Patent Publication Number: US-2022220925-A1

Title: Thrust reverser cascade including accoustic treatment

Description:
TECHNICAL FIELD 
     The invention relates to the acoustic treatment of sound waves emitted by a turbomachine of an aircraft, and more particularly to the treatment of sound waves at the thrust reversers of the turbomachine. 
     PRIOR ART 
     When a turbomachine is in operation, the interaction between the flow and the solid portions of the turbomachine are responsible for the generation of noise which propagates on either side of the turbomachine. 
     One of the means of attenuating this acoustic radiation is to integrated acoustic treatment means in the surfaces in contact with the sound waves. 
     Conventionally, the acoustic treatment of a turbojet, and more precisely of the noise radiated by the interaction of the rotor and its environment, is accomplished by means of absorbing panels positioned at the wetted surfaces of the duct in which the sound waves propagate. What is meant by wetted surfaces are the surfaces in contact with a fluid flow. These panels are generally composite material of the sandwich type confining a honeycomb forming acoustic absorption cells. 
     Known for example in the prior art are acoustic panels with a single degree of freedom, or SDOF, which have a conventional honeycomb acoustic treatment structure lining the walls of the nacelle of a turbomachine. 
     Because of the principle of operation of the technologies of the acoustic treatment panel using resonant cavities, the radial bulk, i.e. the radial thickness, of the acoustic treatment panels depends on the treatment frequency targeted for obtaining the maximum effectiveness in acoustic attenuation. 
     However, engine architectures increasingly have speeds of rotation of the bladed wheels that are slower and slower, and a number of blades on the bladed wheels that are smaller and smaller, which causes a reduction in the dominant frequencies of the noise associated with the module comprising the fan and the straightener stage, or fan-OGV for “outlet guide vane” module. As a result, matching between the optimal thickness of the acoustic panels and the volume available in the nacelles is currently not satisfied. 
     To slow down an aircraft, a turbomachine generally comprises thrust reversers. There exist primarily two technologies of thrust reverser that are based on the action of a cascade. Two types of cascade type thrust reversers are distinguished: fixed cascade type thrust reversers and cascade type thrust reversers with a sliding connection. 
     Schematic section views are shown in  FIGS. 1A and 1B  in a horizontal plane of a turbomachine  1  according to a first known embodiment of the prior art, respectively in a position in which the thrust reversal is inactivated and in a position in which the thrust reversal is activated. 
     The turbomachine  1  comprises a nacelle  2  with axial symmetry around an axis X defining an axial direction DA, a radial direction DR and a circumferential direction DC, a fan  3 , a primary stream  4 , a secondary stream, a primary straightener stage  5 , a secondary straightener stage  6 , and a cascade type thrust reverser device  7  including a cascade  8 . 
     As illustrated in  FIGS. 1A and 1B , which show a turbomachine provided with a fixed cascade type thrust reverser, in fixed cascade thrust reversers the cascade  8  is embedded in, i.e. secured to an upstream portion  21  of the nacelle  2  and in sliding connection with a downstream portion  22  of the nacelle  2 , upstream and downstream being defined with respect to the flow direction of a gas flow F in the turbomachine  1 . Translating downstream, the downstream portion  22  of the nacelle  2  uncovers the cascade  8  which becomes the only interface between the flow internal to the nacelle  2  and the surrounding medium in which the turbomachine  1  moves. 
     Schematic section views are shown in  FIGS. 2A and 2B  in a horizontal plane of a turbomachine  1  according to a second embodiment of the prior art, respectively in a position in which the thrust reversal is inactivated and in a position in which the thrust reversal is activated. 
     As illustrated in  FIGS. 2A and 2B  which show a turbomachine  1  provided with a cascade type thrust reverser with a sliding connection, in a fixed cascade thrust reverser the cascade  8  is in sliding connection with respect to the upstream portion  21  of the nacelle  2  and in embedded connection with respect to the downstream portion  22  of the nacelle  2 . Translating downstream, the downstream portion  22  of the nacelle drives the cascade  8  out of the nacelle  2  to position it at the interface between the flow internal to the nacelle  2  and the ambient medium. 
