Abstract:
An annular air flow passage for a turbine engine such as a turbojet or a turboprop, crossed by an instrumented rod that includes mechanism(s) for measuring characteristics of a flow potentially traveling along the passage, the rod extending between an outer annular wall and an inner annular wall of the passage. Outer connection(s) fasten(s) an outer end of the instrumented rod to the outer wall in a manner that is rigid in all directions, and inner connection(s) fasten(s) an inner end of the instrumented rod to the inner wall, in a manner that is rigid in the circumferential direction and that has at least one degree of freedom to move in a first direction extending between the inner and outer walls of the passage and having at least a radial component.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of French Patent Application 1554724, filed May 26, 2015, which claims the benefit of French Patent Application 1454862, filed on May 28, 2014, the contents of each of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The invention relates to an annular air flow passage having an instrumented rod passing therethrough, the passage being situated in general manner in a turbine engine. 
     BACKGROUND OF THE INVENTION 
     Conventionally, a bypass turbojet  10 , as shown in  FIG. 1 , is constituted by a gas turbine  12  of axis  14  driving a ducted fan  16  which is generally located upstream (UP) from the engine. The mass of air sucked in by the engine is split into a primary air stream (arrow A) that flows through the gas turbine or engine core, and a secondary air stream (arrow B) that comes from the fan  16  and that surrounds the engine core, the primary and secondary air streams being coaxial. 
     In well-known manner, the primary air stream (arrow A) is generally compressed by a first compressor  18  referred to as a low pressure (LP) compressor or booster, having an LP shaft that is connected to the shaft of the fan  14  and that is driven in rotation by the shaft of the downstream low pressure turbine (not shown), the air then being compressed in a second compressor  20  further downstream (DN), referred to as a high pressure (HP) compressor, having an HP shaft that is driven in rotation by the shaft of a high pressure turbine arranged at the outlet from a combustion chamber and located upstream from the low pressure turbine (the combustion chamber and the turbines not being shown). 
     In such a two-spool turbojet, the term “intermediate casing”  22  is commonly used to designate a casing having its hub arranged between a casing  24  of the low pressure compressor  18  and a casing  26  of the high pressure compressor  20 . 
     The intermediate casing  22  has an inner annular wall  28  defining the outside of the annular primary air flow passage  18 , an intermediate annular wall  30  defining the inside of the annular secondary air flow passage  33 , and an outer wall  35  defining the outside of the annular secondary air flow passage  33 . 
     Furthermore, such a turbojet is generally provided with devices known as variable bleed valves (VBVs)  32  that serve to divert a portion of the primary air stream at the outlet from the LP compressor  18  into the annular channel  33  of the secondary air stream. By lowering the pressure downstream from the LP compressor  18 , this bleeding has the effect of lowering its operating point and thus of reducing the risks of the compressor  18 ,  20  surging which would lead to a sudden reversal of the flow direction of the hot gas stream from the combustion chamber, and which could damage the compressor  18 ,  20 . Furthermore, in the event of accidental penetration of water, in particular in the form of rain or hail, or indeed in the event of accidental penetration of various kinds of debris, which can harm the operation of a turbojet, these valves make it possible to recover such water or debris and eject it from the primary passage feeding air to the combustion chamber. 
     Thus, the bleed valves  32  are formed in the inner annular shroud  28  of the hub of the intermediate casing  32  and they communicate with a space lying between the inner annular shroud  28  and the intermediate shroud  30  of the intermediate casing  22 . 
     In order to bleed off air, the hub of the intermediate casing  22  has a downstream transverse plate  34  arranged upstream from the high pressure compressor  20  of the turbojet and connecting together the downstream ends of the inner and intermediate annular shrouds  28  and  30 . The downstream plate  34  has a plurality of first openings  36  distributed around the axis  14  of the turbojet  10 , each communicating upstream with the inside of the hub and downstream with a duct  38  having its downstream end leading to a shroud  40  that is perforated by second openings downstream from an outer annular shroud  42  formed to extend the intermediate annular wall  30  of the intermediate casing  32  downstream. 
