CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to United States Provisional Patent Application No. 61/916,980, filed December 17, 2013.

BACKGROUND OF THE INVENTION

[0002] In pursuit of higher engine efficiencies, higher turbine inlet temperatures have been relied upon to boost overall engine performance. This can result in gas path temperatures that may exceed melting points of turbine component materials. To address this issue, dedicated cooling air is extracted from a compressor section and is used to cool the gas path components in the turbine, such as rotating blades and stator vanes for example.

[0003] One method of cooling turbine airfoils utilizes internal cooling passages. Typically, film cooling holes and significant volumes of cooling air are required to provide the needed amount of cooling. One area that is difficult to effectively cool is a tip of the airfoil. Tip shelves and squealer pockets have been incorporated into the tip of the blade to improve cooling but have not always been capable of effectively cooling a leading edge portion of the tip.

SUMMARY OF THE INVENTION

[0004] In a featured embodiment, a gas turbine engine component comprises an airfoil having a leading edge, a trailing edge, and pressure and suction side walls extending from the leading edge to the trailing edge. The airfoil extends from a base to a tip. A shelf is formed in the tip, and extends from the pressure side wall, around the leading edge, to the suction side wall.

[0005] In another embodiment according to the previous embodiment, the tip defines a distal end surface of the airfoil. The shelf defines a bottom surface that is spaced radially inwardly of the distal end surface, and includes a shelf wall surface extending from the distal end surface to the bottom surface.

[0006] In another embodiment according to any of the previous embodiments, at least one cooling hole or slot is formed within one of the bottom surface and shelf wall. [0007] In another embodiment according to any of the previous embodiments, the airfoil is defined by a length extending in a direction from the leading edge to the trailing edge. A distance between the shelf wall and an outer surface of the pressure side wall varies along the length of the airfoil.

[0008] In another embodiment according to any of the previous embodiments, the shelf wall is defined by a first radius on the pressure side wall and by a second radius on the suction side wall that is different than the first radius.

[0009] In another embodiment according to any of the previous embodiments, the first radius is greater than the second radius.

[0010] In another embodiment according to any of the previous embodiments, the shelf wall is defined by a third radius at the leading edge that is different from at least one of the first radius and second radius.

[0011] In another embodiment according to any of the previous embodiments, the first radius is greater than the second radius. The third radius is less than the second radius.

[0012] In another embodiment according to any of the previous embodiments, the bottom surface extends uninterrupted around the leading edge from the pressure side wall to the suction side wall.

[0013] In another embodiment according to any of the previous embodiments, the shelf extends a greater distance along the pressure side wall than along the suction side wall.

[0014] In another embodiment according to any of the previous embodiments, at least one internal cooling passage is formed within the airfoil and at least one cooling hole formed within the shelf that is in fluid communication with the at least one internal cooling passage.

[0015] In another embodiment according to any of the previous embodiments, the at least one cooling hole comprises a plurality of cooling holes formed in the shelf. The cooling holes are located at the leading edge, pressure side wall, and suction side wall.

[0016] In another embodiment according to any of the previous embodiments, the tip includes a squealer pocket.

[0017] In another featured embodiment, a gas turbine engine comprises a compressor section, a combustor section downstream of the compressor section, and a turbine section downstream of the combustor section. The turbine section includes at least one airfoil having a leading edge, a trailing edge, and pressure and suction side walls extending from the leading edge to the trailing edge. The airfoil extends from a base to a tip. A shelf formed in the tip, and extends from the pressure side wall, around the leading edge, to the suction side wall.

[0018] In another embodiment according to the previous embodiment, the tip defines a distal end surface of the airfoil. The shelf defines a bottom surface that is spaced radially inwardly of the distal end surface, and includes a shelf wall surface extending from the distal end surface to the bottom surface.

[0019] In another embodiment according to any of the previous embodiments, a plurality of cooling holes or slots are formed within the bottom surface and/or shelf wall. The holes or slots are located at the pressure side wall, leading edge, and suction side wall.

[0020] In another embodiment according to any of the previous embodiments, the airfoil is defined by a length extending in a direction from the leading edge to the trailing edge. A distance between the shelf wall and an outer surface of the pressure side wall varies along the length of the airfoil.

