Patent Publication Number: US-2022235936-A1

Title: Combustion chamber comprising means for cooling an annular casing zone downstream of a chimney

Description:
TECHNICAL FIELD 
     The present invention relates to the field of combustion chambers of turbomachines, in particular turbomachines used for the propulsion of aircraft. 
     The invention relates more particularly to a combustion chamber comprising at least one annular casing delimiting an inner volume of the combustion chamber and provided with a chimney extending to the outside of the inner volume and delimiting a passage for a penetrating part through the annular casing, and, possibly, a bushing mounted floating on the chimney. 
     PRIOR ART 
     The internal temperature of combustion chambers is such that it is in general necessary to cool the annular casings that delimit the inner volume of these combustion chambers. 
     A common solution to limit the heating of such an annular casing consists of circulating a relatively cool film of air along the annular casing, within the inner volume of the combustion chamber. 
     Such a parietal film of air is in general formed by means of a multitude of microperforations formed in the annular casing, and through which relatively cool air coming from a bypass space of the combustion chamber is introduced into the inner volume of the latter. 
     However, in the cases where the annular casing is provided with a chimney intended for the passage of a penetrating part, such as a spark plug, through the annular casing, the chimney and the penetrating part degrade the efficiency of the cooling of a zone of the annular casing located immediately downstream of this chimney. 
     Indeed, the penetrating part constitutes, within the inner volume of the combustion chamber, an obstacle that interrupts the parietal film of air. 
     In addition, the region of location of the chimney in the annular casing and the passage delimited by the chimney constitute themselves a region devoid of microperforations. 
     Finally, outside the combustion chamber, the chimney also constitutes an obstacle to the flow of cool air circulating in the bypass space of the combustion chamber and supplying the microperforations. The microperforations possibly located in the wake of the chimney are therefore under-supplied with cooling air. 
     Document WO2015/049468A1 discloses a chimney of an annular casing of a combustion chamber provided with lateral conduits able to deviate, to a median axial plane of the chimney, air circulating around the chimney in the bypass space of the combustion chamber. This document also discloses a deflector fastened on an outer casing arranged around a combustion chamber, in order to deviate, to the external annular casing of the combustion chamber, air circulating in the bypass space of the combustion chamber. 
     These solutions are however not optimal regarding the cooling of the zone located immediately downstream of a chimney. 
     Document WO2018/050999A1 discloses a chimney provided with a deflector arranged opposite microperforations so as to participate in the formation of a parietal cooling film of air. 
     The supplying with air of these microperforations is however not optimal due to the fact that the chimney masks the microperforations with regards to the flow of air circulating in the bypass space of the combustion chamber. 
     DISCLOSURE OF THE INVENTION 
     The invention has in particular for purpose to provide a simple, economical and efficient solution to this problem, making it possible to avoid at least partially the disadvantages described hereinabove. 
     For this purpose, the combustion chamber further comprises a main air collection chamber open to the upstream and closed to the downstream, arranged facing a downstream portion of the chimney; and at least one through-opening formed in the annular casing and putting into direct communication the inner volume of the combustion chamber and the main air collection chamber. 
     The main air collection chamber makes it possible to capture air coming from upstream of the chimney and to inject it, via the through-opening, into the inner volume of the combustion chamber, where this air allows for a cooling of the annular casing. 
     In a preferred embodiment of the invention, the combustion chamber further comprises a deflector arranged in the inner volume of the combustion chamber, connected to a region of the annular casing that is closer to a central axis of the chimney than the through-opening or each through-opening is, and extending facing and beyond the through-opening or each through-opening, whereupon a space of formation of parietal cooling air film, closed to the upstream and open to the downstream, is defined between the annular casing and the deflector. 
     The deflector makes it possible to deviate the air injected beforehand into the inner volume of the combustion chamber via the through-opening. The deflector thus favours, in combination with the through-opening, the formation of a parietal cooling film of air circulating along the annular casing. 
