Turbine blades

Abstract: A convectively cooled turbine blade 10 has two distinct cooling air passage systems. The first system 30 cools the blade leading edge 18 and emits cooling air through outlet passageways 36 in the leading edge 18 arranged in showerhead array. The second system 38 includes a five-pass series flow passage comprising five cooling passage sections 40-44 that extend in series through the remainder of the blade. Cooling air resupply passages 82,84 inject additional cooling air into the third and fifth cooling passage sections 42,44.

Description: This invention relates in general to turbine blades and deals more particularly with an improved convectively cooled turbine blade particularly but not exclusively adapted for use in the first stage of a gas turbine engine. In gas turbine engines a turbine operated by combustion product gases drives a compressor which furnishes air to a burner. Gas turbine engines operate at relatively high temperatures, and the capacity of such an engine is limited to a large extent by the ability of the turbine blades to withstand the thermal stresses that develop at such relatively high operating temperatures. The ability of the turbine blades to withstand such thermal stresses is directly related to the materials from which the blades are made, and the material's strength at high operating temperatures. To enable higher operating temperatures and increased engine efficiency without risk of blade failure, hollow, convectively cooled turbine blades are frequently utilized. Such blades generally have intricate interior passageways which provide torturous, multiple pass flow paths to assure efficient cooling that are designed with the intent that all portions of the blades may be maintained at relatively uniform temperature. However, as cooling air flows through the relatively long interior passageways, a significant portion of the cooling air escapes through cooling holes in the side walls of the blade to provide film cooling. This reduces the pressure, velocity, and mass flow rate of the cooling air as it flows through the interior passageways which reduces the rate at which heat from the turbine blade is transferred to the cooling air. Localized overheating of the side walls may occur in the side walls immediately adjacent the areas where the cooling airflow pressure, velocity, and mass flow rate are reduced. As a result of such overheating, the turbine blade may be weakened or damaged, thereby shortening the useful life of the turbine blade. GB-A-2,250,548 and US-A-5,387,086 disclose turbine blades having multipass coding passages. What is needed is a turbine blade that maintains cooling air pressure, velocity, and mass flow rate at such levels as to avoid localized overheating of the turbine blade. It is therefore an object of the present invention to provide a turbine blade that maintains cooling air pressure, velocity, and mass flow rate at such levels as to avoid localized overheating of the turbine blade. In accordance with the invention there is provided a turbine blade as claimed in claim 1. A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIG. 1 is a longitudinal sectional view of an airfoil shaped turbine blade embodying the present invention. FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1. FIG. 3 is a somewhat enlarged fragmentary sectional view taken along the line 3-3 of FIG. 1. Turning now to the drawings, the invention is illustrated and described with reference to an air cooled turbine blade, designated generally by the numeral 10, and particularly adapted for use in the first stage of an axial flow gas turbine engine (not shown) which has a plurality of airfoil shaped turbine rotor blades mounted in angularly spaced relation on a rotor disc. The turbine blade 10 has a more or less conventional outer configuration and comprises a hollow elongated body, indicated generally at 12, which includes a concave inner side wall 14 and an opposing convex inner side wall 16 as shown in FIG. 2. The side walls terminate at longitudinally extending leading and trailing edges indicated, respectively at 18 and 20. The body 12 further includes a root portion 22 at one end 33 and an elongated blade portion 24 which extends from the root portion 22 and terminates at a closed tip 26 at the other end 27 of the blade 10. A platform 28 extends outwardly from the body at the junction 49 between the root portion 22 and the blade portion 24. The root portion 22 is preferably provided with attachment shoulders (not shown) which may have a conventional fir tree configuration for mounting the turbine blade 10 in complementary slots in a rotor disc. Two distinct cooling air passageway systems are provided for convectively cooling the blade 10. The first passageway system 30, includes a substantially straight longitudinally extending first passage 32 which opens through the root end 33 of the blade 10 and extends through the root portion 22 and into the blade portion 24 along the leading edge 18. A first root rib 31 extends from the root end 33 toward the blade portion 24, and a first blade rib 34 disposed between the side walls 14 and 16 extends from the tip end 27 to the first root rib 31. The first blade rib 34 is integral