Patent Publication Number: US-2022228504-A1

Title: Device for cooling an outer casing of a turbomachine and turbomachine provided with such a device

Description:
FIELD OF THE INVENTION 
     The invention lies in the field of aircraft turbomachines. 
     The present invention relates to a device for cooling, using air jets, an outer casing of a turbomachine, comprising a housing for supplying air and an attachment device for this housing, on this same casing. 
     The invention also relates to a turbomachine comprising a cooling device using air jets as mentioned previously. 
     PRIOR ART 
     One example of a double flow turbomachine, intended to be installed on air aircraft (not shown) to propel it in the air, is shown in the appended  FIG. 1 . 
     Conventionally, this turbomachine  1  extends along a main axis  10  and comprises an air intake  11  by which the flow of gas penetrates into the turbomachine  1  and in which the flow of gas passes through a fan  12 . Downstream of the fan  12 , the gas flow separates into a primary gas flow flowing in a primary stream  13  and a secondary gas flow flowing in a secondary stream  14 . 
     In the primary stream  13 , the primary flow passes, from upstream to downstream (i.e. from left to right in the figure), through a low-pressure compressor  131 , a high-pressure compressor  132 , a combustion chamber  133 , a high-pressure turbine  134 , a low-pressure turbine  135 , and a gas exhaust casing to which is connected an exhaust nozzle  136 . In the secondary stream  14 , the secondary flow passes through a fan straightener  141  then mixes with the primary stream at the exhaust nozzle. 
     An inter-stream casing  15  separates the primary stream  13  from the secondary stream  14 . 
     Each compressor or turbine of the turbomachine comprises several states, each stage being formed by fixed blading (or a stator) or even a straightener, and rotating blading (or a rotor) which rotates around the main axis  10  of the turbomachine. 
     The stator and the rotor of a stage each comprise a plurality of blades distributed regularly around the main axis  10  of the turbomachine and extending radially relative to this axis inside the primary stream, so as to have the primary flow pass through them. 
     All the stages of a compressor or of a turbine are housed between an inner casing  16  extending around the main axis  10  and the inter-stream casing  15 , the latter being provided coaxially around the inner casing  16  so as to delimit the primary stream  13 . 
     The inter-stream casing  15  comprises, from upstream to downstream, an outer low-pressure compressor casing  151 , an outer high-pressure compressor casing  152 , an outer high-pressure turbine casing  153  and an outer low-pressure turbine casing  154 . 
     The radial clearances between the tip of the blades of a rotor and the outer casing which surrounds it are managed by a cooling device using air jets of this casing. 
     A part of an outer low-pressure turbine casing  154  can thus be seen in the appended  FIG. 2 , equipped with a cooling device  2  using air jets. This device  2  comprises at least one supply housing  20  for air under pressure, connected to an air source (for example a part of the secondary air flow) by a connector  21 . Each housing  20  is also connected to several cooling tubes  22 , (seven in number here for example, on either side of the housing  20 ). Each tube  22  is curved and disposed around the outer casing  154 . In addition, each tube  22  is drilled with a series of air ejection holes (not visible in the figures) opening at right angles (i.e., facing) to the outer face of the outer casing  154 . 
     The cooling device  2  can be of the type known by the acronym “LPTCC” (for “Low Pressure Turbine Clearance Control”) or of the type known by the acronym “LPTACC”(for “Low Pressure Turbine Active Clearance Control”). 
     In the case of a cooling device of the LPTCC type, the flow rate of air circulating in the device is directly proportional to the flow rate of air (secondary flow) circulating in the secondary stream. 
     In the case of a cooling device of the LPTACC type, the flow rate of air circulating in the device  2  is controlled via a motorized valve (not visible in the figures), connected to the computer of the aircraft, which adapts this air flow rate depending on the phases of flight (takeoff, climb, cruise, etc.). 
     In the cooling devices of the prior art, the housing  20  is attached at its upstream and downstream ends respectively to an upstream flange BAM and to a downstream flange BAV, these two flanges being themselves attached to the two ends of the outer casing  154 . 
