Patent Publication Number: US-11028801-B2

Title: Grating for the formation of a reverse flow of an aircraft turbofan engine

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the French patent application No. 1761914 filed on Dec. 11, 2017, the entire disclosures of which are incorporated herein by way of reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a grating for the formation of a reverse flow of a turbofan engine of an aircraft, a turbofan engine comprising at least one such grating, and an aircraft comprising at least one such turbofan engine. 
     An aircraft comprises a fuselage, on each side of which is fixed a wing. Under each wing, there is suspended at least one turbofan engine. Each turbofan engine is fixed under the wing via a pylon which is fixed between the structure of the wing and the structure of the turbofan engine. 
     The turbofan engine comprises an engine in the form of a core and a nacelle which is fixed around the engine to a fixed structure of the jet engine. Between the engine and the nacelle, the jet engine has a secondary jet in which there flows, from upstream to downstream, a secondary flow of gasses originating from a fan positioned upstream of the engine. 
     The nacelle comprises a cowl that is fixed relative to the fixed structure and, forward, a mobile cowl which moves translationally aft to free a window between the mobile cowl and the fixed cowl and which allows the passage of gasses between the secondary jet and the outside. 
     Initially, one or more blocker doors are displaced from an inactive position to an active position. In the inactive position, the blocker door is outside of the secondary jet and does not prevent the flow of the secondary flow. In the active position, the blocker door is across the secondary jet and directs the secondary flow from the secondary jet to the window and therefore to the outside. 
     The displacements of the mobile cowl and of the blocker doors are produced by a control system comprising, for example, thrusters and rods. 
     To best guide the flow outgoing through the window, gratings, also called “cascades,” are positioned across the window to enhance the efficiency of the reverser by more accurately controlling the direction of the diverted secondary flow. 
     These gratings take the form of profiled fins which divert the secondary flow. Each fin has a curved profile whose rounding is oriented aft and whose center of curvature is forward relative to the fin. While these fins allow a good deflection of the secondary flow forward, the air flow at the output of the grating tends to separate at the trailing edge of each fin, which tends to reduce the performance of the grating. 
     To ensure a better efficiency of these gratings, it is necessary to find fin forms which are more efficient from an aerodynamic point of view and from a weight point of view. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to propose a grating for the formation of a reverse flow of a turbofan engine of an aircraft. 
     To this end, a grating is proposed for the formation of a reverse flow of a turbofan engine having a forward end and an aft end, the grating comprising fins of a first type having a curved profile whose rounding is intended to be oriented aft and whose center of curvature is forward relative to the fin of the first type, the grating being characterized in that it comprises fins of a second type, in that each fin of one of the two types is inserted between two fins of the other type moving from forward to aft, in that each fin of the second type has a curved profile whose rounding is configured to be oriented aft and whose center of curvature is forward relative to the fin of the second type, and in that the cord of the fins of the second type is smaller than the cord of the fins of the first type. 
     Such a grating allows for a reduction of the weight while ensuring an efficient diversion. 
     Advantageously, the trailing edges of the fins of the first type and the trailing edges of the fins of the second type are in one and the same output plane. 
     Advantageously, the leading edges of the fins of the first type are in one and the same input plane parallel to the output plane, and in that the leading edge of each fin of the second type is in an intermediate plane between the input plane and the output plane and at a distance from each of them. 
     Advantageously: 
     
       
         
           
             
               
                 
                   
                     