     As shown in  FIG. 1 , the hub of the intermediate casing  22  carries stator vanes  44  that extend between the intermediate wall  30  and the outer wall  35  of the intermediate casing  22 . The stator vanes  44 , also known as outlet guide vanes (OGVs), are for straightening out the secondary air stream coming from the upstream fan  16 . 
     In the context of developing a turbine engine, it is necessary to measure and verify its performance. It is desired in particular to measure the flow parameters of the stream flowing in the secondary passage, such as its speed, its pressure, and its temperature. For this purpose, it has been found that it is preferable to arrange measurement sensors at certain precise locations in the secondary passage. One of these locations is situated downstream from the stator vanes  44  of the intermediate casing  22 , in a plane lying at a particular angle of inclination relative to the axis of the turbine engine and passing via the perforated shroud  40 . This location makes it possible to take good measurements of the performance of the assembly comprising the fan  16  and the guide vanes  44 . In order to take exhaustive measurements of the stream in this location, it is desirable to arrange a plurality of sensors at different heights in the secondary passage, while remaining in this plane. Even though these sensors are incorporated in intrusive manner, they must not influence the normal operation of the turbine engine, and they must be capable of withstanding the environment in which they are to be found during testing, where such environments generally cover all of the possible operating ranges of the turbine engine. In particular, during such tests, it is possible to observe variations in temperature, in pressure, and in relative positioning of parts because of various assembly clearances and because of differential expansions. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution that is simple, effective, and inexpensive for incorporating instruments for measuring the stream flowing through the above-mentioned passage. 
     To this end, the invention provides an annular air flow passage for a turbine engine such as a turbojet or a turboprop, the passage being crossed by an instrumented rod including means for measuring characteristics of a flow potentially traveling along the passage, said rod extending between an outer annular wall and an inner annular wall of the passage, the passage being characterized in that outer connection means fasten an outer end of the instrumented rod to the outer wall in a manner that is rigid in all directions, and in that inner connection means fasten an inner end of the instrumented rod to the inner wall, in a manner that is rigid in the circumferential direction of the passage and that has at least one degree of freedom to move in a first given direction extending between the inner and outer walls of the passage and having at least a radial component. 
     By means of the invention, it is possible to position sensors along the entire length of the rod, and thus over the full height of the passage, thereby making it possible to measure exhaustively the flow of the stream in the predefined plane. By way of example, the rod may have a duct for passing cables that opens out through the outer wall of the passage so as to connect the sensors of the rod to external devices for collecting information. Because of the degree of freedom to move in at least said first direction extending between the inner and outer walls of the passage that is made possible at the inner end of the rod relative to the inner wall of the passage, the rod is not subjected to structural stresses in the event of differential expansion between the inner wall of the passage and the outer wall, or in the event of those two walls moving in operation as made possible by the various assembly clearances of the structure. 
     In another characteristic of the invention, the inner connection means fasten the inner end of the instrumented rod to the inner wall with a degree of freedom to move in a second given direction substantially perpendicular to the first given direction. 
     With such an arrangement, it is thus possible to allow the rod to move in translation in a first direction and in a second direction that is substantially perpendicular to the first direction. 
     Advantageously, the inner connection means comprise a shoe fastened rigidly to the inner wall and fastened rigidly to the inner end of the instrumented rod in the circumferential direction, and fastened thereto with at least one degree of freedom to move in a first direction having at least a radial component. 
     Preferably, the shoe and the inner end of the instrumented rod are engaged relative to each other with the ability to slide in at least said first direction. 
     In an embodiment, the shoe comprises a first shoe portion and a second shoe portion that are secured to each other and that define a housing in which the inner end of the rod is suitable for moving at least in said first given direction. 
     The fit between the shoe and the inner end of the instrumented rod may be of the H7/g6 type. Relative movement is thus allowed between the shoe and the inner end of the rod. 