[0021] In another embodiment according to any of the previous embodiments, the shelf wall is defined by a first radius on the pressure side wall and by a second radius on the suction side wall that is different than the first radius.

[0022] In another embodiment according to any of the previous embodiments, the first radius is greater than the second radius. The shelf wall is defined by a third radius at the leading edge that is less than the second radius.

[0023] In another embodiment according to any of the previous embodiments, the shelf extends a greater distance along the pressure side wall than along the suction side wall.

[0024] The foregoing features and elements may be combined in any combination without exclusivity, unless expressly indicated otherwise.

[0025] These and other features may be best understood from the following drawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic representation of one example of a gas turbine [0027] Figure 2 is a side perspective view of a turbine blade. [0028] Figure 3 is a schematic cross-sectional view of a root section of the blade of Figure 2.

[0029] Figure 4 is a perspective view of a tip shelf in the tip of the airfoil section of the blade of Figure 2.

[0030] Figure 5 shows an enlarged top view of the tip of the airfoil section showing the shelf extending from a pressure side, around a leading edge, and to a suction side of the airfoil.

[0031] Figure 6 is a leading edge side view of Figure 5.

[0032] Figure 7 is a pressure side view of Figure 5.

[0033] Figure 8 shows an example of cooling holes formed in the shelf.

DETAILED DESCRIPTION

[0034] Figure 1 schematically illustrates a gas turbine engine 20. The gas turbine engine 20 is disclosed herein as a two-spool turbofan that generally incorporates a fan section 22, a compressor section 24, a combustor section 26 and a turbine section 28. Alternative engines might include an augmentor section (not shown) among other systems or features. The fan section 22 drives air along a bypass flow path B in a bypass duct defined within a nacelle 15, while the compressor section 24 drives air along a core flow path C for compression and communication into the combustor section 26 then expansion through the turbine section 28. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three- spool architectures.

[0035] The exemplary engine 20 generally includes a low speed spool 30 and a high speed spool 32 mounted for rotation about an engine central longitudinal axis A relative to an engine static structure 36 via several bearing systems 38. It should be understood that various bearing systems 38 at various locations may alternatively or additionally be provided, and the location of bearing systems 38 may be varied as appropriate to the application.

[0036] The low speed spool 30 generally includes an inner shaft 40 that interconnects a fan 42, a first (or low) pressure compressor 44 and a first (or low) pressure turbine 46. The inner shaft 40 is connected to the fan 42 through a speed change mechanism, which in exemplary gas turbine engine 20 is illustrated as a geared architecture 48 to drive the fan 42 at a lower speed than the low speed spool 30. The high speed spool 32 includes an outer shaft 50 that interconnects a second (or high) pressure compressor 52 and a second (or high) pressure turbine 54. A combustor 56 is arranged in exemplary gas turbine 20 between the high pressure compressor 52 and the high pressure turbine 54. A mid-turbine frame 57 of the engine static structure 36 is arranged generally between the high pressure turbine 54 and the low pressure turbine 46. The mid-turbine frame 57 further supports bearing systems 38 in the turbine section 28. The inner shaft 40 and the outer shaft 50 are concentric and rotate via bearing systems 38 about the engine central longitudinal axis A which is collinear with their longitudinal axes.

[0037] The core airflow is compressed by the low pressure compressor 44 then the high pressure compressor 52, mixed and burned with fuel in the combustor 56, then expanded over the high pressure turbine 54 and low pressure turbine 46. The mid-turbine frame 57 includes airfoils 59 which are in the core airflow path C. The turbines 46, 54 rotationally drive the respective low speed spool 30 and high speed spool 32 in response to the expansion. It will be appreciated that each of the positions of the fan section 22, compressor section 24, combustor section 26, turbine section 28, and fan drive gear system 48 may be varied. For example, gear system 48 may be located aft of combustor section 26 or even aft of turbine section 28, and fan section 22 may be positioned forward or aft of the location of gear system 48.

[0038] The engine 20 in one example is a high-bypass geared aircraft engine. In a further example, the engine 20 bypass ratio is greater than about six (6), with an example embodiment being greater than about ten (10), the geared architecture 48 is an epicyclic gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3 and the low pressure turbine 46 has a pressure ratio that is greater than about five. In one disclosed embodiment, the engine 20 bypass ratio is greater than about ten

(10:1), the fan diameter is significantly larger than that of the low pressure compressor 44, and the low pressure turbine 46 has a pressure ratio that is greater than about five 5:1. Low pressure turbine 46 pressure ratio is pressure measured prior to inlet of low pressure turbine

46 as related to the pressure at the outlet of the low pressure turbine 46 prior to an exhaust nozzle. The geared architecture 48 may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about 2.3:1. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans.

