TURBINE BLADE RETENTION AND DAMPING DEVICE

Abstract: Damping of a turbine rotor is attained by a weighted member (26) trapped between pockets (24) formed in the neck of adjacent blades (10) at one end and a space between the disk (36) and rotor seal (34) and forward extending blade lug (50) at the other end. The feather seal (52) which is a curved plate fits over the top of the weighted member (26) and is trapped between nubs (54,56) formed on the front and rear underside of the blade platform (20). The front face (46) of the rim of the disk (36) at the disk cavity is open ended and blocked off at the rear face. This assembly allows for individual blade removal and viewing from the rear face by removing a single rim cavity cover without disturbing the remaining compo­ nents of the assembly. The inverted ring (76,78) sup­ ports take up the axial loads alleviating the loads heretofore taken up by the TOBI rotor seal (36), allowing for a lighter weight installation.

Description: Technical Field This invention relates to gas turbine engines and particularly to the rim configuration of the disk of the turbine rotor and retention means of the blades, seals and dampers. Background of the Invention With the advent of high speed aircraft with its advanced type of engines, in order to enhance the high cycle fatigue life of component parts, particularly the turbine rotor blades, it has become necessary to incorporate damping techniques so as to reduce vibratory stresses occasioned by the higher speeds. For turbine rotors that utilize fir tree attachments to secure the blades to the disk, such dampers have been incorporated in the space between blades at the blade root/disk attachment sections. Examples of dampers of this sort are disclosed in US-A-4,182,598, 4,101,245, 4,455,122 and 3,887,298. The turbine blade damper of US-A-4,182,598 referred to (on which the two-part form of independent claim 1 is based) is mounted in a cavity between the neck portions of adjacent blades. A toggle damper is mounted in a slot of the cover plate of the turbine rotor. The damper disclosed in US-A-3,887,298 has a seal plate extension on the high pressure side of the rotor and a damper support has a seal plate extension on the low pressure side of the rotor. The seal plate extensions fit into spaces between the rotor disk and side plate fixed thereto. While those embodiments exemplified in the above noted patents disclose means for achieving damping, they all to some extent require complex means of assembly and disassembly necessitating the removal of more than one blade to replace another blade or component in the disk/blade assembly, or to install a blade, damper and/or seal. Disclosure of the Invention According to the invention there is provided a rotor assembly for a gas turbine engine, having a disk, said disk having a rim portion and radially outwardly extending disk lugs in said rim portion, defining disk slots therebetween, said disk lugs each having a front face and a rear face, a plurality of blades, each blade having a root section and a neck section radially outwardly of the root section, each blade having its root section received in a corresponding one of said disk slots, there being formed a dead rim cavity radially outwardly of each disk lug between the neck sections of adjacent blades, said rotor assembly further having means for absorbing excessive vibratory motions occasioned by the rotation of the turbine, said means including a damper formed from a weighted element having a radial inner end portion and a radial outer end portion in its assembled position and opposing side edges, a rotor seal adjacent said disk and extending radially adjacent said neck sections of the blades, the radial inner end portion of said weighted element being trapped in a space bounded on one side by a radially extending annular portion of said rotor seal, characterized in that the other side of said space is bounded by the front face of the disk lug and each blade root section has a portion extending axially beyond the front face of said disk lugs toward the rotor seal and under a portion of said radial inner end portion of said weighted element radially inwardly thereof, said axially extending root portions of two adjacent blades defining with the annular portion of the rotor seal and the front side of the disk lug between said two adjacent blades a pocket for receiving and positioning the inner end portion of said weighted element, the side edges at the radial outer end portion of the element being received in opposing pockets formed in the blade neck sections. In one embodiment there can be provided an improved retention system for the turbine rotor components by incorporating a unique rim configuration that employs snap rings to secure the blades in the disk. To this end, rearward retention of the blades is by a snap ring supported by hooks integral to the rear of the disk, and forward blade retention is by an inverted snap ring supported by a lug integral to the front of the disk lug. In this configuration the axial retention of the blades is provided by this snap ring and not the TOBI (Tangential On Board Injector) rotor seal which has been the common heretofore practice. To have designed the system incorporating heretofore design practices would have added an intolerable amount of weight to be capable of absorbing these axial loads. Among the advantages afforded by this inverted snap ring are: (1) improved producibility of the snap ring groove, (2) lighter weight than heretofore known retention systems, and (3) full ring support for the snap ring for improved durability, leakage control and life. In another embodiment of this invention an improved means is provided for supporting an interplatform seal adjacent the undersurface of the blade platforms to extend across the gap between platforms. Nubs cast on the underside of the platform and a buttress on the rear of the platform provide a retention and orientation system for the seal which may be assembled and disassembled from either the front and rear end of the disk. Thus, this invention contemplates an easily accessible damper and interstage platform seal to facilitate the assembly and disassembly of those components without the necessity of removing more than