TURBINE BALANCE ARRANGEMENT WITH INTEGRAL AIR PASSAGE

Abstract: A gas turbine rotor includes a disk (50) with axial dovetail slots (64) and air cooled blades (52) having mating, but shortened dovetails (66). The axial flow path (68) so formed is blocked at the far end and is in fluid communication with the blade cooling passages. Balance weights (70) fit within the openings in a manner which does not interfere with the cooling airflow.

Description: This invention relates to balancing of gas turbine rotors and in particular to rotors having air cooled blades and of the type recited in the precharacterizing portion of independent claim 1 (US-A-3,853,425) Gas turbine rotors rotate at high speed and any unbalance causes vibration and reduces the life of the components. Therefore, it is known to balance such rotors by selective addition of weights. Balancing of a bladed turbine or compressor rotor is disclosed in CH-A-659 288. The blades are not air cooled and each blade dovetail is received in a dovetail slot of the disk having a greater length than the length of the blade dovetail. Two keys are mounted in the dovetail slot in abutment with the blade dovetail to retain the blade. A balancing slot for receiving a balancing weight is formed in the key. Location of balance weights on collars attached to the disks is also known but involves the additional weight of the collar and elaborate machining of the collar. Such collars are conventionally of thin cross section and therefore susceptible to handling damage. Balance weights attached thereto are usually close tolerance highly machined parts. Depending on the weight retention means, the weights can be improperly installed, endangering balance weight retention. Removal of the balance weights is often difficult, for instance involving drilling out of a rivet. The collar may be bent or otherwise damaged during this procedure. Often the balance weights are not positively trapped so that they may come off the collar or the collar itself may crack off causing substantial damage to the engine. Location of the weights within the disk itself often creates complicated machining and possibly causes stress concentrations at highly stressed points. Such locations may interfere with the cooling passages for air cooled blades. The object of the invention to balance a gas turbine rotor having air cooled blades in a manner which does not compromise cooling airflow to the blade while avoiding the recited drawbacks of the known balance means. According to the invention, to achieve this, there is provided a gas turbine rotor having a rotating disk and a plurality of air cooled blades extending from said disk and a supply of cooling air located on a first side of said disk, a plurality of axially extending dovetail slots extending through the outer edge of said disk, a mating dovetail on each of said blades, said dovetail being shorter than the depth of said dovetail slots, thereby providing an axial opening through said dovetail slot, said axial opening being open at a first side of said disk in direct fluid communication with said supply of cooling air, blocking means provided at a second side of said disk extending to the full depth of said dovetail slot whereby said axial opening is closed at the second side, each blade having at least one cooling flow path therethrough including radial inlet means in fluid communication with said axial opening, characterized in that a balance weight is located in at least one of said axial openings filling less than all of said axial opening leaving a portion of the opening in fluid communication with said radial inlet. Advantageous features of the gas turbine rotor balance means are recited in the dependent claims. Embodiments of the gas turbine rotor balance means will now be described with reference to the accompanying drawings, wherein: Figure 1 is a partial section through the disk and blade of the sinuous blade cooling embodiment; Figure 2 is a section through Figure 1; Figure 3 is a partial section through the disk and blade of the parallel flow cooling embodiment and Figure 4 is a section through Figure 3. The gas turbine rotor includes a disk 10 carrying a plurality of turbine blades 12. The blades are located in the hot gas stream while the supply of relatively low temperature cooling air 14 exists on a first side of the disk. The blade of the Figure 1 embodiment is sinuously cooled with air flowing through the sinuous passage 16 and out through a plurality of downstream openings 18. The air inlet opening to each blade should be generous and substantially unrestricted to insure a sufficient flow of cooling air restricted primarily by the openings 18. The disk 10 includes a plurality of axially extending dovetail slots 24 with each of the blades 12 carrying a dovetail 26 which mates with the slots. The dovetail is shorter than the depth of the slots so that an axial opening or passageway 28 is formed through the dovetail slot. While these slots are illustrated as directly axial, it is understood that in certain embodiments they may be at various angles, still maintaining a substantial axial component. The blade retaining plates 30 extend to the bottom of the axial slot 24 thereby blocking the second side of the axial opening (28) and closing the end of the passage. A plate 30 is located in each axial slot. Each blade has radial openings 32 in fluid communication with the cooling flow path 16 and with the axial opening 28. Accordingly, cooling air from the supply 14 passes through the axial opening 28 and through the passageways 32 into and through the blade. Internal support webs 34 located within the radial opening serve to strengthen the root of the blade and also function to make the flow path of air entering the blade more uniform. The inlet portion 36 of these passageways is generously sized to minimize pressure drop at this location where the cooling air must make a 90° bend. A dead air space 38 is a lightening hole and forms no significant portion of the airflow path. The rotor assembly is spun on a balancing machine with the amount and location of needed weights being determined. The required weights 40 are then located at appropriate locations within the axial opening 28. Each blade has rails 42 toward the first or inlet side of the disk with these rails terminating toward the second side forming a recess 44. The weight 40 is located at the second side being retained from axial movement toward the upstream side by the rails. It is restrained from axial movement in the other direction by the blade retaining plates 30 which in turn are held in place by a snap ring 46 which engages slots 48 on the disk. A snap ring 47 engages slots 49 for axial retention of the blades in the other direction. Accordingly, the blades are restrained from axial movement in either direction and the weight is retained at the upstream location. It can be seen that the flow path from the air supply 14 through the axial opening 28 and into the blades is unrestricted. Figure 3 illustrates an alternate embodiment where a parallel flow path through the blade is used for cooling and wherein the blade retaining plate is omitted. Disk 50 carries a plurality of turbine blades 52 with the supply of high pressure cooling air 14 located on the upstream side of the disk. Each blade 52 includes parallel flow paths 54, 56 and 58 with corresponding inlets 55, 57, 59 and 60. Internal baffle 61 distributes the air with a discharge of air of paths 56 and 58 through openings 62. Air passing through path 54 discharges through openings (not shown) in the leading edge. Again, a generous inlet opening must be provided for an adaquate flow of cooling air. In particular, the downstream opening, 59 and 60 should not be unduly restricted. Slots 64 extend axially through the disk forming an axial opening or flow passage 68. Each blade 52 has a dovetail 66 which is shorter than the depth of the opening 64, thereby forming the axial flow path 68. During trim balancing of the rotor balance weights 70 are located as required within the axial opening 68 toward the second or aft side of the disk. Each weight is of substantially U-shaped as seen in Figure 4 and is restrained from movement toward the first side by a step 72 in a dovetail of the blade. Recess 74 located at the second or aft side of the disk accepts and retains the weight. A downwardly extending lip 76 forming a portion of the dovetail of the blade closes off the second side of the flow passage 68 and also serves to retain the weight 68. A snap ring 46 engaging a plurality of hooks 48 located on both the disk and the blades retains the blades from axial movement with respect to the disk. The entire cooling airflow must pass through inlet 80 of the axial passage with portions of this flow passing upwardly through inlets 55, 57, 59 and 60, respectively. With the location of the weight at the second or aft side it can be seen that the majority of the required flow has exited from axial passageway 68 before the location of weight 70 is reached. The weight 70 has an outwardly facing U-shape with the opening in fluid communication with inlets 59 and 60. This provides a residual flow path 90 past the weight. Accordingly, the restriction in flow area caused by the weight 70 is minor and because of the reduced flow passing thereby the airflow to the blade is not compromised.

