Abstract:
A fan-turbine rotor assembly for a tip turbine engine includes a fan hub with an outer periphery scalloped by a multitude of elongated openings which extend into a fan hub web. Each elongated opening defines an inducer section and a blade receipt section to retain a hollow fan blade section. The blade receipt section retains each of the hollow fan blade sections adjacent each inducer section. The inducer sections are cast directly into the fan hub which minimizes leakage between each fan blade section and each of the respective inducer sections to minimize airflow leakage and increase engine efficiency.

Description:
[0001]    This invention was made with government support under Contract No.: F33657-03-C-2044. The government therefore has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a tip turbine engine, and more particularly to a fan-turbine rotor assembly which includes an inducer formed therein. 
         [0003]    An aircraft gas turbine engine of the conventional turbofan type generally includes a forward bypass fan, a compressor, a combustor, and an aft turbine all located along a common longitudinal axis. A compressor and a turbine of the engine are interconnected by a shaft. The compressor is rotatably driven to compress air entering the combustor to a relatively high pressure. This pressurized air is then mixed with fuel in a combustor and ignited to form a high energy gas stream. The gas stream flows axially aft to rotatably drive the turbine which rotatably drives the compressor through the shaft. The gas stream is also responsible for rotating the bypass fan. In some instances, there are multiple shafts or spools. In such instances, there is a separate turbine connected to a separate corresponding compressor through each shaft. In most instances, the lowest pressure turbine will drive the bypass fan. 
         [0004]    Although highly efficient, conventional turbofan engines operate in an axial flow relationship. The axial flow relationship results in a relatively complicated elongated engine structure of considerable longitudinal length relative to the engine diameter. This elongated shape may complicate or prevent packaging of the engine into particular applications. 
         [0005]    A recent development in gas turbine engines is the tip turbine engine. Tip turbine engines locate an axial compressor forward of a bypass fan which includes hollow fan blades that receive airflow from the axial compressor therethrough such that the hollow fan blades operate as a centrifugal compressor. Compressed core airflow from the hollow fan blades is mixed with fuel in an annular combustor and ignited to form a high energy gas stream which drives the turbine integrated onto the tips of the hollow bypass fan blades for rotation therewith as generally disclosed in U.S. Patent Application Publication Nos.: 20030192303; 20030192304; and 20040025490. 
         [0006]    The tip turbine engine provides a thrust to weight ratio equivalent to conventional turbofan engines of the same class within a package of significantly shorter length. 
         [0007]    One significant rotational component of a tip turbine engine is the fan-turbine rotor assembly. The fan-turbine rotor assembly includes a multitude of components which rotate at relatively high speeds to generate bypass airflow while communicating a core airflow through each of the multitude of hollow fan blades. A large percentage of the expense associated with a tip turbine engine is the manufacture of the fan-turbine rotor assembly and the integration of the inducer with the fan hub. 
         [0008]    Accordingly, it is desirable to provide an inducer arrangement for a fan-turbine rotor assembly, which is relatively inexpensive to manufacture yet provides a high degree of reliability. 
       SUMMARY OF THE INVENTION 
       [0009]    The fan-turbine rotor assembly for a tip turbine engine according to the present invention includes a fan hub which has an outer periphery scalloped by a multitude of elongated openings which extend into a fan hub web. Each elongated opening defines an inducer section and a blade receipt section to retain a hollow fan blade section. The blade receipt section retains each of the hollow fan blade sections adjacent each inducer section. An inner fan blade mount is located adjacent an inducer exhaust section to communicate a core airflow communication path from within each inducer section into the core airflow passage within each fan blade section. 
         [0010]    The inducer is cast directly into the fan hub which minimizes leakage between each fan blade section and each inducer section to provide increased engine efficiency. Manufacturing and assembly is also readily facilitated. 