     However, in order for cooling using air jets to be effective, it is necessary that the air gap between the tubes  22  and the external face of the outer casing  154  be constant and with a low value. The tubes  22  themselves being attached to the housing  20 , it follows that the air gap between this housing  20  and the outer casing  154  must also be constant and with a low value. 
     However, during the operation of the turbomachine and particularly during the takeoff of the aircraft, it is noted that a high thermal gradient exists between the upstream and downstream flanges that are considered to be “cold,” and the outer surface (called the “skin”) of the outer casing  154  that is considered to be “hot.” Thus the flanges dilate radially less than the rest of the casing  154  and the latter easily takes on the shape of a barrel. Consequently, the air gap between the center of the housing  20  and the casing  154  does not vary in the same way as the air gap between the upstream and downstream ends of the housing  20  and the casing  154 . 
     Moreover, the attachment of the housing  20  to the flanges BAM and BAV imposes a relatively large chain of dimensions of the cooling device  2 , which translates into a considerable increase (on the order of several millimeters) of the nominal value of the air gap between the housing  20  and the outer surface of the casing  154  to avoid any risk of contact between them. 
     Also known from document WO 2015/65 525 is a device for attaching an oil reservoir to the outer casing of the fan of a turbomachine. This device comprises a ball-joint connection, however, this document does not describe the attachment device of the invention. 
     DISCLOSURE OF THE INVENTION 
     The invention therefore has as its object to propose an attachment device for an air supply housing, as previously mentioned, to the outer casing of a turbine (high or low pressure) or of a compressor (high or low pressure) of a turbomachine, which avoids the previously mentioned disadvantages of the prior art. An attachment device of this type has as its object of maintaining a relatively constant air gap between the housing and the casing during the flight phase of the aircraft and avoiding contact between the housing and the casing during the transitional phases, such as the takeoff of the aircraft, during which the casing dilates further. 
     To this end, the invention relates to a cooling device using air jets for an outer turbomachine casing, this cooling device comprising an air supply housing for the cooling tubes of this casing, said housing comprising an upstream end and a downstream end, upstream and downstream being defined relative to the flow direction of the flow in said turbomachine. 
     According to the invention, said housing comprises an attachment device on said outer casing, in that the attachment device comprises two retention devices using ball-joint connection, called “upstream,” configured to connect each the upstream end of the housing to an outer face of the outer casing while allowing the movement of this upstream end relative to the outer face of the outer casing, in that each upstream retention device comprises a cupped washer and a recessed washer, the cupped washer comprising a cupped face received in a concave face of the recessed washer, said cupped washer being able to move relative to said recessed washer to form said ball-joint connection and at least one of the upstream retention devices comprises a lateral flange attached to the housing and a connection assembly attached to the outer casing, the connection assembly comprises a connecting screw attached to a boss and a hollow cylindrical socket, the socket having a part with a large cross section for receiving the head of the screw, this part with a large cross section having, at its outer end, a first shoulder, like a collar, forming a stop for an elastic return member in the radial direction and this part with a large cross section being extended at its inner end by a part with a narrow cross section for receiving the body of the screw, the part with the narrow cross section of the socket is housed both in an opening of the flange of the housing and in a central orifice provided in the cupped washer. 
     Due to these features of the invention, the housing and the casing can follow the relative movements of one with respect to the other due to differential dilations during operation, which retaining an air gap which varies little between the cooling tubes and the casing, and while avoiding contact between the casing and the housing. 
