Abstract:
Devices for intaking gases from the boundary layer through ducts hollowed out in blades. These devices are suitable for variable setting blades, installed on the stator using pivots. The seal is maintained despite the variation in the relative position between the moving pivots through which ducts pass, and the fixed intake header pipe.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject of this invention is air bleed on a pivoting blade of a turbomachine stator. 
     2. Discussion of Background 
     A large number of turbomachines include stator blades with a pivoting assembly so as to modify the gas guiding characteristics depending on the speed of the machine. Specialists say that the blade setting is variable. The blade setting is varied by a throttle control surrounding the stator and usually including an actuation ring to which connecting rods are articulated, the opposite ends of the connecting rods engaging with extreme portions of pivots of blades that extend outside the stator. Rotation of the ring around the stator tilts the connecting rods and pivots the blades about the pivot axis. 
     It is also known that gases can be taken in on the surface of the blades. Such an arrangement is normally applied to compressor blades to suck in the boundary layer and consequently increase the compression ratio. Intake takes place through hollow channels formed in the blades and opening up on their surface, and air is recovered and reinjected into another portion of the machine. Although this process has been known for several decades, it has been suggested particularly for fixed setting blades that can be used to build intake ducts that are also fixed. This description discloses satisfactory solutions to the seal problem that arises when an intake system is applied to variable setting blades, necessarily adjusted with a clearance through the stator case. 
     However, we will mention document U.S. Pat. No. 5,795,128 in which pivoting blades are provided with an air intake system including a header pipe covering the outside ends of the pivots and in which the hollow intake drillings drilled at the centre of the pivots open up. This design imposes a header pipe applied to the stator at the blades, which is a design constraint that cannot always be respected. One disadvantage of this design is due to the control rods that pass through the header pipe and require a particular sealing means. 
     Document FR-A-2 433 106 discloses a similar system except that the header pipe is made in the case in front of the central portions of the blade pivots. The hindrance associated with interference between the control rods and the header pipe disappears, but layout constraints are even greater. The airflow is affected by sudden direction and section variations that induce large head losses. 
     Document U.S. Pat. No. 5,472,314 describes a system in which the blade includes a pivoting part at the leading edge, a fixed part at the trailing edge, and an intermediate flexible part; air passes through the fixed part and the flexible part between the outside of the case and the pivoting part. This innovative design is expensive and complicated. 
     SUMMARY OF THE INVENTION 
     Thus, the invention relates to a device comprising a stator blade stage with variable setting, the blades each being fitted with a pivot passing through the stator and including an end portion extending outside the stator, characterised in that it includes an air bleed system comprising a header pipe surrounding the stator, connections to the header pipe prolonging the corresponding end portions of the pivots in a leaktight manner, and ducts hollowed out in the pivots and the faces of the blades. 
     The arrangement of connections to the header pipe prolonging the end portions of the pivots by spreading around them, results in the channels hollowed out in the pivots and passing through the stator opening up directly into the connections to the header pipe with no discontinuity or flow head loss. Seals arranged between the connections and the pivots reduce leaks to a low flow. 
     The design of the blades and the entire device remains simple, and the header pipe may be placed at any location at which it does not cause a hindrance, adjacent to or around the blade pivots. 
     However, it is important to be sure that junctions between connections to the header pipe and the end portions of the pivots do not hinder pivoting of the blades or cause excessive wear that would unacceptably increase leaks. In a first embodiment of the invention, connections to the header pipe include flexible pipes. One particularly simple means of connection to the blade pivots consists of arranging nuts free to rotate about the end of the pipe and connected to the ends of the pipe through stops, the end portions of the pivots being threaded to hold the connection nuts. All that is necessary then is to screw the nuts to the ends of the pivots to tighten the ends of the pipes in contact with the pivot end faces, the seals being arranged judiciously at the junctions. The threads may be the same as those used to install stop nuts in contact with the stator and that retain blade pivots preventing them from sliding in their housing. 
