EP1555390B1 - Cooling air exit openings for turbine blade - Google Patents

Description

Background of the invention

The present invention relates to the general field of turbine blades, and more particularly to the geometry of the cooling air discharge slots located on the trailing edge of moving blades or fixed turbomachine turbine.

A turbomachine turbine (for example, the high-pressure turbine) consists of a plurality of stages each formed of a distributor and a moving wheel. The turbine distributor has a plurality of fixed vanes for straightening the flow of gas therethrough and the impeller of the turbine is formed of a plurality of blades.

The moving and fixed blades of such a turbine are subjected to very high temperatures of the gases from the combustion chamber and which pass through the turbine. These temperatures reach values much higher than those that can withstand without damage the vanes that are in contact with these gases, which has the effect of limiting their service life.

In order to limit the damage caused by these hot gases on the blades, it is known to provide these vanes with internal cooling circuits to reduce the temperature of the latter. By means of such circuits, cooling air is introduced into the vane which traverses the vane along a path formed by cavities formed in the vane before being ejected by slots opening on the surface. of dawn, between the foot and the top of it.

However, in practice, it is found that for a turbine blade blade, the slot closest to the root of the blade is poorly cooled. Similarly, for a fixed turbine blade, the slots closest to the foot and the blade tip are also poorly cooled. Indeed, cracks tend to form on the trailing edge of the dawn, at these slots. Such cracks compromise the life of the dawn by decreasing their mechanical strength.

Figure 7 illustrates the location of such cracks for a turbine blade. This figure is a partial view in perspective of a moving blade 100 of high-pressure turbine. The blade 100 has an aerodynamic surface 102 which is connected at the level of the blade root 104 to a platform 106 via a connection zone 108. The aerodynamic surface 102 of the blade extends axially between a leading edge (not shown in the figure) and a trailing edge 110. In order to ensure the cooling of the blade 100, air passes through it along a path formed by cavities (no shown) practiced in the blade before being evacuated by evacuation slots 112 opening to the aerodynamic surface 102 of the blade, at its trailing edge 110.

Each discharge slot 112 is formed in particular of a side wall 114 provided with an opening (not shown) opening in the cavities traversed by the cooling air. Each slot also has a recessed wall 116 extending between the side wall 114 and the trailing edge 110 of the blade, an upper wall 118 and a bottom wall 120 which extend between the recessed wall 116 and the surface. aerodynamic 102 of dawn.

In practice, it is found that one or more cracks 122 (only one is shown in the figure) are formed at the discharge slot 112a which is the slot closest to the platform 106 (hereinafter called lower slot). More specifically, the cracks 122 are formed at the recessed wall 116 of the lower slot 112a and propagate axially from the trailing edge 110 of the blade to the side wall 114.

Such cracks result mainly from a high concentration of mechanical stresses at the lower slot 112a which are generated in particular by the lower wall 120 of this lower slot. There is a risk that such cracks propagate over the entire aerodynamic surface 102 of the blade, thus limiting its service life.

For a fixed blade of turbine, identical cracks appear both at the level of the evacuation slot nearest to the platform arranged on the side of the blade root, but also at the level the nearest evacuation slot to another platform connected to the dawn by its top (hereinafter called upper slot).

In order to limit the appearance of these cracks, US Pat. No. 6,062,817 provides, for a moving blade, to partially remove the bottom wall of the evacuation slot closest to the platform so that the recessed wall of this slot extends radially partially between the upper wall and the platform of the blade.

This solution is however insufficient. Indeed, the lower slot of the blade of this patent always has sharp edges at its lower wall. The sudden change in thickness that results leads to a bad flow of the cooling air evacuated by this slot. The evacuated air then no longer makes it possible to cool the connection zone between the platform and the foot of the blade and cracks particularly prejudicial to the service life of the dawn appear at this zone.

Document US2003 / 0108423 A1 presents another turbine blade according to the prior art.

Object and summary of the invention

The present invention therefore aims to overcome such drawbacks by proposing a turbine blade whose slot (s) closest to the platform (s) has a geometry that makes it possible both to avoid the formation of cracks and to ensure cooling of the connection area between the platform (s) and the blade.

