EP1703084B1 - Device for varying the cross-section of a turbine stator - Google Patents

Description

Background of the invention

The present invention relates to the general field of turbine distributors. It is more particularly a device for varying the neck section of a turbine distributor.

To obtain a thrust gain in a turbomachine, it is known to use a variation of the gas flow section at the weakest section, called a collar, of a high pressure or low pressure turbine distributor. pressure. The variation of the neck section of a distributor is intended to adapt the flow rate of the gas passing through the distributor as a function of the different operating phases of the turbomachine. In particular, it is necessary to be able to open the neck section of the distributor during idling phases of the turbomachine and reduce the rest of the time to increase the margin pumping and reduce the specific consumption of the turbomachine.

In known devices, the variation of the neck section is obtained by means of articulated systems. Thus, systems are known having flaps provided on the walls of the gas flow passage between the vanes (or blades) of the distributor at its neck. These flaps, which are articulated with pivots, rods and a control ring, can thus make a jump in the flow of gas flow to reduce the section. See for example the document EP 0 191 687 . Articulated-blade systems are also known in which all or part of the blades can pivot in the gas flow path in order to reduce the section thereof. Such systems also require pivots and other articulation parts.

The document FR 2708311 describes a device also representing the state of the art.

These various known devices have the disadvantage of being based on the articulation of small parts. Due to the hot environment of the dispenser area, there is a risk of galling, burning and accelerated erosion of the joints. In addition, these devices require assembly and maintenance difficult and expensive.

Object and summary of the invention

The main object of the present invention is therefore to overcome such disadvantages by proposing a device for varying the neck section of a dispenser requiring few parts, of easy and reliable assembly in the hot environment of the dispenser.

For this purpose, there is provided a device for varying the neck section of a turbine distributor, the dispenser being formed by a plurality of fixed blades which extend radially between outer and inner annular platforms spaced apart. from one another to define a flow of combustion gas flow through the turbine, the vanes being spaced from each other to define a neck having a minimum flow section, the device being characterized in that it comprises an annular element of coefficient of expansion less than that of the platforms of the distributor, said annular element being fixed on the external platform and being able to take two positions: a position corresponding to a lack of expansion of the platforms; forms in which it ensures the continuity of the profile of the flow vein, and another position corresponding to a presence of expansion of the platforms in which it is made. protruding into the flow vein so as to reduce the section thereof.

The presence of an annular element having a coefficient of expansion lower than that of the platforms of the distributor aims to take advantage of the temperature difference of the platforms of the distributor between the idling phases of the turbomachine and the other phases of operation of it for which the platforms dilate. In this way, the proposed device has very few parts and does not rely on any articulation hence the advantages in assembly, maintenance and reliability.

According to a particular embodiment of the invention, the annular element is held axially in an annular groove of the external platform of the distributor in the absence of expansion of the platforms of the distributor and is able to move radially relative to this one in the presence of a dilatation of the platforms.

According to another particular provision of the invention, the annular element comprises at least one radial lug which is housed in a notch of the external platform so as to prevent the element annular to offset itself from the external platform. In this case, the device advantageously comprises at least one member for axially holding the lug of the annular element on the external platform.

According to yet another particular embodiment of the invention, the annular element has, at an upstream portion, a cross section which decreases downstream upstream. When the platforms of the dispenser expand, this feature prevents the ring from forming too abrupt a step in the flow channel which would have the effect of reducing the performance of the dispenser.

The annular element can be made from a composite material. Alternatively, it can be obtained from a ceramic material.

The present invention also relates to a turbine distributor comprising a device for varying its neck section as defined above.

Brief description of the drawings

• la figure 1 est une vue partielle en coupe longitudinale d'une turbomachine illustrant l'emplacement du dispositif selon l'invention ;
• la figure 2 est une vue partielle, en perspective et en éclaté d'un distributeur muni d'un dispositif selon l'invention ;
• la figure 3 est une vue à plat du distributeur de la figure 2 ; et
• les figures 4A et 4B illustrent le dispositif selon l'invention dans ses deux positions de fonctionnement.