     According to other advantageous and nonlimiting features, taken alone or in combination:
         said recessed washer is drilled with a central orifice and has a flat radially inner face and an opposite radially outer face of which the central part is flat and of which the peripheral part is concave, and this recessed washer is arranged so that its flat inner face rests against a flat face of the boss and that the free end of the part with a narrow cross section of the socket rests against the flat central part of the radially outer face of the recessed washer;   the lateral flange and the cupped washer are in a single piece and the boss and the recessed washer are in a single piece;   the upstream retention device comprises a cylindrical washer drilled with an orifice, arranged around the connection assembly, against the flange attached to the housing via an elastic return member supported on the first shoulder;   said socket has on its external surface a third shoulder between its part with a narrow cross section and its part with a large cross section, and this third shoulder forms a stop for limiting the travel of the lateral flange of the housing relative to said casing;   the opening provided in the flange of the housing has an oblong shape, its largest dimension being oriented circumferentially around the longitudinal axis of the casing;   said attachment device comprises a retention device using a ball-joint connection, called “downstream,” which is configured to connect the downstream end of the housing to the outer casing, while allowing the movement of this downstream end of the housing relative to the casing;   said downstream retention device comprises a cupped washer and a recessed washer, the cupped washer comprising a cupped face received in a concave face of the recessed washer, said cupped washer being able to move relative to said recessed washer to form the ball-joint connection;   the downstream retention device comprises a downstream flange attached to the housing and an connection assembly attached to the outer casing and extending through an opening provided in said downstream flange, the connection assembly of the downstream retention device comprises a connecting screw and a hollow cylindrical socket, the socket having a part with a large cross section for receiving the head of the screw, this part with a large cross section having, at its outer end, a first shoulder, like a collar, forming a stop for an elastic return member in the radial direction and this part with a large cross section is extended at its inner end by a part with a narrow cross section for receiving the body of the screw, the part with the narrow cross section of the socket is housed both in the opening of the downstream flange of the housing and in the central orifice of the cupped washer, and a female blocking element is configured to be screwed into the inner end of the screw, against an attachment tab attached to the casing;   said socket has on its external surface a third shoulder between its part with a narrow cross section and its part with a large cross section and this third shoulder forms a stop for limiting the travel of the downstream flange of the housing relative to the attachment tab attached to said casing;   the opening provided in the downstream flange of the second retention device has an oblong shape, its largest dimension being oriented along the longitudinal axis of the casing.       

     Finally, the invention relates to a turbomachine. In conformity with the invention, this turbomachine comprises an outer casing, particularly a turbine or compressor outer casing, and a cooling device using air jets as previously mentioned, said cooling tubes being drilled with air ejection holes and being intended to be arranged around the outer face of said outer casing so that the air ejection holes face the outer face of said outer casing. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       Other features, objects and advantages of the invention will be revealed by the description that follows, which is purely illustrative and not limiting, and which must be read with reference to the appended drawings in which: 
         FIG. 1  is a schematic showing an axial section of an example of a turbomachine on which the attachment device of the air supply housing in conformity with the invention can be used. 
         FIG. 2  is a perspective view showing schematically an attachment device of the air supply housing according to the prior art. 
         FIG. 3  is a perspective view of the attachment device of an air supply housing according to the invention. 
         FIG. 4  is an exploded perspective view of a part of the air supply housing and of a first embodiment of one of the two upstream retention devices which form a part of the attachment device according to the invention. 
         FIG. 5  is a detail perspective view of a part of the housing and of a part of the upstream retention device of  FIG. 4 . 
         FIG. 6  is a transverse section view of the upstream retention device of  FIG. 4 . 
         FIG. 7  is a transverse section view of a second embodiment of the upstream retention device of  FIG. 4 . 
         FIG. 8  is a section view of the downstream retention device which forms a part of the attachment device according to the invention, this downstream retention device being shown in a first position. 
         FIG. 9  is a section view of the downstream retention device which forms a part of the attachment device according to the invention, this downstream device being shown in a second position. 
         FIG. 10  is a section view of the downstream retention device which forms a part of the attachment device according to the invention, this downstream device being shown in a third position. 
         FIG. 11  is a detail perspective view of a part off the downstream retention device of  FIGS. 8 to 10 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 3 , it can be seen that the attachment device  3  according to the invention allows attaching an air supply housing  20  to an outer casing  154 , by allowing a certain degree of freedom to this housing relative to the casing. 
     In the example shown in the figures, this outer casing is that of a low-pressure turbine. In conformity with the invention, this casing could be that of a high-pressure turbine or of a high or low-pressure compressor. 
