Abstract:
A plurality of hatches are distributed on the rear periphery of an engine cowl. The hatches are opened only when turbojet engine power is greater than cruising power. In an open position, the hatches draw hot air jets passing through an intermediate chamber before ejecting the jets through longitudinally-distributed communication components.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a turbine engine with attenuated jet noise, designed to be fitted to an aircraft. 
     BACKGROUND OF THE RELATED ART 
     It is known that, at the rear of a turbofan turbine engine, the cold flow and the hot flow travel in the same direction toward the downstream of said turbine engine and come into contact with one another. Since the speeds of said flows are different from each other, the result of this is fluid shear of penetration between said flows, said fluid shear generating noise, called “jet noise” in aviation technology. 
     To attenuate such a jet noise, thought has already been given to generating turbulence at the boundary between said hot flow and said cold flow. It has therefore already been proposed to make recesses in the outlet edge of the hot flow, said recesses being distributed on the periphery of said outlet edge and each of them generally having at least the approximate shape of a triangle, whose base is indistinguishable from said outlet edge and whose apex is in front of this outlet edge. These recesses are usually called “chevrons” in aviation technology. 
     These known chevrons are effective in attenuating the jet noise; however, they have the disadvantage of generating considerable drag. 
     In addition, it must be noted that the reduction of the jet noise is truly useful only when the aircraft fitted with said turbine engine is close to the ground with a high speed of said turbine engine, in order not to annoy the people who are in an airport or who reside in the vicinity of the latter. On the other hand, in the cruising phase at high altitude, the attenuation of the jet noise is of only little importance. 
     Therefore, at cruising speed, the performance of the aircraft is unnecessarily penalized by said chevrons creating increased drag. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to remedy this disadvantage, by generating turbulence at the boundary between said hot and cold flows only when the attenuation of the jet noise is really useful. 
     Accordingly, according to the invention, the turbofan turbine engine for an aircraft, comprising:
         a hollow nacelle having a longitudinal axis and comprising, at the front, an air inlet and, at the rear, an air outlet;   a fan placed axially in said nacelle opposite said air inlet and capable of generating the cold flow of said turbine engine;   a generator placed axially in said nacelle, behind said fan, said generator being capable of generating the axial hot flow of said turbine engine surrounded by said cold flow and being enclosed in an engine cowl; and   a fan channel inner cowl coaxially surrounding said hot flow generator so as:
           to delimit with the nacelle a channel of annular section for said cold flow, a channel that terminates in said air outlet of the nacelle;   to delimit with said engine cowl an intermediate chamber of annular section; and   to converge via its rear portion with the rear portion of said engine cowl so that the respective rear edges of these rear portions form the edge of the outlet orifice of said hot flow at the rear portion of said intermediate chamber,
 
is noteworthy:
   
           in that, provided in the rear portion of said intermediate chamber are communication means placed about said longitudinal axis and capable of placing said intermediate chamber in communication with the outside, in the vicinity of the boundary between said cold flow and said hot flow;   in that a plurality of hatches are provided that are arranged in the rear portion of said engine cowl, while being distributed on the periphery of the latter rear portion;   in that said hatches are opened only when the speed of said turbine engine is greater than a threshold corresponding to at least the cruising speed of the aircraft; and   in that, in the open position, said hatches draw off, from said hot flow, individual jets of hot air flowing into said intermediate chamber before leaving the latter through said communication means while being distributed about said longitudinal axis.       

     Therefore, in the flight phases in which the engine speed is less than said threshold, the hatches are closed and the turbine engine of the invention operates like a turbine engine with no chevrons, with no attenuation of the jet noise nor increase in drag. 
     On the other hand, on take-off, the speed of the turbine engine is high and greater than said threshold, so that the hatches are opened and draw off individual jets of hot air. These individual jets, distributed on the periphery of the rear portion of the engine cowl (in accordance with the distribution of said hatches), enter said chamber and leave it via said communication means, generating turbulence at the boundary between the hot and cold flows, in the manner of chevrons. They therefore cause a reduction in the jet noise, accompanied by an increase in drag. 
     It will be noted that, when the aircraft is in the approach phase for the purpose of a landing (engine at low speed), but the pilot is obliged to reapply throttle because said landing is momentarily impossible, the engine speed when the throttle is reapplied is high and comparable to that of take-off. Consequently, on such a reapplication of the throttle, the hatches are opened and the jet noise is attenuated, which is favorable since the aircraft is then close to the ground. 
     It will also be noted that, when the aircraft comprises a plurality of turbine engines, of which at least one has failed, the speed of the turbine engines that are operating is greater than their normal speed to compensate for said failure and, in this case, it is advantageous that said hatches are opened to attenuate the noise generated. 