one blade. Hence, individual blades can be installed and removed without disrupting the rotor or changing the dynamics of the rotor. By virtue of this invention, a significant improvement in turbine maintainability and assembly is evidenced coupled with a reduction in tooling requirements and a less complex rim assembly. The foregoing and other features and advantages of the present invention will become more apparent from the following description and accompanying drawing. Brief Description of the Drawings FIG 1 is a view in elevation of the blade. FIG 2 is a perspective view of the damper. FIG 3 is a partial view in section and elevation showing the disk, blade, TOBI seal, rotor and retention system. FIG 4 is a sectional view taken substantially along the lines 4-4 of FIG 3 with the damper shown in full. FIG 5 is a perspective view of the interstage seal. FIG 6 is a partial rear end view of the rim and assembled rotor. Best Mode for Carrying Out the Invention For an understanding of the invention, reference is being made to FIGS 1-6 of the drawings. As is well known, the turbine of a gas turbine engine is comprised of a disk supported to the engine shaft that supports a plurality of radially projecting turbine blades uniformly mounted about the circumference of the disk and supported thereto in fir tree broaches formed in the disk. The blade 10 itself, as shown in FIG 1, consists of a root generally illustrated by reference numeral 12 having a conventional fir tree shaped root section 14 extending radially in the neck 16 of the blade 10 and configured to fit into the fir tree broach in the disk. A depression 18 in the neck 16 of the blade 10 adjacent the rim of the disk defines a dead rim cavity which is directly under the platform 20. The platform 20 extends circumferentially and axially from the airfoil 22 of the blade 10 and overlies the rim of the disk. The platform of the next adjacent blade abuts the side surface of the platform of its adjacent blade and leaves a laterally extending gap which is sealed by sealing mechanism to be described hereinbelow. As noted from FIG 1, the blade 10 has cast therein a pocket 24 adapted to receive the radial outer end portion of damper 26 (FIG 2). Each of the blades has identical pockets cast on the forward and rearward faces of the neck. The side edges 28 and 30 of damper 26 are adapted to fit into these pockets which provide axial and circumferential positioning of the radial outer end portion of the damper 26 (see FIGS 3 and 4). The inner leg 32 of damper 26 is captured between the annular shaped TOBI seal rotor 34 which is secured in any well-known manner to the disk 36, or splined to the shaft common to the shaft to which disk 36 is mounted. Suffice it to say TOBI seal rotor 34 and disk 36 rotate at the same RPM. The outer diameter of TOBI seal rotor 34 carries a rim 44 that has a rear face 42 that bears against the side face of disk 36, but is designed so as not to absorb the loads generated by the blades. Extending from the rim but spaced from the rear face 42 is a radially extending annular portion 44 that, together with the end face 46 of disk 36 and the extended portion 48 formed on the side face of lug 50 of the fir tree 14 of blade 10, defines a pocket receiving the inner leg of damper 26. This pocket, provided by the TOBI rotor seal and extended blade lug, provides axial and circumferential positioning of the radial inner end portion of damper 26. This method of retention allows the damper to seat freely on pocket base 77 without restraint to achieve effective damping, thus dissipating the energy of the vibrations of the blades, but still prevents the damper from separating from the rotor or locking up. The damper 26 is contoured to include central extensions 27 that provide sufficient mass in the proper location to attain the desired centrifugal load, which in conjunction with the friction induced component damps out vibratory stresses produced by the blades. As mentioned above, the gap between the platform 20 is sealed by a relatively thin, generally flat member 52 that is contoured to fit and be trapped on the underside of the plaform by using a cast seal finger 53 extending radially downwardly from the platform and leading edge nub 54 and trailing edge nub 56. The seal member 52 (see FIG 3) is installed from the front of the disk 36 through a gap formed between the seal finger 53 and platform 20 and slides along the platform until it strikes the rear buttress nub 56. The trailing edge nub 56 prevents seal 52 from leaving the rear of the blade. With the platform seal 52 against the rear buttress, an installation pressure exerted outwardly against the forward edge of seal 52 will seat the seal member 52 to the inner surface of the platform 20. Likewise, the leading edge nub 54 prevents the seal member 52 from coming out the front of the platform 20. Removal of the seal member 52 is a relatively simple procedure. It requires sliding a tool between the blade platform that flexes the forward edge of the seal member 52 over the leading edge nub 54. The seal member 52 can then be easily gripped and removed by the operator. As is apparent from the foregoing, retaining the seal member 52 and damper 26 in the manner described hereinabove allows installation and removal of individual blades and greatly reduces the effort necessary to maintain the turbine since the tooling requirements are reduced and the rim assembly is less complex than heretofore known systems. As was described above, the retention system for securing the blades 10 to the disk 36 is designed so that any load imposed by the blades is not absorbed by the TOBI rotor seal 34, but rather is absorbed by the snap ring assembly generally illustrated by reference numeral 70. In this assembly, an interrupted annular lug 72 with a complete groove cross-section 74 is integral to the front face of each disk lug 99. A full ring 76 fits into this complementary groove 74 and bears against the side face of the fir tree root section 14 of blade 10. The full ring is retained radially by the rim 40 of the TOBI rotor seal 34 overlying the groove 74 and is designed to resist the loads imparted by the rotating blades 10. As is apparent from the drawing, the groove 74 faces away from the engine's