     According to other advantageous aspects of the invention, the combustion chamber has one or more of the following characteristics, taken individually or according to any technically permissible combinations:
         the deflector comprises a proximal portion in the form of a portion of a ring through which the deflector is connected to said region of the annular casing, and a free distal portion extending facing and beyond the through-opening or each through-opening;   the main air collection chamber is in the form of a portion of a ring and has two opposite respective circumferential ends open to the upstream;   the main air collection chamber is closed on the side opposite the annular casing;   the combustion chamber furthermore comprises a secondary air collection chamber, open to the upstream and closed to the downstream, arranged facing the downstream portion of the chimney, and the downstream portion of the chimney comprises air passage orifices putting into direct communication the passage and the secondary air collection chamber;   the secondary air collection chamber is in the form of a portion of a ring and has two opposite respective circumferential ends open to the upstream;   the secondary air collection chamber is arranged between the chimney and a portion at least of the main air collection chamber;   the annular casing is formed at least by an annular wall provided with an orifice, and an annular flange of an additional part, housed in the orifice of the annular wall; and the additional part further comprises a tubular wall forming the chimney and from which the annular flange extends by moving away from the central axis of the chimney, said annular flange comprising the through-opening or each through-opening; and the additional part further comprises the main air collection chamber;   the additional part further comprises said region of the annular casing to which the deflector is connected, and the deflector;   the additional part further comprises the secondary air collection chamber.       

     The invention also relates to a turbomachine for an aircraft, comprising a combustion chamber of the type described hereinabove, and a penetrating part extending through the chimney. 
     In embodiments of the invention, the penetrating part is a spark plug. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention shall be better understood, and other details, advantages and characteristics of the latter will appear when reading the following description given by way of a non-limiting example and in reference to the accompanying drawings wherein: 
         FIG. 1  is a partial schematic view as an axial cross-section of a turbomachine for an aircraft; 
         FIG. 2  is a partial schematic half-view as an axial cross-section of a combustion chamber of a turbomachine of a known type; 
         FIG. 3  is a partial schematic view of the top of an external annular casing of the combustion chamber of  FIG. 2 ; 
         FIG. 4  is a partial schematic view in perspective and as an axial cross-section of a combustion chamber of a turbomachine according to a preferred embodiment of the invention; 
         FIG. 5  is a schematic view in perspective and as an axial cross-section of an additional part that is part of the combustion chamber of  FIG. 4 ; 
         FIG. 6  is a schematic view of the bottom of the additional part of  FIG. 5 ; 
         FIG. 7  is a schematic view in perspective of the additional part of  FIG. 5 . 
     
    
    
     In all of these figures, identical references can designate identical or similar elements. 
     DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS 
     The  FIG. 1  shows a turbomachine  10  for an aircraft, including in general a fan  12  intended for the aspiration of a flow of air being divided downstream of the fan into a primary flow circulating in a flow channel for primary flow, hereinafter called primary duct PF, within a gas generator, and a secondary flow that bypasses this gas generator in a flow channel for secondary flow, hereinafter called secondary duct SF. 
     The turbomachine is for example a bypass turbo turbine engine. The gas generator thus includes, generally, a low-pressure compressor  14 , a high-pressure compressor  16 , a combustion chamber  18 , a high-pressure turbine  20  and a low-pressure turbine  22 . The respective rotors of the high-pressure compressor and of the high-pressure turbine are connected by a shaft called “high-pressure shaft”, while the respective rotors of the low-pressure compressor and of the low-pressure turbine are connected by a shaft called “low-pressure shaft”, in a manner known per se. The turbomachine is furthermore shrouded by a nacelle  24 . The different rotors are rotatably mounted about a longitudinal axis  28  of the turbomachine. 