     According to a characteristic of the invention, the housing may be defined by a downstream lug extending outwards from the second shoe portion and by a U-shaped recess that is open in the downstream direction in the first shoe portion. 
     The second shoe portion may be L-shaped with an axial wall carrying the downstream lug extending between the first shoe portion and the inner wall. 
     According to another characteristic of the invention, the axial wall of the second shoe portion is engaged axially in an axial groove in an inner face of the first shoe portion. 
     Preferably, the thickness of said axial wall is greater than the depth of said axial groove, thus making it possible to fasten the second shoe portion by clamping against the inner annular wall of the first shoe portion. 
     In a practical embodiment of the invention, the inner end of the rod is mounted with initial assembly clearance J, e.g. of 3 millimeters (mm), relative to the second shoe portion. This clearance J may be formed between the inner end of the rod and the axial wall of the second shoe portion. 
     In another embodiment of the invention, at least one through orifice is formed in the inner end of the instrumented rod and is aligned in the circumferential direction with at least one through orifice in the shoe, a locking member being engaged through the above-mentioned orifices in the shoe and in the inner end of the instrumented rod. 
     According to an important feature, the section of the at least one orifice in the shoe is contained strictly within the section of the at least one orifice in the inner end of the rod, or vice versa. Thus, the locking member, which logically fits the size of the smaller of the orifices in the shoe or the inner end of the rod, can move freely within the other orifices that are of greater size, thereby allowing relative movement between the shoe and the inner end of the rod in the plane perpendicular to the axis of the orifices. 
     Preferably, at least one orifice in the shoe or in the inner end of the rod is of oblong shape, being elongate in alignment with the instrumented rod. In this way, greater relative movement is made available in the long direction of the rod. 
     The locking member engaged through the orifices in the shoe and the inner end of the rod is preferably a self-locking bolt configured so as to avoid clamping the shoe against the instrumented rod. 
     Advantageously, the shoe is fastened rigidly to a first shroud forming the inner wall of the passage, said shroud being arranged downstream from an annular row of stationary vanes extending across the passage and upstream from a perforated second shroud for bleeding air, and the outer end of the rod is fastened relative to the outer wall downstream from said row of stationary vanes. The perforated shroud through which the air bleed duct opens out is not suitable for supporting the instrumented rod in this type of configuration. 
     The shoe may have a downstream portion arranged axially facing the perforated second shroud and radially at a distance therefrom, the shoe being fastened to the inner end of the rod at said downstream portion. This enables the rod to be connected to the inner wall of the passage while lying in the measurement plane passing through the shroud through which the air bleed ducts open out in the above-defined configuration. 
     In order to lie in the measurement plane, the inner end of the instrumented rod may be situated upstream relative to the outer end of the instrumented rod. 
     A spacer may be mounted between the outer end of the instrumented rod and the outer wall of the passage. 
     The invention also provides a turbine engine, such as a turbojet or a turboprop, including an annular passage as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and characteristics of the invention appear on reading the following description made by way of non-limiting example and with reference to the accompanying drawings, in which: 
         FIG. 1 , described above, is a diagrammatic half-view in axial section of an aircraft turbojet of known type; 
         FIG. 2  is a half-view of a passage suitable for being fitted in the turbojet shown in  FIG. 1 ; 
         FIGS. 3 and 4  are complementary views of the connection between the shoe and the inner end of the instrumented rod in one embodiment; 
         FIGS. 5 and 6  are complementary views of the connection between the outer end of the instrumented rod and the outer wall of the passage; 
         FIG. 7  is an enlargement of  FIG. 2  in the region of the shoe; 
         FIGS. 8 to 10  are diagrammatic perspective views of a second embodiment of an instrumented rod; 
         FIGS. 11A, 11B, and 11C  are diagrammatic views of the sequence for assembling the inner end of an instrumented rod in the second embodiment; and 
         FIG. 12  is a view on a larger scale of the region defined by a dashed line in  FIG. 11C . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows an instrumented rod incorporated in a turbine engine of the type shown in  FIG. 1 . There can thus be seen a secondary passage  33  having a plurality of OGVs  44  passing radially therethrough from an intermediate casing  22 . From upstream to downstream, the inner boundary of the passage is formed respectively by the intermediate wall  30  of the intermediate casing, by a first shroud  42 , and by a perforated second shroud  40  into which there open out the bleed ducts of the primary passage  18  of the turbine engine. 
