Abstract:
A vane for a stator of a variable-geometry turbine, in particular for aeronautical engines, has an airfoil profile and a pair of hinge portions, which are carried by the airfoil profile and enable the airfoil profile to be coupled to a support structure of the stator so as to be rotatable about an axis of adjustment; the vane also has internal channels that allow a flow of air to pass through in order to cool the hinge portions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority under 35 U.S.C. §119 of application number TO2001A 000446, filed May 11, 2001 in Italy.  
         BACKGROUND OF INVENTION  
         [0002]    The present invention relates to a vane for a stator of a variable-geometry turbine, in particular of an axial turbine for aeronautical engines.  
           [0003]    As is known, an axial turbine for an aeronautical engine comprises at least one stator and one rotor arranged in succession to each other and comprising respective arrays of vanes delimiting between them associated nozzles through which a flow of gas can pass.  
           [0004]    In aeronautical engines, it has been found necessary to use axial turbines having relatively high efficiency in all operating conditions and, therefore, over a relatively wide range of values for the rate of flow of the gases that pass through the turbine itself.  
           [0005]    This requirement could be met by producing variable-geometry turbines, i.e. turbines in which it is possible to vary the transverse area of the nozzles of at least one stator, in particular by adjusting the angular position of the stator vanes about respective axes incident to the axis of the turbine.  
           [0006]    In use, however, the operating temperatures of the turbine are extremely high and involve considerable thermal expansion of the vanes and other components, so that jamming or outright seizure could occur between the movable vanes and the fixed parts of the stator, consequently compromising the functionality of the turbine.  
         SUMMARY OF INVENTION  
         [0007]    The purpose of this invention is to produce a vane for a stator of a variable-geometry turbine, in particular for aeronautical engines, which allows the problems set out above to be solved simply and economically.  
           [0008]    According to the present invention, a vane is produced for a stator of a variable-geometry turbine, in particular for aeronautical engines; the vane comprising an airfoil profile and means for coupling said airfoil profile to a support structure of said stator; characterised in that said coupling means comprise hinge means carried by said airfoil profile to allow rotation of the airfoil profile itself with respect to said support structure about an axis of adjustment, and in that it comprises means for cooling said hinge means.  
           [0009]    The present invention also concerns a stator of a variable-geometry turbine, in particular for aeronautical engines.  
           [0010]    According to the present invention, a stator of a variable-geometry turbine is produced, in particular for aeronautical engines; the stator comprising a support structure and a plurality of vane members delimiting between them a plurality of passages for a flow of gas; each vane comprising an airfoil profile and means for coupling said airfoil profile to said support structure; characterised in that said coupling means comprise hinge means carried by said airfoil profile to allow the rotation of the airfoil profile with respect to said support structure about an axis of adjustment, and in that it comprises means for cooling said hinge means. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    The invention will now be described with reference to the attached drawings, which illustrate a non-limiting embodiment of the invention, in which:  
         [0012]    [0012]FIG. 1 is a schematic radial section of a preferred embodiment of the vane for a stator of a variable-geometry turbine, in particular for aeronautical engines, produced according to the present invention;  
         [0013]    [0013]FIG. 2 illustrates in radial section and at a larger scale the vane in FIG. 1; and  
         [0014]    [0014]FIG. 3 is a perspective view, with parts in section, of the vane in FIGS. 1 and 2. 
     
    
     DETAILED DESCRIPTION  
       [0015]    In FIG. 1, the number  1  indicates a variable-geometry axial turbine (shown schematically and in part), which constitutes part of an aeronautical engine, not shown.  
         [0016]    The turbine  1  is axially symmetrical with respect to an axis  3  coinciding with the axis of the associated aeronautical engine and comprises an engine shaft  4  rotatable about the axis  3  and a case or casing  8  housing a succession of coaxial stages, only one of which is shown as  10  in FIG. 1.  
         [0017]    With reference to FIGS. 1 and 2, the stage  10  comprises a stator  11  and a rotor  12  keyed to the engine shaft  4  downstream from the stator  11 . The stator  11  in turn comprises a hub  16  (shown schematically and in part), which supports the engine shaft  4  in a known manner and is integrally connected to the casing  8  by means of a plurality of spokes  17  (FIG. 2) angularly equidistant from each other about the axis  3 .  
         [0018]    As shown in FIG. 2, the stator  111  also comprises two annular platforms or walls  20 ,  21 , which are arranged in an intermediate radial position between the hub  16  and the casing  8  and have the spokes  17  passing through them. The walls  20 ,  21  are coupled, one with the casing  8  and the other with the hub  16  in substantially fixed datum positions by means of connecting devices  24  that allow the walls  20 ,  21  themselves the possibility of axial and radial displacements of relatively limited amplitude with respect to the casing  8  and the hub  16  in order to compensate, in service, for the differences in thermal expansion between the various components.  
         [0019]    The walls  20 ,  21  have respective surfaces  27 ,  28  facing each other and radially delimiting an annular duct  30  with a diameter increasing in the direction of travel of the gas flow that passes through the turbine  1 . The walls  20 ,  21  carry an array of vanes  32  (only one of which is shown) angularly equidistant from each other about the axis  3  with the spokes  17  passing through them and comprising respective airfoil profiles  33 , which are housed in the duct  30  and between them circumferentially delimit a plurality of nozzles.  
         [0020]    With reference to FIGS. 2 and 3, each vane  32  also comprises a pair of circular hinging flanges  36 ,  37 , integral with the associated profile  33 , arranged at opposite ends of the profile  33  itself and coaxial with each other along an axis  40 , which is incident to the axis  3  and forms an angle other than 90° with the axis  3 .  