     In all of this description, the axial direction X is the direction of the longitudinal axis  28 . Except where it is stipulated otherwise, the radial direction R is at any point a direction orthogonal to the longitudinal axis  28  and passing through the latter, and the circumferential or tangential direction C is at any point a direction orthogonal to the radial direction R and to the longitudinal axis  28 . Except where it is stipulated otherwise, the terms “inner” and “outer” refer respectively to a relative proximity, and a relative separation, of an element in relation to the longitudinal axis  28 . Finally, the qualifiers “upstream” and “downstream” are defined by reference to the direction D of the flow of the gases in the primary PF and secondary SF ducts of the turbomachine. 
       FIG. 2  shows on a larger scale the combustion chamber  18  and its immediate environment, in a known configuration of the prior art. 
     The combustion chamber  18  comprises two coaxial annular casings, respectively inner  30  and outer  32 , centred with respect to a longitudinal axis of the combustion chamber, that is confounded with the longitudinal axis  28  of the turbomachine. 
     These two annular casings  30  and  32  are fastened downstream at inner  34  and outer  36  casings of the combustion chamber, and are connected to one another at their upstream end by an annular casing of a chamber bottom  38  wherein injection systems  40  are mounted respectively associated with an annular row of fuel injectors  42 . Each injection system  40  comprises openings intended for the injection, in the combustion chamber, of a median portion of a flow of air  44  coming from a diffuser  46  mounted at the outlet of the high-pressure compressor  16  of the turbomachine. 
     The annular casings  30 ,  32  and  38  thus delimit an inner volume  47  of the combustion chamber  18 . 
     Moreover, the inner  30  and outer  32  annular casings of the combustion chamber are for example connected at their upstream end to an annular shroud  48  that makes it possible to protect the annular casing of a chamber bottom  38  and the injection systems  40 , and that makes it possible to guide downstream a radially internal portion  50  of the flow of air  44 , hereinafter called inner bypass flow of air, and a radially external portion  52  of the flow of air  44 , hereinafter called outer bypass flow of air, respectively along inner  30  and outer  32  annular casings, within inner  54  and outer  56  bypass spaces. The inner  30  and outer  32  annular casings of the combustion chamber include for example each one of the air inlet orifices  58  and  60  intended for injecting a portion of the inner bypass flow of air  50  and of a portion of the outer bypass flow of air  52  into the ignited gases within the combustion chamber. 
     The coaxial annular casings  30  and  32  are furthermore provided with many microperforations, distributed substantially over the entire surface of these walls, and intended to create a parietal cooling film of air along each one of these walls within the combustion chamber  18 . These microperforations are not shown in  FIG. 2  for reasons of scale, but are shown in  FIG. 3 , where these microperforations, designated by the reference  62 , are shown larger and distributed according to a lesser density than in reality. The microperforations  62  in general have diameters comprised between 0.3 and 0.6 mm approximately, and are, in any case, clearly smaller than the air inlet orifices  58  and  60 . 
     Moreover, at least one of the annular casings  30  and  32  comprises at least one chimney delimiting a passage for a penetrating part, such as a spark plug, through said casing. 
     For example, the external annular casing  32  thus includes a chimney  64  extending according to a central axis  66  for example locally orthogonal to the annular casing  32 , and delimiting a passage  68  opening onto the combustion chamber  18  and through which extends a spark plug  70  mounted on the outer casing  36 . Such a spark plug  70  is intended to initiate the combustion of the air and fuel mixture within the combustion chamber  18 , at the starting of the turbomachine. In a manner known per se, the seal between the spark plug  70 , or a similar through-part, and the chimney  64 , is advantageously provided by means of a bushing mounted floating in the chimney. 
     Generally, the absence of microperforations in the zone corresponding to the chimney  64  and to its periphery penalises the cooling of this zone of the annular casing concerned  32 . 
     Furthermore, the spark plug  70  constitutes, in the inner volume  47  of the combustion chamber, an obstacle of a nature to interrupt a parietal film of air coming from upstream. 