     Said communication means may comprise a plurality of individual communication openings distributed on the periphery of the rear portion of said intermediate chamber. 
     Such individual openings may be specifically made for the needs of the present invention. However, if, as is described in French patent application No. 05 09260 filed on Sep. 12, 2005 in the name of the applicant, on the periphery of said outlet orifice of the hot flow, only one of said rear edges of said fan channel inner cowl or of said engine cowl is notched by recesses capable of attenuating the jet noise of the turbine engine without generating excessive drag, it is advantageous that said recesses form at least in part said communication means. In addition, to optimize the blow-through of said recesses, and therefore increase the attenuation of the jet noise, it is preferable, if each recess has at least the approximate shape of a triangle as indicated above, that an individual jet of hot air flows out in the corresponding recess through a side edge of said recess. 
     Furthermore, if, in a usual manner in certain turbine engines, said rear edges of the fan channel inner cowl and of the engine cowl arrange between them a slot, at least portions of said slot may also form at least in part said communication means. 
     Preferably, with each hatch is associated a closing and opening system, sensitive to the value of a physical magnitude characterizing the state of said hot flow. 
     Therefore, the closing and opening of said hatches may be automatic according to the engine speed. 
     For example, such a closing and opening system may comprise a calibrated spring, acting on the corresponding hatch in the closing direction. Therefore, by choosing the appropriate calibration for this spring, the hatch may remain closed when the value of the pressure of said hot flow is less than the high values that said pressure has at high engine speeds and is open in the converse case. 
     However, preferably, each closing and opening system of a hatch comprises a bimetallic strip being triggered for a hot flow temperature corresponding to the take-off speed. 
     In an advantageous embodiment, each hatch comprises an elastic strip capable of interacting with an opening made in said rear portion of the engine cowl, said elastic strip being fixedly attached to said rear portion along an edge of said opening and said bimetallic strip being fixedly attached, on one side, to said rear portion and, on the other side, to said elastic strip. 
     Preferably, so as not to create obstacles in the path of the hot flow (which would risk degrading the performance of said turbine engine), it is advantageous for said hatches to open in the direction of said intermediate chamber. 
     For a reason similar to the foregoing, the system for closing and opening each hatch is advantageously on the side of said intermediate chamber. 
     On the latter side, each hatch may be protected by a rearward-opening casing to allow said jets of hot air to reach said communication means. 
     Advantageously, particularly in order to be able to adjust the inclination of said jets of hot air relative to the edge of the outlet orifice of the hot flow, means for the guidance of said jets of hot air are provided behind said hatches. Such guidance means may consist of walls, obstacles, etc. They may also consist of said casings for protecting the hatches. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The figures of the appended drawing will clearly explain how the invention may be embodied. In these figures, identical reference numbers indicate similar elements. 
         FIG. 1  represents, in schematic axial section, a known turbine engine, designed to be enhanced by the present invention. 
         FIGS. 2 and 3  illustrate schematically the principle of the present invention applied to the turbine engine of  FIG. 1 . 
         FIGS. 4 and 5  illustrate schematically, in views respectively similar to  FIGS. 2 and 3 , a variant application of the present invention to the turbine engine of  FIG. 1 . 
         FIG. 6  shows in perspective an exemplary embodiment of the hatches used in the implementation of the present invention. 
         FIG. 7  shows in schematic perspective the rear portion of the engine cowl of the turbine engine corresponding to  FIGS. 2 to 5 , said rear portion being fitted with a plurality of hatches distributed on its periphery and protected by protective casings. 
         FIG. 8  illustrates, in enlarged perspective from the rear, a hatch protected by a protective casing and fitted with means for guiding the jet of hot air. 
         FIG. 9  illustrates, also in enlarged perspective from the rear, a variant embodiment of said guidance means associated with the hatches. 
         FIG. 10  shows a variant embodiment of the invention, in a view similar to  FIG. 7 . 
         FIG. 11  illustrates the variant embodiment of  FIG. 10 , the rear portion of the fan channel inner cowl being represented as an overlay of said rear portion of the engine cowl and comprising chevrons. 
         FIGS. 12 and 13  further illustrate another variant embodiment in views comparable to  FIGS. 10 and 11 . 
         FIG. 14  is a variant embodiment of that of  FIGS. 10 to 13 . 
         FIG. 15  represents, in schematic axial section, another known turbine engine, different from that of  FIG. 1  and also intended to be enhanced by the present invention. 