     A casing  154  of this type has an annular shape, preferably frustoconical or substantially frustoconical. It extends around a main axis X-X′ coaxial with the axis  10  when the casing is mounted in the turbomachine. This casing  154  further has, at its downstream end, an annular radial flange  1540 . 
     In  FIG. 3 , it can also be seen that the housing  20  has an outer face  23  to which the connector  21  connects, two opposite lateral faces  24 , (only one being visible in the figure) and to which the cooling tubes  22  connect so as to be in air communication with this housing, and an inner face  25  which is more visible in  FIG. 4  and which is located facing the outer face of the casing  154 . 
     Finally, this housing  20  has a downstream end  26  and an upstream end  27 . 
     In the description and the claims, the terms “upstream” and “downstream” are defined by reference to the flow direction of the flow, particularly of the primary flow, in the turbomachine. 
     The shape of the inner face  25  of this housing substantially follows the contour of the outer face of the casing  154 . 
     The attachment device  3  according to the invention comprises at least two (and preferably three) retention devices using ball-joint connection, each of which connect said housing  20  to said outer casing  154 . 
     Still preferably, the attachment device  3  according to the invention comprises two retention device  4  using ball-joint connection, called an “upstream devices,” because they are arranged at the upstream end of the housing  20 , preferably on either side of the upstream end  27  of the housing. 
     Preferably, too, the attachment device  3  further comprises a retention device  5  using a ball-joint connection, called a “downstream device” because it connects the downstream end  26  of the housing  20  to the casing  154 , more precisely to the downstream flange  1540  of the casing  154 . 
     The upstream retention device  4  using a ball-joint connection will now be described in more detail in connection with  FIGS. 3 to 7 . 
     This upstream retention device  4  comprises a lateral flange  28 , attached to the housing  20 , and a connection assembly  40  attached to the outer face of the outer casing  154 . The lateral flange  28  extends in a circumferential direction relative to the casing. 
     As can be seen in the figures, the lateral flange  28  preferably has the shape of a plate, attached to the housing  20  in proximity to the upstream end  27  of the latter, for example by welding between two adjacent cooling tubes  22  or between two sockets  29  leading out of the housing  20  and which allow the connection of the cooling tubes  22  to this housing. 
     Still preferably, the upstream retention device  4  is arranged at the zone of the casing  154  that is most deformed. 
     This lateral flange  28  is drilled with an opening  280 , this opening having a cross section allowing the movement of the lateral flange  28  relative to the connection assembly  40  which will be described subsequently. 
     Still preferably, the opening  280  has an oblong shape, its largest dimension being oriented circumferentially relative to the longitudinal axis XX′ of the casing  154  (see  FIG. 5 ). 
     One possible embodiment of the connection assembly  40  will now be described with reference to  FIGS. 4 and 6 . This connection assembly  40  extends on either side of the lateral flange  28  while defining, relative to it, an outer part  401 , i.e. located outside the flange  28  (toward the top of  FIG. 6 ) and an inner part  402 , the latter extending between the lateral flange  28  and the outer surface of the casing  154 . 
     The connection assembly  40  generally comprises a boss  41 , a connection pin  42 , a socket  43 , an elastic return member  44 , a recessed (or concave) washer  45 , a convex (or cupped) washer  46  and preferably, to limit wear, a cylindrical washer  47 . 
     These various elements will now be described in more detail. 
     The connection pin  42  extends in a direction Y 1 -Y′ 1 , called “radial.” 
     The boss  41  comprises a cylindrical part  410 , drilled with a bore  411 , which is preferably blind and which opens to the radially outer surface of the part  410 . 
     This bore  411  is tapped on its internal surface (tap  412 ) and extends along the longitudinal axis Y 1 -Y′ 1 . 
     The boss  41  can be a single piece with the casing  154 , or be welded to it or even, as shown in the figures, be screwed to this casing. 
     In the latter case and to this end, the cylindrical part  410  is extended for example by at least two attachment tabs  413 , arranged on either side of the cylindrical part. Each attachment tab  413  is drilled with an orifice  414 . A bolt  415  is inserted through the orifices  414  and the wall of the casing  154  and is retained in place by a nut  416 , thus providing the attachment of the boss  41  to the casing  154 . 
