Patent Publication Number: US-2023151769-A1

Title: Optimised discharge line grid and optimized discharge valve

Description:
TECHNICAL FIELD 
     The invention relates to the field of noise in aircraft propulsion systems, and specifically noise from bleed valves used on aircraft propulsion systems. 
     PRIOR ART 
     In most configurations, aircraft propulsion systems, such as turbofans, turboprops, or open rotors, are constituted in a similar way to the turbojet engine, of which a section view in a longitudinal plane of the turbojet engine is illustrated in  FIG.  1   . 
     The turbojet engine  1  comprises a nacelle  2 , an intermediate casing  3  and an inner casing  4 . The nacelle  2  and the two casings  3  and  4  are coaxial and define an axial direction of the turbojet engine DAT and a radial direction of the turbojet engine D RT . The nacelle  2  defines at a first end an inlet channel  5  of a fluid flow and at a second end, opposite the first end, an exhaust channel  6  of a fluid flow. The intermediate casing  3  and the inner casing  4  together delimit a primary fluid flow path  7 . The nacelle  2  and the intermediate casing  3  together delimit a secondary fluid flow path  8 . The primary flow path  7  and the secondary flow path  8  are disposed along an axial direction of the turbojet engine DAT between the inlet channel  5  and the exhaust channel  6 . 
     The turbojet engine  1  further comprises a fan  9  configured to deliver an air flow F as the fluid flow, the air flow F being divided at the outlet of the fan into a primary flow Fp circulating in the primary flow path  7  and into a secondary flow Fs circulating in the secondary flow path  8 . 
     The secondary flow path  8  comprises a ring of stators  10 , and the primary flow path  7  comprises a stage of low-pressure compression  11 , a stage of high-pressure compression  12 , a combustion chamber  13 , a high-pressure turbine  14  and a low-pressure turbine  15 . 
     The propulsion systems of an aircraft generally comprise bleed valves  16  such as for example valves known as Variable Bleed Valves (VBV), Transient Bleed Valves (TBV) or Handling Bleed Valves (HBV). These valves  16  have the function of controlling the operation of the turbojet engines  2 , by adjusting the air flow rate at the inlet and/or outlet of the high-pressure compressor  12 , to increase the surge margin, at low ratings, or during the acceleration or deceleration phases. The flow rate thus drawn is expelled through a duct  17 , then reinserted into the secondary flow path  8  conveying the secondary flow Fs, or further downstream into the primary flow Fp, depending on the strategy used. 
     If the air flow rate is reinserted downstream of the primary flow path  7  conveying the primary flow Fp as illustrated in  FIG.  1    (a commonly-occurring situation in the control of transient ratings), a common system optimization consists in the partial obstruction of the duct by a multi-perforated grid or a diaphragm. The benefit of this optimization is to generate a load loss, making it possible to adapt the thermodynamic conditioning of the flow to the fluid environment into which it will be reinserted, under controlled mass and bulk limitations. The situation in which the grid is positioned in the duct is referred to as a duct configuration. 
     In the situation illustrated in  FIG.  2   , in which the air flow rate is reinserted into the secondary flow path  8  conveying the secondary flow Fs, or in the situation in which the air flow rate is reinserted into the ambient environment (a commonly-occurring situation in the control of the lower ratings), the duct  17  of the bleed system is shorter and is conventionally, without a diaphragm. This being the case, it is common to position a grid at the downstream end of this duct  17 , to reduce the aero-acoustic phenomena generated by the expulsion of gas at high speed. The situation where the grid is positioned at the end of the duct is referred to as free configuration. 
     In the two scenarios illustrated in  FIGS.  1  and  2   , a significant amount of acoustic radiation results from the interaction between the perforated grid and the flow that traverses it. This noise, which can reach a high level on the effective perceived noise scale in decibels, known by the abbreviation EPNdB (Effective Perceived Noise in deciBels) contributes to the airplane noise, during rating transitions and at low ratings. 
     From the document WO 2015/110748 a strategy is known for reinserting the drawn load, as well as the use of a micro-perforated diaphragm to minimize the acoustic penalties associated with the supersonic phenomena generated downstream of this diaphragm. 
     Among the noise sources identified during the passing of the flow through the grid, two forms of noise are particularly troublesome: mixing noise, generated as its name suggests by the mixing of the flow in the jets generated by the grid, and shock noise, which can appear when the flow becomes supersonic at the outlet of the grid. 
     SUMMARY OF THE INVENTION 
     The invention aims to make provision for an improved grid making it possible to optimize the mixing downstream of the grid and thus minimize the intensity of the aero-acoustic phenomena generated by this type of bleed system and specifically to reduce mixing noise and shock noise, while providing a perforated surface making it possible to ensure the operability of the air system. 