     Thrust reversers represent both a cost, a mass and a bulk that are very penalizing for the performance of the propulsive assembly, while they are used only at the end of the landing phase. The volume that they use in the nacelle can in particular not be used in the prior art, for acoustic treatment of the sound waves emitted by the turbomachine. 
     In the propulsive assembly architectures using door type thrust reversers which are deployed inside the secondary flow to deflect the flow upstream outside the nacelle, a known practice for integrated the conventional acoustic treatment consists of integrating acoustic panels in the cavities of the reverser doors. This practice consists simply of integrating conventional absorbing panels into the available volumes, as is done in the fan casing. 
     DISCLOSURE OF THE INVENTION 
     The invention seeks to supply a cascade type thrust reverser which allows both reorienting a flow of air upstream of the turbomachine outside the nacelle and minimizing the head losses through the cascade when the thrust reversal is activated, and controlling the effectiveness of acoustic absorption when the thrust reversal is inactive. 
     One object of the invention proposes a cascade type thrust reverser device for a turbomachine of an aircraft. The device comprises a thrust reverser cascade and a casing. The cascade extends in a first plane defining a first direction and a second direction and includes first partitions positioned successively in the first direction and parallel to one another, second partitions intersecting said first partitions and each extending in planes parallel to one another and parallel to the first direction, and cavities each defined by two first partitions and two second partitions. The casing comprises an opening extending in a plane orthogonal to said first direction and a housing in which the cascade can be inserted in said first direction via said opening. The casing and said cascade are in relative translation with respect to one another in the first direction between a first position of the device in which the cascade is entirely positioned in the housing and a second position of the device in which said cascade is at least partially outside said housing. 
     According to a general feature of the invention, the casing comprises a perforated wall intended to be in contact with an air flow and to be positioned between said air flow and the cascade when the device is in the first position. 
     Preferably, the perforated wall includes a plurality of orifices and a plurality of wall strips with no orifices and intended to face the first walls of the cascade when the device is in the first position, at least one orifice being positioned between two successive wall strips in the first direction and facing a cavity when the device is in the first position. 
     The thrust reverser cascade can be formed by an annular one-piece cascade or by a plurality of cascade sections which can be assembled together to form a hollow cylinder with a circular or polygonal base. 
     When the cascade type thrust reverser device is mounted on the turbojet, the first direction corresponds to an axial direction of the turbojet and the second direction corresponds to a circumferential direction of the turbojet when the cascade is at least partially annular or to a direction tangent to the circumferential direction when the cascade is plane, not curved in other words. 
     The first partitions are intended to be oriented in a direction intersecting the flow direction of a gas flow inside a turbomachine including a cascade type thrust reverser device of this type. When the thrust reverser device is mounted on a turbomachine, the first partitions, oriented in an azimuthal or radial direction of the turbomachine, are indispensable for guaranteeing the functionality of thrust reversal. It is in fact due to these first partitions that the air flow circulating in a stream, inside the nacelle in which the thrust reverser device is mounted, can be captured and reoriented upstream of the turbomachine, with respect to the flow direction inside the nacelle, outside the nacelle. The second partitions are intended to be oriented in the direction of gas flow inside a turbomachine including a cascade type thrust reverser device of this type. When the thrust reverser device is mounted on a turbomachine, the second partitions, oriented in an axial direction of the turbomachine, are not indispensable for the functionality of thrust reversal. On the other hand, they allow the formation of resonant cavities allowing attenuating the acoustic waves generated by the turbomachine. 
     When the thrust reverser device according to the invention is mounted on a turbomachine and is in the first position, the device allows, on the one hand, having the cavities formed by the reverser cascade communicate with the fluid medium of the secondary flow of the turbomachine and, on the other hand, providing quality contact between the reverser cascade and the material(s) located at the interface with the fluid medium of the secondary flow. 
     When the thrust reverser device according to the invention is mounted on a turbomachine and in the first or the second position, the device allows guaranteeing its aerodynamic sealing. 
