Abstract:
A turbine engine has a first disk and a second disk, each extending radially from an inner aperture to an outer periphery. A coupling, transmits a torque and a longitudinal compressive force between the first and second disks. The coupling has first means for transmitting a majority of the torque and second means, radially outboard of the first means, for transmitting a majority of the force.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to gas turbine engines. More particularly, the invention relates to gas turbine engines having center-tie rotor stacks. 
   A gas turbine engine typically includes one or more rotor stacks associated with one or more sections of the engine. A rotor stack may include several longitudinally spaced apart blade-carrying disks of successive stages of the section. A stator structure may include circumferential stages of vanes longitudinally interspersed with the rotor disks. The rotor disks are secured to each other against relative rotation and the rotor stack is secured against rotation relative to other components on its common spool (e.g., the low and high speed/pressure spools of the engine). 
   Numerous systems have been used to tie rotor disks together. In an exemplary center-tie system, the disks are held longitudinally spaced from each other by sleeve-like spacers. The spacers may be unitarily-formed with one or both adjacent disks. However, some spacers are often separate from at least one of the adjacent pair of disks and may engage that disk via an interference fit and/or a keying arrangement. The interference fit or keying arrangement may require the maintenance of a longitudinal compressive force across the disk stack so as to maintain the engagement. The compressive force may be obtained by securing opposite ends of the stack to a central shaft passing within the stack. The stack may be mounted to the shaft with a longitudinal precompression force so that a tensile force of equal magnitude is transmitted through the portion of the shaft within the stack. 
   Alternate configurations involve the use of an array of circumferentially-spaced tie rods extending through web portions of the rotor disks to tie the disks together. In such systems, the associated spool may lack a shaft portion passing within the rotor. Rather, separate shaft segments may extend longitudinally outward from one or both ends of the rotor stack. 
   Desired improvements in efficiency and output have greatly driven developments in turbine engine configurations. Efficiency may include both performance efficiency and manufacturing efficiency. 
   U.S. patent application Ser. No. 10/825,255, Ser. No. 10/825,256, and Ser. No. 10/985,863 of Suciu and Norris (hereafter collectively the Suciu et al. applications, the disclosures of which are incorporated by reference herein as if set forth at length) disclose engines having one or more outwardly concave inter-disk spacers. With the rotor rotating, a centrifugal action may maintain longitudinal rotor compression and engagement between a spacer and at least one of the adjacent disks. This engagement may transmit longitudinal torque between the disks in addition to the compression. 
   SUMMARY OF THE INVENTION 
   One aspect of the invention involves a turbine engine having a first disk and a second disk, each extending radially from an inner aperture to an outer periphery. A coupling, transmits a torque and a longitudinal compressive force between the first and second disks. The coupling has first means for transmitting a majority of the torque and second means, radially outboard of the first means, for transmitting a majority of the force. 
   In various implementations, the second means may include spacers (e.g., as in the Suciu et al. applications or otherwise). The first means may comprise radial splines or interfitting first and second pluralities of teeth on the first and second disks, respectively. The first plurality of teeth may be formed at an aft rim of a first sleeve extending aft from and unitarily-formed with a web of the first disk. The second plurality of teeth may be formed at a forward rim of a second sleeve extending forward from and unitarily-formed with a web of the second disk. The first and second disks may each have an inboard annular protuberance inboard of the respective first and second sleeves. The second means may comprise a spacer having an outwardly longitudinally concave portion having a thickness and a longitudinal extent effective to provide an increase in said force with a rotation speed of the first and second disks. The engine may have a high speed and pressure compressor section and a low speed and pressure compressor section. The first and second disks may be in the high pressure compressor section. A plurality of circumferentially-spaced anti vortex tubes may be carried by the first means. A tension shaft may extend within the inner aperture of each of the first and second disks and be substantially nonrotating relative to the first and second disks. There may be means for sealing between the first disk and the shaft. A third disk may extend radially from an inner aperture to an outer periphery. A second coupling may transmit a torque and a longitudinal compressive force between the third and second disks. The second coupling may include first means for transmitting a majority of the torque and second means, radially outboard of the first means, for transmitting a majority of the force. There may be no off-center tie members holding the first and second disks under longitudinal compression. 