     One possible embodiment with strong pipes in such an application consists of making them from a metallic braid provided with an inside coating of a polymer such as tetrafluoroethylene (Teflon). This solves the problem of making a sealed mechanical connection between a fixed header pipe and mobile pivots placed at any position with respect to the header pipe. 
     The seal can be completed if the pipes are provided with sealing bellows penetrating the ducts hollowed out in the pivots. The bellows conceal the junctions between the pivots and the flexible pipes and reinforce the effectiveness of the seals. 
     In another embodiment, flexible pipes are no longer used. The connections of blade pivots to the header pipe are then made by tubular parts, in this case called rigid barrels, prolonging the pivots and fixed to the header pipe. This design supports the header pipe by blade pivots by means of rigid barrels, possibly without needing to use any other means of connecting the header pipe to the case. The header pipe at a distance from the case does not hinder the layout of the case. In one particular design, the assembly is possible if the header pipe and the connections are composed of two halves assembled at a joint, extending in the plane or in the cone of the blade pivoting axes. 
     In one particular design, the connections include sockets composed of two discontinuous halves surrounding the end portions of the pivots. The pivots are then tightly adjusted, with moderate clamping so as not to make pivoting more difficult. 
     In another embodiment in which the connections always include rigid barrels fixed to the header pipe, there are also prolonging pivots prolonging the blade pivots, in which ducts are hollowed out prolonging the ducts of blade pivots, rotational drive means connecting the prolonging pivots to the blade pivots, and bearings and seals between the barrels and the prolonging pivots. This more complicated construction has the advantage that it gives a better seal due to a greater assembly precision. The prolonging pivots may include axial support shoulders stopping in contact on the barrels, the header pipe then being composed of two concentric assembled parts. Greater cohesion of the device is then possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the following figures: 
         FIG. 1  is a general view of a device according to the invention, 
         FIG. 2  is a view of the most innovative portions of the device, and 
         FIGS. 3 and 4  show two other possible embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  contains a partial view of a turbomachine in which the annular gas flow path delimited by a stator  1  and a concentric rotor  2 , is occupied alternately by fixed blade stages connected to the stator  1 , and the mobile blade stages connected to the stator  2 . Some blade stages, for example belonging to the high pressure compressor, are hollowed out from intake ducts, the general shape of which may be compared to a comb and that include a main intake duct  3 , hollowed out in the blade approximately in the radial direction, and affluents  4  hollowed out in the blade substantially in the axial direction and that open up at its surface at an intake point  5 . The main ducts  3  open up in front of intake systems, most of which will not be described in detail, and are included inside the rotor  2  or the stator  1  depending on the case. In this case the description will apply to a particular stage  6  of fixed blades, in which the setting of the blades  7  is variable and pivots  8  passing through the stator  1  and that are connected to it by bearings  9 . The main ducts of the blades  7  pass through the pivots  8 . A circular header pipe  10  draws in air sucked in at the outside face of the stator  1 , through connections  11  that are connected to the ends of the main ducts  3  respectively on the end portions of the pivots  8 . 
       FIG. 2  shows the layout at this location. The pivots  8  are provided with connection portions  12  usually with a square section outside the stator  1 , control rods  13  controlling the setting of the blades  7  (that are only shown roughly) and threaded parts  14  on which nuts  46  are engaged retaining the pivots  8  preventing them from sliding in their bearings  9 . Rotation retainers, not shown here, hold the nuts  46  at fixed positions on the threaded portions  14 . According to the invention, the pivots  8  are prolonged towards the outside of the end portions  15  that make a junction with the connections  11 . In this embodiment, these connections are flexible pipes for which the connection ends each carry a ring  16  in which a groove  17  is hollowed out. Nuts  18  have interfaces fitted with collars  19  retained in grooves  17  and enabling free rotation of the nuts  18  around the ends of the connections  11 . The junctions are made by screwing the nuts  18  onto the threaded end portions  15  of the pivots  8  until the plane end faces of the connections  11  and pivots  8  touch each other through seals  20 . The main channels  3  then open up in the connections  11 . The seal is beneficially completed by bellows  50  engaged in the ends of the main ducts  3  and for which the outside folds touch their walls so as to limit the airflow reaching the seals  20 . It has been found that the connections  11 , that are fairly flexible in torsion and resistant to mechanical fatigue produced by pivoting of blades  7 , and the heat of the bleed air, were obtained by constructing them from a metallic braid coated on the inside with a polymer such as tetrafluoroethylene. The bellows  50  can also be composed of tetrafluoroethylene. 