     In a first aspect of the thrust reverser device, the casing can also comprise a porous interface formed by at least one layer of porous material and positioned at the interface between the perforated wall and the cascade when the thrust reverser device is in the first position. 
     The addition of a porous interface allows improving the interface between the thrust reverser cascade and the perforated wall by providing better sealing at the junctions between the partitions of the thrust reverser cascade and the wall strips, which offering useful clearance for improving the sliding of the thrust reverser cascade at the time when the thrust reverser function is used, i.e. when the device is in the second position. 
     In a second aspect of the thrust reverser device, the porous interface can have a thickness comprised between 0.2 and 2 mm, the thickness extending in a third direction perpendicular to said first plane. 
     In a third aspect of the thrust reverser device, a layer of porous material of the porous interface can comprise a web or a foam or a material with a cellular structure. 
     In a fourth aspect of the thrust reverser device, the device can also comprise a sealed frame positioned in the housing between the perforated wall and the cascade when the device is in the first position, on the periphery of the perforated wall in the first plane. 
     The sealing frame defines a contact surface which forms a span. This span allows guaranteeing the aerodynamic sealing of the device and thus avoiding any leak which penalizes the performance of the turbomachine. 
     In a fifth aspect of the thrust reverser device, the distance separating two first partitions in the first direction and the distance separating two second partitions in the second direction can each be defined as a function of the frequencies of the sound waves to be treated by said cavities. 
     The thrust reverser cascade can thus be dimensioned to tune the cavities to the frequencies of the sound waves radiated by the turbomachine in which the thrust reverser device is mounted, and in particular with respect to the frequencies of the sound waves radiated by the pair formed by the fan and the straightener vane stage of the turbomachine. 
     To this end, the following relation is used, which is valid for the dimensioning of a conventional Helmholtz resonator. 
     
       
         
           
             
               
                 
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     With F the tuning frequency in Hertz, C the speed of sound in meters per second, S the cross section area of the neck in square meters, V the volume of the resonant cavity in meters, and l′ the corrected length of the neck, the neck being formed by an orifice of the perforated wall facing a cavity. The corrected length of the neck l′ being calculated based on the sum of the geometric length of the neck l in a direction perpendicular to the plane in which the perforated wall extends with the channel correction d where, for juxtaposed resonators: 
     
       
         
           
             
               
                 
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     with r the radius of an orifice, and s the level of perforation. 
     In the case of simple resonator type operation, the volume V corresponds to the volume of the cavities formed by the structure of the thrust reverser cascade. 
     In a sixth aspect of the thrust reverser device, the first partitions of the cascade can have a height comprised between 10 mm and 300 mm. 
     In a seventh aspect of the thrust reverser device, the first partitions can comprise a thickness comprised between 0.5 and 5 mm to be sufficiently thick to withstand the loads to which they are subjected, but also as thin as possible to minimize the mass and the head losses in the cascade. The thickness of the first partitions is measured at a given point of the second partition, perpendicular to the tangent to the surface at this point of the second partition. 
     In an eight aspect of the thrust reverser device, the casing also comprises an acoustically reflecting wall movable in a third direction orthogonal to said first plane and positioned parallel to the first plane between an outer wall and the cascade when the device is in the first position, the outer wall being intended to be in contact with a nacelle of a turbomachine when the device is mounted in a turbomachine. 
     The acoustically reflecting wall allows ensuring the operation of cavities as resonant cavities. 
     In a ninth aspect of the thrust reverser device, the acoustically reflecting wall can have a thickness in a third direction greater than 2 mm so that is has sufficient inertia to reflect acoustic waves. 
     In a tenth aspect of the thrust reverser device, the casing can comprise elastic means mounted between the outer wall and the acoustically reflecting wall and configured to push said acoustically reflecting wall toward the cascade. 
     The pressure retention of the acoustically reflecting wall against the cascade when the device is in the first position allows ensuring good acoustic sealing of the resonant cavities formed by the cascade, the perforated wall and the acoustically reflecting wall. 
     In an eleventh aspect of the thrust reverser device, the acoustically reflecting wall has dimensions at least equal to the dimensions of the cascade in said first plane to cover all the cavities of the cascade and thus maximize the acoustic treatment when the device is in the first position. 