   Another aspect of the invention involves a thermally-controlled, center-tied, rotor. The rotor has a central shaft and a plurality of blade disks. The disks each have a central aperture surrounding the shaft. The disks define annular cavities between adjacent pairs of the disks. One or more circumferentially distributed anti-vortex tubes extend within at least a first of said cavities between a first and second of said disks. A radially compliant seal is between the shaft and at least one of said disks. 
   In various implementations, a radial spline torque coupling may be between the first and second disks and carry the one or more circumferentially distributed anti-vortex tubes. The radially compliant seal may be a metallic bellows seal positioned to thermally isolate at least a portion of or more of the cavities from one or more others of the cavities. The one or more circumferentially distributed anti-vortex tubes may be a plurality of evenly circumferentially-spaced tubes at a common longitudinal position. 
   Another aspect of the invention involves a turbine engine rotor having a plurality of disks and a plurality of stages of blades. Each disk extends radially from an inner aperture to an outer periphery. Each stage is borne by an associated one of said disks. There are a plurality of spacers, each spacer between an adjacent pair of said disks. A central shaft carries the plurality of disks and the plurality of spacers to rotate about an axis with the plurality of disks and the plurality of spacers. A first of the spacers transmits a longitudinal compressive force between a first and a second of the disks. Interfitting first and second portions of said first and second disks radially inboard of said first spacer transmit longitudinal torque between the first and second disks. 
   In various implementations, the interfitting first and second portions may comprise radial splines. The first spacer may be unitarily-formed with the first disk. The first spacer may have an end portion essentially interference fit within a portion of the second disk. The stator may comprise a plurality of stages of vanes. The first spacer may have a longitudinal cross-section, said longitudinal cross-section having a first portion being essentially outwardly concave in a static condition The stages of vanes may include at least a first stage of vanes having inboard vane tips in facing proximity to an outer surface of said first spacer at said first portion. The inboard tips of the first stage of vanes may be longitudinally convex. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial longitudinal sectional view of a gas turbine engine. 
       FIG. 2  is a partial longitudinal sectional view of a high pressure compressor rotor stack of the engine of  FIG. 1 . 
       FIG. 3  is a longitudinal sectional view of a disk bore of the stack of  FIG. 2 . 
       FIG. 4  is a radial view of interfitting splines of two disks of the stack of  FIG. 2 . 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a gas turbine engine  20  having a high speed/pressure compressor (HPC) section  22  receiving air moving along a core flowpath  500  from a low speed/pressure compressor (LPC) section  23  and delivering the air to a combustor section  24 . High and low speed/pressure turbine (HPT, LPT) sections  25  and  26  are downstream of the combustor along the core flowpath  500 . The engine may further include a transmission-driven fan  28  driving air along a bypass flowpath  501  and/or an augmentor (not shown) among other systems or features. 
   The exemplary engine  20  includes low and high speed spools mounted for rotation about an engine central longitudinal axis or centerline  502  relative to an engine stationary structure via several bearing systems. The low speed spool includes a low speed shaft  29  ( FIG. 2 ) carrying LPC and LPT rotors and their blades. The high speed spool includes the HPC and HPT rotors and their blades.  FIG. 2  shows an HPC tie shaft  30  concentrically surrounding the low speed shaft  29 . Each shaft  29  and  30  may be an assembly, either fully or partially integrated (e.g., via welding). 
     FIG. 2  shows an HPC rotor stack  32  mounted to the high speed shaft  30 . The exemplary rotor stack  32  includes, from fore to aft and upstream to downstream, an exemplary nine blade disks  34 A- 34 I each carrying an associated stage of blades  36 A- 36 I. A plurality of stages of vanes  38 A- 38 I are located along the core flowpath  500  sequentially interspersed with the blade stages. The vanes have airfoils extending radially inward from roots at outboard platforms  39  formed as portions of a core flowpath outer wall  40 . The first (#1) and second (#2) vane stage airfoils extend inward to inboard platforms  42  forming portions of a core flowpath inboard wall  46 . As is discussed in further detail below, the exemplary airfoils of the subsequent vane stages extend to inboard airfoil tips  48 . 
