TURBOMACHINE COMBUSTION CHAMBER SHELL RING
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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
5 with the combustion gases downstream from the shell ring before entering the turbines.
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
10 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,
15 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
20 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.
In a general form, it relates to a turbomachine combustion chamber shell ring,
25 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
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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
5 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
10 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
15 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.
20 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 shdpe, 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,
25 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
30 said respective dilution hole by the inner edge and between the attachment sectors. In
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order to help continue the flow on the downstream side of the dilution hole, more
advantageously, the dilation 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.
The invention will now be described with reference to the following figures:
- figure 1 is a general view of a turbomachine combustion chamber and the shell
ring thereof; and
- figures 2 and 3 disclose the invention more specifically.
A turbomachine combustion chamber where the invention may be present is
represented schematically in Figure 1. It should be noted that these combustion
chambers are annular about the turbomachine axis, such that figure 1 is merely a halfsection
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 casing6 and an inner casing7 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 casing6 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
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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.
1 5 Remarks will now be made in relation to figures 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 orifice43
extending in front of the respective dilution hole 39 but having a smaller radius, an inner
10 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 figure 3 that the insert 40 has a somewhat triangular
15 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
edge44. This inner edge44 and the attachment sectors46 define air flow sectors
20 traversing the holes45 of the inserts40, including, herein, two symmetrical lateral
sectors 47 in relation to an axial direction of the shell ring2 or 3 and