Abstract:
The relief device is designed to divert a portion of a main flow toward a by-pass flow in a turbojet that includes a main flow stream, a by-pass flow stream and an intermediate casing. The relief device includes inner openings of the inner shroud, outer openings of the outer shroud, a relief circuit connecting the inner openings to the outer openings, and a blanking device capable of opening and closing the relief circuit. The relief circuit includes upstream holes of the intermediate casing, downstream holes of the intermediate casing, and an annular channel defined between the intermediate casing, the outer shroud and a connecting partition. The connecting partition rests on the intermediate casing so as to encompass the downstream holes of the intermediate casing in the annular channel and resting on the outer shroud so as to encompass the outer openings of the outer shroud in the annular channel.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the field of turbofan aircraft engines. 
     It relates more precisely to a relief device for a turbojet and to a turbojet fitted with such a relief device. 
     In a known manner, an aircraft turbofan engine comprises a main stream of gas flow and a by-pass stream of gas flow that are separated by an intermediate casing that is a structural part. In the main stream are placed, from upstream to downstream in the direction of flow of the gases, a low-pressure compressor and a high-pressure compressor. The air thus compressed is carried to a combustion chamber in which it is mixed with the pressurized fuel that is burnt to supply, downstream of the combustion chamber, energy to a high-pressure turbine that drives the high-pressure compressor, then to a low-pressure turbine that drives the fan and the low-pressure compressor. The gases leaving the turbines supply a residual thrust that is added to the thrust generated by the gases traveling in the by-pass stream in order to provide the propulsion of the aircraft. 
     In certain flight conditions, the quantity of air delivered by the low-pressure compressor is too great to ensure correct operation of the turbojet, so it is necessary to divert a portion of this air toward the by-pass stream in order to prevent the occurrence of the phenomenon called pumping that is due to the separation of fluid wisps along the blades and causes an instability of the flow. 
     The air diversion is also called air relief. It is carried out by means of a relief device. 
     DESCRIPTION OF THE PRIOR ART 
     A well-known relief device uses movable flaps that are articulated and actuated simultaneously by a set of actuation means. Such a flap relief device is described in document U.S. Pat. No. 3,638,428. An example of a flap relief device is shown in  FIG. 10 , which illustrates the main flow stream  110  in which the low-pressure compressor  112  is placed and the by-pass flow stream  114  that surrounds the main flow stream  110 . The two streams  110 ,  114  are annular and are separated by an interstream compartment  117  shown in the form of an annular compartment having an inner shroud  116  and an outer shroud  118 . An intermediate casing  120  that is a structural part extends over one section of the turbojet and connects the inner shroud  116  and the outer shroud  118 . The intermediate casing  120  comprises support arms  122  that extend radially from the outer shroud  118  to the inside of the by-pass stream  114 . These support arms  122  allow the forces of the engine to pass to the structure of the aircraft. They are usually eight to twelve in number. 
     Upstream of the support arms  122 , the inner stream  114  also contains contravanes  124  which extend radially from the outer shroud  118  and have the function of rectifying the flow of air after it has passed through the blades of a fan (not shown in the figure). 
     The flow in the main stream  110  is represented by the arrows  190 . The flow in the by-pass stream  114  is represented by the arrows  192 . The air relief or diversion from the main stream  110  to the by-pass stream  114  is shown by the arrows  194 . This relief takes place through inner openings  126  of the inner shroud  116  and outer openings  128  of the outer shroud  118 , by means of movable flaps  130  placed in the interstream compartment  117 , between the inner shroud  116  and the outer shroud  118 . The movable flaps  130  are actuated by cylinders  164  so as to be able to blank off the inner openings  126  in a synchronous manner. The outer openings  128  are not blanked off. They have the form of grilles distributed over the circumference of the outer shroud  118  and positioned at the intermediate casing between the support arms  122 . 
     SUMMARY OF THE INVENTION 
     The relief device of the prior art that has just been described with reference to  FIG. 10  is not suitable for recent aviation turbojet designs which are increasingly tending to reduce the weight and space requirement of the turbojets. Accordingly an effort is being made to shorten the axial dimension of turbojets, and it has been proposed to place the contravanes on the same axial section of the intermediate casing as the support arms, and even to give these support arms a stator profile. For example, on the intermediate casing, there are support arms between which the countervanes are distributed. Consequently there is no more room on this section to place the outer opening grilles necessary for relief. In addition, even if it were possible to clear positions to place such relief grilles, another disadvantage would be of concern. Specifically, the main flow (arrows  190 ) often contains debris such as ice particles. If they are in the relief flow (arrows  194 ), this debris is likely to damage the countervanes placed between the support arms, because these countervanes are usually made of composite material or aluminum. 