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     where “c” is the cord of the fins of the first type, 
     “c′” is the cord of the fins of the second type, 
     “s” is the distance between two consecutive fins of the first type, 
     “s′” is the distance between a fin of the first type and a consecutive fin of the second type, 
     “h” is the height of the fins of the first type, 
     “h′” is the height of the fins of the second type, 
     “θ 1 ” is the input angle between the tangent to the curvature of the leading edge of the fins of the first type and the vertical axis, 
     “θ 1 ′” is the input angle between the tangent to the curvature of the leading edge of the fins of the second type and the vertical axis, 
     “θ 2 ” is the output angle between the tangent to the curvature of the trailing edge of the fins of the first type and the vertical axis, 
     “θ 2 ′” is the output angle between the tangent to the curvature of the trailing edge of the fins of the second type and the vertical axis, 
     “st” is the offset angle of the fins of the first type, and 
     “st′” is the offset angle of the fins of the second type. 
     According to a particular embodiment, the heights of the fins of the second type vary from one fin of the second type to another fin of the second type. 
     According to a particular embodiment, the distance between a fin of the first type and the consecutive fin of the second type in the forward to aft direction, is different from the distance between another fin of the first type and the fin of the second type consecutive in the forward to aft direction to this other fin of the first type. 
     According to a particular embodiment, the input angles of the fins of the second type vary from one fin of the second type to another fin of the second type. 
     The invention also proposes a turbofan engine comprising at least one grating for the formation of a reverse flow according to one of the preceding variants. 
     The invention also proposes an aircraft comprising at least one turbofan engine according to the preceding variant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention mentioned above, and others, will become more clearly apparent on reading the following description of an exemplary embodiment, the description being given in relation to the attached drawings, in which: 
         FIG. 1  is a side view of an aircraft comprising a turbofan engine according to the invention, 
         FIG. 2  is a cross-sectional view through a median plane of the jet engine according to the invention in closed position, 
         FIG. 3  is a cross-sectional view similar to that of  FIG. 2  in open position, 
         FIG. 4  shows a side view of a grating according to the invention, 
         FIG. 5  shows an enlargement of a part of the grating of  FIG. 4 , and 
         FIG. 6  shows a side view of a grating according to different embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, the terms relating to a position are taken with reference to an aircraft in an advancing position as is represented in  FIG. 1 . 
       FIG. 1  shows an aircraft  10  which comprises a fuselage  12 , on each side of which is fixed a wing  14  which bears at least one turbofan engine  100  according to the invention. The turbofan engine  100  is fixed under the wing  14  via a pylon  16 . 
     In the following description, and by convention, X will denote the longitudinal axis of the nacelle  102  and of the turbofan engine  100  which is overall parallel to the longitudinal axis X of the aircraft  10 , or roll axis, oriented positively in the direction of advance of the aircraft  10 , Y denotes the transverse axis or pitch axis of the aircraft which is horizontal when the aircraft is on the ground, and Z denotes the vertical axis or vertical height or yaw axis when the aircraft is on the ground, these three directions X, Y and Z being mutually orthogonal and forming an orthonormal reference frame whose origin is the center of gravity of the aircraft. 
     The turbofan engine  100  comprises a nacelle  102  which comprises, forward, a fixed cowl  106  and, rearward of the fixed cowl  106  relative to the longitudinal axis X, a mobile cowl  108 . 
     As is shown in  FIGS. 2 and 3 , the turbofan engine  100  comprises an engine  20  in the form of a core which is housed inside the nacelle  102 . The jet engine  100  has a jet  202  delimited between the nacelle  102  and the engine  20  and in which circulates a secondary flow  208  originating from an upstream fan. 
     The fixed cowl  106  is fixedly mounted on a fixed structure  209  of the nacelle  102  and constitutes an outer wall of the nacelle  102 . 
     The mobile cowl  108  is mounted to be translationally mobile on the fixed structure  209  in a direction of translation that is overall parallel to the longitudinal axis X. The translation is produced by any appropriate means such as, for example, runners, or by any actuation systems such as, for example, thrusters or motors. 
     In the embodiment of the invention presented here, the mobile cowl  108  comprises an inner wall  207   a  and an outer wall  207   b  which surrounds the inner wall  207   a.    
     The mobile cowl  108  is mobile between a position of closure ( FIG. 2 ) in which the mobile cowl  108  is against the fixed cowl  106  and a position of opening ( FIG. 3 ) in which the mobile cowl  108  is moved away from the fixed cowl  106  aft so as to open a window  210  open to the outside of the nacelle  102  and which opens a passage between the secondary jet  202  and the outside. In the position of closure, the fixed cowl  106  and the outer wall  207   b  are extended to form the outer jacket of the nacelle  102  and to close the window  210 , and in the position of opening, the fixed cowl  106  and the outer wall  207   b  are separated from one another. 
     At the same time, in the position of closure, the inner wall  207   a  comes into contact with the fixed structure  209  and constitutes an outer wall of the secondary jet  202 , and, in the position of opening, the inner wall  207   a  is moved away from the fixed structure  209  so as to open the passage between the secondary jet  202  and the window  210 . 
     The nacelle  102  comprises at least one blocker door  104 . In particular, there can be two blocker doors  104  positioned facing one another, or several, for example four, blocker doors  104  distributed regularly over the periphery of the nacelle  102 . 
     The thrust reversing system which is described here is described only by way of illustration and the invention can be applied to any type of thrust reverser for which cascades are used in order to increase the efficiency of the thrust forward of the nacelle. 
     Furthermore, here, the invention is more particularly described for a single blocker door  104 , but it applies in the same way for each blocker door  104  when there are several thereof. 
