Patent Application
20150132139
The invention relates generally to the field of turbomachines, and more particularly that of turbine blades of these turbomachines and to their manufacture.
Turbine blades are subjected to strong thermal stresses due to the heat in gases in which they are plunged at the outlet of the combustion chamber, and need to be cooled to support these temperatures. They are accordingly hollow and traversed by internal cavities in which cooling gas circulates, taken at the outlet of a stage of one of the compressors.
More precisely, a turbine blade of a turbomachine comprises an aerodynamic surface (or blade) extending between a blade foot and a blade tip. The blade has a leading edge arranged opposite the flow of hot gases coming from the combustion chamber of the turbomachine, as well as a trailing edge opposite the leading edge and the lateral intrados and extrados walls which connect the leading edge to the trailing edge.
The internal cavities extend over the height of the blade, and comprise, from upstream to downstream in the direction of the flow of gases from the combustion chamber, a leading edge cavity and a trailing edge cavity, adjacent to the leading edge and the trailing edge of the blade respectively, and at least one central cavity, extending between the leading edge cavity and the trailing edge cavity. These cavities are fed with cooling gas via tubing connecting them to the foot of the blade.
The blade also comprises, at the level of its tip, a hollow form or bath, which is defined by the extension of the intrados and extrados walls, as well as by a bottom wall which close off the internal cavities.
To make these different cavities, which have complex forms and whereof the geometry must be respected with great precision, the blades are classically produced by a technique known under the name of lost wax smelting. This technique consists schematically of making a blade draft of wax in which cores made of ceramic which reproduce the resulting cavities are embedded. The wax blade is then embedded in a carapace, for example made of refractory material, then the cores are eliminated chemically, leaving in their place the preferred internal cavities and bath. Embodiments of this method are described in particular in documents FR 2 875 425, FR 2 874 186, or FR 2 957 828 in the name of the applicant.
The cores for these modern turbine blades are constituted by internal cavity cores, having classically the form of columns, which are positioned side by side and held together by conventional means.
These cores have increasingly more complex forms, as the specifications required for cooling of blades grow and the blades diversify. It is necessary to position them in the carapace with extreme precision.
A core generally comprises a first core element designed to form the cavities and a second core element designed to form the bath, the second core element being connected to the first core element by linking rods made of alumina or quartz.
The aim of these rods is to hold between them the parts of the core and stiffen the resulting assembly, and they are involved in making dedusting holes in the upper part of the blade. These rods are stored in the holes which they tend to make in the bottom of the bath. The dedusting holes enable circulation of the cooling gas in the cavities and evacuation of various particles entering the turbomachine.
To improve the aerodynamic performance of the blade and minimise energy losses, it has been proposed to use turbine blades for turbomachines having an advanced blade tip of the type “offset of tip sections” according to the French patent application registered on Nov, 17 2011 No. FR 11 60465 in the name of the applicant.
Such turbine blades are adapted to minimise energy losses. They comprise a blade which can be broken down into blade sections stacked according to a stacking direction along the blade. In the case of the blade tip with tip section offset, the stacking of the sections at the level of the tip of the blade is offset in the direction of the intrados wall, preferably progressively.
For this, as described in patent application No. FR 11 60465, the blade can comprise a cavity at the level of its tip, open in the direction of its free end and delimited by the bottom wall and a rim which extends between the leading edge and the trailing edge. The stacking of the blade sections of the blade at the level of this rim presents offset in the direction of the intrados, this offset increasing as the free end of the tip of the blade is approached. The blade also comprises cooling channels, inclined relative to the intrados, and connecting the internal cavities to the intrados wall.
The intrados wall of the blade can also present a projecting portion, whereof the outer face is inclined relative to the rest of the intrados of the blade and has at its end a terminal face, turned towards the rim. The bottom wall is connected to the intrados wall at the level of the terminal face of the projecting portion, and the cooling channels can be arranged in the projecting portion of the intrados wall such that they terminate on the terminal face of the projecting portion, the distance between the axis of the cooling channels and the outer limit of the free end of the rim of the intrados side being greater than zero.
However, this tip section offset and the small size of the blade, and therefore of the cores used for its manufacture, make it difficult to hold the rods of the second core element which is designed to former the bath on the first core element.
It has therefore been proposed to orient the rods individually, with big angles relative to the main direction of the blade. However, the cores are complex to produce due to the strong inclination of the linking rods relative to the main direction of the cores (and therefore of the injection of ceramic), which can raise problems of wear of the cores at the level of the bottom of the bath. Also, executing this manufacturing method needs knowhow and experience which are accessible to all those skilled in the art, specifically the founders, as here.
It has also been proposed to use linking rods anchored conventionally in the core elements, but with anchoring strongly reduced in comparison with conventional techniques, due to the minimal dimension of the internal cavities of the blade. But, the anchoring depth and the thickness of the cores (generally made of ceramic) about the linking rods cause problems of cracking (partial ruptures which occur under the action of forces resulting from uneven withdrawal) in the core elements, and therefore an excessive rate of discard.
The invention proposes as such an assembly forming a core for the manufacture of a turbomachine blade cooled by circulation of fluid in internal cavities, comprising a first core element of elongated form for the formation of different internal cavities and a second core element for the formation of a bath cavity, the second core element being designed to be arranged in the extension of the first core element. The first core element comprises an internal core of a leading edge cavity, at least one central cavity internal core and a trailing edge cavity internal core designed to form respectively, from upstream to downstream in the direction of flow of gases in the turbine, a leading edge cavity, at least one central cavity and a trailing edge cavity of the blade. The core of the central internal cavity adjacent to the internal core of the trailing edge cavity has, in the immediate vicinity of the second core element, a bulge which extends in the direction of the core of the leading edge cavity.