     In a subject of the invention, provision is made for an acoustic treatment grid intended to be mounted inside or at the outlet of a duct of a bleed valve of a turbomachine of an aircraft intended to convey a gas flow (F), the grid comprising a perforated plate and circular orifices traversing the perforated plate along a first direction, the orifices having a diameter and a geometrical center. 
     According to a general feature of the invention, each orifice ( 230 ) is separated from an adjacent orifice by a space, the length (e) of which is equal to the product of the diameter (D) of said orifice ( 230 ) and a spacing coefficient of a value between 1.1 and 6. 
     The grid according to the invention makes it possible to optimize the spatial distribution of the perforations on the surface of the grid, and thus to limit the interaction of the jets above each perforation of the grid which promotes a quick dissipation of the turbulent structures generated downstream of the grid-flow system, and thus makes it possible to minimize low-frequency noise, while ensuring the operability of the bleed valve. 
     The acoustic radiation is indeed mainly governed by the expansion of the flow through the grid, and is therefore closely linked to the geometry of the grid. The adjustment of the space of the orifices of the plate as a function of the diameters of the orifices makes it possible to significantly shift the acoustic radiation into the high frequencies and thus take it partially outside the audible range. 
     Furthermore, since high-frequency radiation is easier to reduce, using porous materials for example, the acoustic absorption of the acoustic radiation is made easier. 
     The range chosen for the spacing coefficient makes it possible to ensure a good trade-off between the shifting of the radiation into the high frequencies and the various compactness requirements related to the application. 
     According to a first aspect of the acoustic treatment grid, the diameter of the orifices of the perforated plate is preferably between 0.5 mm and 20 mm. 
     Such a range of diameters for the orifices of the perforated plate makes it possible to maximize the shifting of the acoustic radiation into the high frequencies. 
     According to a second aspect of the acoustic treatment grid, the perforated plate preferably has a thickness along the first direction between 1 mm and 20 mm. 
     The range chosen for the thickness of the perforated plate makes it possible to resist the forces exerted and the temperatures prevailing in the turbomachine in which the bleed valve is mounted including such a bleed grid. 
     According to a third aspect of the acoustic treatment grid, the perforated plate may comprise, with respect to the gas flow intended to traverse the perforated plate, an upstream face intended to receive the gas flow and a downstream face, opposite the upstream face, from which the gas flow is intended to escape, the grid further comprising a layer of porous material disposed on said downstream face of the perforated plate. 
     The use of a porous material on the downstream face of the grid makes it possible to attenuate acoustic resonance phenomena in the outlet duct, and thus to reduce the longitudinal modes that are set up. 
     According to a fourth aspect of the acoustic treatment grid, the layer of porous material disposed on said downstream face of the perforated plate includes a thickness along the first direction preferably between a first thickness equal to half the diameter of an orifice around which the layer of porous material is disposed and a second thickness equal to twenty times the greatest length of the perforated plate measured in a plane orthogonal to the first direction. 
     Thus, if the perforated plate has the shape of a disc, its thickness is preferably less than twenty times the diameter of the perforated plate. 
     According to a fifth aspect of the acoustic treatment grid, the perforated plate may comprise between 2 and 500 orifices. 
     According to a sixth aspect of the acoustic treatment grid, the orifices may be uniformly distributed over the perforated plate. 
     According to a seventh aspect of the acoustic treatment grid, the perforated plate may comprise at least a first orifice with a first diameter and at least a second orifice with a second diameter separate from the first diameter. 
     In another subject of the invention, provision is made for a bleed valve for an aircraft turbojet engine comprising a duct intended to convey a gas flow mainly along a first direction from at least one inlet of the duct to at least one outlet of the duct, and at least one acoustic treatment grid as defined above mounted inside the duct or on an outlet of the duct. The first direction of the acoustic treatment grid is colinear with the first direction of the bleed valve. 
     According to a first aspect of the bleed valve, the duct may comprise at least one wall equipped with an acoustic treatment means and located downstream of the bleed grid with respect to the direction of flow of the gas flow intended to be conveyed through the duct. 
     The application of an acoustic treatment means on one or more wall(s) of the duct makes it possible to reduce the high-frequency acoustic radiation generated by the expansion of the gas flow through the grid. 
     According to a second aspect of the bleed valve, the acoustic treatment means of said at least one wall may comprise a layer of porous material and/or an acoustic treatment panel. 