     In the embodiment of the invention presented here, the blocker door  104  is positioned between the inner wall  207   a  and the outer wall  207   b  in the position of closure. 
     The blocker door  104  is mounted to rotate freely about an axis of rotation  50  on the fixed structure of the nacelle  102  between an inactive position ( FIG. 2 ) in which it is not in the jet  202  and an active position ( FIG. 3 ) in which it at least partly blocks the jet  202 . 
     When the mobile cowl  108  is in the position of closure, the blocker door  104  is in the inactive position, and when the mobile cowl  108  is in the position of opening, the blocker door  104  is in the active position so as to divert at least a part of the secondary flow  208  to the outside of the nacelle  102 . 
     The displacement of the blocker door  104  is linked to the displacement of the mobile cowl  108 . The displacement of the blocker door  104  is controlled by any appropriate means, such as a system of rods, thrusters or motors. 
     Thus, in the position of opening of the mobile cowl  108  and in the active position of the blocker door  104 , the secondary flow  208  is diverted to the outside through the window  210 . 
     For each window  210 , the nacelle  102  is equipped with gratings  250  which allow the formation of a reverse gas flow of the jet engine  100  from the secondary gas flow  208 , also known as “cascades”, which are positioned across the window  210  to enhance the efficiency of the reverser by more accurately controlling the direction of a diverted secondary flow  208  and, in particular, by orienting the secondary flow into a direction forward of the nacelle  102 .  FIG. 4  shows the grating  250  on its own and in cross section. 
     The number of gratings  250  per window  210  varies according to the dimensions of the gratings  250  and of the window  210 . In the following description, the invention is more particularly described for a single grating  250 , but it applies in the same way for each grating  250  when there are several thereof. 
     The grating  250  takes the form of a frame having an upstream edge  252  and a downstream edge  254  parallel to the upstream edge  252 , and lateral edges  253  at right angles to the upstream  252  and downstream  254  edges. The grating  250  is fixed to the fixed structure of the nacelle  102 , for example by screws. 
     Inside the frame, the grating  250  has fins  256  of a first type and fins  258  of a second type, where each fin  256 ,  258  of one of the two types is inserted between two fins  258 ,  256  of the other type going along the longitudinal axis X, that is to say, from forward to aft of the jet engine  100 . 
     Each fin  256  of the first type has a curved profile whose rounding is oriented aft of the jet engine  100  and whose center of curvature is forward relative to the fin  256  of the first type. Each fin  256  of the first type therefore makes it possible to divert the secondary flow  208  forward. 
     Each fin  258  of the second type also has a curved profile whose rounding is oriented aft of the jet engine  100  and whose center of curvature is forward relative to the fin  258  of the second type, but whose chord is smaller than the chord of the fins  256  of the first type. 
     Thus, with respect to the secondary flow  208  entering into the grating  250 , each fin  258  of the second type has a drag which is lower than the drag of the fins  256  of the first type. Since the fins  258  of the second type are smaller than the fins  256  of the first type, they are less heavy, hence a weight saving, and they make it possible, by reducing the output surface of the secondary flow  208 , to create a convergent section and speed up the secondary flow  208  at the output of the grating  250  and thus reduce the separation of the air flow at the fins  256  of the first type. 
     The trailing edges of the fins  256  of the first type and the trailing edges of the fins  258  of the second type are aligned in a direction that is overall parallel to the longitudinal axis x. In other words, the trailing edges of all the fins  256  and  258  are all in one and the same output plane that is overall parallel to the longitudinal axis X. This output plane may be curved to follow the curvature of the nacelle, such as a surface of revolution about the longitudinal axis of the engine. 
     On the other hand, the leading edges of the fins  256  of the first type and the leading edges of the fins  258  of the second type are not aligned in a direction that is overall parallel to the longitudinal axis X. The leading edges of the fins  256  of the first type are all in one and the same input plane parallel to the output plane and the leading edge of each fin  258  of the second type is in an intermediate plane between the input plane and the output plane and at a distance from each of them. The input plane and the intermediate plane may also be curved in the same manner as the output plane to follow the curvature of the nacelle, such as a surface of revolution about the longitudinal axis of the engine, with all of the input, output and intermediate planes being concentric. 
       FIG. 5  shows an enlargement of the grating  250  where: 
     “c” is the chord of the fins  256  of the first type, 
     “c′” is the chord of the fins  258  of the second type, 
     “s” is the distance between two consecutive fins  256  of the first type in the forward to aft direction, 
     “s′” is the distance between a fin  256  of the first type and a consecutive fin  258  of the second type in the forward to aft direction, 
     “h” is the height of the fins  256  of the first type, 
     “h′” is the height of the fins  258  of the second type, 
     “θ 1 ” is the input angle between the tangent to the curvature of the leading edge of the fins  256  of the first type and the vertical axis, 
     “θ 1 ′” is the input angle between the tangent to the curvature of the leading edge of the fins  258  of the second type and the vertical axis, 
     “θ 2 ” is the output angle between the tangent to the curvature of the trailing edge of the fins  256  of the first type and the vertical axis, 
     “θ 2 ′” is the output angle between the tangent to the curvature of the trailing edge of the fins  258  of the second type and the vertical axis, 
     “st” is the offset angle of the fins  256  of the first type, that is to say the angle between the chord and the vertical axis, and 
     “st′” is the offset angle of the fins  258  of the second type, that is to say the angle between the chord and the vertical axis. 
     The vertical axis is taken here with reference to  FIGS. 2 to 6 , but this axis is more generally a radial direction of the turbofan engine  100 . Furthermore, different thickness laws can be applied to the profile of the fins. 
     According to a particular embodiment, the fins  256  of the first type and the fins  258  of the second type are such that: 
     
