Abstract:
A turbomachine combustion chamber shell ring in which dilution holes in the turbomachine combustion chamber shell ring are covered with inserts defining chambers around same on an inner face of the shell ring. Ventilation holes, through the insert, induce ventilation of portions of the shell ring surrounding the dilution holes, cool the portions, and prevent crack formation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a turbomachine combustion chamber shell ring. 
     The shell ring in question herein defines a flame tube, which is thus subject to considerable overheating on the inner face thereof, whereas the outer face thereof is crossed by a cool gas flow, originating from the turbomachine compressors and mixing with the combustion gases downstream from the shell ring before entering the turbines. 
     2. Description of the Related Art 
     Such a shell ring is traversed by a plurality of types of holes, including dilution holes having a relatively large diameter intended to allow the entry of a portion of the outer flow into the flame tube so as to improve the composition of the combustion mixture, and finer ventilation holes, which are more numerous and distributed on most of the surface area of the shell ring, to also enable the entry of air from the outer flow, but which have the effect of protecting the shell ring from overheating, by forming a flush flow in the downstream direction on the inner face of the shell ring and thus a boundary layer cooler than the combustion gases. 
     This boundary layer is reformed poorly downstream from the large diameter holes, interrupting the flush flow, and the corresponding portions of the shell ring, all or almost all subject to overheating, are subject to deformation and stress arising from differential expansions, which may give rise to cracks. 
     The document EP-A-1 703 207 describes a combustion chamber whereon the invention may be implanted. In addition, the above problems are mentioned in the French patent application registered under the number 11 53232 disclosing a modification of the conventional shell ring arrangement to reform the boundary layer immediately downstream from the large-diameter holes and thus relieve the shell ring. A further solution is however proposed with the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     In a general form, it relates to a turbomachine combustion chamber shell ring, comprising dilution holes and ventilation holes surrounding the dilution holes and finer and more numerous than said holes, characterised in that it comprises inserts extending over and around the dilution holes on an outer face of the shell ring, the shell ring is devoid of ventilation holes at portions situated above the inserts, the inserts each comprising an edge for attaching to the shell ring and an orifice extending over one of the respective dilution holes, and the inserts are traversed by holes directed towards said portions of the shell ring. 
     The essential effect obtained is that the high pressure present around the shell ring allows the entry of air via the holes of the insert, in streams striking the outer face of the shell ring and producing the sought cooling at this location, with a greater intensity than ventilation holes arranged through the shell ring, traversed very quickly by the air. Instead, the air sucked in below the insert flows on the outer face of the shell ring after reaching same, towards the dilution hole, and this flow time causes a greater elimination of heat. When the air enters the dilution hole, the relatively low speed driving same may make it possible for it to resume a tangent downstream direction relatively easily, which will help restore the boundary layer on the inner face of the shell ring and will enhance the ventilation further. 
     According to requirements, the inserts may be parallel with the shell ring or inclined relative thereto in an axial direction of the shell ring. The holes of the inserts are advantageously perpendicular to the shell ring, but they may also be positioned obliquely; all these adaptations are to be decided in each design. 
     Advantageously, the inserts extend more in the downstream direction of the shell ring than in other directions from the centres of the dilution holes, since the portions of the shell ring subject to intense overheating are specifically downstream from these holes. The inserts may however be subject to retraction in this downstream direction of the shell ring, since the boundary layer is reformed according to the same shape, bypassing the dilution holes. 
     A further favourable feature is obtained if the inserts each comprise an inner edge surrounding the respective orifice and extending towards the respective dilution passage, making it possible to channel both the air sucked in directly by the dilution holes via the insert orifice, and the air sucked in by the insert holes and blowing onto the shell ring, then flowing around this inner edge. 
     Satisfactory cohesion is obtained if the inner edge is enclosed between the attachment sectors situated in the respective dilution hole, flow sectors being defined in said respective dilution hole by the inner edge and between the attachment sectors. In order to help continue the flow on the downstream side of the dilution hole, more advantageously, the dilution holes and the inner edge have centres offset in an axial direction of the shell ring, such that the flow sectors have a main surface area downstream from the inner edge. 