     The acoustic treatment panel can be a panel comprising a honeycomb structure. The acoustic treatment means can be optimized as a function of the size of the orifices to act on the range of frequencies radiated by said grid. 
     According to a third aspect of the bleed valve, the shortest distance between the acoustic treatment means and the grid is less than or equal to a length equal to forty times the greatest length of the section of the duct, the section of the duct extending orthogonally to the first direction. 
     According to a fourth aspect of the bleed valve, the length along the first direction of the acoustic treatment means is preferably between a first length equal to half the greatest length of the section of the duct and a second length equal to fifty times the greatest length of the section of the duct, the section of the duct extending orthogonally to the first direction. 
     According to a fifth aspect of the bleed valve, the thickness of the acoustic treatment means along a direction orthogonal to the first direction is preferably between a first thickness equal to half the diameter of an orifice of the perforated plate and a second thickness equal to twenty times the greatest length of the section of the duct, the section of the duct extending orthogonally to the first direction. 
     According to a sixth aspect of the bleed valve, the duct may comprise at least one segment, the diameter of which varies along the first direction. 
     According to a seventh aspect of the bleed valve, the duct may comprise at least one segment, in which the geometrical shape of the section of the duct varies, the section of the duct extending orthogonally to the first direction. 
     According to an eighth aspect of the bleed valve, the duct may comprise at least two outlets, at least a fork, at least a first segment extending between the inlet of the duct and a fork, a second segment extending between a fork and a first outlet, a third segment extending between a fork and a second outlet, at least one of said at least one grid being mounted in one of the first, second or third segment, or on one of the first or second outlets. 
     The use of a duct with a variable section and/or of a non-circular geometrical shape and/or forks makes it possible to minimize any areas of recirculation or stalling of the ducts (source of additional noise) and to adapt the system to the overall dimensions available on the architecture of the engine. 
     According to a ninth aspect of the bleed valve, said at least one grid and/or said at least one acoustic treatment means can be made of ceramic material. 
     The advantage of using a ceramic material is that it reduces the weight of the grid by ensuring the resistance of the part to the engine environment (high temperatures etc.) Furthermore, acoustic treatment made of Ceramic Matric Composite (CMC) material have good properties at high temperatures. 
     In another subject of the invention, provision is made for a turbojet engine comprising a nacelle, an intermediate casing and an inner casing, coaxial, and a bleed valve as defined above, the intermediate casing and the inner casing together delimiting a primary fluid flow path, the nacelle and the intermediate casing together delimiting a secondary fluid flow path, and the bleed valve being mounted between the primary flow path and the secondary flow path and configured to draw a portion of the air from the primary flow path and deliver it into the secondary air path. 
     In another subject of the invention, provision is made for a turbojet engine comprising a nacelle, an intermediate casing and an inner casing, coaxial, and a bleed as defined above, the intermediate casing and the inner casing together delimiting a primary fluid flow path in which is mounted a combustion chamber, the nacelle and the intermediate casing together delimiting a secondary fluid flow path, and the bleed valve being configured to draw a portion of the air from the primary flow path upstream of the combustion chamber and deliver it into the primary flow path downstream of the combustion chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1   , already described, shows a section view in a longitudinal plane of a turbojet engine of the prior art with a bleed valve reinjecting into the primary flow. 
         FIG.  2   , already described, shows a section view in a longitudinal plane of a turbojet engine of the prior art with a bleed reinjecting into the primary flow. 
         FIG.  3    schematically shows a section view of a bleed valve fitted with an acoustic treatment grid according to a first embodiment of the bleed valve. 
         FIG.  4    shows a front view of the acoustic treatment grid of  FIG.  3   . 
         FIG.  5    schematically shows a section view of a bleed valve according to a second embodiment of the bleed valve. 
         FIG.  6    shows a front view of a perforated plate of the acoustic treatment grid according to a third embodiment of the acoustic treatment grid. 
         FIG.  7    shows a front view of a perforated plate of the acoustic treatment grid according to a fourth embodiment of the acoustic treatment grid. 
         FIG.  8    shows a front view of a perforated plate of the acoustic treatment grid according to a fifth embodiment of the acoustic treatment grid. 
         FIG.  9    shows a front view of a perforated plate of the acoustic treatment grid according to a sixth embodiment of the acoustic treatment grid. 
         FIG.  10    shows a front view of a perforated plate of the acoustic treatment grid according to a seventh embodiment of the acoustic treatment grid. 
         FIG.  11    shows a front view of a perforated plate of the acoustic treatment grid according to an eighth embodiment of the acoustic treatment grid. 
         FIG.  12    schematically shows a view of a bleed valve according to a third embodiment of the invention of the bleed valve. 