     The connection pin  42  is for example a screw comprising a body  420 , equipped at one of its ends with a head  421  and which has a thread  423  at its opposite end  422 . 
     The screw  42  cooperates with a female blocking element  424 , having a thread  425  on its external surface and a tap  426  on its internal surface. 
     The socket  43  has the general shape of a cylinder with longitudinal axis Y 1 -Y′ 1 . 
     The socket  43  is bordered at one of its ends by a collar  431 , which defines a first shoulder the role of which will be explained subsequently. This socket  43  continues inward from the collar  431 , by a first part  432  with this large cross section, allowing the passage of the screw  42 , including its head  421  and even possibly the passage of an installation or screwing tool for this head  421 . 
     This first part  432  continues with a second part  433  with a narrow cross section, allowing the passage of the body  420  of the connection pin, of the screw here, but prohibiting the passage of the head  421 . The free end of the second narrow part  433  carries the reference symbol  434 . 
     The passage between the first part with a large cross section  432  and the second part with a narrow cross section  433  defines a second shoulder  435  toward the inside of the central passage of the socket and a third shoulder  436  toward the outside. The shoulder  435  retains the screw head  421 . 
     According to a variant embodiment not shown in the figures, the socket  43  and the connection pin  42  could form only a single piece. 
     The elastic return member  44  is for example a helical compression spring. It is arranged around the first part  432  of the socket  43 , so that one of its ends is supported against the collar  431  and its other end is supported on the lateral flange  28 . It will be noted that it is possible to interleave a cylindrical washer  47  between the lateral flange  28  and the helical spring  44 , in order to prevent damage to the lateral flange  28 . This cylindrical washer  47 , drilled with an orifice  470 , is the arranged around the part with the narrow cross section  433  of the socket  43 . 
     The recessed washer  45  is a cylindrical part with a small thickness, drilled with a central orifice  450 . It has a radially inner face  451  and an opposite radially outer face of which the central part  452  is flat and of which the peripheral part  453  is concave and curved in a circular arc from this flat part to the periphery of the washer. 
     This recessed washer  45  is arranged so that its flat inner face  451  rests against the flat radially outer face  417  of the cylindrical part  410  of the boss  41  and that the free end  434  of the socket  43  rests against the flat central face  452  (reference symbol  417  visible only in  FIG. 4 ). 
     The cupped washer  46  is drilled with a central orifice  460  of larger dimensions than that  450  of the recessed washer  45 . It has a flat radially outer face  461  and an opposite convex and cupped (dome shaped) inner face  462 . The cupped washer  46  is arranged around the part  433  with a narrow cross section of the socket, so that its flat outer face  461  is in contact with the lateral flange  28  and in particular with its radially inner face  281  and that its convex face  462  is in contact with the concave face  453  of the recessed washer  45 . 
     The assembly of the retaining device  4  is as follows. 
     The female blocking element  424  is screwed inside the bore  411  of the cylindrical part  410  by the cooperation of its external thread  425  with the tap  412  of the bore. 
     The socket  43 , the return member  44  and the different washers  45 ,  46  and  47  are positioned as disclosed previously, the narrow part  433  of the socket being inserted into the orifices  470 ,  280  and  460 . 
     The screw  42  is introduced into the socket  43 , as well as through the orifices  470 ,  280  and  460 , then screwed inside the female blocking element  424  by cooperation of its thread  423  with the tap  426  of the nut. This screwing continues until the screw head  421  comes into abutment against the shoulder  435  and the end  434  of the socket  43  comes into abutment against the recessed washer  45 . 
       FIG. 7  illustrates a variant embodiment of the upstream retention device shown in  FIG. 6 . A device of this type bears the reference symbol  4 ′. This device differs from the preceding one in that the lateral flange  28  and the cupped washer  46  are a single piece and form a same single lateral flange with reference  28 ′. 