     A slightly different design is shown in  FIG. 3 . It is distinguished from the previous design particularly by the absence of a flexible pipe to make the connections to the header pipe. Furthermore, the header pipe bolted to the stator is replaced by a header pipe  21  extending along the prolongation of the axes of the pivots  8 . The header pipe  21  is fixed to the tubular shaped barrels  22  directed towards the pivots  8  and that surround their end portions  23 . The bond is completed by bushings  24  retained in grooves hollowed out in the inside face of the barrels  22  and acting as bearings between the barrels  22  and the end portions  23 . Seals  25  and  26  arranged at the two ends of the bushings  24  held in place in other grooves of the barrels  22  and in friction on the end portions  23 , improve the seal of the device. The main ducts  3  open up almost directly into the header pipe  21 . One advantage of this design is that it eliminates the need for flexible connections  11  that are fragile elements of the intake device and occupy a fairly large volume on the surface of the stator  1 . Finally, the header pipe  21  is not retained by the stator  1  but by the pivots  8 . An easy and sufficiently rigid assembly is possible if the header pipe  21  and the barrels  22  are composed of two halves  27  and  28  that are substantially symmetric and are assembled to each other by a seal  29  passing through the plane or the cone of the rotation axes of the pivots  8 . The assembly is made through flanges  29  and  30  produced on the outside and inside edges of the halves  27  and  28 . The seal  29  is restored by the addition of a hardening material. Furthermore, the bushings  24  are also formed from two separate halves  30  and  31  for which the limits are close to the seal  29 . When the header pipe  21  and the barrels  22  are assembled, the halves  30  and  31  of the bushings  24  are brought towards each other and apply a fairly tight fit onto the end portions  23  of the pivots  8 , which produces good cohesion of the device without genuinely opposing rotation of the pivots  8 . This device is suitable, regardless of whether or not the end portions  23  of the pivots  8  are threaded. Although this embodiment of the device is very simple and compact, its seal is not as good. 
     One possible improvement to this type of embodiment is shown in  FIG. 4 . The shape of the header pipe  32  for this embodiment is similar to the shape of the header pipe  21 , but its composition is slightly different as will be seen later. It also includes barrels  33  similar to the barrels  22  but with an individual structure. One essential difference is that the barrels  33  contain prolonging pivots  34  that rotate in them about bearings  35  and are held in place by shoulders  36  at the ends arranged on the side of the header pipe  32  and by nuts  37  adjacent to the pivots  8 , something like the pivots  8  installed on the stator  1 . The pivots  8  and the prolonging pivots  34  are aligned and installed one on the other, the prolonging pivots  34  being adjusted around the end portions of the pivots  8 . Central channels  44  passing through the prolonging pivots  34  prolong the ducts  3  of the pivots  8  of the blades  7  and open up into the header pipe  32 . The prolonging pivots  34  are driven in rotation by the pivots  8  through notches  45  that bring them together. Since the bushings  35  and the barrels  22  are individual, the seal is much better if seals  38  and  39  are placed on each side of the bushings  35 , similar to the previous embodiment. The header pipe  32  remains composed of two portions  40  and  41  assembled together by opposite flanges  42  and  43 , but the seal is perpendicular to the rotation axes of the pivots  8 , one of the portions  40  is an external portion and the other portion  41  is an internal portion comprising barrels  33 , and flanges  42  and  43  are arranged on the side faces of the header pipe  32 .