         FIG.  13    schematically shows a view of a bleed valve according to a fourth embodiment of the invention of the bleed valve. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG.  3    schematically illustrates a section view of a bleed valve  20  fitted with an acoustic treatment grid  22  according to an embodiment of the invention. 
     The bleed valve  20  for an aircraft turbojet engine according to the first embodiment of the invention comprises a cylindrical duct  21  with a circular base of a first diameter De and intended to convey a gas flow F, and a grid  22  comprising a perforated plate  23 , also cylindrical and comprising orifices  230 . 
     The duct  21  defines an axial direction D A  parallel to the cylindrical axis of symmetry of the duct  21  and a radial direction D R  orthogonal to the axial direction D A . The section view of the bleed valve  20  of  FIG.  3    is embodied in a plane comprising the axial direction D A  and the radial direction D R . 
     The perforated plate  23  comprises an upstream face  232  receiving the gas flow F and a downstream face  234  opposite the upstream face  232  through which the gas flow F escapes after traversing the perforated plate  23 . 
     The duct  21  is only partially obstructed by the grid  22  in the sense that the flow F can flow through the orifices  230  of the perforated plate  23  forming the grid  22 , and only through these orifices  23 . 
     The perforated plate  23  of the grid  22  may be made of a metallic material or of a ceramic matrix material or another material resistant to thermal conditions, in particular when the bleed valve  20  is operational. 
     The grid  22  can be mounted at an outlet end of the duct  21  or else inside the duct  21  as indicated by the portion of the duct  21  in dotted lines. 
     Furthermore, as indicated in  FIG.  3   , the grid  22  further comprises a layer of porous material  24  disposed on the downstream face  234  without covering the orifices  230 . The plate  23  and the layer of porous material  24  thus form channels from the orifices  230  of the perforated plate  23 . 
     The perforated plate  23  comprises a thickness h between 1 mm and 20 mm, and the layer of porous material  24  comprises a thickness he. 
       FIG.  4    illustrates a front view of the perforated plate  23  of  FIG.  3    according to a first embodiment. The perforated plate  23  extends in a radial plane comprising the radial direction D R  and orthogonal to the axial direction D A . 
     In a variant, the perforated plate  23  can convex along the axial direction D A . In another variant, the plate  23  can be disposed inside the duct in such a way as to form an angle between 0 and 10° with a plane orthogonal to the axial direction D A , the orifices  230  extending along the axial direction D A  which makes it possible to slightly elongate the length of the channel formed by the orifice  230  with a reduced thickness h of the plate  23 . 
     As illustrated in  FIG.  4   , the perforated plate  23  comprises, in this example, 37 orifices  230  each having the shape of a circle with a second diameter D between 0.5 mm and 20 mm and a geometrical center C. 
     The thickness he of the layer of porous material  24  is contained between a half second diameter D of the orifice  230  and twenty times the first diameter De of the duct  21 , which corresponds to the diameter of the perforated plate  23  when the grid is mounted inside the duct  21 . 
     Each orifice  230  is separated from the other adjacent orifices by a length e between 1.1 times and 6 times the second diameter D of the orifice. The term “adjacent orifices” should be understood to mean two orifices not having any other orifices between them. The length e separating the two orifices is measured from the center of the first orifice to the center of the second orifice. 
       FIG.  5    illustrates a section view of a bleed valve  20  according to a second embodiment of the invention. 
     The second embodiment differs from the first embodiment illustrated in  FIG.  3    and in that the duct  21  comprises a duct portion  210  located downstream of the grid  22  with respect to the direction of the gas flow F, this duct portion  210  being fitted with an acoustic treatment panel  25 . In a variant, the acoustic treatment panel could be replaced by a layer of porous material. 
     The acoustic treatment panel  25  comprises a core having a honeycomb structure forming resonant acoustic absorption cavities. The cavities are tuned over a range of frequencies to be treated. 
     The acoustic treatment panel  25  extends along the wall of the duct portion  210 , i.e. along the axial direction D A , over a length Lm between an upstream end  251  and a downstream end  252  with respect to the direction of the gas flow F. The length Lm is between a first length equal to half the first diameter De of the duct  21  and a second length equal to fifty times the first diameter De of the duct  21 . 
     The upstream end  251  of the acoustic treatment panel  25  is separated from the grid  22  by a length Sm along the axial direction D A  less than or equal to forty times the first diameter De of the duct  21 . 
     The acoustic treatment panel  25  further comprises a thickness hm along the radial direction D R  between a first thickness equal to half of the second diameter D of a orifice  230  of the perforated plate  23  and a second thickness equal to twenty times the first diameter De of the duct  21 . 
