Patent Application
20110268579
The present invention relates generally to rotor structures in gas turbine engines and, more particularly, to a rotor structure including a spindle bolt structure for reducing stresses in turbine spindle bolts of gas turbine engines.
Turbomachines, such as gas turbine engines, generally include a compressor section, a combustor section and a turbine section. A rotor is typically provided extending axially through the sections of the gas turbine engine and includes structure supporting rotating blades in the compressor and turbine sections. In particular, a portion of the rotor extending through the turbine section comprises a plurality of turbine disks joined together wherein each turbine disk is adapted to support a plurality of turbine blades. Similarly, a portion of the rotor extending through the compressor section comprises a plurality of compressor disks joined together wherein each compressor disk is adapted to support a plurality of compressor blades. The portions of the rotor in the turbine and compressor sections are connected by a torque tube.
In a known construction of the rotor, the turbine disks are joined together by a plurality of spindle bolts extending longitudinally through the turbine disks in the axial direction. The spindle bolts are subjected to stresses which may comprise preload stresses and stresses resulting from thrust, centrifugal force, and/or thermal effects.
In accordance with an aspect of the invention, a spindle bolt structure is provided in a gas turbine engine. The gas turbine engine includes a rotor including a plurality of turbine disks for supporting rows of blades, a torque tube located on a compressor side of the turbine disks, and a seal disk located between the torque tube and a first stage turbine disk. The spindle bolt structure comprises a spindle bolt extending through the turbine disks and disposed offset from a rotational axis of the turbine disks. The spindle bolt includes a first terminal end located adjacent to the compressor side of the turbine disks, and a sleeve member is provided extending over a portion of the first terminal end of the spindle bolt and embedded within a compressor side of the seal disk for effecting a reduction in fretting movement of the spindle bolt relative to the seal disk.
In accordance with another aspect of the invention, a spindle bolt structure is provided in a gas turbine engine. The gas turbine engine includes a rotor including a plurality of turbine disks for supporting rows of blades, a torque tube located on a compressor side of the turbine disks, and a seal disk located between the torque tube and a first stage turbine disk. The spindle bolt structure comprises spindle bolts extending through the turbine disks, the spindle bolts being disposed circumferentially around and offset from a rotational axis of the turbine disks. The spindle bolts include a first terminal end located adjacent to the compressor side of the turbine disks. A plurality of holes are provided in the seal disk aligned with corresponding holes in the turbine disks for receiving the spindle bolts. Each hole in the seal disk comprises a stepped portion defining a shoulder between opposing axial faces of the seal disk. A sleeve member extends over a portion of the first terminal end of each of the spindle bolts and is embedded within a compressor side of the seal disk. Each of the sleeve members includes an engagement end engaged on a shoulder within a respective hole in the seal disk for effecting a reduction in fretting movement of the spindle bolt relative to the seal disk.
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:
In the following detailed description of the preferred embodiment, 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, a specific preferred embodiment 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
The turbine section 16 includes a plurality of turbine stages, illustrated as first through fourth stages 28a, 28b, 28c, 28d. Each of the turbine stages 28a, 28b, 28c, 28d comprises a respective one of first through fourth turbine disks 30a, 30b, 30c, 30d that define a portion of the rotor 20, and each of the turbine disks 30a, 30b, 30c, 30d supports a plurality of blades 32 for converting the energy of the hot working gases into rotational movement of the rotor 20. The rotor 20 further comprises a torque tube 34 extending between the compressor section 12 and the turbine section 16 for transferring output power from the turbine section 16 to the compressor section 12, where a portion of the output power is used to drive the compressor disks 18 and blades 22, and the remaining portion of the output power is used to drive an output device, such as electrical generator (not shown) in a power generation plant.
In addition, the rotor 20 includes a seal disk 36 at a location between the turbine section 16 and the combustor section 14, supported between the first stage turbine disk 30a and the torque tube 34. The seal disk 36 includes a rotating seal 38 cooperating with a stationary seal structure 40 adjacent to the combustor shell 24 and forming a seal between the turbine section 16 and the combustor section 14.
A plurality of spindle bolts 42 (only one shown) extend through the turbine disks 30a-d, and pass through the seal disk 36 and an end portion 80 (
In accordance with an aspect of the invention, it has been determined that a failure of a spindle bolt 42 may occur in existing turbine engines 10 having a rotor construction, such as is described above with reference to
Various factors are typically anticipated in specifying the design for the spindle bolts 42 in order to ensure that the spindle bolts 42 are capable of withstanding stresses exerted in the rotors 20. Such factors include possible effects from stresses induced by loads due to thrust, a centrifugal force, or thermal effects. In addition, a preload stress is typically present on the spindle bolts 42, which comprises a stress induced by a predetermined tension applied on the bolts 42 during assembly of the rotor 20 for maintaining the turbine disks 30a-d, seal disk 36 and torque tube 34 joined together.