         FIGS. 16 and 17  illustrate schematically, in views respectively similar to  FIGS. 2 and 3 , the principle of the present invention applied to the turbine engine of  FIG. 15 . 
         FIGS. 18 and 19  illustrate schematically, in views respectively similar to  FIGS. 16 and 17 , a first variant application of the present invention to the turbine engine of  FIG. 15 . 
         FIG. 20  shows, in a view similar to  FIG. 11 , an exemplary embodiment of the rear portion of the hot flow generator of the turbine engine of  FIG. 15  that can be used in the first variant of  FIGS. 18 and 19 . 
         FIGS. 21 and 22  illustrate schematically, in views respectively similar to  FIGS. 16 and 17 , a second variant application of the present invention to the turbine engine of  FIG. 15 . 
         FIG. 23  shows, in a view similar to  FIG. 11 , an exemplary embodiment of the rear portion of the hot flow generator of the turbine engine of  FIG. 15  that can be used in the second variant of  FIGS. 21 and 22 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The turbofan turbine engine of a known type for an aircraft, shown in  FIG. 1 , comprises a hollow nacelle  1  with a longitudinal axis L-L, comprising, at the front, an air inlet  2  provided with a leading edge  3  and, in its rear portion  1 R, an annular air outlet  4  provided with a trailing edge  5 . 
     Placed axially inside said hollow nacelle  1  are:
         a fan  6  directed toward the air inlet  2  and capable of generating the cold flow  7  for the turbine engine;   a central generator  8  comprising, in a known manner and not shown, low-pressure and high-pressure compressors, a combustion chamber and low-pressure and high-pressure turbines, said generator  8  generating the axial hot flow  9  of said turbine engine surrounded by said cold flow  7  and being enclosed in an engine cowl  15 ;   a fan channel inner cowl  14  surrounding said hot flow generator  8 ; and   sound attenuation coverings  12 , designed to absorb the internal noises generated by the fan  6  and the hot flow generator  8 .       

     The fan channel inner cowl  14  delimits with the nacelle  1  a fan channel  13 , of annular section, culminating at the annular outlet  4 . The cold flow  7  passes through the fan channel  13  and leaves the turbine engine through said annular outlet  4 . 
     In addition, the cowl  14  delimits with the engine cowl  15  an intermediate chamber  16 , of annular section, surrounding said central generator  8  and traversed longitudinally by an air flow  17  for the ventilation of said central generator  8 , the air flow  17  being drawn off at the front from the cold flow  7 . 
     The respective rear portions  14 R and  15 R of said cowls  14  and  15  converge on each other and their respective rear edges  14   r  and  15   r  form the edge of the outlet orifice  11  of the hot flow  9  at the rear portion  16 R of the intermediate chamber  16 , while arranging between them a slot  18 , through at least portions of which said ventilation air flow  17  escapes. 
     Therefore, at the outlet of the known turbine engine represented in the figure, the central hot flow  9  is surrounded by the annular cold flow  7 . Clearly, at the boundary  19  between these two flows, the fluids in contact have different speeds, which at least partly generates the jet noise described above. 
     To attenuate this jet noise, the edge of the outlet orifice  11  of the hot flow  9  is provided, in a known manner, with recesses  20  distributed on its periphery. These recesses  20  pass right through the thickness of the two rear edges  14   r  and  15   r  and generate considerable drag. 
     As mentioned above, the object of the present invention is to remove these through-recesses and, to do this, to modify the rear portion  16 R of the intermediate chamber  16  in the manner illustrated schematically by  FIGS. 2 to 7 . 
     As these figures show, on the periphery of the rear portion  15 R of the engine cowl  15  and on the side of the intermediate chamber  16 , a plurality of hatches  21  are arranged and distributed. It will be noted that, in  FIG. 7 , each hatch  21  is protected, on the side of the intermediate chamber  16 , by a casing  22  provided with an opening  23  directed toward the rear of the turbine engine. 
     Each hatch  21  comprises an elastic strip  24  capable of closing off an opening  25  made in said rear portion  15 R of the engine cowl  15  (see  FIG. 6 ). Along an edge of said opening  25 , one end  24 E of said elastic strip  24  is fixedly attached, for example by welding, to said rear portion  15 R. In addition, a bimetallic strip system  26  is fixedly attached, at one of its ends  26 E 1 , to said rear portion  15 R and, at its other end  26 E 2 , to said elastic strip  24 . The bimetallic strip system  26  is designed to deform only when the temperature reached by the hot flow  9  corresponds to a speed of the turbine engine that is greater than a threshold at least equal to the cruising speed, said threshold corresponding for example to the take-off speed or to a high speed capable of compensating for the failure of at least one other turbine engine of the aircraft. 