     Moreover, the boss differs from the previous one in that the cylindrical part  410  and the recessed washer  45  are a single piece, the boss then bearing the reference symbol  41 ′. The other parts are identical. 
     The operation of the upstream retention device  4  is the following. 
     The spring  44  is dimensioned so as to be loaded in compression and therefore constrained between the collar  431  and the lateral flange  28  or the washer  47  if it is present, when the screw  42  is screwed into the female blocking element  424 . In other words, the elastic return member  44  is arranged and retained between the outer part  401  of the connection assembly  4  and the flange  28 , so as to be loaded in compression. 
     This spring  44  therefore tends to constantly seek to return to its original position and therefore the separate the lateral flange  28  from the collar  431 . 
     This original position is that shown in  FIG. 6 . 
     The spring  44  is configured so that the lateral flange  28  can approach the collar  431  by further compressing the turns of the spring  44 , i.e. by working against the return force of said elastic return member. 
     Moreover, the collar  43  is configured so that in the original configuration shown in  FIG. 6 , when the socket  43  constrains the spring  44  due to the collar  431 , there exists a clearance j between the shoulder  436  and the radially outer face of the washer  47  or the radially outer face of the lateral flange  28  if this washer  47  is absent. 
     When the lateral flange  28 , secured to the housing  20 , moves radially slightly outward (toward the top of  FIG. 6 ) to follow the movement of the housing  20 , then the washer  47  comes into abutment against the shoulder  436 . 
     In this position, the spring  44  is then more strongly compressed. However, the clearance j is calculated to be sufficiently small and to prevent complete crushing, or even the deformation of the spring  44 . The shoulder  436  therefore serves as an end-of-travel stop for the movement of the lateral flange  28 . This allows permitting a radial but limited movement between the lateral flange  28  and the casing  154 . 
     Moreover, the lateral flange  28  can move so that the central axis of its orifice  280  is no longer parallel with the axis Y 1 -Y′ 1 . 
     A movement of this type is made possible by the cooperation of the cupped convex face  462  of the cupped washer  46  with the curved outer concave face  453  of the recessed washer  45 . During this movement, the cupped washer  46  still rests against the recessed washer  45 , but slides on it so that its axis is slightly offset relative to the axis Y-Y′ 1  of the screw  42 . The cupped washer  46  thus follows the movement of the lateral flange  28 . This sliding of the cupped washer  46  on the recessed washer  45  provides the function of the “ball-joint connection” of the upstream retention device  4 . 
     In this case, the spring  44  is crushed more on one side than on the other. 
     Finally, it will be noted that the orifice  280  is oblong; it also allows movement of the flange  28  in a circumferential direction around the casing  154  (see arrows F 1  in  FIG. 5 ). 
     The downstream retention device  5  of the downstream end  26  of the housing  20  on the downstream flange  1540  of the casing will now be described in more detail while referring to  FIGS. 7 to 9 . 
     As can be seen in  FIG. 11 , the second retention device  5  comprises a retention element  6  (such as a downstream flange), attached to the air supply housing  20 , and a connection assembly  7  connected to the downstream flange  1540  of the casing. 
     As can be seen in  FIG. 11 , the downstream flange  6  preferably has the form of an attachment tab which comprises for example a plate  61  and a plate  62  assembled together. 
     The plate  61  is attached on the housing on the housing  20 , more precisely on its outer face  23 . 
     The plate  61  also has a downstream part  612  which protrudes out of the housing  20  in the downstream direction and which is drilled with an orifice  613 . 
     The plate  62  also comprises an upstream part which matches the shape of the downstream end  26  of the housing  20  and which is attached to it by screwing or by welding for example. This plate  62  is extended by a downstream part  621  which protrudes downstream relative to the housing  20  and which extends below the downstream part  612  of the plate  61 , parallel to it. It is drilled with an orifice  622  (see  FIG. 8 ). 
     The two orifices  613  and  622  are superimposed and coaxial. 
     Advantageously, they have an oblong shape, of which the larger dimension (length) is oriented in the axial direction x-x of the housing. 