     The object of the invention is to remedy the disadvantages explained above. It proposes a relief device making it possible to provide an air diversion or relief from the main stream to the by-pass stream that is suitable for a turbojet design in which the countervanes are positioned on the same section as the support arms. 
     According to a first aspect, the invention relates to a relief device designed to divert a portion of a main flow toward a by-pass flow in a turbojet, said turbojet having a main flow stream and a by-pass flow stream between which there is an interstream compartment having an inner shroud separating it from said main stream and an outer shroud separating it from said by-pass stream, said turbojet having an intermediate casing furnished with an upstream wall and a downstream wall, the relief device comprises:
         inner openings of the inner shroud, positioned upstream of the intermediate casing,   outer openings of the outer shroud, positioned downstream of the intermediate casing,   a relief circuit connecting said inner openings to said outer openings through the interstream compartment,   blanking means capable of opening and closing said relief circuit and wherein the relief circuit comprises:       

     upstream holes of the intermediate casing, 
     downstream holes of the intermediate casing, 
     an annular channel defined between the intermediate casing, the outer shroud and a connecting partition, said connecting partition resting on the intermediate casing so as to encompass the downstream holes of the latter in said annular channel and resting on the outer shroud so as to encompass the outer openings of the latter in said annular channel. 
     According to the invention, the upstream holes of the intermediate casing are made through an upstream wall of the latter and the downstream holes of the intermediate casing are made through a downstream wall of the latter. 
     According to the invention, the relief device comprises a manifold placed upstream of the intermediate casing and comprising relief passageways placing the inner openings of the inner shroud in communication with the upstream holes of the intermediate casing. 
     According to an optional variant embodiment, the relief circuit comprises as many upstream holes as downstream holes, and it also comprises guide tubes installed between the upstream wall and the downstream wall of the intermediate casing, each guide tube connecting an upstream hole with a downstream hole opposite. 
     The blanking means comprise a relief ring furnished with relief apertures and placed upstream of the intermediate casing. Said relief ring is capable of moving in axial rotation between an open position of the relief circuit in which said relief apertures coincide at least partially with passageways of the relief circuit, and a closed position of the relief circuit in which said relief apertures do not at all coincide with said passageways of the relief circuit. 
     In the completely open position of the relief circuit, each relief aperture of the relief ring is completely superposed with a relief passageway of the manifold. In a partially open position of the relief circuit, each relief aperture of the relief ring is partially superposed with a relief passageway of the manifold. In the completely closed position of the relief circuit, no relief aperture of the relief ring is superposed with a portion of a relief passageway of the manifold. 
     The blanking means comprise means for actuating said relief ring in order to command a movement of the latter between said completely open and completely closed positions of the relief circuit. 
     The actuation means comprise at least one guide slot cut into the upstream wall of the intermediate casing, in a circumferential direction. 
     The actuation means comprise at least one shaft for controlling the relief ring. The travel of the latter is limited by the ends of said guide slot. 
     The actuation means comprise at least one cylinder associated with said control shaft and placed inside the interstream compartment between the upstream wall and the downstream wall of the intermediate casing. 
     According to a second aspect, the invention relates to a turbojet comprising a relief device according to the first aspect. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood on reading the following detailed description of a particular embodiment of the invention, provided as an indication and in no way limiting, and illustrated by means of the appended drawings, in which: 
         FIG. 1  illustrates, in axial section, the relief device according to the invention; 
         FIG. 2  is a view in perspective of the relief device cut along a longitudinal plane; 
         FIG. 3  is another view in perspective, on a larger scale, of the relief device cut along a longitudinal plane, showing more particularly the assembly of the relief ring with the manifold; 
         FIG. 4  is a front view in perspective of the relief ring; 
         FIG. 5  is a rear view in perspective of the manifold; 
         FIGS. 6 ,  7  and  8  represent in front perspective the assembly formed by the manifold and the relief ring, when the relief circuit is respectively completely open, partially open and completely closed; and 
         FIG. 9  illustrates a view in perspective showing the means for actuating the relief ring; and 
         FIG. 10 , already described, is a view in axial section of a relief device of the prior art. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In everything that follows, the terms “radial”, “axial” and “circumferential” refer to the “radial”, “axial” and “circumferential” directions of the turbojet and the terms “upstream” and “downstream” refer to the direction of flow of the gases in the turbojet. 