     In addition, as schematically shown in  FIG. 3 , the chimney  64  constitutes, outside the combustion chamber, a local obstacle to the flow of the corresponding inner  50  or outer  52  bypass flow of air, generating a wake  72  in this flow of air. 
     Such a wake  72  tends to reduce the supply with air of microperforations located in the zone  73  of the annular casing  32  located to the right of the wake  72 , immediately downstream of the chimney, and therefore prevent good cooling of this zone. 
     The presence of the chimney  64 , and, where applicable, of the spark plug  70 , is because of this able to cause, within the annular casing  32 , high thermal gradients, of a magnitude of several hundred degrees Celsius, over a very short distance, of a magnitude of a few millimetres. Such thermal gradients generally result in a lessening in the service life of the annular casing  32 . 
     Other types of penetrating parts, such as start-up injectors, can cause similar problems. 
     The invention, which shall be described in reference to  FIGS. 4 to 7 , makes it possible to at least partially overcome the problem described hereinabove. 
       FIGS. 4 to 7  partially show the combustion chamber  18 , in a configuration in accordance with a preferred embodiment of the invention. 
       FIG. 4  shows in particular the external annular casing  32  provided with the chimney  64  that extends towards the exterior of the combustion chamber  18 , from the annular casing  32 , by delimiting the passage  68  for the penetrating part (this penetrating part is not visible in the  FIGS. 4-7  for increased clarity). The description that follows relates to an example wherein the penetrating part is a spark plug. This description can however be directly transposed to other types of penetrating parts such as those indicated hereinabove. 
     In the example shown, the chimney  64  is formed in an additional part  74 , shown alone in  FIGS. 5-7 . 
     This additional part comprises in particular a tubular wall  76  forming the chimney  64 , and an annular flange  78  extending from the tubular wall  76  by moving away from the central axis  66 , for example transversally to the tubular wall  76  ( FIGS. 4-7 ). 
     The annular casing  32  is thus formed by an annular wall  80 , and by the annular flange  78 , through which the additional part  74  is fastened on the annular wall  80 . This annular flange  78  has in particular a peripheral edge  82  connected to an inner edge  84  of an orifice of the annular wall  80  ( FIG. 4 ). 
     The chimney  64  is advantageously provided with a bushing  90  ( FIGS. 4 and 5 ) mounted floating in the chimney  64 , for example in the radially external end of the latter, and intended to provide the contact with the spark plug by avoiding air leaks between the chimney  64  and the spark plug. For this purpose, the chimney  64  comprises for example a collar  92  arranged at the radially external end of the chimney and delimiting, for example with a washer  93 , an annular groove  94  opening onto the central axis  66  of the chimney. In addition, the bushing  90  comprises an end flange  95  engaged in the annular groove  94  with a transversal play at the central axis  66 . The additional part  74  further comprises a main air collection chamber  100  ( FIGS. 4 and 5 ) arranged around a downstream portion  102 A of the chimney  64  ( FIG. 5 ) and configured to collect an incident flow of air F 1  ( FIG. 4 ) on the chimney  64  from upstream, and inject this air into the inner volume  47  of the combustion chamber in such a way that this air forms a parietal film F 1  ( FIG. 5 ) allowing for the cooling of the zone of the annular casing  32  located immediately downstream of the chimney  64  (i.e. the zone  73  located to the right of the wake  72 , in reference to  FIG. 3 ), as shall appear more clearly in what follows. 
     For this purpose, the main air collection chamber  100  is open to the upstream. The main air collection chamber  100  is for example in the form of a portion of a ring with two opposite respective circumferential ends  104 A ( FIG. 4 ) and  104 B (FIG.  7 ) open to the upstream. The main air collection chamber  100  has an angle range, shown by the angle θ in  FIG. 6 , preferably comprised between 120 degrees and 240 degrees, with respect to the central axis  66  of the chimney. In the preferred example shown, this angle range is equal to 180 degrees, whereupon the respective circumferential ends  104 A,  104 B of the main air collection chamber  100  are diametrically opposite. The respective circumferential ends  104 A,  104 B are then defined in a plane P 1  that includes the central axis  66  of the chimney and that is orthogonal to an axial plane P 2  of the combustion chamber also comprising the central axis  66  of the chimney (the axial plane P 2  corresponding to the plane of  FIG. 2 ). 