     The outer boundary of the passage  33  is formed from upstream to downstream by the outer wall  35  of the intermediate casing  22 , by an air/oil heat exchanger  46 , and by an outer casing  48  of the turbine engine. 
     It is proposed to arrange an instrumented rod  50  through the above-described passage  33  so as to take the desired flow measurements. The rigid rod  50  is of the longitudinal type, and at its upstream edge it carries nozzles  52  with openings facing into the secondary stream B. The nozzles  52  are connected to cables  54  running along a duct formed within the rod  50  and leading to the outside of the passage  33  so as to enable the cable  54  to be connected to devices (not shown) for collecting and processing the measured information. 
     The instrumented rod  50  extends between the inner wall  30  and the outer wall  35  of the passage in a first given direction  51  situated in a plane perpendicular to a circumferential direction. This direction  51  has a component along a radial axis  53  and a component along an axial axis  55 . This first direction  51  is contained in a radial plane, i.e. a plane containing the axis of the passage. 
     The rod  50  is inclined from upstream to downstream respectively from its inner end  56  to its outer end  58 . Its angle of inclination follows the optimum plane for measuring flow in the selected location. The outer end  58  of the rod  50  bends upstream and outwards, and it is fastened to the outer casing  48  of the turbine engine downstream from the air/oil heat exchanger  46  by means of a spacer  60 . The inner end  56  of the instrumented rod  50  is connected to a shoe  62 , which is itself connected to the first shroud  42  of the inner wall of the passage, being situated axially between the intermediate wall  30  of the intermediate casing  22  and the perforated shroud  40  having the openings of the bleed ducts from the primary passage. 
       FIGS. 3 and 4  show in greater detail the shoe  62  and how it is connected to the inner end  56  of the instrumented rod  50 . The shoe has an upstream toe  64  that has a radial hole for passing a screw  66  for fastening to the above-mentioned shroud  42  of the inner wall of the passage  33 . A small amount of clearance is left between the above-mentioned screw  66  and the orifice  68  in the toe  64  so as to be able to accommodate dimensional dispersions in the passage, both axially and circumferentially, when assembling the described assembly. The toe  64  is connected downstream to a downstream portion or stud  70  extending downstream and outwards. The stud  70  has a circumferentially directed hole forming an orifice  72  of oblong shape having its long direction oriented in the same direction as the rod and extending over a distance referenced  72   a , and having its short direction perpendicular to its long direction  72   a  and extending over a distance referenced  72   b.    
     The inner end  56  of the instrumented rod  50  has a housing  74  of dimensions suitable for receiving the stud  70  of the shoe  62 . The inner end  56  of the instrumented rod  50  thus has two walls or fingers  76 ,  78  with facing inside faces that are arranged circumferentially on opposite sides of the stud  70 . Each of the two walls  76  and  78  has a circumferentially extending hole so as to form orifices  80 ,  82  that are in alignment with the oblong orifice  72  in the stud  70 . The orifices  80 ,  82  in the fingers  76 ,  78  of the rod are circular and of sections that are contained within the oblong orifice  72  of the stud  70 . More particularly, the diameter of each of the orifices  80 ,  82  is less than the long dimension  72   a  and less than the short dimension  72   a  of the oblong orifice  72 . A threaded rod  84  of diameter corresponding to the orifices  80 ,  82  in the fingers  76 ,  78  is inserted and locked through the above-mentioned orifices  80 ,  82  and the oblong orifice  72  of the stud  70 . The threaded rod has a head  85  at one of its ends that presses against one of the outside faces of the fingers  76 ,  78 , and a clamping nut  87  is applied against the other one of the outside faces of the fingers  76 ,  78 . 