     In a twelfth aspect of the thrust reverser device, the casing can comprise an actuator configured to disengage the acoustically reflecting wall from the cascade when the device is in the second position. 
     The use of an actuator for disengaging the acoustically reflecting wall from the cascade during the actuation of the thrust reverser device so that it passes from the first position to the second position or conversely allows optimizing the compactness of the thrust reverser device and therefore of the turbomachine comprising said device. 
     The actuator can comprise at least two devices complementary to one another operating in translation or in rotation, distributed azimuthally at the axial ends of the acoustically reflecting wall. When the thrust reverser device is mounted in a turbomachine, the actuator can be communalized with the translation system of the nacelle. 
     In a thirteenth aspect of the thrust reverser device, the acoustically reflecting wall can comprise at least one layer of flexible material. 
     The flexible material can be a polymer. The production of the acoustically reflecting wall of flexible material allow ensuring good sealing at its interface with the thrust reverser cascade. 
     In a fourteenth aspect of the thrust reverser device, that acoustically reflecting wall can comprise a stack of a plurality of layers of at least two different materials. 
     The use of a stack of layers of possibly different materials for producing an acoustically reflecting wall allows obtaining different combinations of useful properties for accomplishing different function relating for example to overall stiffness, or to the flexibility of the interface at the contact with the cascade to improve sealing. 
     In a fifteenths aspect of the thrust reverser device, the acoustically reflecting wall can be made in a single piece. 
     The advantage of an acoustically reflecting wall in a single piece resides in the simplicity of implementation, because it allows not having to manage alignments between the acoustically reflecting wall and the cascade. 
     In a sixteenth aspect of the thrust reverser device, the acoustically reflecting wall can be segmented into at least two pieces/The advantage of an acoustically reflecting wall segmented into a plurality of pieces is not having any limitation on the stiffness of the material which constitutes the acoustically reflecting wall. 
     In a seventeenth aspect of the thrust reverser device, the cascade can be movable and the casing fixed to use the thrust reverser device in a turbomachine provided with a cascade type thrust reverser with a sliding connection or the cascade can be fixed and the casing movable to use the thrust reverser device in a turbomachine provided with a fixed cascade thrust reverser. 
     In another object of the invention, a turbomachine intended to be mounted on an aircraft is proposed, the turbomachine comprising an axially symmetrical nacelle defining an axial direction and a radial direction, the nacelle including a thickness in the radial direction and a housing extending in the axial direction in its thickness to receive a cascade of a cascade type thrust reverser device. 
     According to a general feature of this object of the invention, the turbomachine can comprise a cascade type thrust reverser device as defined above, the cascade being positioned, when thrust reversal is not required, in the corresponding housing of the nacelle of the turbomachine. 
     In another object of the invention, an aircraft is proposed comprising at least one turbomachine as defined above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood, upon reading performed hereafter, by way of indication and without limitation, with reference to the appended drawings in which: 
         FIGS. 1A and 1B , already described, show schematic section views in a longitudinal plane of a turbomachine according to a first known embodiment of the prior art, respectively in a position in which the thrust reversal is inactive and in a position in which the thrust reversal is activated. 
         FIGS. 2A and 2B , already described, show schematic section views in a longitudinal plane of a turbomachine according to a second known embodiment of the prior art, respectively in a position in which the thrust reversal is inactive and in a position where the thrust reversal is activated. 
         FIG. 3  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is inactive according to a first embodiment of the invention. 
         FIG. 4  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is activated according to a first embodiment of the invention. 
         FIG. 5  illustrates schematically a section view in a plane comprising the axial direction and the circumferential direction of a cascade of the thrust reverser device of  FIGS. 3 and 4 . 
         FIG. 6  illustrates schematically a front view in the radial direction of a perforated wall of the thrust reverser device of  FIGS. 3 and 4 . 
         FIG. 7  shows a schematic section view in a plane comprising the axial direction and the radial direction of a thrust reverser device in a position in which the thrust reversal is inactive according to a second embodiment of the invention. 