     In addition, the annular flange  78  comprises at least one through-opening  106  ( FIGS. 5 and 7 ) putting the inner volume  47  of the combustion chamber  18  ( FIG. 4 ) and the main air collection chamber  100  ( FIGS. 4 and 5 ) into direct communication. The through-opening  106  or each through-opening  106  is thus, more generally, formed in the annular casing  32 . 
     In other words, the main air collection chamber  100  is delimited by a portion of the annular flange  78  comprising the through-opening  106  or each through-opening  106 . 
     In the example shown, the annular flange  78  includes a single through-opening  106  taking the form of a curved slot around the central axis  66  of the chimney. As an alternative, the annular flange  78  can include a plurality over through-openings separated from one another, for example each one in the form of an orifice with a circular section. 
     The main air collection chamber  100  is furthermore delimited by a solid outer wall  108  ( FIGS. 4, 5 and 7 ) extending facing and at a distance from the downstream portion  102 A of the chimney  64  ( FIGS. 4 and 5 ). This outer wall  108  thus closes the main air collection chamber  100  downstream. 
     In the example shown, the outer wall  108  connects the annular flange  78  to the collar  92 , whereupon the main air collection chamber  100  extends to the collar  92 . The main air collection chamber  100  is thus closed on the side opposite the annular casing  32 , i.e. the radially external side. In the example shown, the closing of the main air collection chamber  100  of the side opposite the annular casing  32  is provided by the collar  92 . 
     In the preferred embodiment of the invention, the additional part  74  further comprises a deflector  110  extending in the inner volume  47  of the combustion chamber ( FIG. 4 ). More precisely, the deflector  110  extends facing the through-opening  106  and beyond the latter ( FIG. 5 ), from a region  112  of the annular flange  78  (and therefore of the annular casing  32 ) that is closer to the central axis  66  of the chimney  64  than the through-opening is  106  ( FIGS. 4 and 5 ). Thus, a space  114  of formation of parietal cooling air film ( FIGS. 5 and 7 ), closed to the upstream and open to the downstream, is defined between the annular flange  78  (and therefore the annular casing  32 ) and the deflector  110 . 
     The deflector  110  comprises a proximal portion  110 A ( FIGS. 5 and 7 ) in the form of a portion of a ring, through which the deflector  110  is connected to the region  112  of the annular flange  78  (or, more generally, of the annular casing  32 ), and a free distal portion  110 B ( FIGS. 5, 6 and 7 ) extending facing the through-opening  106  and beyond the latter. 
     In the preferred example shown, the free distal portion  110 B extends substantially parallel to the annular flange  78  (and therefore to the annular casing  32 ). More generally, the free distal portion  110 B advantageously forms an angle less than 30 degrees with the annular casing  32 , in a cross-section view along the axial plane P 2 . 
     In addition, in the preferred example shown, the deflector  110  comprises a median portion  110 C curved downstream, that connects the free distal portion  110 B to the proximal portion  110 A of the deflector. 
     The proximal portion  110 A of the deflector has an angle range a with respect to the central axis  66  which is preferably less than or equal to 180 degrees ( FIG. 6 ). 
     In the example shown, the through-opening  106  has an angle range, defined with respect to the central axis  66 , which is less than that of the proximal portion  110 A of the deflector, as is shown in  FIG. 7 . This makes it possible to maximise the proportion of the air, coming from the through-opening  106 , that is deviated downstream by the deflector  110 . 
     The free distal portion  110 B of the deflector  110  has for example a free end of which the angle range ϕ, defined with respect to the central axis  66 , is less than the angle range a of the proximal portion  110 A ( FIG. 6 ). 