       FIG.  6    shows a front view of a perforated plate  23  of the acoustic treatment grid  22  according to a third embodiment of the acoustic treatment grid. 
     In this third embodiment, the perforated plate  23  comprises 22 orifices  230  distributed over a single half  231  of the disk formed by the perforated plate  23 . 
       FIG.  7    shows a front view of a perforated plate  23  of the acoustic treatment grid  22  according to a fourth embodiment of the acoustic treatment grid. 
     In this fourth embodiment, the perforated plate  23  comprises 30 orifices  230  distributed over a ring  233  formed between the outer perimeter of the circular perforated plate  23  and an inner circle Ci of a diameter smaller than that of the outer perimeter. 
       FIG.  8    shows a front view of a perforated plate  23  of the acoustic treatment grid  22  according to a fifth embodiment of the acoustic treatment grid. 
     In this fifth embodiment, the perforated plate  23  comprises 32 orifices  230  distributed over the perforated surface to form first areas  235  without orifices and second areas  236  provided with orifices  230 . 
       FIG.  9    shows a front view of a perforated plate  23  of the acoustic treatment grid  22  according to a ninth embodiment of the acoustic treatment grid. 
     In this sixth embodiment, the perforated plate  23  comprises 36 orifices  230  distributed over the entire surface of the perforated plate  23  as in the first embodiment illustrated in  FIG.  4   . The sixth embodiment differs from the first embodiment illustrated in  FIG.  4    in that the orifices  230  comprise orifices of different diameters, the diameter of the orifices  230  increasing from a first embodiment 237 of the circular perforated plate  23  to a second end  238  of the circular perforated plate  23 . 
       FIG.  10    shows a front view of a perforated plate  23  of the acoustic treatment grid  22  according to a seventh embodiment of the acoustic treatment grid. 
     The seventh embodiment differs from the sixth embodiment illustrated in  FIG.  9    and in that the diameter of the orifices  230  increases as it gets further from the center of the circular perforated plate  23 . 
       FIG.  11    shows a front view of a perforated plate  23  of the acoustic treatment grid  22  according to an eighth embodiment of the acoustic treatment grid. 
     The eighth embodiment differs from the sixth embodiment illustrated in  FIG.  9    in that the diameter of the orifices  230  increases as it gets closer to the center of the circular perforated plate  23 . 
       FIG.  12    schematically illustrates a view of a bleed valve according to a third embodiment of the bleed valve. 
     In the third embodiment of the bleed valve  20 , the duct  21  comprises a single inlet  211 , a first outlet  212 , a second outlet  213 , a fork  214 , a first segment  215  extending between the inlet  211  of the duct  21  and the fork  214 , a second segment  216  extending between the fork  214  and the first outlet  212 , and a third segment  217  extending between the fork  214  and the second outlet  213 . 
     In the third embodiment, the bleed valve  20  comprises a grid  22  mounted in the first segment  215 , as well as a first acoustic treatment panel  25   a  mounted on the first segment  215 , between the grid  22  and the fork  214 , and a second acoustic treatment panel  25   b  mounted on third section  217  between the fork  214  and the second outlet  213 . 
     The first acoustic treatment panel  25   a  extends over a first length Lm 1  of the first segment  215  and is separated from the grid  22  by a first space of length Sm 1 , and the second acoustic treatment panel  25   b  extends over a second length Lm 2  of the third segment  217  and is separated from the grid  22  by a second space of length Sm 2 . 
       FIG.  13    schematically illustrates a view of a bleed valve according to a fourth embodiment of the bleed valve. 
     The fourth embodiment of the bleed valve  20  differs from the third embodiment illustrated in  FIG.  12    in that it comprises two grids  22   a  and  22   b  and two acoustic treatment panels  25   a  and  25   b , the first grid  22   a  and the first acoustic treatment panel being mounted on the second segment  216  of the duct  21  and the second grid  22   b  and the second acoustic treatment panel being mounted on the third segment  217  of the duct  21 . 
     The first acoustic treatment panel  25   a  extends over a first length Lm 1  of the second segment  216  and is separated from the first grid  22   a  by a first space of length Sm 1 , and the second acoustic treatment panel  25   b  extends over a second length Lm 2  of the third segment  217  and is separated from the second grid  22   b  by a second space of length Sm 2 . 
     The grid and the bleed valve according to the invention make it possible to optimize the mixing downstream of the grid and thus to minimize the intensity of the aero-acoustic phenomena generated by this type of bleed system and specifically to reduce mixing noise and shock noise, while providing a perforated plate making it possible to ensure the operability of the air system.