     Therefore, for any turbine engine speed below said threshold, the bimetallic strip system  26  is not deformed and the strip  24  closes off the opening  25  (see  FIG. 2 ). 
     On the other hand, for a turbine engine speed greater than said threshold, the bimetallic strip system  26  deforms and the strip  24  is moved away from the rear portion  15 R. The hatch  21  therefore opens (see  FIGS. 3 ,  5  and  6 ). The result of this is therefore that said hatch  21  draws off, from the hot flow  9 , a jet of hot air  9   d , passing through the opening  23  of the casing  22 , then passing into the intermediate chamber  16  before being discharged to the outside through at least portions of the slot  18 . 
     In the embodiment of  FIGS. 2 and 3 , the jets of hot air  9   d  leave the intermediate chamber  16  in common with the ventilation air  17 , through the slot  18 . On the other hand, in the embodiment of  FIGS. 4 and 5 , on the one hand a partition  10 A inside the intermediate chamber  16  and, on the other hand, openings  10 B in the fan inner cowl  14  have been provided in front of the hatches  21 . Therefore, the ventilation air  17  can escape through the openings  10 B, while only the jets of hot air  9   d  escape through at least portions of the slot  18 . 
     If, as illustrated in  FIGS. 2 to 5 , the edge of the outlet orifice  11  of the hot flow  9  is smooth (that is to say not provided with the through-recesses  20  of  FIG. 1 ), the turbine engine of the invention behaves, from the point of view of jet noise and below said speed threshold, like a known turbine engine not furnished with chevrons. On the other hand, above said threshold, it attenuates the jet noise like a turbine engine furnished with chevrons, even though it does not have any, because each jet of hot air  9   d  drawn off by each hatch  21  generates, at the rear of said turbine engine, turbulence similar to that produced by said recesses  20 . 
     Naturally, although  FIG. 7  shows the jets of hot air  9   d  as being parallel to the axial direction L-L, the orientation of said jets could be different, inclined relative to the edge of the outlet orifice  11  and not orthogonal as shown. 
     In addition, as illustrated in  FIGS. 8 and 9 , behind said hatches  21 , guidance means  27 ,  28  can be provided to orient said jets of hot air  9   d  relative to the edge of the outlet orifice  11  of the hot gas  9 . These guidance means may be walls  27 , grooved obstacles  28  or similar members, forming orientation channels with the rear portion  14 R of the fan cowl  14  (not shown in these figures). 
     In the embodiments of  FIGS. 10 ,  11  and  12 ,  13 , the means for guiding the jets of hot air  9   d  consist of the casings  22 , formed for this purpose. 
     Furthermore, in the latter embodiments, the rear edge  15   r  of the rear portion  15 R is smooth while the rear edge  14   r  of the rear portion  14 R is notched by recesses  29  of triangular shape and the opening  23  of each casing  22  opens into a recess  29  through a side edge of the latter. Therefore, in this case, the jets of hot air  9   d  leave the rear portion  16 R of the intermediate chamber  16  mainly through the recesses  29  opening into the slot  18 . 
     In the variant of  FIG. 14 , the rear edge  14   r  is smooth and, on the contrary, the rear edge  15   r  of the rear portion  15 R is notched with recesses  30 , into which said casings  22  open, in a similar manner to what has been indicated above. Also, in this embodiment, the jets of hot air  9   d  leave the rear portion  16 R of the intermediate chamber  16  mainly through the recesses  30  opening into the slot  18 . 
       FIG. 15  shows a known turbine engine, similar to the turbine engine of  FIG. 1 , except with respect to the rear portion  16 R of the intermediate chamber  16 . In this case, the rear edges  14   r  and  15   r  are joined and do not arrange the slot  18  between them. 
     Consequently, for the escape of the jets of hot air  9   d  to the outside for the purpose of forming turbulence capable of attenuating the jet noise of said turbine engine, it is possible:
         as illustrated by  FIGS. 16 and 17 , to make openings  31  in the fan inner cowl  14 , in the vicinity of the outlet orifice  11  of the hot flow  9 ;   as illustrated by  FIGS. 18 ,  19  and  20 , to make recesses  29  only in the rear edge  14   r , the rear edge  15   r  remaining smooth; or   as illustrated by  FIGS. 21 ,  22  and  23 , to make recesses  30  only in the rear edge  15   r , the rear edge  14   r  remaining smooth.       

     Therefore, in the embodiments of  FIGS. 16 to 23 , the openings  31  and the recesses  29  and  30  are used specifically for the jets of hot air  9   d  to pass through.