     Thus, the free distal portion  110 B of the deflector  110  is essentially arranged facing the zone of the annular casing  32  located downstream of the chimney  64  (i.e. the zone  73  located to the right of the wake  72 , visible in  FIG. 2 ), which makes it possible to maximise the cooling of this zone by the parietal cooling film of air formed in the space  114 . 
     In the embodiment shown, the additional part  74  further comprises a secondary air collection chamber  120  arranged facing the downstream portion  102 A of the chimney  64  ( FIGS. 4 and 5 ) and configured to collect an incident air flow F 3  ( FIG. 4 ) on the chimney  64  from upstream. In addition, the downstream portion  102 A of the chimney  64  comprises air passage orifices  121 A ( FIG. 4 ) putting into direct communication the passage  68 , delimited by the chimney, and the secondary air collection chamber  120 , in order to allow air coming from the secondary air collection chamber  120  to penetrate into the passage  68  ( FIG. 5 : F 4 ) and to thus cool a downstream side  122 A of the spark plug ( FIGS. 2 and 3 ). 
     So as to be supplied with air, the secondary air collection chamber  120  is open to the upstream. For this purpose, the secondary air collection chamber  120  is for example in the form of a portion of a ring with two opposite respective circumferential ends  120 A,  120 B open to the upstream ( FIGS. 4 and 5 ). 
     The respective circumferential ends  120 A,  120 B of the secondary air collection chamber  120  are advantageously in the same plane as the respective circumferential ends  104 A,  104 B of the main air collection chamber  100 , and are therefore also diametrically opposite. 
     In the example shown, the two respective circumferential ends  120 A,  120 B of the secondary air collection chamber  120  are therefore defined in the plane P 1 . 
     In alternative embodiments, the respective circumferential ends  120 A,  120 B of the secondary air collection chamber  120  are offset upstream outside the main air collection chamber  100 . 
     In other alternative embodiments, the respective circumferential ends  120 A,  120 B of the secondary air collection chamber  120  are offset downstream inside the main air collection chamber  100 . 
     More generally, the secondary air collection chamber  120  preferably has an angle range, shown by the angle Ω in  FIG. 6 , comprised between 120 degrees and 240 degrees with respect to the central axis  66  of the chimney. 
     The secondary air collection chamber  120  is arranged between the chimney  64  and a portion of the main air collection chamber  100 . 
     More precisely, in reference to  FIGS. 4 and 5 , the main air collection chamber  100  comprises an inner portion  1001  extending from the outer wall  108  to the tubular wall  76  (or, more generally, to the chimney  64 ) and delimited by the annular flange  78  (or, more generally, by the annular casing  32 ), and an outer portion  100   e  extending from the outer wall  108  to a partition  124 , and delimited by the collar  92 . The cloison  124  is arranged between the outer wall  108  and the chimney  64 , and the secondary air collection chamber  120  is formed between the chimney  64  and the partition  124 . The partition  124  thus closes the secondary air collection chamber  120  downstream. 
     For example, the partition  124  comprises an outer portion  124   e  extending coaxially to the tubular wall  76  in the direction of the annular flange  78  from the collar  92 , and an inner portion  124   i  connecting the outer portion to the tubular wall  76 . 
     This particular arrangement allows the through-opening  106  to be arranged as close as possible to the chimney  64 , to the right of the secondary air collection chamber  120  in the direction of the central axis  66  of the chimney, which makes it possible to prevent the existence of a non-cooled region of the annular casing  32  immediately downstream of the chimney  64 . 
     Moreover, the chimney  64  comprises for example other air passage orifices  121 B, formed in an upstream portion  102 B of the chimney  64  ( FIGS. 4-6 ), defined outside the angle Ω and the angle C) of  FIG. 6 , i.e. upstream of the region of the chimney  64  located facing main  100  and secondary  120  air collection chambers. These orifices  121 B thus allow for the cooling of an upstream side  1226  of the spark plug ( FIG. 3 ) by incident air on the upstream portion  102 B of the chimney  64 . In the example shown, the orifices  121 A and the other orifices  121 B together form an annular row of orifices regularly distributed around the central axis  66 . 