     One possible embodiment of the connection assembly  7  will now be described with reference to  FIG. 8 . The connection assembly  7  extends on either side of the downstream flange  6  while defining, with reference to it, an outer part  701 , i.e. located outside the element  6  (toward the top of  FIG. 9 ), and an inner part  702 , the latter extending between the downstream flange  6  and the outer surface of the casing  154 , as can be seen in  FIG. 9 . 
     The connection assembly  7  generally comprises an attachment tab  71 , a socket  72 , an elastic return member  73 , a connection pin  74 , as well as a recessed washer  76  and a cupped washer  77 , and preferably, to limit wear, two cylindrical washers  75 ,  78 . 
     These various elements will now be described in more detail. 
     The connection pin  74  extends in a direction Y-Y′, called “radial,” due to its orientation relative to the downstream end of the casing  154 . 
     The attachment tab  71  appears in the form of an L-shaped bracket, one  711  of the two branches of which is intended to be attached to the downstream flange  1540  of the casing  154 . This attachment can be accomplished for example by screwing or by welding. When it is attached, this branch  711  extends in a plane parallel to the axis (direction) Y-Y′. 
     The second branch  712 , perpendicular to the first  711 , is drilled with an orifice  713 . 
     The connection pin  74  is for example a screw comprising a body  740 , equipped at one of its ends with a head  741 , and which has at its opposite end  742  a thread  743 . The screw  74  cooperates with a tapped nut  744 , which can be screwed onto the thread  743 . The free end  742  of the screw  74  and the nut  744  form part of the inner part  702  of the assembly  7 . 
     The socket  72  has a generally cylindrical shape. 
     The socket  72  is bordered at one of its ends by a collar  721  which defines a first shoulder the role of which will be explained subsequently. This socket is extended inward from the collar  721  by a first part  722  with a large cross section, allowing the passage of the connection pin  74 , including its head  741  and even possibly the passage of an installation or screwing tool for this head  741 . This first part  722  is extended by a second part  723  with a narrow cross section, allowing the passage of the body  740  of the connection pin but prohibiting the passage of the head  741 . The free end of the second part  723  bears the reference symbol  724 . 
     The passage between the first part with a large cross section  722  and the second part with the narrow cross section  723  defines a second shoulder  725  on the inside of the central passage of the socket and a third shoulder  726  on the outside. The shoulder  725  retains the screw  74  head. 
     According to a variant embodiment not shown in the figures, the socket  72  and the connection pin  74  could form only a single piece. 
     The elastic return member  73  is for example a helical compression spring. It is arranged around the first part  722  of the socket  72 , so that one of its ends is supported against the collar  721  and its other end is supported on the downstream flange  6 . It is possible to interleave a cylindrical washer  75  drilled with a central orifice  750 , between the downstream flange  6  and the helical spring  73 , in order to prevent damage to the element  6 . A washer  75  of this type is then arranged around the second part  723  of the socket  72 . 
     Similarly, a cylindrical washer  78  drilled with an orifice  780  can be interleaved between the lower face of the branch  712  of the attachment tab  71  and the nut  744  in order to avoid damage to the nut  744  on the tab  712 . The body  740  of the pin  74  passes through the orifice  750 . 
     The recessed washer  76  is a cylindrical part with a small thickness drilled with a central orifice  760 . It has a flat radially inner face  761  and an opposite radially outer face of which the central part  762  is flat and of which the peripheral part  763  is concave and curved from this flat part to the periphery of the washer. 
     This washer  76  is arranged so that its flat inner face  761  is in contact with the branch  712  of the attachment tab  71  and the free end  724  of the socket  72  rests against its central flat face  762 . 
     The cupped washer  77  is drilled with a central orifice  770  of larger dimensions than the orifice  760 . It has a flat outer face  771  and an opposite convex and cupped inner face  772 . 
     The cupped washer  77  is arranged around the part with the narrow cross section  723  of the socket  72 , so that its flat outer face  771  is in contact with the downstream flange  6  and its convex inner face  772  is in contact with the concave outer face  763  of the washer  76 . 
     The assembly of the second retention device  5  is as follows. 