     A further aspect of the invention is a turbomachine combustion chamber comprising such a shell ring. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will now be described with reference to the following figures: 
         FIG. 1  is a general view of a turbomachine combustion chamber and the shell ring thereof; and 
         FIGS. 2 and 3  disclose the invention more specifically. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A turbomachine combustion chamber where the invention may be present is represented schematically in  FIG. 1 . It should be noted that these combustion chambers are annular about the turbomachine axis, such that  FIG. 1  is merely a half-section along the axis. A fillet  1  comprises an outer shell ring  2 , an inner shell ring  3 , both substantially conical and mutually concentric, and an annular chamber back face  4  joining the shell rings  2  and  3 . The inner volume of the combustion chamber, forming a flame tube  16 , is defined by the shell rings  2  and  3  and the chamber back face  4  and opens on the side opposite the chamber back face  4  via an opening  5 . The combustion chamber is surrounded by an outer casing  6  and an inner casing  7  defining a flow stream  10  separated by the fillet  1  into two outer stream portions  8  and  9  bypassing and running along the fillet  1 . The air of the flow stream  10  comes from a nozzle  11  situated opposite an opening  12  provided between rear fillets  13  and  14  of the shell rings  2  and  3  (in this description, “rear” and “front” refer to the direction of the air flow). Fuel injectors  15  extend through the outer casing  6 , the opening  12  and the chamber back face  4  to the flame tube  16 . Plugs  17  also traverse the outer casing  6  to the front of the fuel injectors  15  and also traverse the outer shell ring  1  to level with the flame tube  16 . Most of the air flow thus follows the streams  8  and  9 , even though a portion enters below the fillets  13  and  14  via the opening  12 . 
     The shell rings  2  and  3  are traversed by numerous holes, including numerous fine ventilation holes  38  and less numerous larger diameter dilution holes  39 , distributed on a circle or a small number of circles. The common effect of these holes is that of allowing air from the streams  8  and  9  to enter the flame tube  16  at a lower pressure for a variety of purposes. 
     The invention may be used on either of the shell rings  2  and  3 . 
     Remarks will now be made in relation to  FIGS. 2 and 3 . Inserts  40  are arranged on the outer face of the shell ring  2  or  3  and around the dilution holes  39 . They each comprise a main portion  41  extending over the shell ring  2  or  3 , an outer edge  42  surrounding the main portion  41  and attached to the shell ring  2  or  3 , an orifice  43  extending in front of the respective dilution hole  39  but having a smaller radius, an inner edge  44  surrounding the orifice  43  and extending to most of the depth of the dilution hole  39 , and holes  45  through the main portion  41  and opening in front of a portion facing the shell ring  2  or  3 , which is devoid of ventilation holes  38  there. The insert  40  thus defines a chamber  49  almost closed in front of the shell ring  2  or  3  of the respective dilution hole  39 . It can be seen in  FIG. 3  that the insert  40  has a somewhat triangular general shape, extending more in the downstream direction of the flow while becoming increasingly narrow, so as to correspond as much as possible to the area of the shell ring  2  or  3  where cracks may appear. The dilution hole  39  is provided with attachment sectors  46  protruding towards the centre of said hole, touching and enclosing the inner edge  44 . This inner edge  44  and the attachment sectors  46  define air flow sectors traversing the holes  45  of the inserts  40 , including, herein, two symmetrical lateral sectors  47  in relation to an axial direction of the shell ring  2  or  3  and a downstream sector  48 . It should be noted that the centres O 1  and O 2  of the inner edge  44  and the dilution hole  39  are axially offset, such that the sectors  47  or  48  have an irregular shape and the downstream sector  48  is wider, promoting the flow from the chamber  49  via this downstream sector  48  and the reconstruction of a boundary ventilation layer downstream from the dilution hole  39 . 
     The specific flow provided by the insert  40  is as follows. Air from the flow of the flow of the stream  8  or  9  at a high pressure is blown into the chamber  49  via the holes of the inserts  45  and cools the shell ring  2  or  3  around the respective dilution hole  39 , and particularly the portion downstream therefrom, via the outer face thereof. This air then flows into the flame tube  16  via the flow sectors  47  and  48  and particularly through same. On reaching the flame tube  16 , the flow thereof may rapidly return to an axial direction downstream from the combustion chamber and reform a boundary layer in the above-mentioned area of the shell ring  2  or  3  downstream from the dilution hole  38  and helps protect same further. 
     The main portions  41  of the inserts  40  may be optionally parallel with the portion opposite the shell ring  2  or  3 , and the holes  45  optionally perpendicular to this portion. The main portions  41  may particularly be inclined in relation to the shell ring  2  or  3 , along the contour  41 ′ rising in a downstream direction, to better intercept the flow air by creating a larger obstacle.