with the first root rib 31, and together the first root rib 31 and the first blade rib 34 define, in part, the first passage 32 as shown in FIG. 1. The first fluid passageway system 30 is separated from the second fluid passageway system 38 by the first root rib 31 and the first blade rib 34. The first passage includes a leading edge impingement rib 35 that extends from the rib portion 22 to the tip 26. The leading edge impingement rib 35 includes a plurality of impingement holes 39 for allowing air to pass therethrough. At least one longitudinally spaced series of fluid outlet passages 36 extend through the leading edge 18 and communicate with the first passage 32 through the impingement holes 39. The fluid outlet passages 36 terminate in a showerhead array of passage openings in the leading edge 18. The first passage 32 terminates within the blade portion 24 adjacent the tip 26, and a first tip orifice 37 opens into the tip end 27 and extends through the tip 26 and into the first passage 32 of the first fluid passageway system 30. The turbine blade 10 further includes a second distinct passageway system 38 which generally comprises a plurality of longitudinally extending and series connected passage sections 40, 41, 42, 43, 44 which provide a five-pass flow passage through the remainder of the blade portion 24. The five-pass flow passage includes two pathways: a first pathway that extends from the root end 33 along the blade portion 24 adjacent the trailing edge 20 to a second tip orifice 47 that opens through the tip 26 into the tip end 27, and a second pathway that extends between the root end 33 of the turbine blade 10 and a longitudinally spaced series of pedestal slots 45 that open through the trailing edge 20 and are defined by a longitudinally spaced series of elongated pedestal members 54 disposed between the side walls 14, 16. The passageway system 38 further includes two inlet branch passages 46 and 48 which are disposed within the root portion 22 and open through the root end 33 of the turbine blade 10. Referring again to FIG. 1, the first passage section 40 extends along the trailing edge 20, and a plurality of branch passages 46, 48 in the root portion 22 open through the root end 33 and merge with each other and with the first passage section 40 at the junction 49 between the root portion 22 and the blade portion 24. The pedestal immediately adjacent the tip end 27 defines a tip pedestal 55. The first passage section 40 includes first and second impingement ribs 56, 57, and each of these impingement ribs 56, 57 extends from the root portion 22 to the tip pedestal 55. The first impingement rib 56 is in spaced relation to the second impingement rib 57, and each of the impingement ribs includes a plurality of impingement holes 58, 59 for allowing air to pass therethrough. The impingement hole in each of the impingement ribs 56, 57 nearest the root end 33 defines a root impingement hole 60, and the impingement hole in the first impingement rib 56 nearest the tip pedestal 55 defines a tip impingement hole 62. Each of the impingement holes 58 between the root impingement hole 60 and the tip impingement hole 62 in the first impingement rib 56 is aligned with one of the pedestals 54 to impinge cooling air thereon. Each of the impingement holes 59 between the root impingement hole 60 and the tip pedestal 55 in the second impingement rib 57 is aligned with one of the pedestal slots 45 so as to impinge cooling air upon the first impingement rib 56. A second passage section 41 adjacent the first passage section 40 is connected thereto at a first outer turning region 50 adjacent the tip end 27. The second passage section 41 is separated from the first passage section 40 and from the two branch passages 46, 48 by a second blade rib 66 connected to the first root rib 31 at the junction 49. The second blade rib 66 and extends toward the tip end 27 in generally parallel relation to the first blade rib 34 and terminates in spaced relation to the tip 26 at the first outer turning region 50. A third passage section 42 adjacent the second section 41 is connected thereto at a first inner turning region 68 proximate the junction 49. The third passage section 42 is separated from the second passage section 41 a third blade rib 70 extending from the tip 26 toward the root end 33 in generally parallel relation to the second blade rib 66. The third blade rib 70 terminates in spaced relation to the first root rib 31 at the first inner turning region 68. A fourth passage section 43 adjacent the third section 42 is connected thereto at a second outer turning region 72 adjacent the tip 26. The fourth passage section 43 is separated from the third passage section 42 by a fourth blade rib 74. The fourth blade rib 74 is connected to the first root rib 31 at the junction 49 and extends toward the tip 26 in generally parallel relation to the third blade rib 70. The fourth blade rib 74 terminates in spaced relation to the tip 26 at the second outer turning region 72. A fifth passage section 44 adjacent the fourth section 43 is connected thereto at a second inner turning region 76 proximate the junction 49. The fifth passage section 44 is separated from the fourth passage section 43 by a fifth blade