       
         
           
             
               
                 
                   
                     
                       0.2 
                       × 
                       s 
                     
                     ≤ 
                     
                       s 
                       ′ 
                     
                     ≤ 
                     
                       0.8 
                       × 
                       s 
                     
                   
                   ; 
                 
               
             
             
               
                 
                   
                     
                       0.2 
                       × 
                       h 
                     
                     ≤ 
                     
                       h 
                       ′ 
                     
                     ≤ 
                     
                       0.8 
                       × 
                       h 
                     
                   
                   ; 
                   
                     
                       with 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       30 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       mm 
                     
                     ⁢ 
                     
                         
                     
                     ≤ 
                     h 
                     ≤ 
                     
                       70 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       mm 
                     
                   
                   ⁢ 
                   
                       
                   
                   ; 
                 
               
             
             
               
                 
                   
                     
                       
                         - 
                         1.5 
                       
                       × 
                       
                         θ 
                         1 
                       
                     
                     ≤ 
                     
                       θ 
                       
                         1 
                         ′ 
                       
                     
                     ≤ 
                     
                       1.5 
                       × 
                       
                         θ 
                         1 
                       
                     
                   
                   ; 
                   
                     
                       with 
                       ⁢ 
                       
                           
                       
                       - 
                       
                         10 
                         ⁢ 
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                     ≤ 
                     
                       θ 
                       1 
                     
                     ≤ 
                     
                       70 
                       ⁢ 
                       ° 
                     
                   
                   ; 
                 
               
             
             
               
                 
                   
                     
                       
                         - 
                         1.5 
                       
                       × 
                       
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                         2 
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                         θ 
                         2 
                       
                     
                   
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                       ⁢ 
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       FIG. 6  shows different variants which can be implemented independently of one another or in combination with one another. 
     According to a first variant, the heights of the fins  258  of the second type vary from one fin  258  of the second type to another fin  258  of the second type. These variations are represented by different heights h 1 ′, h 2 ′. 
     According to a second variant, the distance between a fin  256  of the first type and the consecutive fin  258  of the second type in the forward to aft direction, is different from the distance between another fin  256  of the first type and the fin  258  of the second type consecutive in the forward to aft direction to this other fin  256  of the first type. These variations are represented by different distances s 1 ′, s 2 ′. 
     According to a third variant, the input angles of the fins  258  of the second type vary from one fin  258  of the second type to another fin  258  of the second type. These variations are represented by different angles θ 1 ′, θ 2 ′. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.