[0039] A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section 22 of the engine 20 is designed for a particular flight condition - typically cruise at about 0.8 Mach and about 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, with the engine at its best fuel consumption - also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')" - is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point. "Low fan pressure ratio" is the pressure ratio across the fan blade alone, without a Fan Exit Guide Vane ("FEGV") system. The low fan pressure ratio as disclosed herein according to one non- limiting embodiment is less than about 1.45. "Low corrected fan tip speed" is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram °R) / (518.7 °R)] ^0'5 . The "Low corrected fan tip speed" as disclosed herein according to one non- limiting embodiment is less than about 1150 ft / second.

[0040] Airfoils located downstream of combustor section 26, such as stator vanes and rotor blades in the turbine section 28, for example, operate in a high-temperature environment. Airfoils that are exposed to high temperatures typically include cooling circuits with internal cooling channels that direct a flow of cooling air through the airfoil to remove heat and prolong the useful life of the airfoil. Figure 2 is a side view of a turbine rotor blade 60 having a root section 62, a platform 64, and an airfoil section 66. Root section 62 is connected to a rotor in the turbine section 28 (Figure 1) as known. The airfoil section 66 includes a leading edge 68, a trailing edge 70, a suction side wall 72, and a pressure side wall 74. The airfoil section 66 extends from a base at the platform 64 to a tip 76, and includes a plurality of surface cooling holes, such as film cooling holes 78, and a plurality of trailing edge cooling slots 80.

[0041] The platform 64 connects one end of airfoil section 66 to root section 62. The leading edge 68, trailing edge 70, suction side wall 72, and pressure side wall 74 extend outwardly away from the platform 64. The tip 76 closes off an opposite end of the airfoil section 66 from the platform 64. Suction side wall 72 and pressure side wall 74 connect leading edge 68 and trailing edge 70. Film cooling holes 78 are arranged over a surface of the airfoil section 66 to provide a layer of cool air proximate the surface of airfoil section 66 for protection from high- temperature combustion gases. Trailing edge cooling slots 80 are arranged along trailing edge 70 to provide an exit for air circulating within airfoil section 66.

[0042] Figure 3 is a schematic section view of the root section 62 of the rotor blade 60 of Figure 2. The rotor blade 60 includes one or more internal cooling channels. In the example shown, there is at least a first cooling channel 82 near the leading edge 68, and a second cooling channel 84 positioned aft of the first cooling channel 82. The cooling channels 82, 84 direct cooling flow F radially outwardly toward the tip 76 of the blade 60. The cooling channels 82, 84 deliver cooling flow to the film cooling holes 78 and the cooling slots 80.

[0043] As shown in Figure 4, a tip shelf 90 is formed in the tip 76. The shelf 90 extends from the pressure side wall 74, around the leading edge 68, to the suction side wall 72. In other words, the tip shelf 90 comprises a wrap-around shelf that wraps around the leading edge 68 in an uninterrupted fashion from the pressure side wall 74 to the suction side wall 72.

[0044] The tip 76 defines a distal end surface 92 of the airfoil 66 and the shelf 90 defines a bottom surface 94 that is spaced radially inwardly of the distal end surface 92 in a direction toward the axis A. A shelf wall surface 96 extends from the distal end surface 92 to the bottom surface 94. In the example shown, the shelf wall surface 96 cooperates with the distal end surface 92 and bottom surface 94 to form an L-shape; however, other profiles could also be utilized. For example, the entire shelf may be provided as a continuous radiussed surface, such as a quarter-pipe shape.

[0045] As shown in Figure 8, one or more cooling slots and/or holes 98 are formed within the bottom surface 94. The cooling slots or holes 98 could also be formed in the wall surface 96 or a corner/radius between the wall surface 96 and the bottom surface 94 and/or end surface 92. The cooling slots or holes 98 are in fluid communication with the internal cooling channels 82, 84 (Figure 3). In one example, the cooling slots or holes 98 are located at the leading edge 68, and at the pressure 74 and suction 72 side walls.