         FIG. 8  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is activated according to a second embodiment of the invention. 
         FIG. 9  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is inactive according to a third embodiment of the invention. 
         FIG. 10  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is activated according to a second embodiment of the invention. 
         FIG. 11  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is inactive according to a fourth embodiment of the invention. 
         FIG. 12  shows a schematic section view in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device in a position in which the thrust reversal is activated according to a fourth embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Shown in  FIGS. 3 and 4  are schematic section views in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device mounted on an aircraft turbomachine according to the first embodiment of the invention and respectively in a position in which the thrust reversal is inactive and in a position in which the thrust reversal is activated. 
     In  FIGS. 3 and 4 , the turbomachine  1  comprises a thrust reverser device  70  which can operate according to the operation described in  FIGS. 2A and 2B . The turbomachine  1  comprises a nacelle  2  with axial symmetry around an axis X defining an axial direction DA, a radial direction DR and a circumferential direction DC. 
     The thrust reverser device  70  comprises a plurality of cascades  80  assembled to form a cascade ring. The ring can have a cylindrical base or a polygonal base, the cascades  80  extending respectively either in a curved plane comprising the axial direction DA and the circumferential direction DC of the turbomachine, or in a straight plane comprising the axial direction DA and a direction tangent to the circumferential direction DC. 
     In the embodiments illustrated, the cascades  80  are curved to facilitate the explanation and the labels, and extend mainly in a curved plane, called the first plane here, comprising the axial direction DA and the circumferential direction DC. 
     As shown in  FIG. 5 , which is a section view of a cascade  80  in a section plane parallel to the first plane, each cascade  80  comprises a frame  81  inside which extend first partitions  82  in the circumferential direction DC and first transverse partitions  83  in the axial direction DA. The frame  81 , the first partitions  82  and the first transverse partitions  83  have a height in the radial direction DR comprised between 10 mm and 300 mm. 
     The thickness of the first partitions  82  is comprised between 0.5 mm and 5 mm to be sufficiently thick to withstand the loads to which they are subjected, but also as thin as possible to minimize the mass and the head losses in the cascade. 
     The first partitions  82  are azimuthal partitions intended to orient the gas flow F toward the outside of the nacelle  2  and upstream of the turbomachine  1  for the reversal of thrust when the thrust reverser device is activated. The first transverse partitions  83  are axial partitions intended to define, with the first partitions  82 , first cavities  84  for the absorption of acoustic waves generated by the turbomachine, when the thrust reverser device is inactive. 
     The distance in the circumferential direction DC separating two first transverse partitions  83  adjacent to one another is equal to the distance in the axial direction D A  separating two first partitions  82 , to thus favor acoustic propagation in plane waves inside the cavities. 
     The cascade  80  comprises, in the axial direction DA of the turbomachine  1  on which the device  70  is mounted, a first axial end  810  and a second axial end  812 . As illustrated in  FIGS. 3 and 4 , the second axial end  812  of the cascades  80  is fixed to a downstream portion  22  of the nacelle  2 , movable with respect to an upstream portion  21  of the nacelle  2 . 
     Housed in the upstream portion  21  of the nacelle  2  of the turbomachine  1 , the thrust reverser device  70  comprises a plurality of casings  71  assembled to form a panel ring. The ring can have a cylindrical base or a polygonal base, the casings  71  extending respectively either in a curved plane comprising the axial direction DA and the circumferential direction DC of the turbomachine  1 , or in a straight plane comprising the axial direction DA and a direction tangent to the circumferential direction DC. 
     In the embodiments illustrated, the casing&#39;s  71  are curved to facilitate the explanation and the labels, and extend mainly in a curved plane comprising the axial direction DA and the circumferential direction DC. 
     Each casing  71  includes successively in the radial direction DR moving away from the axis of revolution, a perforated wall  72 , a porous interface  77 , a housing  75  configured to accommodate the cascade  80 , and an acoustically reflecting wall  73 . The porous interface  77  is glued to the perforated wall  72  inside the casing  71  and the housing  75  extends, in the radial direction DR, between the porous interface  77  and the acoustically reflecting wall  73 . 