rib 78. The fifth blade rib 78 extends from the tip 26 toward the root end 33 in generally parallel relation to the fourth blade rib 74. The fifth blade rib 78 terminates in spaced relation to the first root rib 31 at the second inner turning region 76. The fifth passage section 44 terminates within the blade portion 24 adjacent the tip 26. Air flows into and through the turbine blade 10 from the rotor disc and in directions indicated by the flow arrows in FIG. 1. More specifically, cooling air from the rotor disc enters the first passageway system 30, flows outwardly through the passage 32, flows through the leading edge impingement rib 35 and is eventually discharged at the blade leading edge through the showerhead holes 36. Additional air from the rotor disc enters the branch passages 46 and 48 which comprises the second passageway system 38 and flows into and through the first passage section 40 between the second blade rib 66 and the second impingement rib 57. As shown in FIG. 1, some of this air flows through the impingement holes 59 of the second impingement rib 57, impinges the first impingement rib 56 and then flows through the impingement holes 58 thereof, then through the slots 45 and out the trailing edge 20 of the blade portion 24. The flow path for the remaining air is through the second 41, third 42, fourth 43, and fifth 44 passage sections is series flow. As the cooling air flows through these sections, a portion is escaping through the side walls 14, 16 through cooling holes (not shown) that perforate the side walls 14, 16 along the length of the passage sections 40, 41, 42, 43, 44. The escaping cooling air provides both convective cooling and film cooling of the side walls 14, 16. Cooling air that does not escape through the cooling holes along the length of the second passageway system is dumped at the blade tip 26 through the second tip orifice 47. Trip strips 80 are incorporated into the side walls 14, 16 along each passage section 40, 41, 42, 43, 44 to improve convective cooling. Each trip strip 80 produces downstream agitation or turbulence which effectively breaks up the boundary layers and causes the cooling air to scrub the walls of the passages. Further, the surface areas of the various passage walls are increased by the provision of trip strips with a resulting increase in fluid cooling efficiency. As the cooling air flows through the passage sections 40, 41, 42, 43, 44, a significant portion of the cooling air escapes through the impingement holes 59 and the cooling holes (not shown) in the side walls 14, 16. This in turn reduces the pressure, velocity, and mass flow rate of the cooling air as it flows through the passage sections 40, 41, 42, 43, 44, which reduces the rate at which heat from the blade 10 is transferred to the cooling air. Localized overheating of the side walls 14, 16 immediately adjacent the third, fourth and fifth passage sections 42, 43, 44 may occur as a result of such reduction in heat transfer, which may in turn weaken the blade 10. To compensate for the loss in the pressure, velocity, and mass flow rate of the cooling air, first and second resupply passages 82, 84, are incorporated into the first root rib 31. The first resupply passage 82 extends from the first inner turning region 68 through the first root rib 31 to one of the branch passages 46. The second resupply passage 84 extends from the second inner turning region 76 through the first root rib 31 to the first fluid passageway system 30. As shown in FIG. 3, the first resupply passage 82 is substantially aligned with the third passage section 42 and the second resupply passage 84 is substantially aligned with the fifth passage section 44. Through the resupply passages 82, 84, cooling air from the root portion 22 is injected directly into the third 42 and fifth 44 passage sections, thereby increasing the pressure and mass flow rate of the cooling air through the third, fourth and fifth passage sections 42, 43, 44. The increase in pressure and mass flow rate through the third 42 and fifth 44 passage sections increases rate of heat transfer from the side walls 14, 16 to the cooling air, thereby reducing the temperature of the side walls 14, 16 immediately adjacent the third 42 and fifth 44 passage sections. Additionally, since the resupply passages 82, 84 are aligned with the third 42 and fifth 44 passage sections, the streams of cooling air entering the third 42 and fifth 44 passage sections through the resupply passages 82, 84 act as ejectors for the second 41 and fourth 43 passage sections, respectively. As those skilled in the art will readily appreciate, the ejector streams produced by the resupply passages 82, 84 draw the cooling air from the second 41 and fourth 43 passage sections, respectively, increasing the velocity of the cooling air through these passage sections. This higher velocity increases rate of heat transfer from the side walls 14, 16 to the cooling air, thereby reducing the temperature of the side walls 14, 16 immediately adjacent the second 41 and fourth 43 passage sections. Although this invention has been shown and described with respect to a detailed embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the scope of the claimed invention.