Known design practice permits specification of the spindle bolts 42 to withstand the conventionally anticipated stresses experienced by the spindle bolts 42 as a result of forces generated by thrust, rotation of the rotor 20 and thermal effects, which are generally referenced herein as baseline or mean stresses. That is, the mean stresses generated by thrust, rotation of the rotor 20 and thermal effects, and substantially due to centrifugal forces with rotation of the rotor 20, are generally predictable, permitting the spindle bolts 42 to be designed, including a factor of safety, to withstand these predicted stresses.
The above noted area of potential failure in the spindle bolt 42, i.e., along the incremental length section DA, indicates an area where a failure may occur in spite of the application of conventional design practice to configure the spindle bolts 42 to withstand the predicted stresses applied through the rotor 20. In accordance with the present invention, a theory of failure and solution are presented to address the unexpected spindle bolt failures at the exemplary location along the incremental length section DA. Specifically, it may be observed that the rotor 20 normally experiences a sag between the bearings 46, 50, resulting in a certain amount of axial elongation of the spindle bolts 42 as the bolts 42 each rotate with the rotor 20 from top-dead-center (TDC) to bottom-dead-center (BDC). For example, a cyclically occurring bolt stretch or elongation in the axial direction A1 is associated with the incremental length section DA (
It is believed that a further factor contributing to failure of the spindle bolt 42 comprises a fretting effect (fretting fatigue) associated with the cyclically occurring lengthwise or axial movement of the spindle bolt 42 relative to the spindle bolt hole 58 in the seal disk 36 and the torque tube 34 as the length of the seal bolt 42 changes in the section DA. The fretting effect comprises an alternating stress, S, produced by high traction forces formed at an interface between the contacting surfaces of the spindle bolt 42 and the spindle bolt hole 58. The traction force is related to the force, F, with which the spindle bolt 42 engages the surface of the spindle bolt hole 58 and the coefficient of friction, p, at the interface between the spindle bolt 42 and the spindle bolt hole 58, i.e., the traction force is proportional to F×μ, such that the traction force may be decreased by providing increased lubrication (decreased friction) between the spindle bolt 42 and the surface of the spindle bolt hole 58. Further, the magnitude of the fretting effect may be described in terms of the energy produced along the section DA by the relative axial movement between the spindle bolt 42 and the seal disk 36. Specifically, the energy associated with the fretting effect may be expressed in terms of the energy per unit area, E, as follows:
E=S×L
e
where,
The stress contributing to the failure of the spindle bolt 42 within the seal disk 36 comprises the sum of the mean stress and the fretting stress applied along the section DA.
Referring to
A sleeve member 64 is positioned within an enlarged diameter portion 66 of the spindle bolt hole 58 and extends over a portion of the first terminal end 45a of the spindle bolt 42a. The sleeve member 64 is rigidly attached to the first terminal end 45a and includes an engagement end 68 that is engaged on the stepped portion 62, i.e., engaged on the shoulder, for defining a fixed upstream end of the disk structure for the turbine section 16. The first terminal end 45a preferably comprises a threaded end and the sleeve member 64 is preferably threadably engaged on the first terminal end 45a.
An anti-rotation key member 70 may be provided adjacent to the upstream axial face 54a and extending into slots 72, 74 formed in the seal disk 36 and the sleeve member 64, respectively. The sleeve member 64 may be formed with a generally cylindrical outer surface, and the key member 70 prevents rotation of the sleeve member 64 relative to the seal disk 36a, permitting the spindle bolt 42a to be threaded into the sleeve member 64 by rotation of the second terminal end (not shown in
The torque tube 34 may comprise spindle bolt hole portions 58a, such that the same torque tube may be used for the present spindle bolt structure 60 as is provided for the prior structure described with reference to
The spindle bolt structure 60 is configured to provide a reduction in the energy associated fretting at the locations of contact between the spindle bolt 42a and the spindle bolt hole 58 within the seal disk 36a. In particular, the shoulder defined by the stepped portion 62 is located at a distance D8 from the downstream axial face 56a less than one-half the distance between the upstream and downstream axial faces 54a, 56a. Hence, the length along which relative movement of the spindle bolt 42a may take place due to alternative elongation of the spindle bolt 42a is substantially reduced with a corresponding reduction of the relative movement between the spindle bolt 42a and the seal disk 36a. Further, the surface contact area between the spindle bolt 42a and the seal disk 36a is substantially shortened to comprise the portion of the bolt 42a along the length DB, substantially reducing the energy that may be produced due to cyclical fretting movement in the axial direction. For example, the length of the contacting section DB may be reduced approximately 14% relative to the length DA, which is believed to result in approximately 10% reduction in the relative movement, Le, with a corresponding reduction in contact stress, S, of approximately 49% and a resulting reduction in energy, E, of 4.9% below that provided by the configuration of
It may also be noted that in accordance with the structure disclosed for the present invention, the configuration of the seal disk 36a provides a reduced unsupported section of the spindle bolt 42a between the first turbine disk 30a and the downstream face 56a of the seal disk 36a. In particular, an inner diameter portion 94a, located inwardly from a cavity 95a of the seal disk 36a, is extended downstream toward an axial location 98a of a curvic coupling 96a between the seal disk 36a and the first turbine disk 30a. A distance db from a downstream end of the inner diameter portion 94a to the axial location 98a is substantially less than a corresponding distance da (
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.