     It can thus be understood that the inner end of the rod has a degree of freedom in the first direction corresponding to the direction  51  and in a given second direction  111  that is substantially perpendicular to the given first direction  51 . 
     The fit between the stud  70  of the shoe  62  and the housing  74  in the rod  50  is of the sliding type, preferably of the H7/g6 type. The bolt formed by the threaded rod  84  and the nut  87  is self-locking, and the self-locking clamping of the bolt is configured so as to avoid deforming the walls  76 ,  78  of the housing  74  and so as to avoid pressing them against the stud  70  in order to conserve a sliding fit. It is thus possible for the stud  70  to slide axially and radially in the housing  74  within the movement limits available for the threaded rod  84  in the oblong hole  72  in the stud  70 , while blocking the rod  50  relative to the shoe  62  in the circumferential direction. This serves in particular to avoid the rod  50  being set into vibration while performing measurements, while allowing the rod to expand longitudinally in testing. 
     A minimum clearance of 2 mm is preferably formed all around the threaded rod  84  in the oblong hole  72  in the stud  70 , in order to make it possible while assembling the described assembly to accommodate axial and radial dimensional fabrication tolerances or dispersions of the parts that are assembled together to constitute the passage. 
     With reference to  FIGS. 5 and 6 , it can be seen that the outer end  58  of the instrumented rod  50  is fastened to the outer casing  48  of the turbine engine by means of a spacer  60 . By means of this spacer  60 , it is possible to form the rod  50  with a length that makes it easier to install in the passage. The spacer  60  co-operates with the outer end face of the rod  50  and the inside face of the outer casing  48 . The spacer has through holes  86 ,  88  in alignment with holes (not shown) in the outer casing  48  and holes  86 ′,  88 ′ formed on flanges at the outer end  58  of the rod  50 , these flanges being lateral and extending in a circumferential direction. It is thus possible to insert threaded rods  86 ″,  88 ″ through the sets of aligned holes in order to lock the outer end of the rod  50  rigidly against the outer casing  48 , bolting using nuts. 
       FIG. 7  makes it easier to understand how the shoe  62  is positioned relative to the inner wall of the passage  33 . The perforated second shroud  40  possesses a structure and mechanical strength that are not suitable for fastening the instrumented rod  50  thereto. The optimum plane for performing flow measurements in the passage nevertheless passes via the shroud  42 . The shoe  62  thus makes it possible, by using fastener means that are axially offset, to fasten respectively both with the rod  50  and with the inner wall of the passage, thereby keeping the rod  50  in the above-mentioned optimum measurement plane, while nevertheless using the first shroud  42  situated immediately downstream from the intermediate casing  22  as the support for fastening to the inner wall of the passage, which first shroud  42  has the structural strength needed for supporting the rod  50  during testing. 
     Furthermore, although the toe  64  of the shoe  62  is in direct contact via its inner surface with the first shroud  42  situated immediately downstream from the intermediate casing  22  in order to ensure reliable pressure and good relative fastening, the downstream portion of the toe  64 , in contrast, is not in contact with the perforated second shroud  40 , with the inner surface of the toe  64  having a raised downstream portion  90  or outward setback at that location. This ensures that the toe  62  does not press at all against the perforated second shroud  40 . 
       FIGS. 8 to 12  show another way of incorporating an instrumented rod  92  in an annular secondary air flow passage of a turbojet as described above with reference to  FIG. 1 . Although not shown in  FIGS. 8 to 12 , the inner end  93  of the rod  92  is axially offset relative to its outer end. The rod also has an inner end  93  connected to the remainder of the rod  92  via a shoulder  94 . 
     In this embodiment, and unlike the above-described embodiment, the shoe  95  has a first portion  96  and a second portion  97 . 