center line and hence is viewed as being inverted since it is typical to orient the slots and grooves to face the center line of the engine. This serves to improve producibility of the grooves since it facilitates the manufacturing thereof, reduces weight, and improves the life of the assembly since the ring supports the blades over the entire circumference. Sealing of the dead rim cavity adjacent the juncture of the blade roots and disk rim is by use of a plurality of individual seal plates 80 (FIGS 3 and 6) supported on the rear face of disk 36. Each plate is contoured to fit into the space adjacent the root of blades 10 and are retained by hooks 82 integral to the rear face of disk lugs 99 of disk 36. The hooks' slots support the full split snap ring 86 which bear against each of the plates 80. This system supports the aerodynamic thrust load of the blades 10, while sealing up the dead rim cavity. To remove dampers 26, this snap ring 86 and seal plates 80, need not be disturbed. On the other hand in the preferred instances it may be advantageous to view into the dead rim cavity or cooling air supply slot 100 by removing snap ring 86 and seal plates 80 without disturbing the dampers 26 or TOBI seal rotor 34 such as may be required for trim balance operations. This seal plate installation is highly advantageous at a 0° fir tree broach angle, i.e. fir tree slot is perpendicular to disk face 46, since the seal plate is of lightest weight design. However, it is to be understood and as will be apparent to those skilled in the art, this invention can be employed where the broach angle is greater than 0°. It is apparent from the foregoing that the rim configuration as described serves to allow individual blade installation and removal, blade-to-blade damping and platform sealing of an extended neck blade. In addition, and without limitation, this invention improves high cycle fatigue life while at the same time decreases weight over other heretofore known disk rim configurations.

Claims: Rotor assembly for a gas turbine engine, having a disk (36), said disk (36) having a rim portion and radially outwardly extending disk lugs (99) in said rim portion, defining disk slots therebetween, said disk lugs (99) each having a front face and a rear face, a plurality of blades (10), each blade (10) having a root section (14) and a neck section (16) radially outwardly of the root section (14), each blade (10) having its root section (14) received in a corresponding one of said disk slots, there being formed a dead rim cavity radially outwardly of each disk lug (99) between the neck sections of adjacent blades (10), said rotor assembly further having means for absorbing excessive vibratory motions occasioned by the rotation of the turbine, said means including a damper (26) formed from a weighted element having a radial inner end portion and a radial outer end portion in its assembled position and opposing side edges (28, 30), a rotor seal (34) adjacent said disk (36) and extending radially adjacent said neck sections (16) of the blades (10), the radial inner end portion of said weighted element being trapped in a space bounded on one side by a radially extending annular portion (44) of said rotor seal (34), characterized in that the other side of said space is bounded by the front face of the disk lug (99) and each blade root section (14) has a portion (48) extending axially beyond the front face of said disk lugs (99) toward the rotor seal (36) and under a portion of said radial inner end portion of said weighted element radially inwardly thereof, said axially extending root portions (48) of two adjacent blades (10) defining with the annular portion (44) of the rotor seal (34) and the front side of the disk lug (99) between said two adjacent blades (10) a pocket for receiving and positioning the inner end portion of said weighted element, the side edges (28, 30) at the radial outer end portion of the element being received in opposing pockets (24) formed in the blade neck sections (16). Rotor assembly according to claim 1, characterized in that said weighted element includes a front face and rear face, centrally disposed axially extending portions (27) on said element adding weight thereto in a given amount and location to absorb the energy induced by said rotating rotor assembly. Rotor assembly according to claim 1 or 2, characterized in that said pockets (24) are cast into said blades (10). Rotor assembly according to claim 1, characterized in that said blades (10) are axially retained in the rotor disk slots by a first retaining ring (76) supported by first hooks (72) formed on the front face of said disk lugs (99) and a second retaining ring (86) supported by second hooks (82) formed on the rear face of said disk lugs (99), and that the first hooks (72) formed on the front face of the rotor disk (36) are radially outwardly directed and the first retaining ring (76) received in grooves (74) defined between the hooks (72) and the front face of the rotor disk (36) is retained against radial outward movement by the rotor seal (34). Rotor assembly according to claim 1, characterized in that a plurality of individual seal plates (80) are supported on the rear face of the disk (10) to block the flow of cooling air admitted into the dead air cavity between the blade neck sections (16) through the front face of the disk (10), said plates (80) being retained by said second retaining ring (86). Rotor assembly according to claim 1, wherein each blade (10) has a platform (20) radially outwardly of said neck section (16) and, said rotor assembly further characterized by including an interplatform seal (52) comprising a relatively flat rectangular plate member curved at either end fitting underneath adjacent blade platforms (20) to seal between adjacent platforms (20), nubs (54, 56) formed on the forward and rearward underside surface of said platform (20) for receiving and retaining said plate member, and a finger (53) on the blade (10) defining a gap for permitting said plate member to slide along the platform (20).

Inventors: BROWN, WESLEY DAVID, HILL, EDWARD CLARENCE, VERCELLONE, PETER THOMAS
Applicants: UNITED TECHNOLOGIES CORPORATION
Application year: 1989
Main classification: F01D5
IPC codes: F01D11, F01D5