For this purpose, there is provided a turbomachine turbine blade having an aerodynamic surface extending radially between a blade root and a blade tip and axially between a leading edge and a trailing edge, at least a lower platform connected to the root of the blade by a lower connection zone, and a cooling circuit consisting of at least one cavity extending radially between the top and the blade root, of at least one air inlet opening at a radial end of the or the cavities, a plurality of discharge slots arranged along the trailing edge of the blade including a lower discharge slot disposed in the vicinity of the foot of the d vane, the lower discharge slot having a side wall provided with an opening opening into the cavity or cavities, a recessed wall, a bottom wall disposed on the side of the blade root, a lower edge formed between the wall recessed and the wall in and a ledge lower section formed between the lower wall and the lower connection zone, characterized in that the lower edge and the lower edge of the lower discharge slot each have a substantially rounded cross section so as to eliminate any salient angle between the opening of the slot and the lower connection area.

In this way, the rounded shape of the cross section of the lower edge and the lower edge of the lower discharge slot avoids any formation of cracks at the wall recess of this slot. Moreover, thanks to this rounded shape, a cooling air film is created at the lower connection area between the platform and the blade root to cool this area. The temperature of the connection zone is thus lowered.

According to a particular provision of the invention, applicable to the case of a fixed distributor blade, the blade further comprises an upper platform connected to the top of the blade by an upper connection zone, the cooling circuit comprising in addition an upper discharge slot disposed in the vicinity of the blade tip and having a side wall provided with an opening opening in the cavity or cavities, a recessed wall, an upper wall disposed on the side of the apex of blade, an upper edge formed between the recessed wall and the upper wall, and an upper ridge formed between the upper wall and the upper connection zone; characterized in that the upper edge and the upper edge of the upper discharge slot each have a substantially rounded cross section so as to eliminate any projecting angle between the opening of said slot and the upper connection area.

Preferably, the rounded shapes of the straight section of the ridges and flanges each extend axially from the opening of the discharge slot to an outlet plane extending axially between said opening of the discharge slot and the trailing edge of dawn.

The rounded shapes of the straight section of the edges and edges advantageously each have a radius of curvature which is increasing from the opening of the discharge slot to the exit plane. In this case, these radii of curvature are preferably such that the recessed wall of the evacuation slot and the connection area are combined.

In the case of a moving blade, the recessed wall of the lower discharge slot may have an inclination towards the blade tip and the opening of the side wall of the lower discharge slot may be formed essentially in the lower connection area.

The invention also relates to a core for obtaining a blade as described above, comprising a main part intended to reserve a location for the cooling cavity of the blade, the main part being provided with a plurality terminal tabs which are intended to reserve as many locations for the ventilation slots of the cooling circuit of the blade, characterized in that the main part of the core further comprises, at a location reserved for the slot lower discharge, a lower tab of complementary shape to this lower slot.

The invention also relates to a turbomachine high-pressure turbine having a plurality of blades as defined above, and a turbine engine valve having a plurality of blades as defined above.

Brief description of the drawings

• la figure 1 est une vue en perspective d'une aube mobile de turbine selon l'invention ;
• la figure 2 est une vue partielle et en perspective de la fente d'évacuation inférieure de l'aube de la figure 1 ;
• les figures 3A, 3B et 3C sont des vues en coupe respectives selon IIIA, IIIB et IIIC de la figure 2 ;
• la figure 4 est une en perspective d'une aube fixe de turbine selon l'invention ;
• la figure 5 est une vue partielle et en perspective de la fente d'évacuation supérieure de l'aube de la figure 4 ;
• la figure 6 est une vue partielle et en perspective d'un noyau pour l'obtention de l'aube de la figure 1 ; et
• la figure 7, déjà décrite, est une vue partielle et en perspective d'une aube mobile de turbine selon l'art antérieur.

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures:

• Figure 1 is a perspective view of a turbine blade according to the invention;
• Figure 2 is a partial view in perspective of the lower discharge slot of the blade of Figure 1;
• Figures 3A, 3B and 3C are respective sectional views along IIIA, IIIB and IIIC of Figure 2;
• Figure 4 is a perspective view of a fixed turbine blade according to the invention;
• Figure 5 is a partial view in perspective of the upper discharge slot of the blade of Figure 4;
• Figure 6 is a partial perspective view of a core for obtaining the blade of Figure 1; and
• Figure 7, already described, is a partial view in perspective of a turbine blade according to the prior art.

Zero-valued description of an embodiment

FIG. 1 is a perspective view of a moving blade 10 of a high-pressure turbomachine turbine. The blade 10 is fixed on a turbine wheel (not shown) by means of a fitting 12 in the form of fir.

The blade 10 is in the form of an aerodynamic surface 14 which extends radially between a blade root 16 and a blade tip 18 and axially between a leading edge 20 and a trailing edge 22. The aerodynamic surface 14 of the blade thus defines the intrados 14a and the extrados 14b of the blade.

