hot combustion gas H G ingestion into the cooling passage(s) 46 a - 46 d . In the embodiment shown, the outlet 52 d of the fourth primary cooling passage 46 d is angled away from the flow of hot combustion gases H G .

As shown in FIG. 2 , the built-up surface 54 may comprise, for example, a high heat tolerant weld material that is applied to form a non-axisymmetric contour on the platform 16 A, although other suitable materials may be used. The built-up surface 54 may comprise a bump or bulge that extends radially outwardly from the radially outer surface 55 A of the platform 16 A. The built-up surface 54 increases the area through which the cooling passages 46 a - 46 d may be formed and allows the cooling passages 46 a - 46 d to extend radially inwardly so as to release cooling fluid in a direction toward the platform 16 A, which may provide film cooling on the platform 16 A.

The built-up surface 54 in the embodiment shown comprises a radially outermost surface 70 on the pressure side adjacent to the airfoil leading edge 24 A. The built-up surface 54 decreases in height in each of forward, aft, and circumferential directions away from the radially outermost surface 70 , as most clearly shown in FIG. 2 . The built-up surface 54 extends in the forward direction to a location forward of the leading edge 24 A of the airfoil 10 A, at which location the built-up surface 54 comes together with the surface 55 A of the platform 16 A, such as a location adjacent to a leading edge 72 A of the platform 16 A, see FIGS. 1 and 2 . The built-up surface 54 extends in the aft direction to a location between the airfoil leading and trailing edges 24 A, 26 A, at which location the built-up surface 54 comes together with the surface 55 A of the platform 16 A. Further, the built-up surface 54 extends in the circumferential direction toward the gap G to a location between the pressure sidewall 20 A of the airfoil 10 A and the gap G, at which location the built-up surface 54 comes together with the surface 55 A of the platform 16 A.

The majority of the built-up surface 54 in the embodiment shown is located adjacent to the leading edge 24 A of the airfoil 10 A and along the pressure sidewall 20 A thereof at the intersection 56 between the pressure sidewall 20 A of the first airfoil 10 A and the platform 16 A. However, a portion of the built-up surface 54 in the embodiment shown extends around the leading edge 24 A of the airfoil 10 A to the suction side 22 A, at which location the built-up surface 54 decreases in height and comes together with the surface 55 A of the platform 16 A. It is noted that the particular configuration of the built-up surface 54 may depend upon the engine in which the airfoils 10 A, 10 B are located and the desired effects on the flow of the hot combustion gases H G .

The built-up surface 54 is preferably configured and located so as to reduce the strength of the horseshoe vortices 36 a , 36 b and thereby improve the efficiency of the engine. Additional details in connection with the configuration and location of built-up surfaces (without cooling passages formed therein) and the effects thereof on the flow of hot combustion gases H G and the horseshoe vortices 36 a , 36 b can be found in U.S. Pat. No. 7,134,842.

The cooling fluid from the cooling passages 46 a - 46 d provides direct convection cooling to the built-up material 54 and the platform 16 A while passing through the cooling passages 46 a - 46 d , and also provides film cooling to the outer surface 55 A of the platform 16 A and the built-up surface 54 upon exiting the cooling passage outlets 52 a - 52 d.

As noted above, the cooling passages 46 a - 46 d provide cooling fluid directly from the main cooling channel 38 A to the platform 16 A, i.e., without requiring the cooling fluid to traverse other cooling fluid circuits or passageways associated with or within the airfoil 10 A or the platform 16 A before being delivered to the platform 16 A. Thus, an amount of cooling fluid provided through the cooling passages 46 a - 46 d to the platform 16 A is believed to be increased over prior art airfoils in which cooling fluid delivered to the platform traverses such other cooling circuits or passageways. The cooling passages 46 a - 46 d may be provided in addition to or in place of an existing cooling channel structure such as is described, for example, in U.S. Pat. No. 5,344,283, the entire disclosure of which is hereby incorporated by reference herein.

The built-up surface 54 and cooling passages 46 according to aspects of the invention are believed to provide advantages over the prior art by supplying cooling fluid directly from the main cooling channel 38 A to the radially outer surface 55 A of the platform 16 A at the location adjacent to the leading edge 24 A of the airfoil 10 A. Since the cooling fluid supplied to the platform 16 A comes directly from the main cooling channel 38 A, it is believed that a greater flow of cooling fluid at a lower temperature may be provided than is provided in platform cooling systems that distribute the cooling fluid through multiple locations within the platform. Thus, adequate cooling of the radially outer surface 55 A of the platform 16 A adjacent to the leading edge 24 A of the airfoil 10 A is believed to be provided, such that a lifespan of the airfoil/platform assembly according to the invention is believed to be increased.

The aspects of the invention described herein may be performed during a repair process to repair/replace damaged airfoil/platform assemblies, such as the airfoil illustrated in U.S. Pat. No. 5,344,283, in situations where platforms 16 A adjacent to the leading edge 24 A of the airfoil 10 A have become damaged/destroyed during engine operation due to overheating and oxidation. Alternatively, the airfoil/platform assembly described herein may be provided as a new component in an engine.