Claims: A turbine blade having a hollow elongated body including a root portion (22) at one end (33) and a blade portion (24) extending from said root portion (22) and terminating at a tip (26) at the other end (27) of said body, said body having opposing side walls (14,16) and longitudinally extending leading and trailing edges (18,20) and having a plurality of generally longitudinally extending blade ribs therein extending between said side walls (14,16) of the blade and a plurality of generally longitudinally extending root ribs therein extending from said one end. said blade ribs and said root ribs partially defining a first fluid passageway system (30) and a second fluid passageway system (38) within said body, said first fluid passageway system (30) distinctly separate from said second fluid passageway system (38), a first tip orifice (37) opening through said other end (27) and extending through said tip (26) into said first fluid passageway system (30) and a second tip orifice (47) opening through said other end (27) and extending through said tip (26) into said second fluid passageway system (38), a first root rib (31) extending from said one end (33) toward said blade portion (24), a first blade rib (34) extending from said tip end (27) to said first root rib (31) and integral therewith, said first fluid passageway system (30) being separated from said second fluid passageway system (38) by said first root rib (31) and said first blade rib (34), said first passageway system (30) having a substantially straight longitudinally extending first fluid passage (32) opening through said one end (33) and extending through said root portion (22) into said blade portion (24) and along said leading edge (18) and terminating within said blade portion (24) generally adjacent said tip end (27), said second fluid passageway system (38) having a multiple-pass fluid passage including a plurality of generally longitudinally extending and series connected passage sections (40-44) defining a reversing flow path through the remainder of said blade portion (24), said passage sections including a first passage section (40) in said blade portion (24), a second passage section (41) adjacent said first section (40) and connected thereto at a first outer turning region (50) adjacent said tip end (27), said second passage section (41) being separated from said first passage section (40)and from said two branch passages (46,48) by a second one (66) of said blade ribs connected to said first root rib (31) at said junction (49) and extending toward said tip end (27) in generally parallel relation to said first blade rib (34) and terminating in spaced relation to said tip (26) at said first outer turning region (50), a third passage section (42) adjacent said second section (41) and connected thereto at a first inner turning region (68) proximate said junction (49), said third passage section (42) being separated from said second passage section (41) by a third one (70) of said blade ribs extending from said tip (26) toward said one end (33) in generally parallel relation to said second blade rib (66) and terminating in spaced relation to said first root rib (31) at said first inner turning region (68), a fourth passage section (43) adjacent said third section (42) and connected thereto at a second outer turning region (72) adjacent said tip end (27), said fourth passage section (43) being separated from said third passage section (42) by a fourth one (74) of said blade ribs connected to said first root rib (31) at said junction (49) and extending toward said tip (26) in generally parallel relation to said third blade rib (70) and terminating in spaced relation to said tip (26) at said second outer turning region (72), a fifth passage section (44) adjacent said fourth section (43) and connected thereto at a second inner turning region (76) proximate said junction (49), said fifth passage section (44) being separated from said fourth passage section (43) by a fifth one (78) of said blade ribs extending from said tip (26) toward said one end (33) in generally parallel relation to said fourth blade rib (74) and terminating in spaced relation to said first root rib (31) at said second inner turning region (76), said fifth passage section (44) terminating within said blade characterised by said first passage section (40) extending along said trailing edge (20) and a plurality of branch passages (46,48) in said root portion (22) opening through said one end (33) and merging with each other and with said first passage section (40) at a junction (49) between said root and blade portions (22,24) portion (24) and adjacent said tip (26), and a first resupply passage (82) extending from said first inner turning region (68) through said first root rib (31) to one of said branch passages (46,48). The turbine blade of claim 1 wherein the first resupply passage (82) is substantially aligned with said third passage section (42). The turbine blade of claim 1 or 2 further comprising a second resupply passage (84) extending from said second inner turning region (76) through said first root rib (31) to said first fluid passageway system (30). The turbine blade of claim 3 wherein said second resupply passage (84) is substantially aligned with said fifth passage section (44).

Inventors: LIANG GEORGE P, LIANG, GEORGE P.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1998
Main classification: F01D5
IPC codes: F01D5