         [0011]    The present invention therefore provides an inducer arrangement for a fan-turbine rotor assembly which is relatively inexpensive to manufacture yet provides a high degree of reliability. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0013]      FIG. 1  is a partial sectional perspective view of a tip turbine engine; 
           [0014]      FIG. 2  is a longitudinal sectional view of a tip turbine engine along an engine centerline; 
           [0015]      FIG. 3  is an exploded view of a fan-turbine rotor assembly; 
           [0016]      FIG. 4  is an assembled view of a fan-turbine rotor assembly; 
           [0017]      FIG. 5A  is an expanded radial sectional view of an inducer section; 
           [0018]      FIG. 5B  is a sequential sectional view of the fan hub illustrating the inducer sections therewith; 
           [0019]      FIG. 6  is a schematic view of airflow through the last stage of an axial compressor and into the inducer; 
           [0020]      FIG. 7A  is an expanded phantom perspective view of a fan blade mounted to a hub of a fan-turbine rotor assembly; 
           [0021]      FIG. 7B  is an expanded partially sectioned perspective view of a fan blade mounted to a hub of a fan-turbine rotor assembly; and 
           [0022]      FIG. 7C  is an expanded partially sectioned perspective view of a diffuser section of a fan blade. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0023]      FIG. 1  illustrates a general perspective partial sectional view of a tip turbine engine type gas turbine engine  10 . The engine  10  includes an outer nacelle  12 , a rotationally fixed static outer support structure  14  and a rotationally fixed static inner support structure  16 . A multitude of fan inlet guide vanes  18  are mounted between the static outer support structure  14  and the static inner support structure  16 . Each inlet guide vane preferably includes a variable trailing edge  18 A. 
         [0024]    A nose cone  20  is preferably located along the engine centerline A to smoothly direct airflow into an axial compressor  22  adjacent thereto. The axial compressor  22  is mounted about the engine centerline A behind the nose cone  20 . 
         [0025]    A fan-turbine rotor assembly  24  is mounted for rotation about the engine centerline A aft of the axial compressor  22 . The fan-turbine rotor assembly  24  includes a multitude of hollow fan blades  28  to provide internal, centrifugal compression of the compressed airflow from the axial compressor  22  for distribution to an annular combustor  30  located within the rotationally fixed static outer support structure  14 . 
         [0026]    A turbine  32  includes a multitude of tip turbine blades  34  (two stages shown) which rotatably drive the hollow fan blades  28  relative a multitude of tip turbine stators  36  which extend radially inwardly from the static outer support structure  14 . The annular combustor  30  is axially forward of the turbine  32  and communicates with the turbine  32 . 
         [0027]    Referring to  FIG. 2 , the rotationally fixed static inner support structure  16  includes a splitter  40 , a static inner support housing  42  and an static outer support housing  44  located coaxial to said engine centerline A. 
         [0028]    The axial compressor  22  includes the axial compressor rotor  46  from which a plurality of compressor blades  52  extend radially outwardly and a compressor case  50  fixedly mounted to the splitter  40 . A plurality of compressor vanes  54  extend radially inwardly from the compressor case  50  between stages of the compressor blades  52 . The compressor blades  52  and compressor vanes  54  are arranged circumferentially about the axial compressor rotor  46  in stages (three stages of compressor blades  52  and compressor vanes  54  are shown in this example). The axial compressor rotor  46  is mounted for rotation upon the static inner support housing  42  through a forward bearing assembly  68  and an aft bearing assembly  62 . 
         [0029]    The fan-turbine rotor assembly  24  includes a fan hub  64  that supports a multitude of the hollow fan blades  28 . Each fan blade  28  includes an inducer section  66 , a hollow fan blade section  72  and a diffuser section  74 . The inducer section  66  receives airflow from the axial compressor  22  generally parallel to the engine centerline A and turns the airflow from an axial airflow direction toward a radial airflow direction. The airflow is radially communicated through a core airflow passage  80  within the fan blade section  72  where the airflow is centrifugally compressed. From the core airflow passage  80 , the airflow is turned and diffused toward an axial airflow direction toward the annular combustor  30 . Preferably the airflow is diffused axially forward in the engine  10 , however, the airflow may alternatively be communicated in another direction. 