     The first portion  96  of the shoe has an upstream toe  98  and a downstream portion or downstream stud  99  extending outwards in the direction  51 . The inner surface of the toe  98  has an axial groove  100 . The toe  96  also has a radial orifice  101  passing through it and opening out inwardly into the end wall of the groove  100 . The stud  99  has a U-shaped recess  102  that is open in the downstream direction and that communicates inwardly with the downstream end of the groove  100 . The toe  98  has an outer surface with a substantially plane upstream first surface portion  103  arranged axially between the upstream end of the toe  98  and the orifice  101 , and with two lateral second surface portions  104  that are substantially convex. In a plane containing the axial axis  55  and the radial axis  53 , the first surface portion  103  presents an angle of inclination relative to the inner surface of the toe  98  that is such that air striking this outer surface  103  is not deflected towards the nozzles  52  near the inner end of the rod  92 . 
     The second portion  97  of the shoe is L-shaped, having both a downstream lug  105  extending outwards in the above-mentioned given direction  51 , and also a wall  106  extending axially upstream from the downstream lug  105  for the purpose of engaging axially in the groove  100  of the inner face of the toe  98 . The thickness of the axial wall  106  of the second portion  97  of the shoe is greater than the depth of the groove  100  so as to enable the axial wall  106  to be clamped between the toe  98  and the inner shroud ( FIG. 11C  and  FIG. 12 ). The upstream end of the axial wall  106  of the second portion  97  of the shoe includes an orifice  107 . 
     In the invention, the U-shaped recess  102  in the stud  99  and the downstream lug  105  of the second portion  97  of the shoe define between them a housing in which the inner end  93  of the rod  92  is engaged as a tight sliding fit, as shown in  FIGS. 10 and 11C . 
     The inner end  93  of the rod  92  is mounted in the housing with initial assembly clearance J relative to the axial wall  106  of the second portion  97  of the shoe. This clearance J may for example be of the order of 3 mm. 
     The inner end  93  of the rod  92  is assembled with the shoe  95  as follows. The first portion  96  of the shoe is moved axially downstream so that the inner end  93  of the rod  92  is received in the U-shaped downstream recess  102  of the stud  99  of the first shoe portion  96 , the shoulder  94  of the rod  92  then facing the outer edge  108  of the stud ( FIG. 10  and  FIG. 11A ). Simultaneously with the above step, the second shoe portion  97  is engaged axially from upstream so that its axial wall  106  is received in the groove  100  of the inner surface of the toe  98  ( FIG. 11B ). In the assembled position ( FIG. 11C ), the axis of the orifice  101  in the toe  98  and the axis of the orifice  107  in the second shoe portion  97  are in radial alignment. As can be seen in  FIGS. 11A, 11B, and 11C , and more precisely in  FIG. 12 , the orifice  101  in the toe  98  presents an outer first portion  109  of greater diameter than its inner second portion  110  so that the head of a fastener screw can be received fully therein in order to avoid having any impact on the stream of air flowing in the secondary passage. The second portion  110  of the orifice  101  in the toe  98  presents a diameter that is identical to that of the orifice  107  in the axial wall  106  of the second shoe portion  97 . 
     The means for connecting the outer end of the rod  92  may be entirely similar to those described with reference to the above-described embodiment. 
     In this second embodiment, the rod  92  extends likewise along the first given direction  51  that has a component along a radial axis  53  and a component along an axial axis  55 . The instrumented rod  92  is movable in translation only in the given direction  51 , with movement solely in the second direction  111  substantially perpendicular to the first direction  51  being prevented by the downstream stud  99  and the downstream lug  105 . 
     It can be understood that the first direction extends substantially along a mean line of the rod  50 ,  92 . The invention is naturally applicable to a rod that is not rectilinear as in the embodiments shown in the figures, but, for example, that has undulations between its inner and outer ends. 
     Although the above description is made with reference to an annular passage of type that can be found in a turbine engine, it can clearly be seen that, in a manner that is obvious to the person skilled in the art, the invention can also be applied to any passage defined transversely between two walls, or by way of example by a single annular wall, and that has the instrumented rod arranged therein in the manner described above.