   In the exemplary embodiment, each of the disks has a generally annular web  50 A- 50 I extending radially outward from an inboard annular protuberance known as a “bore”  52 A- 52 I to an outboard peripheral portion (blade platform bands)  54 A- 54 I. The bores  52 A- 52 I encircle central apertures of the disks through which a portion  56  of the tie shaft  30  freely passes with clearance. The blades may be unitarily formed with the peripheral portions  54 A- 54 I (e.g., as a single piece with continuous microstructure), non-unitarily integrally formed (e.g., via welding so as to only be destructively removable), or non-destructively removably mounted to the peripheral portions via mounting features (e.g., via fir tree blade roots captured within complementary fir tree channels in the peripheral portions or via dovetail interaction, circumferential slot interaction, and the like). 
   A series of spacers  62 A- 62 H connect adjacent pairs of the disks  34 A- 34 I. In the exemplary engine, the first spacer  62 A is formed integrally with (e.g., unitarily formed or welded to) the first disk web  50 A and extends aft to a contacting engagement with the second disk. In the exemplary engine, the first spacer  62 A is outwardly concave (e.g., as disclosed in the Suciu et al. applications) so that its contacting engagement with the second disk  34 B produces a longitudinal engagement force increasing with speed due to centrifugal action tending to straighten/flatten the spacer section. In the exemplary engine, the second spacer  62 B is formed integrally with the second disk (e.g., with the blade platform band  54 B) and extends aft to a contacting engagement with the third disk  34 C (e.g., at the blade platform band  54 C). The remaining exemplary spacers  62 C- 62 H are separately formed from their adjacent disks and in contacting engagement with the blade platform bands of the adjacent disks. The spacers  62 B- 62 H have outboard surfaces in close facing proximity to the inboard tips of the associated vanes (e.g., as disclosed in the Suciu ′863 application). Outward concavity of these spacers  62 B- 62 H also provides the speed-increasing longitudinal compression force. 
   The first spacer  62 A thus separates an inboard/interior annular inter-disk cavity  64 A from an outboard/exterior annular inter-disk cavity  65 . The cavity  65  may accommodate the platform  42  of the second vane stage  38 B and the first spacer  62 A may have features for sealing with that platform. As is discussed above, one or more of the remaining spacers (e.g., all the remaining spacers in the exemplary rotor stack), however, are shifted radially outward. The spacer upstream and downstream portions may substantially merge with or connect to the platform bands  54 B- 54 G of the adjacent disks. Thus, the exemplary remaining spacers  62 B- 62 H separate associated first annular inter-disk cavities  64 B- 64 H from the core flowpath  500 . 
   Additional inter-disk coupling is provided between at least some of the disks.  FIG. 2  shows couplings  66 C- 66 H radially inboard of the associated spacer  62 C- 62 H. The couplings  66 C- 66 H separate the associated first annular cavity  64 C- 64 H from a second annular cavity  67 C- 67 H. Each exemplary coupling  66 C- 66 H includes a first tubular ring- or sleeve-like structure  70  ( FIG. 3 ) extending aft from the disk thereahead and a second such structure  72  extending forward from the disk aft thereof. The exemplary structures  70  and  72  are each unitarily-formed with their associated individual disk, extending respectively aft and forward from near the junction of the disk web and bore. Alternative structures may be bonded or welded to or otherwise integrated or attached to remaining portions of the associated disk. At respective aft and fore rims of the structures  70  and  72 , the structures include interfitting radial splines or teeth  74  in a circumferential array ( FIG. 4 ). In the exemplary interfitting, each tooth  74  of one structure  70  or  72  is received in an inter-tooth space of the mating structure  72  or  70 , respectively. 
   The exemplary illustrated teeth  74  have a longitudinal span roughly the same as a radial span and a circumferential span somewhat longer. As is discussed in further detail below, in the exemplary embodiment there may be a longitudinal gap  75  between each of the teeth  74  and their receiving inter-tooth space. In the exemplary embodiment, this gap  75  is between the longitudinal apex  76  of the tooth and the base  77  of the intertooth space. The sides  78  of each tooth  74  may extend longitudinally in sliding engagement with the adjacent side  78  of the adjacent interfitting tooth to permit relative longitudinal movement. 