         [0030]    A gearbox assembly  90  aft of the fan-turbine rotor assembly  24  provides a speed increase between the fan-turbine rotor assembly  24  and the axial compressor  22 . Alternatively, the gearbox assembly  90  could provide a speed decrease between the fan-turbine rotor assembly  24  and the axial compressor rotor  46 . The gearbox assembly  90  is mounted for rotation between the static inner support housing  42  and the static outer support housing  44 . The gearbox assembly  90  includes a sun gear shaft  92  which rotates with the axial compressor  22  and a planet carrier  94  which rotates with the fan-turbine rotor assembly  24  to provide a speed differential therebetween. The gearbox assembly  90  is preferably a planetary gearbox that provides co-rotating or counter-rotating rotational engagement between the fan-turbine rotor assembly  24  and an axial compressor rotor  46 . The gearbox assembly  90  is mounted for rotation between the sun gear shaft  92  and the static outer support housing  44  through a forward bearing  96  and a rear bearing  98 . The forward bearing  96  and the rear bearing  98  are both tapered roller bearings and both handle radial loads. The forward bearing  96  handles the aft axial loads while the rear bearing  98  handles the forward axial loads. The sun gear shaft  92  is rotationally engaged with the axial compressor rotor  46  at a splined interconnection  100  or the like. 
         [0031]    In operation, air enters the axial compressor  22 , where it is compressed by the three stages of the compressor blades  52  and compressor vanes  54 . The compressed air from the axial compressor  22  enters the inducer section  66  in a direction generally parallel to the engine centerline A and is turned by the inducer section  66  radially outwardly through the core airflow passage  80  of the hollow fan blades  28 . The airflow is further compressed centrifugally in the hollow fan blades  28  by rotation of the hollow fan blades  28 . From the core airflow passage  80 , the airflow is turned and diffused axially forward in the engine  10  into the annular combustor  30 . The compressed core airflow from the hollow fan blades  28  is mixed with fuel in the annular combustor  30  and ignited to form a high-energy gas stream. The high-energy gas stream is expanded over the multitude of tip turbine blades  34  mounted about the outer periphery of the fan-turbine rotor assembly  24  to drive the fan-turbine rotor assembly  24 , which in turn drives the axial compressor  22  through the gearbox assembly  90 . Concurrent therewith, the fan-turbine rotor assembly  24  discharges fan bypass air axially aft to merge with the core airflow from the turbine  32  in an exhaust case  106 . A multitude of exit guide vanes  108  are located between the static outer support housing  44  and the rotationally fixed static outer support structure  14  to guide the combined airflow out of the engine  10  to provide forward thrust. An exhaust mixer  110  mixes the airflow from the turbine blades  34  with the bypass airflow through the fan blades  28 . 
         [0032]    Referring to  FIG. 3 , the fan-turbine rotor assembly  24  is illustrated in an exploded view. The fan hub  64  is the primary structural support of the fan-turbine rotor assembly  24  ( FIG. 4 ). The fan hub  64  is preferably forged and then milled to provide the desired geometry. The fan hub  64  defines a bore  111  and an outer periphery  112 . The outer periphery  112  is preferably scalloped by a multitude of elongated openings  111 . The fan hub  64  is the primary structural support of the fan-turbine rotor assembly  24 . The fan hub  64  supports the multitude of fan blades  28 , a diffuser  114 , and the turbine  32 . The diffuser  114  defines a diffuser surface  119  formed about the outer periphery of the fan blade sections  72  to provide structural support to the outer tips of the fan blade sections  72  and to turn and diffuse the airflow from the radial core airflow passage  80  ( FIG. 3 ) toward an axial airflow direction. The turbine  32  is mounted to the diffuser surface  119  as one or more turbine ring rotors  118   a ,  118   b  which may include a multitude of turbine blade clusters. 
         [0033]    Referring to  FIG. 4 , the fan hub  64  itself forms the multitude of inducer sections  66 . Each inducer section  66  formed by the fan hub  64  is essentially a conduit that defines an inducer passage  118  between an inducer inlet section  120  and an inducer exit section  128   FIGS. 5A ,  5 B). 
         [0034]    Referring to  FIGS. 5A and 5B , the inducer sections  66  together form the inducer  116  of the fan-turbine rotor assembly  24 . The inducer inlet section  120  of each inducer passage  118  extends forward of the fan hub  64  and is canted toward a rotational direction of the fan hub  64  such that inducer inlet  120  operates as an air scoop during rotation of the fan-turbine rotor assembly  24 . Each inducer passage  118  provides separate airflow communication to each core airflow passage  80  when each fan blade section  72  is mounted within each elongated opening  114 . Preferably, each fan blade section  72  includes an attached diffuser section  74  such that the diffuser surface  119  is formed when the fan-turbine rotor assembly  24  is assembled. 