     With reference first of all to  FIG. 1 , it represents, in axial section, a portion of a turbojet  2  centered on a portion of the intermediate casing  20 , and showing the main stream  10  in which the main flow travels, indicated by the arrows  90 , and the by-pass stream  14  in which the by-pass flow travels, indicated by the arrows  92 . The intermediate casing comprises an upstream wall  202  and a downstream wall  204 . It also comprises support arms  22  that extend radially in the by-pass stream  14  from the outer shroud  18  and are attached to the upstream wall  202  and to the downstream wall  204 . It also comprises countervanes  24  that extend radially in the by-pass stream  14  from the outer shroud  18 . They are distributed between the support arms  22  and are attached to the upstream wall  202  and downstream wall  204  of the intermediate casing  20 . Between the main stream  10  and the by-pass stream  14  there is an interstream compartment  17  that is separated from the main stream by an inner shroud  16  and from the by-pass stream by an outer shroud  18 . In particular, the interstream compartment  17  comprises an intermediate portion called the interstream cavity  19  delimited by the outer shroud  18 , the inner shroud  16 , the upstream wall  202  of the intermediate casing  20  and the downstream wall  204  of the intermediate casing  20 . 
     The relief flow from the main stream  10  to the by-pass stream  14  is identified by the arrows  94 . It leaves the main stream  10  through inner openings  26  of the inner shroud  16  and enters the by-pass stream  14  through outer openings  28  of the outer shroud  18 . It passes through upstream holes  32  of the upstream wall  202  and downstream holes  34  of the downstream wall  204 . 
     Between the inner openings  26  and the upstream holes  32  of the intermediate casing  20 , the relief flow  94  is guided by a manifold  36 . This manifold  36  is represented in rear perspective in  FIG. 5 . It is an annular part having an upstream zone  38  and a downstream zone  40 . The upstream zone  38  is an annular zone which extends in the extension of the inner shroud  16 . The downstream zone  40  comprises a fastening flange  42  for it to be fastened to the upstream wall  202  of the intermediate casing  20 . The manifold  36  comprises, on its downstream zone  40 , relief passageways  44  identical in number to the number of upstream holes  32  of the upstream wall  202 . In the example illustrated, the relief passageways  44  are ten in number. They extend from an inner face  46  to a downstream face  48  of the downstream zone  40 , said downstream face  48  being the face of contact between the fastening flange  42  and the intermediate casing  20  when the manifold  36  is fastened to the latter. They open onto said inner face  46  through inner orifices  50 . 
     Between the downstream holes  34  of the intermediate casing  20  and the outer openings  28 , the relief flow  94  is guided by an annular channel  52 . The latter is delimited by the downstream wall  204  of the intermediate casing  20 , the outer shroud  18  downstream of the intermediate casing  20 , and a connecting partition  54  that links said outer shroud  18  to said downstream wall  204  so as to encompass the outer openings  28  and the downstream holes  34  in said annular channel  52 . 
     According to an optional variant embodiment, that is illustrated in the figures, the relief flow  94  is guided, between the upstream holes  32  and the downstream holes  34  of the intermediate casing  20 , by guide tubes  56  that extend substantially in an axial direction through the interstream cavity  19  of the interstream compartment  17  situated between the upstream wall  202  and downstream wall  204  of the intermediate casing  20 . When the guide tubes  56  are provided, preferably the same number of upstream holes  32  and downstream holes  34  are provided. In the example illustrated, they are ten in number. These guide tubes  56  have the advantage of completely guiding the relief flow  94 , which otherwise would fill the interstream cavity  19  of the interstream compartment  17  between the upstream wall  202  and the downstream wall  204  of the intermediate casing  20 , with the risk of depositing in this interstream cavity  19  debris such as for example fragments of ice or sand. 
     The manifold  36 , the upstream holes  32 , the downstream holes  34 , the annular channel  52  and the guide tubes  56 , when they are present, define a relief circuit  36 ,  32 ,  56 ,  34 ,  52  between the inner openings  26  of the inner shroud  16  and the outer openings  28  of the outer shroud  18 . 
     The relief device according to the invention comprises said inner openings  26 , said outer openings  28  and said relief circuit. It also comprises blanking means  58 ,  60 ,  62 ,  64 ,  66  of said relief circuit. 