The fitting 12 of the blade 10 is connected to the blade root 16 at a lower platform 24 defining a wall for the flow of the flue gas through the turbine. The platform 24 is connected to the blade root 16 by a lower connection zone 26.

The blade which is subjected to the very high temperatures of the combustion gases passing through the turbine needs to be cooled. For this purpose, and in a manner known per se, the blade 10 comprises one or more internal cooling circuits.

Each cooling circuit consists of at least one cavity 28 extending radially between the root 16 and the blade tip 18. The cavity is supplied with cooling air at one of its radial ends by an air inlet opening (not shown). This air intake opening is generally provided at the fitting 12 of the blade 10.

In order to evacuate the cooling air flowing in the cavity 28 of the cooling circuits, a plurality of slots 30 are distributed along the trailing edge 22, between the foot 16 and the blade tip 18. These evacuation slots 30 open into the cavity 28 and open at the intrados 14a of the blade, at its trailing edge 22.

More particularly as illustrated in Figures 2 and 3A to 3C, the blade 10 has a lower discharge slot 30a which is disposed near the blade root 16. Compared to other slots 30, this lower slot 30a is the one which is closest to the lower platform 24.

The lower discharge slot 30a consists of a recessed (or recessed) wall 32, a lower wall (or step) 34, and a side wall 36 provided with an opening 38 opening into the cavity 28 of the cooling circuit.

By bottom wall, is meant the wall which is disposed on the side of the blade root 16. The recessed wall 32 extends radially from the bottom wall 34 to the blade tip 18 and axially between the side wall 36 and the trailing edge 22 of dawn. In addition, the bottom wall 34 extends between the recessed wall 32 and the lower connection zone 26.

Thus, for the lower discharge slot 30a, a lower edge 40 formed between the recessed wall 32 and the lower wall 34 can be defined. Likewise, a lower rim 42 is formed between the lower wall 34 and the bottom connection 26.

This particular geometry of the lower discharge slot 30a ensures a guiding of the air coming from the cavity of the cooling circuit via the opening 38 and thus makes it possible to cool the trailing edge 22 of the blade which is the part of the blade is the thinnest and therefore the most exposed to the high temperatures of the combustion gases.

According to the invention, the lower edge 40 and the lower edge 42 of the lower discharge slot 30a each have a substantially rounded cross section so as to eliminate any projecting angle between the opening 38 of the slot 30a and the In this way, any formation of cracks at the recessed wall 32 of the lower discharge slot 30a is avoided.

According to a particular characteristic of the invention, the rounded shapes of the straight section of the edge 40 and the lower flange 42 each extend axially from the opening 38 of the lower discharge slot 30a to a plane of P-outlet extending axially between the opening of the discharge slot and the trailing edge 22 of the blade.

The output plane P can be defined with respect to a coordinate system formed by X, Y and Z axes shown in FIG. relative to this coordinate system, the output plane P is parallel to the XY plane.

According to another particular characteristic of the invention, the rounded shapes of the cross-section of the edge 40 and the lower flange 42 each have a radius of curvature which increases from the opening 38 of the lower discharge slot 30a towards the exit plan P.

This characteristic is illustrated in particular in FIGS. 3A to 3C on which it is clearly seen that the radii of curvature of the edge 40 and of the rim 42 which are smaller increase as one moves away from the opening 38. 3A, which is the cut closest to the opening 38 of the lower slot 30a, these radii of curvature are smaller than those of FIG. 3C which represents a section in the exit plane P.

It is also possible to have a different variation of the radii of curvature of the edge 40 and the flange 42 lower. These radii of curvature can indeed be constant or decrease as one moves away from the opening 38.

On the other hand, as one moves away from the opening 38 of the lower slot 30a, the width (in the intrados / extrados direction) of the lower wall 34 decreases until it disappears completely at the level of the section shown. in Figure 3C (i.e., at the exit plane P).

According to yet another particular characteristic of the invention illustrated by this same FIG. 3C, at the level of the exit plane P, the radiuses of curvature of the rounded shapes of the lower edge 40 and edge 42 are such that the recessed wall 32 the lower slot 30a and the lower connection area 26 are combined.

Likewise, the radius of curvature of the rounded shapes of the lower edge 40 and edge 42 are also coincidental at the level of the outlet plane P. This is due to the fact that the width (in the intrados / extrados direction) of the lower wall 34 of the lower slot disappears at the exit plane P.

Thus, it is possible to partially retain the guiding function of the air that comes from the cavity 28 of the cooling circuit and discharged through this slot.

Any abrupt discontinuities in thickness at the lower slot 30a and the connection zone 26 are thus eliminated, which makes it possible to create a cooling film at the intrados 14a of the connection zone 26. The air cooling from the opening 38 of the lower slot 30a is therefore "lick" the connecting zone 26 to lower the temperature.