     The socket  72 , the return member  73  and the different washers  75 ,  76 ,  77  and  78  are positioned as previously disclosed. The screw  74  is introduced into the socket  72  as well as through the orifices  760 ,  713  and  780 . The narrow part  723  of the socket is inserted into the orifices  613 ,  622 ,  750  and  770 . The nut  744  is screwed to the threaded end  743  of the screw and below the branch  712  of the tab  71 . 
     This screwing is performed so that the nut  744  comes into abutment against the washer  78  and the second part  723  of the socket  72 , the washer  76  and the branch  712  are retained and immobilized between the head  741  of the screw  74  and the nut  744 . 
     The operation of the second retention device  5  is the following. 
     The spring  73  is dimensioned so as to be loaded in compression and therefore constrained between the collar  721  and the element  6  or the washer  75  if it is present. 
     In other words, the elastic return member  73  is arranged and retained between the outer part  701  of the connection assembly  7  and the downstream flange  6  so as to be loaded in compression. 
     This spring  73  tends to permanently seek to return to its original position, and therefore to separate said downstream flange  6  from the collar  721 , (i.e. from the outer part of the connection assembly). 
     This original position is shown in  FIG. 8 . 
     However, the elastic return member (spring)  73  is configured so that the downstream flange  6  can approach the outer part  701  of the connection assembly  7  (particularly the collar  721 ) by further compressing the turns of the spring, i.e. by working against the return force of said elastic return member. 
     This other position is shown in  FIG. 9 . 
     Advantageously, moreover, the different elements of the connection assembly  7  and of the downstream flange  6  are configured so that in the original configuration shown in  FIG. 8 , when the socket  72  constrains the spring  73  due to the collar  721 , there exists a clearance j 1  between the shoulder  726  and the upper face of the washer  75  or the upper face of the downstream flange  6  if the washer  75  is absent. 
     In the second position, shown in  FIG. 9 , the downstream flange  6 , secured to the housing  20 , has moved slightly outward (toward the top of the figure) to follow a movement of this housing  20 . In doing so, the washer  75  comes into abutment against the shoulder  726 . The clearance j 1  then extends between the outer face  771  of the cupped washer  77  and the inner face of the downstream flange  6 . In this second position, the spring  73  is more strongly compressed. However, the clearance j 1  is calculated to be sufficiently small to prevent complete crushing, or even the deformation of the spring  73 . The shoulder  726  serves therefore as an end-of-travel stop for the movement of the downstream flange  6 . 
     It is therefore understood that this device according to the invention allows permitting (radial) movement between the downstream flange  6  secured to the housing  20  and the flange  1540  of the casing, in other words movement between the housing  20  and the casing  154 . This movement is exerted in a first direction corresponding to the axis Y-Y′. In addition, the oblong shape of the orifices  613 ,  622  of the downstream flange  6  allows movement of this flange in the axial direction X-X′, around the narrow part  723  of the socket  72 . 
     Finally, the downstream flange  6  can move jointly in the axial direction and in the radial direction (see arrow F in  FIG. 10 ). 
     In this position, the downstream flange  6  is no longer perpendicular to the axis Y-Y′ of the screw  74 , (or in other words, it is no longer parallel to the branch  712  of the attachment tab  71 ). 
     This movement is made possible by the cooperation of the convex face  772  of the cupped washer  77  with the concave outer face  763  of the recessed washer  76 . In this position, the cupped washer  77  still rests against the recessed washer  76 , but slides on it so that its axis is slightly offset relative to the axis Y-Y′ of the screw  74 . The cupped washer  77  thus follows the movement of the downstream flange  6 . This sliding of the washer  77  on the washer  76  provides the function of “ball-joint connection” of the device  5 . 
     The spring  73  is further crushed between the collar  721  and the free end of the downstream flange  6  (to the right in  FIG. 10 ) than between the collar  721  and the part of the downstream flange  6  closest to the housing  20  (to the left in  FIG. 10 ). 
     The downstream flange  6  is therefore always held under pressure by the spring  73  but can thus move relative to the casing  154  and follow its deformation.