   The couplings  66 C- 66 H may provide a preferential transmission of torque rather than compression. Torque may be transmitted by the engagement of the tooth sides  78 . The longitudinal gaps  75 , if present, may permit the couplings  66 C- 66 H to contract and essentially avoid transmission of compression forces. 
   In the exemplary rotor stack, at fore and aft ends  80  and  82  ( FIG. 1 ), the rotor stack is mounted to the tie shaft  30  but intermediate (e.g., at the disk bores) is structurally clear of the shaft  30 . At the aft end  82 , a rear hub  90  (FIG.  2 —which may be unitarily formed with or integrated with an adjacent portion of the tie shaft  30 ) extends radially outward and forward to an annular distal end  92  having an outboard surface and a forward rim surface. The outboard surface is captured against an inboard surface of an aft portion of the platform band  54 I of the aft disk  34 I. Engagement may be similar to the hub engagement of the Suciu et al. applications. 
   As with the spacers of the Suciu et al. applications, increases in speed may tend to radially expand the spacers  62 A- 62 H, especially in intermediate longitudinal positions so as to partially flatten the spacers. Advantageously, the shapes of the tips  48  and spacer outboard surfaces are chosen to provide an essentially minimal gap at a specific steady state running condition and/or transient condition and/or range of such conditions. 
   Thus, the spacers  62 A- 62 H locally take up the compressive load across the rotor stack. There may be an associated tensile load across the tie shaft  30  (subject to net longitudinal force applied to the blades by the airflow). However, at least between certain disks, additional couplings (e.g.,  66 C- 66 H) at least partially take up the inter-disk torsional (torque) load. For example, the spacers  62 A and  62 B may take up essentially all the compressive and torsional loads between the disks  34 A- 34 C. Accordingly, the spacers  62 A and  62 B and their interfaces with the disks must have sufficient robustness to withstand such compressive and torsional loads. For example, there may be interfitting teeth or a particularly robust frictional/interference fit at the contact locations to transmit the torsional loads. However, the remaining spacers  62 C- 62 H, may take up a smaller portion of the torsional load between the disks  34 C- 34 I (e.g., less than half) and preferably essentially none (e.g., close to a deformation-limited minimum). The remainder of the torsional load may be taken up by the couplings  66 C- 66 H. 
   In alternate embodiments, the couplings  66 C- 66 H may take up some portion of the longitudinal load (e.g., if there are no gaps  75  or the gaps are small enough to become bottomed or if there is an additional load path). In such a case, the couplings  66 C- 66 H may take up a similarly low fraction of the longitudinal load between the disks  34 C- 34 I as the spacers  62 C- 62 H take up of the torsional load. However, if the longitudinal load is so split, it may be difficult to predict and may present engineering problems. 
   The bifurcation of torque and compression coupling along at least a portion of the stack may provide design opportunities and advantages relative to configurations lacking such bifurcation (e.g., where all compression and torsion loads between an adjacent pair of disks are carried by a single spacer). By relieving the spacers  62 C- 62 H of the need to carry torsional load, the spacers  62 C- 62 H may be lightened relative to those of a baseline configuration. Particular lightening may be achieved at the contact locations with the associated disks (e.g., by removing tooth engagement features of particularly robust interference fitting portions). The complementary features of the disk bands  54 C- 54 I may also be reduced or eliminated. 
   The additional couplings  66 C- 66 H may represent the addition of more mass than is saved in lightening the spacers and disks. However, there may be one or more potential benefits. If a mass is located at the spacers or the platform bands, the relatively outboard location greatly increases the centrifugal stresses imposed by such mass. The radially inward shift of such mass (including possible net increase in mass) to the inboard structures may reduce the stresses. Reduced stresses may facilitate one or more of several design or redesign opportunities. The engine could be radially expanded. Because such expansion would increase stresses, the stress reduction afforded by the bifurcation allows overall stresses to remain sub-critical. At a given radial size, yet further lightening (e.g., of the disk bores and webs) may be permitted because the bores and webs are subjected to less loading. This potentially allows the achievement of engine sizes, geometries, and increased operating speeds otherwise unattainable or attainable only through much generally greater robustness (and mass) of components. Also even with an overall mass increase, it may be possible to reduce the rotor&#39;s polar moment of inertia, thereby improving acceleration/deceleration performance. 