This particular geometry of the lower discharge slot applies both to a turbine blade as shown in FIG. 1, and to a stationary valve blade as shown in FIG.

FIG. 4 thus illustrates a fixed blade 50 of a high-pressure turbine distributor of a turbomachine. The references in this figure 4 which are identical to those of Figure 1 designate the same elements as those described in connection with Figure 1.

With respect to the fixed blade described in connection with FIG. 1, this fixed blade 50 is mounted between two platforms; namely, a lower platform 52 and an upper platform 54. The upper platform 54 is connected to the top 18 of the blade by an upper connection zone 56, while the lower platform 52 is connected to the blade root 16 by a lower connection zone 58.

As for the moving blade of FIG. 1, the cooling circuit of the fixed blade 50 comprises a plurality of discharge slots 30, a lower slot 30a which opens into the cooling cavity 28, which is arranged at the vicinity of the dawn foot 16 and which opens on the intrados 14a of the dawn. This lower discharge slot 30a has the same features as those of the moving blade of FIG.

Furthermore, the cooling circuit of the fixed vane 50 further comprises an upper discharge slot 30b which also opens into the cooling cavity 28 and which is arranged in the vicinity of the blade tip 18. This upper slot 30b opens at the intrados 14a of the dawn 50.

As illustrated in FIG. 5, this upper slot 30b consists of a side wall 60 provided with an opening 62 opening in the cooling cavity 28, a recessed wall 64, and an upper wall 66 disposed on the side of the blade tip 18. By wall upper 66, is meant the wall which is located on the side of the blade tip 18.

Thus, it is possible to define for this slot 30b an upper edge 70 formed between the recessed wall 64 and the upper wall 66, and an upper flange 72 formed between the upper wall 66 and the upper connection zone 56.

According to the invention, the upper edge 70 and the upper edge 72 of the upper discharge slot 30b each have a substantially rounded cross section so as to eliminate any projecting angle between the opening 62 of the slot 30b and the upper connection area 56.

By simple symmetry, the particular characteristics of the lower slot of the blade which have previously been described in connection with FIGS. 1, 2 and 3A to 3C also apply to the upper slot 30b of this fixed blade 50.

In general, the blades 10 and fixed 50 of the invention are obtained directly by molding.

For this purpose, the blade is produced by casting a metal in a mold containing a ceramic core whose particular function is to reserve a location for the cooling circuit of the blade (that is to say for the cavity 28 and each vent slot 30, 30a and 30b). Once the metal is poured into the mold, the blade is cooled and the ceramic core is removed.

FIG. 6 shows a ceramic core 80 making it possible to reserve a location for the cooling circuit of the moving blade 10 of FIG. 1. This FIG. 6 illustrates this core on the extrados side of the blade.

The core 80 has a main portion 82 for reserving a location for the cooling or cooling cavities of the blade. This main portion 82 is provided with a plurality of terminal tabs (or fingers) 84 which are intended to reserve as many locations for the discharge slots of the cooling circuit of the blade.

In order to obtain directly at the outlet of the foundry the rounded shapes of the cross-section of the lower edge and rim of the lower discharge slot of the blade, the ceramic core 80 presents, at level of the slot for this lower slot, a lower tab 84a of complementary shape to these rounded shapes.

More specifically, the lower tongue 84a has a first edge 86 of complementary shape to the recessed wall of the lower slot, a second edge 88 of complementary shape to the bottom wall of this slot, and a third edge 90 of shape complementary to its side wall.

The lower edge 92 formed between the first 86 and second edge 88 edges thus has a cross section of substantially rounded shape. Similarly, the lower flange 94 formed between the second edge 88 and an edge (not shown) of complementary shape to the lower connection area of the blade to the lower platform also has a cross section of substantially rounded shape.

In this way, it is possible to reproduce in series the same rounded shapes at the cross section of the edges and lower edges of the lower discharge slot of the blade.

Of course, when it is a fixed blade such as that described with reference to FIGS. 4 and 5, the ceramic core of such a blade also has, at the location reserved for the slot of upper discharge, an upper tongue to reproduce the rounded shapes of the cross section of the upper edge and rim.

According to another particular feature of the invention applied to a moving blade, the recessed wall 32 of the lower discharge slot 30a has an inclination towards the blade tip. This inclination (for example of the order of 10 ° to 30 °), which is particularly illustrated in Figure 1, also increases the cooling of the connection zone 26 between the platform 24 and the foot of dawn 16.