     The casing  71  also comprises an opening  76  communicating with the housing  75 , the opening extending in a plane comprising the radial direction DR and the circumferential direction DC at an axial end of the casing  71  facing the downstream portion  22  of the nacelle  2 . 
     When thrust reversal is inactive, the thrust reverser device  70  is in a first position illustrated in  FIG. 3  in which the cascade  80  is positioned in the housing  75  of the casing  71 . 
     When thrust reversal is activated, the thrust reverser device  70  is in a second position illustrated in  FIG. 4  in which the cascade  80  is extracted from the casing  71  in the axial direction DA in translation with the downstream portion  22  of the nacelle, leaving the housing  75  free, at least in part. 
     As shown in  FIG. 6  which is a front view in the radial direction DR of the perforated wall  72  of the thrust reverser device  70  of  FIGS. 3 and 4 , the perforated wall comprises a plurality of orifices  722  and first wall strips  724  with no orifices and second wall strips  726  with no orifices and orthogonal to the first wall strips  724 . 
     When the device  70  is mounted on the turbomachine  1 , the first wall strips  724  extend in the circumferential direction DC and the second wall strips  726  extend in the axial direction DA. 
     The wall strips  724  and  726  thus separate the matrix groups of orifices  723 , each group  728  being in fluid communication with a single cavity  84  of the cascade  80 . 
     The perforated wall  72  is configured so that the first wall strips  724  are aligned with the first partitions  82  and the second wall strips  726  are aligned with the second partitions  83  when the device  70  is in the first position, to thus optimize sealing of the cavities  84 . 
     In addition, the porous interface  77  is formed of several layers of porous material and has a thickness E in the radial direction DR comprised between 0.2 mm and 2 mm to improve the interface between the movable cascade  80  and the perforated wall  72  by ensuring better sealing while still facilitating the sliding of the cascade  80  in the housing  75  during translations. 
     When the thrust reverser device  70  is in its first position as illustrated in  FIG. 3 , the first cavities  84  thus form resonant cavities, or acoustic treatment cells, due to the acoustically reflecting wall  73  and to the first and second partitions  82  and  83 . 
     In addition, as shown in  FIG. 5 , the casing  71  can comprise a sealing span  88  having a rectangular shape in a plane comprising the axial direction DA and the circumferential direction DC. The sealing span  88  is mounted on the porous interface  77  between the thrust reverser cascade  80  and the porous interface  77 . The sealing span  88  is formed on the porous interface  77  so as to extend along the first and second partitions  82  and  83  of the cascade  80  when the device  70  is in the first position, to form a sealed connection with the porous interface  77 . 
     Schematic section views are shown in  FIGS. 7 and 8  in a plane comprising the axial direction and the radial direction of a cascade type thrust reverser device  70  mounted on an aircraft turbomachine according to a second embodiment of the invention, and respectively in a position in which the thrust reversal is inactive and in a position in which the thrust reversal is activated. 
     In  FIGS. 7 and 8 , the turbomachine  1  comprises this time a thrust reverser device  70  which can operate according to the operation described in  FIGS. 1A and 1B . 
     The second embodiment differs from the first embodiment in that the cascade  80  is secured to the upstream portion  21  of the nacelle  2  of the turbomachine  1  and the casing  71  is made in the downstream portion  22  of the nacelle  2 . 
     The casing  71  comprises an opening  76  communicating with the housing  75 , the opening extending in a plane comprising the radial direction DR and the circumferential direction DC at an axial end of the casing  71  facing the upstream portion  21  of the nacelle  2 . 
     When the thrust reversal is inactive, the thrust reverser device  70  is in a first position illustrated in  FIG. 7 , in which the cascade  80  is positioned in the housing  75  of the casing  71 . 
     When the thrust reversal is activated, the thrust reverser device  70  is in a second position illustrated in  FIG. 8  in which the cascade  80  is extracted from the casing  71  in the axial direction DA, the casing  71  being in translation with the downstream portion  21  of the nacelle  2 , leaving the housing  75  free at least in part. 