   Various engineering considerations may influence which inter-disk couplings are bifurcated and which are not. In the exemplary engine, the core flowpath diverges radially outward in the downstream direction. Thus, centrifugal loading may be more significant in downstream regions. Thus, the exemplary upstream couplings are not bifurcated whereas downstream couplings are. A variety of engineering considerations influence the radial position profile of the core flowpath. This may, accordingly, influence the particular bifurcation adopted. 
   Additionally, one or more of the couplings  66 C- 66 H may be used to carry anti-vortex tubes  100  ( FIG. 1 ). A variety of such tubes, otherwise mounted, are known in the art. In the exemplary engine, there are a circumferential array of tubes  100  (e.g., three to eight) at like longitudinal position, radially-extending, and evenly circumferentially-spaced, between the disks  34 G and  34 H. Near their inboard ends  102 , the tubes  100  are mounted to the coupling  66 G. For example, the tubes  100  may be mounted to a ring  103  ( FIG. 3 ). The ring  103  may be snap fit to one of the structures (e.g., the structure  72 ). There may be a longitudinal gap between the tubes  100  and the other structure (e.g.,  70 ) effective to provide similar compliance/freedom as do the gaps  75 . 
   The tube outboard ends  104  are located at an outboard portion of the radial span between the centerline  502  and the flowpath  500 . More particularly, they are well outboard (e.g., in an outboard half of the radial span between the coupling  66 G and the spacer  62 G). The tubes  100  direct a radially inward airflow to the space  67 G. Advantageously, this airflow helps maintain a desired disk temperature profile to control thermal/mechanical stresses. Depending on conditions, the airflow may cool disk portions that are hotter than other portions or heat disk portions that are cooler than other portions. 
   It may be desirable to thermally isolate individual disks or groups of disks (e.g., to limit the particular disk(s) subject to thermal influence of flow through particular groups of tubes  100 ). For example,  FIG. 3  shows a metallic bellows seal  120  extending inward from a narrow circumferential lip  122  at the forward end of the disk bore  52 G. The seal  120  extends into contacting engagement with the outer surface of the tie shaft  30 . Although the seal  120  may be secured to the shaft  30 , advantageously there is circumferential freedom of movement to accommodate twist and circumferential oscillation. Similarly, the bellows cross-section provides a radial compliance to accommodate relative radial movement (e.g., vibration) of the shaft  30  relative to the bore  52 G. The seal  120  isolates the annular volume  67 F ahead of the disk bore  52 G from the volume  67 G therebehind. 
   As noted in the Suciu et al. &#39;863 application, use of spacers such as  62 B- 62 H may have additional advantages. The outward concavity provides radial recessing of the spacer outboard surface near the middle of the spacer. This recessing provides a greater radial span for the core flowpath. The increase in radial span provides an area rule effect, at least partially compensating for reduced flow cross-sectional area caused by the presence of the vane airfoils. This may improve compressor efficiency. The spacers  62  may essentially eliminate air recirculation losses, heat transfer, and the like associated with prior art outboard inter-disk cavities that accommodate vane inboard platforms (e.g., like platforms  42 ). Manufacturing complexity may further be reduced with the absence, for example, of the vane inboard platforms. 
   The foregoing principles may be applied in the reengineering of an existing engine configuration or in an original engineering process. Various engineering techniques may be utilized. These may include simulations and actual hardware testing. The simulations/testing may be performed at static conditions and one or more non-zero speed conditions. The non-zero speed conditions may include one or both of steady-state operation and transient conditions (e.g., accelerations, decelerations, and combinations thereof). The simulation/tests may be performed iteratively. The iteration may involve varying parameters of the spacers  62 C- 62 H such as spacer thickness, spacer curvature or other shape parameters, vane tip curvature or other shape parameters, and static tip-to-spacer separation (which may include varying specific positions for the tip and the spacer). The iteration may involve varying parameters of the couplings  66 C- 66 H such as the thickness profiles of the structures  70  and  72 , the size and geometry of the teeth  74 , the radial position of the couplings, and the like. 
   One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when applied as a reengineering of an existing engine configuration, details of the existing configuration may influence details of any particular implementation. Accordingly, other embodiments are within the scope of the following claims.