     These blanking means  58 ,  60 ,  62 ,  64 ,  66  comprise a relief ring  58 , represented in front perspective in  FIG. 4 . This relief ring  58  comprises relief apertures  60  of which the number, shape and dimensions match the number, shape and dimensions of the inner orifices  50  of the manifold  36 . They are ten in number in the example illustrated. 
     In service, the relief ring  58  is centered on the inner face  46  of the manifold  36  so as to be able to rotate relative to the latter between two extreme positions. More precisely, the relief ring  58  is shown against the inner face  46  of the downstream zone  40  of the manifold  36 , and is guided in rotation by this inner face  46 . 
     The extreme positions, and a partially open intermediate position, are illustrated in  FIGS. 6 to 8 . Therefore:
           FIG. 6  is a view in perspective of the relief ring  58  assembled with the manifold  36  in the completely open position of the relief circuit, in which the relief ring  58  is rotated so that its relief apertures  60  are exactly superposed with the inner orifices  50  of the relief passageways  44  of the manifold  36 ;     FIG. 7  is a view in perspective of the relief ring  58  assembled with the manifold  36  in a partially open—or partially closed—position of the relief circuit, in which the relief ring  58  is rotated so that its relief apertures  60  partially blank off the inner orifices  50  of the relief passageways  44  of the manifold  36  and partially cover the inner face  46  of the latter;     FIG. 8  is a view in perspective of the relief ring  58  assembled with the manifold  36  in the completely closed position of the relief circuit, in which the relief ring  58  is rotated so that its relief apertures  60  are not superposed with the inner orifices  50  of the relief passageways  44  of the manifold  36 , but with the inner face  46  of the latter.       

     The blanking means  58 ,  60 ,  62 ,  64 ,  66  also comprise means  62 ,  64 ,  66 , that are illustrated in  FIG. 9 , for actuating the relief ring  58 . 
     In the exemplary embodiment illustrated in the figures, the relief ring  58  is furnished with at least one control shaft  62  that extends in a substantially axial direction from the relief ring  58 . Preferably, the relief ring  58  is furnished with two control shafts  62 . Such control shafts  62  are placed between the apertures  60  of the relief ring  58 . Each control shaft  62  is connected to a cylinder  64  that is placed either in the interstream cavity  19  between the upstream wall  202  and the downstream wall  204  of the intermediate casing  20 , or in the interstream compartment  17 . Accordingly, each control shaft  62  passes through the upstream wall  202  of the intermediate casing  20 . More precisely, each control shaft  62  passes through a guide aperture  66  cut into this upstream wall  202 , between two upstream holes  32 . The ends of each guide aperture  66  perform a stop function for the control shaft  62  that passes through it. The travel of the control shaft  62  is limited by the ends of the guide aperture  66 . The latter is appropriately dimensioned so that the travel of the control shaft  62  allows the relief ring  58  to move between the two desired extreme positions of the relief circuit. Therefore, one of the stops of the control shaft  62  corresponds to the completely open position of the relief ring  58 , while the other stop of the control shaft corresponds to the completely closed position of the relief ring  58 . 
       FIG. 3  is a view in perspective and in section through the relief circuit. It represents the manifold  36  fastened to the upstream wall  202  of the intermediate casing  20  and the relief ring  58  and the manifold  36  assembled in the completely open position of the relief circuit. It shows, in section, an inner opening  26 , a relief passageway  44  and an upstream hole  32 . In this figure, it appears that the inner shroud  16  of the interstream compartment  17  is materialized, at this level of the turbojet, by an upstream zone  38  of the manifold  36 , then by a spoiler  70 , then by the intermediate casing  20 . The spoiler  70  is an annular connecting part fastened to the upstream wall  202  of the intermediate casing  20  by fastening means  72 , for example screws, and on which the relief ring  58  is centered. For simplification reasons, the guide tubes  56  are not shown in  FIG. 3 . 
       FIG. 2  is another view in perspective, at a greater distance, and in section through the relief circuit. It represents the manifold  36  fastened to the upstream wall  202  of the intermediate casing  20 . This figure also shows, in section, a downstream hole  34  of the downstream wall  204  of the intermediate casing  20  and an outer opening  26  of the outer shroud  18 , and the annular channel  52 . The latter is delimited by the outer shroud  18 , the downstream wall  204  of the intermediate casing  20  and a connecting partition  54 . In addition,  FIG. 2  shows countervanes  24  and a support arm  22  fastened to the upstream wall  202  and downstream wall  204  of the inner casing  20 . For simplification reasons, the guide tubes  56  are not shown in  FIG. 2 .