Similarly, again in order to improve the cooling of the connection zone 26, the opening 38 of the lower discharge slot 30a of such a moving blade 10 is preferably formed essentially in the connection zone 26 between the plate -form 24 and the dawn foot 16.

Claims (12)

1. A turbine blade (10; 50) of a turbomachine, including:

   - an airfoil (14) extending radially from a blade base (16) to a blade tip (18) and axially from a leading edge (20) to a trailing edge (22);

   - at least a bottom platform (24; 52) connected to the base (16) of the blade by a bottom connection zone (26; 58); and

   - a cooling circuit consisting of at least one cavity (28) extending radially from the blade tip (18) to the blade base (16), of at least one air inlet opening at a radial end of the cavity(ies), of a plurality of evacuation slots (30, 30a, 30b) arranged along the trailing edge (22) of the blade, said blade having a bottom evacuation slot (30a) that is disposed near the blade base (16), said bottom evacuation slot (30a) including:

   - an end wall (36) provided with an opening (38) that opens into the cavity(ies) (28);

   - a setback wall (32);

   - a bottom wall (34) disposed beside the blade base (16);

   - a bottom edge (40) formed between the setback wall (32) and the bottom wall (34); and

   - a bottom shoulder (42) formed between the bottom wall (34) and the bottom connection zone (26; 58); where

   the bottom edge (40) of the bottom evacuation slot (30a) has a right section of substantially rounded shape; said blade being characterised in that the bottom shoulder (42) also has a right section of substantially rounded shape, thereby avoiding any protruding angles between the opening (38) of said slot (30a) and the bottom connection zone (26; 58).
2. A blade (50) according to claim 1, further including a top platform (54) connected to the tip (18) of the blade by a top connection zone (56), the cooling circuit further including a top evacuation slot (30b) disposed near the blade tip and having:

   - an end wall (60) provided with an opening (62) that opens into the cavity(ies) (28);

   - a setback wall (64);

   - a top wall (66) disposed beside the blade tip;

   - a top edge (70) formed between the setback wall (64) and the top wall (66); and

   - a top shoulder (72) formed between the top wall (66) and the top connection zone (56);

   said blade being characterised in that the top edge (70) of the top evacuation slot (30b) and the top shoulder (72) of the top evacuation slot (30b) have respective right sections of substantially rounded shape, thereby avoiding any protruding angles between the opening (62) of said slot (30b) and the top connection zone (56).
3. A blade according to claim 1 and claim 2, characterised in that the rounded shapes of the right section of the edges (40, 70) and of the shoulders (42, 72) each extend axially from the opening (38, 62) of the evacuation slot (30a, 30b) to an outlet plane (P) extending axially between said opening (38, 62) of the evacuation slot (30a, 30b) and the trailing edge (22) of the blade.
4. A blade according to claim 3, characterised in that the rounded shapes of the right section of the bottom edges (40, 70) and of the bottom shoulders (42, 72) each have a radius of curvature which increases from the opening (38, 62) of the evacuation slot (30a, 30b) to the outlet plane (P).
5. A blade according to claim 4, characterised in that, at the outlet plane (P), the radii of curvature of the rounded shapes of the right section of the bottom edges (40, 70) and of the shoulders (42, 72) are such that the setback wall (32, 64) of the evacuation slot (30a, 30b) coincides with the connection zone (26, 58, 56).
6. A blade according to claim 1, characterised in that it consists of a moving blade (10) in a high-pressure turbine of a turbomachine.
7. A blade according to claim 6, characterised in that the setback wall (32) of the bottom evacuation slot (30a) slopes towards the blade tip (18).
8. A blade according to claim 6 and claim 7, characterised in that the opening (38) in the end wall (36) of the bottom evacuation slot (30a) is formed essentially in the bottom connection zone (26).
9. A blade according to claim 2, characterised in that it consists of a stator nozzle blade (50) of a high pressure turbine of a turbomachine
10. A core for obtaining a blade according to any one of claims 1 to 9, including a main portion (82) designed for reserving space for the cooling cavity of the blade, said main portion (82) being provided with a plurality of terminal flat tongues (84) that are designed to reserve a corresponding number of spaces for the evacuation slots of the cooling circuit of the blade, said core being characterised in that the main portion (82) of the core further includes a bottom flat tongue (84a) in the space reserved for the bottom evacuation slot, said flat tongue of shape complementary to said bottom slot.
11. A high-pressure turbine of a turbomachine, characterised in that it has a plurality of moving blades (10), according to any one of claims 6 to 8.
12. A turbomachine nozzle, characterised in that it has a plurality of stator blades, according to claim 9.

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