Claims: Gas turbine rotor having a rotating disk (10;50) and a plurality of air cooled blades (12;52) extending from said disk (10;50) and a supply of cooling air located on a first side of said disk (10;50), a plurality of axially extending dovetail slots (24;64) extending through the outer edge of said disk (10;50); a mating dovetail (26;66) on each of said blades (12;52), said dovetail (26;66) being shorter than the depth of said dovetail slots (24;64), thereby providing an axial opening (28;68) through said dovetail slot (24;64) said axial opening (28;68) being open at a first side of said disk (10;50) in direct fluid communication with said supply of cooling air; blocking means provided at a second side of said disk (10;50) extending to the full depth of said dovetail slot (24;64) whereby said axial opening (28;68) is closed at the second side; each blade (12,52) having at least one cooling flow path therethrough including radial inlet means in fluid communication with said axial opening (28;68); characterized in that a balance weight (40;70) is located in at least one of said axial openings (28;68) filling less than all of said axial opening (28;68) leaving a portion of the opening (28;68) in fluid communication with said radial inlet (36). Turbine rotor according to claim 1, characterized in that each blade (12) has a serpentine cooling flow path (16) therethrough; said radial inlet means comprises an inlet (36) located at the first side of said blade (12); and said weight (40) is located at the second side of said blade (12) whereby said axial flow path to said inlet (36) is unrestricted. Turbine rotor according to claim 2, characterized in that said dovetail (26) has a radially extending recess (44) at the second side for accepting and retaining said weight (40). Turbine rotor according to claim 3, characterized in that said dovetail (26) has at the first side an axially elongated radially inwardly extending rail (42), the absence of which establishes said radially extending recess (44). Turbine rotor according to claim 4, characterized by a plurality of annular blade retention plates (30) located at the second side of said disk (10); and said blocking means comprising said retention plate (30) completely covering said axial opening (28). Turbine rotor according to claim 1, characterized in that said weight (70) has a cross sectional area filling less than the cross-sectional area of said axial opening (68), thereby forming a residual opening (90); and said residual opening (90) being in fluid communication with said radial inlet means. Turbine rotor according to claim 6, characterized in that said radial inlet means has a plurality of inlets (55, 57, 59, 60) in fluid communication with said axial opening (68); said weight (70) being located at the second side of said axial opening (68), whereby the axial opening (68) toward said first side is totally unrestricted. Turbine rotor according to claim 7, characterized in that said dovetail (66) has a radially extending recess (74) at the second side for accepting and retaining said weight (70). Turbine rotor according to claims 6 or 8, characterized in that said blocking means comprises an extending lip (76) on said dovetail (66) extending the full depth of said dovetail slot (64).

Inventors: MCCRACKEN, JAMES R.
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1988
Main classification: F01D25
IPC codes: F01D5, F16F15