[0046] The airfoil 66 is defined by a length extending in a direction from the leading edge 68 to the trailing edge 70. In one example, a distance between the shelf wall surface 96 and an outer surface 100 of the pressure side wall 74 varies along the length of the airfoil 66. [0047] As shown in Figure 5, in one example, the shelf wall surface 96 is defined by a first radius Rl on the pressure side wall 74 and is defined by a second radius R2 on the suction side wall 72. In one example, the second radius R2 is different than the first radius Rl . For example, the first radius Rl is greater than the second radius R2.

[0048] Also, in the example shown, the shelf wall surface 96 is defined by a third radius R3 at the leading edge 68 as shown in Figure 5. In one example, the third radius R3 is different from at least one of the first radius Rl and second radius R2. For example, the first radius Rl is greater than the second radius R2, and the third radius R3 is less than the second radius R2. The contour provided by varying the radii further enhances cooling effectiveness. The radii used to define the shelf 90 are application dependent, and can provide different radius combination than that shown in the figures. Further, in certain applications the shelf 90 may be defined by sharp corners instead of radii.

[0049] As shown in Figure 6, the bottom surface 94 extends uninterrupted around the leading edge 68 from the pressure side wall 74 to the suction side wall 72. In one example, the shelf 90 extends a greater distance along the pressure side wall 74 than along the suction side wall 72. In other example configurations, the length of the shelf portions on the pressure 74 and suction 72 side walls may vary as needed for various applications.

[0050] In one example shown in Figure 7, the depth of the shelf 90, which extends from the distal end surface 92 to the bottom surface 94, is generally constant around the leading edge 68. The depth remains generally constant as the shelf 90 extends from the leading edge toward the trailing edge 70. The depth of the shelf 90 decreases to a shallower depth near the trailing edge 70 (see Figure 4).

[0051] The leading edge 68 may include a radially extending trench or groove 102 as best shown in Figures 4-6. Optionally, the leading edge 68 may simply be a rounded surface.

[0052] Also, as indicated schematically in Figure 4, the airfoil section 66 may include a squealer pocket 104 to further enhance cooling. Any squealer pocket shape and/or configuration could be incorporated into the tip 76 of the airfoil section 66. The tip shelf 90 can be used either with or without the squealer pocket 104.

[0053] Thermal distress has been observed in the tip of turbine blades 60 in the form of coating spallation, oxidation, and thermal cracking. The distress has been primarily observed toward the leading edge 68 on surfaces without film cooling on both the pressure 74 and suction 72 sides, as well as the trailing edge 70. Current turbine blade tip designs with internal cores have a geometric configuration, where the distance front the extreme leading edge corner of the external blade tip to the nearest internally cooled cavity surface leaves a relatively large mass of metal in this extreme leading edge tip region that is not as effectively cooled as the remainder of the tip 76. Because of the gas path streamlines around the tip 76, traditional film cooling is far less effective in this region, even when a leading edge trench design is used to funnel showerhead cooling air towards the tip 76. As a result of these cooling limitations of both conductive and convective nature, metal temperature in this extreme leading edge tip region may exceed that of the remainder of the blade, and thus it becomes one of the first regions to experience thermal distress.

[0054] The recessed shelf 90 is incorporated into both the suction 72 and pressure 74 sides of the tip 76 of the airfoil 66, wrapping around the intersection of the leading edge camber/chord line, with integral cooling holes 98 supplied by internal cooling passages 82, 84. The cooling holes 98 in this shelf region supply a cooled fluid boundary layer. Further, incorporation of the wrap-around tip shelf 90 removes the extreme leading edge tip mass of metal and provides a surface through which cooling holes/slots may be created and upon which film cooling may be more efficiently deposited. Additionally, the wrap-around tip shelf 90 effectively locates the remaining extreme leading edge tip edges closer to the internal cooled cavities. Finally, unsteady computational fluid dynamic analysis has shown that the effect of removing this leading edge corner of the blade face (as viewed from the pressure side) when a leading edge wrap-around shelf is included with a pressure-side tip shelf does not allow any more pressure side gas leakage over the tip than with a pressure-side tip shelf alone, so there is no loss of turbine efficiency due to the altered blade geometry.

[0055] Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.