It is noted that the platform 16 A associated with the first airfoil 10 A is slightly offset from the platform 16 B associated with the second airfoil 10 B in the radial direction, as shown in FIG. 3 . This may result from tolerance issues encountered while assembling the row or airfoils 12 . However, since the platform 16 A illustrated in FIG. 3 extends radially outwardly further than the platform 16 B, cooling fluid flowing out of the cooling passages 46 a - 46 d may flow over the radially outer surface 55 A of the platform 16 A associated with the first airfoil 10 A to a radially outer surface 55 B of the platform 16 B associated with the second airfoil 10 B to cool the platform 16 B. It is noted that the platform 16 B associated with the second airfoil 10 B may extend radially outwardly slightly more than the platform 16 A associated with the first airfoil 10 A. In this case, the cooling fluid flowing out of the cooling passages 46 a - 46 d may flow over the radially outer surface 55 A of the platform 16 A associated with the first airfoil 10 A and contact the edge of the platform 16 B associated with the second airfoil 10 B, wherein the cooling fluid could flow radially inwardly into the gap G.

Referring now to FIG. 4 , an airfoil 10 ′ according to another embodiment is shown, where structure similar to that described with reference to FIGS. 1-3 includes the same reference number followed by a prime (′) symbol. Each of a plurality of secondary cooling passages 60 according to this embodiment includes an inlet 62 in fluid communication with a primary cooling passage 46 ′, which primary cooling passage 46 ′ communicates with a main cooling channel (not shown in this embodiment) of the airfoil 10 A′. That is, the secondary cooling passages 60 according to this embodiment are branched off from the primary cooling passage 46 ′ and fan out to provide cooling fluid from outlets 64 thereof to spaced locations of a platform 16 A′. It is noted that the outlet 64 of at least one of the cooling passages 46 ′, 60 according to this embodiment may be angled away from a direction of flow of hot combustion gases passing through the gas turbine engine during operation thereof, so as to avoid or reduce hot combustion gas ingestion into the cooling passage(s) 46 ′, 60 .

Referring now to FIG. 5 , a first airfoil 10 A″ according to yet another embodiment is illustrated, where structure similar to that described above with reference to FIGS. 1-3 includes the same reference number followed by a double prime (″) symbol. In this embodiment, a built-up surface 54 ″ located at an intersection 56 ″ between a pressure sidewall 20 A″ of the first airfoil 10 A″ and a platform 16 A″ extends in the circumferential direction all the way to a gap G″ formed between the platform 16 A″ and an adjacent platform 16 B″. Thus, in this embodiment, cooling fluid delivered by one or more primary cooling passages 46 ″ (and, optionally, one or more secondary cooling passages (not shown in this embodiment)) formed at least partially through the built-up surface 54 ″ can be delivered all the way to the circumferential edge of the platform 16 A″ via an outlet 52 ″ that opens into the gap G″ between platform 16 A″ and the adjacent platform 16 B″. This may be desirable in some engines, as the portion of the platform 16 A″ proximate to the gap G″ in some engines has been found to be prone to damage caused by overheating and oxidation.

Referring now to FIG. 6 , a method 100 of servicing an airfoil, such as the airfoil 10 A described above with reference to FIGS. 1-3 , will be described.

At step 102 , a surface of the airfoil 10 A is built up adjacent to a leading edge 24 A of the airfoil 10 A at an intersection 56 between a pressure sidewall 20 A of the airfoil 10 A and a platform 16 A associated with the airfoil 10 A. The surface is built up by applying a high heat tolerant material, such as a welding material, to the surface. The material may be applied, for example, using laser welding. The built-up surface 54 may be, for example, as described above with reference to FIGS. 1-3 or as described above with reference to FIG. 5 .

At step 104 , one or more primary cooling passages 46 are formed at least partially within the built-up surface 54 at the intersection 56 between the airfoil pressure sidewall 20 A and the platform 16 A. The primary cooling passages 46 may be formed, for example, by drilling a corresponding bore through the built-up surface 54 . The primary cooling passages 46 are in direct fluid communication with a main cooling channel 38 A within the airfoil 10 A and each has an outlet 52 at the platform 16 A for providing cooling fluid directly from the main cooling channel 38 A to the platform 16 A. As noted above, the main cooling channel 38 A may be located radially outwardly from the platform 16 A between the airfoil leading edge 24 A and a trailing edge 26 A of the airfoil 10 A. The primary cooling passages 46 may extend radially inwardly from the main cooling channel 38 A and in the circumferential direction toward a gap G between the platform 16 A and an adjacent platform 16 B through the built-up surface 54 to the outlet 52 at the platform 16 A.

At step 106 , in an optional step, at least one secondary cooling passage 60 is formed at least partially within the built-up surface 54 . The secondary cooling passage(s) 60 has an inlet 62 in communication with the primary cooling passage 46 , as described above with respect to FIG. 4 . The secondary cooling passage(s) 60 has an outlet 64 at the platform 16 A spaced from the outlet 52 of the primary cooling channel 46 for providing cooling fluid from the main cooling channel 38 A to the platform 16 A.

While the cooling passages 46 , 46 ′, 60 and the built-up surface 54 described herein have been described as being formed in stationary vanes, e.g., the airfoils 10 A, 10 B, these features could also be applied to rotating turbine blades without departing from the spirit and scope of the invention.

Further, as noted above, the cooling passages 46 , 46 ′, 60 and the built-up surface 54 described herein may be formed as part of a repair/replacement process or may be implemented in new airfoil designs. Further, the cooling passages 46 , 46 ′, 60 and the built-up surface 54 may be formed by other processes than the one described herein. For example, the built-up surface 54 may be applied as a substantially even layer over all or part of the platform 16 A and may be machined to form the contoured bump or bulge described herein.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.