         [0035]      FIG. 6  schematically illustrates the relationship of the angle of the last stage of the compressor rotor blade  52  (one shown) and the last stage of the compressor vanes  54  in the three stage axial compressor  22  ( FIG. 2 ) prior to communication of the airflow from the axial compressor  22  into the inducer sections  66  in the engine  10 . Referring to the compressor blade velocity triangle Bt, the compressor rotor blade  52  is angled relative to the engine centerline A to provide an angle of a relative velocity vector, Vr 1 . The velocity of the counter-rotating compressor blade  52  gives a blade velocity vector, Vb 1 . The resultant vector, indicating the resultant core airflow from the compressor blade  52 , is the absolute velocity vector, Val. 
         [0036]    Referring to the vane velocity vector St, a stator leading edge  541  of the compressor stator  54  is angled to correspond with the absolute velocity vector, Va 1  from the compressor rotor blade  52  to efficiently receive and compress the core airflow from the compressor blade  52 . The vane trailing edge  54   t  is angled relative to the engine centerline A to compress and redirect the airflow toward the inducer section  66  (one shown) as the inducer  116  rotates relative thereto at a vane absolute velocity vector, Va 1 . 
         [0037]    The inducer inlet  120  of the inducer section  66  is angled to efficiently receive the core airflow from the vane trailing edge  54   t  which flows toward the inducer section  66  at the absolute velocity vector, Va 1  from the vane  54 . The velocity of the inducer section  66  gives an inducer velocity vector, Vb 1 . Referring to the inducer velocity triangle It, the angle of the inducer  66  is selected such that the sum of the inducer relative velocity vector Vr 1  and the inducer velocity vector Vb 1  match the angle of the core airflow incoming from the compressor vane trailing edge  54   t  (absolute velocity vector, Val). 
         [0038]    It should be understood that the specific angles will depend on a variety of factors, including anticipated blade velocities and the design choices made in the earlier stages of the compressor blades  52  and compressor vanes  54  to provide a length sufficient to turn the core airflow from axial flow to radial flow while decreasing the overall length of the engine  10 . It should be understood that the axial compressor  22  may alternatively counter-rotate relative to inducer  116  as disclosed in co-pending application ______ entitled “COUNTER-ROTATING GEARBOX FOR TIP TURBINE ENGINE,” which is assigned to the assignee of the present invention and which is hereby incorporated by reference in its entirety. 
         [0039]    Referring to  FIG. 7A , the fan hub  64  retains each hollow fan blade section  72  through a blade receipt section  122 . The blade receipt section  122  preferably forms an axial semi-cylindrical opening formed along the axial length of the elongated openings  111 . It should be understood that other retention structures such as a dove-tail, fir-tree, or bulb-type engagement structure will likewise be usable with the present invention. 
         [0040]    Each hollow fan blade section  72  includes a fan blade mount section  124  that corresponds with the blade receipt section  122  to retain the hollow fan blade section  72  within the fan hub  64 . The fan blade mount  124  preferably includes a semi-cylindrical portion to radially retain the fan blade  28 . 
         [0041]    Referring to  FIG. 7B , the inner fan blade mount  124  is preferably uni-directionally mounted into the blade receipt section  122  such as from the rear face of the fan hub  64 . The fan blade mount section  124  engages the blade receipt section  122  during operation of the fan-turbine rotor assembly  24  to provide a directional lock therebetween. That is, the inner fan blade mount  124  and the blade receipt section  122  may be frustoconical or axially non-symmetrical such that the forward segments form a smaller perimeter than the rear segment to provide a wedged engagement therebetween when assembled. 
         [0042]    Each inducer section  66  within the fan hub  64  receives core airflow communication from the inducer passages  118  into the core airflow passage  80  and turns and diffuses the airflow through each diffuser section  74  of the diffuser  114  (also illustrated in  FIG. 7C ). 
         [0043]    It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
         [0044]    The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.