         [0021]    The flanges  36 ,  37  of each vane  32  engage rotatably in respective circular seatings  41 ,  42  made in the walls  20  and  21  respectively to allow the associated profile  33  to rotate about the axis  40 .  
         [0022]    With reference to FIG. 2, the flanges  36 ,  37  of each vane  32  terminate in respective coaxial cylindrical sections  48 ,  49 , of which the section  48  is caused to rotate in use by an angular positioning unit  50  (shown in part) comprising in particular a motor-driven actuating and synchronising ring  51  designed to rotate the profiles  33  simultaneously about the respective axes  40  through the same angle, keeping the profiles  33  themselves in the same orientation to each other with respect to the surfaces  27 ,  28 . In particular, the maximum angular deflection of each vane  32  about the associated axis  40  is approximately 6, while the zones of the surfaces  27  and  28  to which the profiles  33  are coupled slidably have a shape complementary to associated ideal surfaces generated by rotation of the profiles  33 .  
         [0023]    The flanges  36 ,  37  of each vane  32  are defined by respective circular plate portions, project from the associated profile  33  radially with respect to the axis  40  and are facing each other in the duct  30 .  
         [0024]    The flange  37  is delimited by a cylindrical surface  59  directly and slidably coupled with the wall  21  in the seating  42  and by a flat surface  60  connecting the surface  59  to the section  49 , which is coupled to the wall  21  via an interposed spacer bush  68  constituting a friction bearing.  
         [0025]    On the other hand, the flange  36  is delimited by a cylindrical surface  61  directly and slidably coupled with the wall  20  in the seating  41  and by a flat surface  62 , which connects the surface  51  to the section  48 , and against which is arranged an axially abutting radial lever  72  connecting the vane  32  to the ring  51 . In particular, the lever  72  is attached to the section  48  and is coupled with the wall  20  via an interposed spacer bush  73  constituting a friction bearing.  
         [0026]    With reference to FIGS. 2 and 3, each vane  32  is cooled in use by a flow of air under pressure, which is conveyed into the case  8  in a known manner, not shown, and flows through a passage  81  made in the vane  32  itself and comprising an inlet  82  defined by the flange  36 , an outlet  84  defined by the flange  37  and an intermediate chamber  85  made in the profile  33 . The chamber  85 , in particular, communicates with the duct  30  via a plurality of holes (not shown) made in a tail portion of the profile  33  to cool the trailing edge of the profile  33  itself which, in use, is subject to severe thermal stresses.  
         [0027]    The flow of cooling air removes heat from the flanges  36 ,  37  by passing through the inlet  82  and the outlet  84  and also by means of channelling  86  inside the flanges  36 ,  37  themselves. This channelling  86  comprises, for each flange  36 ,  37  at least one associated pair of through-holes  87  (FIG. 2) made in positions diametrically opposite to each other and in a substantially radial direction, and an associated continuous circumferential groove  89 , which is made along the surface  59 ,  61  close to the circular edge or corner of separation from the surface  60 ,  62  and communicates with the chamber  85  via the holes  87 .  
         [0028]    In use, the flow of cooling air is sent at a pressure of about 20 bar into the passage  81 , flows through the holes  87  and removes heat from the flanges  36 ,  37  to limit the thermal expansion of the flanges  36 ,  37  themselves.  
         [0029]    The air sent into the grooves  89 , at the same time, forms a film or cushion of air that performs not only a load-bearing function during rotation of the vanes, limiting the friction forces between flanges  36 ,  37  and walls  20 ,  21 , but above all a sealing function preventing the flow of gas from flowing out of the duct  30  through the clearances formed between the vanes  32  and the walls  20 ,  21  in the seatings  41 ,  42 .  
         [0030]    In other words, in the grooves  89  the cushion of air constitutes a sort of virtual sealing ring that avoids the use of sealing gaskets between the vanes  32  and the walls  20 ,  21 .  
         [0031]    From the above, it is evident that the vanes  32  enable the geometry of the nozzles of the stator  11  to be adjusted in use, the vanes being hinged to the walls  20 ,  21 , and at the same time avoid jamming and seizure against the walls  20 ,  21  during adjustment, being cooled at the flanges  36 ,  37 .  
         [0032]    In fact, the removal of heat by means of the flow of air that passes through the passage  81  and the channelling  86  makes it possible to limit the thermal expansion of the flanges  36 ,  37  and thus to control the clearances between the flanges  36 ,  37  themselves and the walls  20 ,  21  in order to obtain correct and always precise angular positioning of the vanes  32  about the respective axes  40 .  
         [0033]    Moreover, as already stated, the fact of causing air to flow along the surfaces  59 ,  61  makes it possible to produce a cushion of air that limits the friction between the flanges  36 ,  37  and the walls  20 ,  21  and therefore contributes significantly to obtaining precise angular positioning of the vanes  32  and thus correct operation of the turbine  1 , achieving high levels of efficiency in all operating conditions of the associated aeronautical engine.  
         [0034]    Finally, it is evident from the above that modifications and variations can be made to the vane  32  described and illustrated, without extending it beyond the scope of protection of the present invention.  
         [0035]    In particular, the vane  32  could have hinge portions different from those described and illustrated and/or cooling fluids or channels different from those indicated could be provided. For example, the cushions of air that are formed in use between the flanges  36 ,  37  and the walls  20 ,  21  could be obtained by producing seatings in the walls  20 ,  21  instead of in the vanes  32 , or a simple chamfer along the corners between the surfaces  59 ,  61  and the surfaces  60 ,  62 . Moreover, a labyrinth seating could be provided instead of a simple groove  89  on the flanges  36 ,  37 .