     In operation, the relatively cool flow of air F 1  coming from upstream ( FIG. 4 ) is captured by the respective circumferential ends  104 A,  104 B of the main air collection chamber  100  and bypasses the chimney  64  by circulating within this main air collection chamber  100  then escapes from the latter through the through-opening  106 , through which the air penetrates into the space  114 . The air is then deviated downstream by the deflector  110  whereupon the air forms a parietal cooling film of air F 2  ( FIG. 5 ) circulating downstream along the inner face of the annular casing  32 . The air thus makes it possible to efficiently cool the zone of the annular casing  32  located immediately downstream of the chimney  64  (i.e. the zone  73  located to the right of the wake  72 ). 
     Moreover, the relatively cool flow of air F 3  coming from upstream ( FIG. 4 ) is captured by the respective circumferential ends  120 A,  120 B of the secondary air collection chamber  120  and bypasses the chimney  64  by circulating within this secondary air collection chamber  120  then penetrates into the passage  68  via the air passage orifices  121 A. The centripetal flow of air F 4  coming from these orifices ( FIG. 5 ) allows for the cooling of the downstream side  122 A of the spark plug ( FIGS. 2 and 3 ). 
     The separation of the flow of air F 1  and F 3  by the partition  124  makes it possible to ensure a homogeneous supply of the air passage orifices  121 A while still controlling the flow rate of the flow of air F 1  intended for forming the parietal cooling film of air F 2 . 
     As an alternative, the annular wall  80  and the elements described hereinabove as belonging to the additional part  74  can be carried out in a single piece. These elements are in particular the chimney  64 , the annular flange  78 , the main air collection chamber  100 , and, where applicable, the deflector  110 , and the secondary air collection chamber  120 . 
     Moreover, the configuration described hereinabove in relation with the external annular casing  32  exteriorly delimiting the inner volume  47  of the combustion chamber can, as an alternative or in a complementary manner, be applied to the cooling of the inner casing  30  that interiorly delimits this inner volume  47 . 
     Similarly, in the cases where the annular casing of a chamber bottom  38  comprises radial ends curved downstream, the additional part  74  can be added in an orifice of this annular casing of a chamber bottom  38 , or, as an alternative, the elements described hereinabove as belonging to the additional part  74  can be integrated into this annular casing of a chamber bottom  38 . 
     In the embodiment shown, the main air collection chamber  100  and the through-opening  106  are centred with respect to the axial plane P 2 . The same applies with regards to the deflector  110  and the secondary air collection chamber  120 . 
     Such a configuration is optimal in the case where the flow of air  44  coming from a diffuser  46  is an axial air flow, i.e. devoid of a gyratory component, whereupon the wake  72  is centred with respect to the axial plane P 2 . 
     As an alternative, in the case where the air flow  44  has a gyratory component at the outlet of the diffuser  46 , whereupon the wake  72  is inclined with respect to the axial plane P 2 , the main air collection chamber  100 , the through-opening  106  and, where applicable, the deflector  110 , the space  114  of formation of parietal cooling air film, and the secondary air collection chamber  120 , can be centred with respect to a plane inclined with respect to the axial plane P 2  and comprising the central axis  66  of the chimney  64 . The flow of the flow of air  44  being in this case locally inclined in relation to the axial direction X, the qualifiers “upstream” and “downstream”, applied to the definition of the air collection chamber  100  and, where applicable, the space  114  of formation of parietal cooling air film, and the secondary air collection chamber  120 , are defined by reference to the local inclined direction of the flow of the flow of air  44 . 
     In the foregoing, the expression “comprising one” must be understood as being a synonym of “comprising at least one”, except if the contrary is specified.