Such a solution enables anchoring of at least one linking rod at the level of an enlarged area of the first core element (at the level of the bulge), and consequently producing turbine blades for turbomachines having an offset of tip sections according to a reliable method with a minimal rate of discard of cores.
The invention also relates to a blade produced by means of such an assembly forming a foundry core, as well as a manufacturing method using such an assembly.
Other characteristics, aims and advantages of the present invention will emerge more clearly from the detailed following description, given in reference to the attached drawings given by way of non-limitation and in which:
a is a side elevation of an example of a blade with tip section offset in keeping with the prior art,
b is a view of the top of the blade of
a is a side elevation of an example of a blade with tip section offset in keeping with the invention, and
b is a view of the top of the blade of
In reference to
The blade can for example present an advanced blade apex of the type “tip section offset” in keeping with French patent application No. FR 11 60465 registered on Nov. 17, 2011 in the name of the applicant.
Especially, from the leading edge 13 to the trailing edge 14, the blade 1 comprises a leading edge cavity 19a, one or more central cavities 19b, 19c, 19d, (in this case three for the blade 1 shown in the figure, specifically a first rising central cavity 19b, a descending central cavity 19c, and a second rising central cavity 19d, which together form assembly an internal cavity “trombone”, and a trailing edge cavity 19e. The blade 1 also comprises, at the level of its tip 11, a bath 18, whereof the bottom wall 17 closes off the internal cooling cavities 19a-19e.
The intercavity wall 20 separating the central cavity 19d adjacent to trailing edge the cavity 19e and the following cavity in the direction of the leading edge 13 (that is, in the case of the blade of
As a variant, when the blade 1 comprises only a single central cavity 19d, it is the intercavity wall 20 which separates this single central cavity 19d from the leading edge cavity 19a which can match, in the vicinity of the bottom wall 17 of the bath, with an offset 16 in the direction of the leading edge 13.
Due to this offset 16 relative to the rest of the intercavity wall 20, the central cavity 19d which is adjacent to the trailing edge cavity 19e has a bulge 34 in the vicinity of the bottom wall 17, said cavity 19d being wider at the level of the blade tip 12 than at the level of the blade foot 11. The particular form of this central cavity 19d simplifies the manufacturing of the blade 7.
Also, as illustrated in
The assembly forming a foundry core 30 for the manufacture of such a turbomachine blade (
The second core element 32 is connected to the first core element 31 by linking rods 40 which can for example be made of aluminium or quartz.
The first core element 31 has an overall elongated form according to the height of the blade 1 and comprises a series of internal cores (or columns) 31a, 31b, 31c, 31d and 31e, designed to form respectively the cavities of a leading edge 19a, the central cavity/cavities 19b, 19c and 19d, and the trailing edge cavity 19e respectively.
The second core element 32 is arranged above the first core element 31, and is separated from the latter by linking rods 40 positioned so as to form dedusting holes 35 in the internal cores 31a to 31e.
The internal core 19d defining the central cavity 31d adjacent to the core 31e of the trailing edge cavity has, at least in an area immediately near the second core element 32, a bulge 34 in the direction of the internal core 31a of the leading edge cavity. The internal core 31c of the corresponding central cavity is therefore wider at this level, for example from 30% to 60% wider, as is evident in
Also, the central cavity internal core 31c immediately adjacent in the direction of the cavity 31a of a leading edge as such matches a complementary counterform 33 such that the intercavity wall 20 made between these two internal cores 31c and 31d has the offset 16 described hereinabove in the direction of the leading edge 13 of the blade 1.
As a variant, when the blade 1 comprises only a single central cavity 19d, the first core 31 comprises only a single central cavity internal core 31c, and it is the internal core 31a of the leading edge cavity which is immediately adjacent to this central core internal core 31d. It is therefore the internal core 31a of a leading edge which matches the complementary counterform such that the intercavity wall 20 made between these two internal cores 31a and 31d has the offset 16 described hereinabove in the direction of the leading edge 13 of the blade 1.
The bulge 34 and the counterform 33 are local, and extend only at the level of the upper part of the internal cores 31b-31d (respectively 31a, in the case of a blade comprising a single central cavity), the core 31d adjacent to the core 31e of the trailing edge cavity being wider at the level of this bulge 34 than at the level of its lower part.
The height of the bulge 34 is sufficient to allow anchoring of the linking rods 40 at the level of the bulge 34, and making dedusting holes 35 in the wall 17 forming the bottom of the bath 18 without formation of cracks in the internal cores 31b-31d. Also, the bulge 34 extends as far as the upper wall of the central cavity internal core 31e.
Making these dedusting holes 35 is made easier by modification of the geometry of the internal core 31d adjacent to the trailing edge core 31e and more particularly by the existence of the bulge 34 in its upper part. In particular, because of the aerodynamic form of the blade 10, which has an increasing transversal cross-section between the trailing edge 14 and the leading edge 13, the presence of the bulge 34 anchors the linking rods 40 in an area of the core 31 wider than with a configuration of a classic core, and consequently limits the angle formed between the linking rods 40 and the main axis of the cores. Making the holes 35 is therefore more favourable for foundry and also improves the possibilities for anchoring the linking rods 40.
Also, the diameter of the retaining rods 40 can be selected so as to be equal to the preferred diameter for the dedusting holes 35 in the final item to avoid an extra step for finishing the blade 10 (capping of holes) after the step of lost wax smelting.
As illustrated in
The linking rods 40 are accordingly oriented obliquely relative to the general direction according to which the second core element 32 they pass through extends to form the dedusting holes 35 of the second core element 32.
The second core element 32 can also comprise bosses 36 (
The assembly forming a foundry core 30 such as illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1251620 | Feb 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP13/52785 | 2/12/2013 | WO | 00 |