     Schematic section views are shown in  FIGS. 9 and 10  in a plane comprising the axial direction DA and the radial direction DR of a cascade type thrust reverser device mounted on an aircraft turbomachine  1  according to a third embodiment of the invention and respectively in a position in which the thrust reversal is inactive and in a position in which the thrust reversal is activated. 
     As for the first embodiment, in the third embodiment illustrated in  FIGS. 9 and 10 , the turbomachine  1  comprises a thrust reverser device  70  which can operate according to the operation described in  FIGS. 2A and 2B . The turbomachine  1  comprises a nacelle  2  with axial symmetry around an axis X defining an axial direction DA, a radial direction DR and a circumferential direction DC. 
     The third embodiment differs from the first embodiment in that the casing  71  also comprises an outer wall  712 , compression springs  78  cooperating with the acoustically reflecting wall  73  and an actuator  79  configured to disengage the acoustically reflecting wall  73  from the cascade  80  when the device  70  is out of its first position. 
     The outer wall  712  of the casing  71  is positioned at a radially outer end of the casing  71 . The compression springs  78  are mounted between the outer wall  712  and the acoustically reflecting wall  73  and exert a radially inner force to press the acoustically reflecting all  73  against the cascade  80  when the device  70  is in the first position, and thus ensure better sealing and optimize the acoustic treatment. The terms “inner” and “outer” are used here with reference to the radial direction DR. 
     The actuator  79  comprises a first beveled surface  792  on the first axial end  810  of the cascade  80  protruding radially from the axial end  810  of the frame  81  of the cascade  80  so as to extend radially outward beyond the first and second partitions  82  and  83  of the cascade  80 . 
     The acoustically reflecting wall  73  comprises a first axial end  732  and a second axial end  734  opposite to the first axial end  732 . The first axial end  732  faces the upstream portion  21  of the nacelle  2 , while the second axial end  734  faces the downstream portion  22  of the nacelle  2 . In other words, the first axial end  732  corresponds to an upstream end while the second axial end  734  corresponds to a downstream end of the acoustically reflecting wall  73 . 
     The actuator  79  comprises a second beveled surface  793  on the second axial end  732  of the acoustically reflecting wall  73 . The second beveled surface  793  cooperates with the first beveled surface  792  when the device  70  is in the first position, to allow the acoustically reflecting wall  73  to be supported in the radial direction DR against the cascade  80 . The first beveled surface  792  and the second beveled surface  793  are parallel to one another and each form an angle of 45° with the first plane, i.e. with a plane comprising the axial direction DA and the circumferential direction DC. 
     The second beveled surface  793  also cooperates with the first beveled surface  793  to allow the cascade  80  to be withdrawn from the housing  75  when the device  70  is extracted from its first position. The actuator  79  causes a compression of the springs  78  and an outward movement of the acoustically reflecting wall  73  in the radial direction DR until the entire cascade  80 , and more particularly the first beveled surface  792 , can pass under the acoustically reflecting wall  73  and thus allow the extraction of the cascade  80  out of the housing  75 . 
     Schematic section views are shown in  FIGS. 11 and 12 , in a plane comprising the axial direction DA and the radial direction DR of a cascade type thrust reverser device mounted on an aircraft turbomachine  1  according to a fourth embodiment of the invention, and respectively in a position in which the thrust reversal is inactive and in a position in which the thrust reversal is activated. 
     The fourth embodiment differs from the third embodiment illustrated in  FIGS. 9 and 10  in that the cascade  80  is secured to the upstream portion  21  of the nacelle  2  of the turbomachine  1  and the casing  71  is made in the downstream portion  22  of the nacelle  2 . 
     In the fourth embodiment, the actuator  79  is located at the downstream ends. The first beveled surface  792  is at the second axial end  812  of the frame  81  of the cascade  80  and the second beveled surface  793  of the actuator  79  is positioned at the second axial end  734 . 
     The invention thus supplies a cascade type thrust reverser which allows both reorienting the air flow upstream of the turbomachine outside the nacelle and minimizing the head losses through the cascade when the thrust reversal is activated, and maximizing the effectiveness of acoustic absorption when the thrust reversal is inactive.