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:

• the figure 1 is a partial view in longitudinal section of a turbomachine illustrating the location of the device according to the invention;
• the figure 2 is a partial perspective and exploded view of a dispenser provided with a device according to the invention;
• the figure 3 is a flat view of the distributor of the figure 2 ; and
• the Figures 4A and 4B illustrate the device according to the invention in its two operating positions.

Detailed description of an embodiment

In connection with the figure 1 , the high-pressure distributor 10 is mounted at the outlet of the combustion chamber 12 of the turbomachine and upstream of the high-pressure turbine 14 thereof.

Of course, the present invention can also be applied to a low-pressure distributor of such a turbomachine.

The high-pressure dispenser 10 is formed by a plurality of fixed blades (or blades) 16 which extend radially between outer and inner annular platforms 18 and 20.

The platforms 18, 20 are spaced radially from one another and are arranged concentrically about an axis of the turbomachine (not shown). By external platform is meant the platform that is furthest from the axis of the turbomachine.

The platforms are typically metallic. They may be in the form of a single ring or a plurality of ring segments placed end to end and they define between them an annular vein 22 for the flow of gases from the combustion chamber 12.

The blades 16 of the distributor are fixed on the platforms 18, 20 between which they extend radially. They also extend axially from upstream to downstream between their leading edge 16a and their trailing edge 16b.

The blades 16 are further spaced from each other in the circumferential direction to define a neck having a minimum flow section. The neck of the dispenser is the portion of the vein 22 having the lowest flow section. As illustrated on the figure 3 this section is defined by the shortest distance d connecting the trailing edge 16b of a blade 16 to the extrados of the adjacent blade.

According to the invention, the dispenser thus defined is provided with a device for varying its neck section including in particular an annular element 24 which has a coefficient of expansion smaller than that of the platforms 18, 20 of the dispenser.

By way of example, the annular element 24 is made from a composite or ceramic material. These materials have the particular property of having a coefficient of expansion virtually zero, therefore necessarily less than that of the metal component platforms 18, 20 of the distributor.

Of course, any other material having a coefficient of expansion lower than that of the platforms of the dispenser may be used to produce the annular element of the variation device of the neck section according to the invention.

The annular element 24 is a single ring which is fixed on the external platform 18 of the dispenser. It is arranged so as to be able to take two positions: a position corresponding to an absence of expansion of the platforms in which it ensures continuity of profile of the flow stream 22, and another position corresponding to a presence of expansion of the platforms 18, 20 in which it projects into the flow channel so as to reduce the section thereof.

More precisely, the annular element 24 is housed in an annular groove 26 provided in the external platform 18 of the distributor, at its downstream portion. The annular groove 26 of the outer platform 18 has a depth (radial height) substantially identical to the thickness of the annular element 24 so that, in the absence of expansion of the platforms 18, 20, this it ensures the continuity of profile of the flow line 22.

As shown on the figure 3 , the annular element 24 extends tangentially over the entire circumference of the outer platform 18 of the distributor, and axially over substantially the entire length of the neck of the dispenser. For this purpose, it has cutouts that conform to the contour of the blades 16, while at the same time providing a small space with them (not shown in FIG. figure 3 ) to account for any expansion of the blades.

On the figure 2 it is noted that the annular element 24 is further provided with one or more pins 28 which extend radially outwardly. This or these lugs 28 (preferably three lugs equidistant over the entire circumference of the annular element) are intended to be housed in as many notches 30 formed at the downstream end of the outer platform 18 of the dispenser.

Each pin 28 of the annular element is associated with an axial retaining member 32 thereof on the outer platform 18 of the distributor. This holding member 32 may be formed by a wafer 34 provided with fixing pins 36 (for example two in number per wafer) fitting into holes 38 formed on the external platform 18. The wafer 34 thus maintained by the pins 36 ensures an axial locking of the annular element 24 on the external platform 18.

The mounting of the annular element 24 on the outer platform 18 of the dispenser thus clearly follows from the foregoing. Once all the segments of the distributor platforms assembled, the annular element 24 is placed in the groove 26 of the outer platform 18 with its lugs 28 housed in the notches 30 provided for this purpose. The annular element 24 is then locked axially by means of the plates 34 held by their pins 36. The lugs 28 also have the function of preventing the annular element from being off-center with respect to the axis of the turbomachine.

With such an arrangement, it is found that the annular element 24 is held axially but a relative displacement between the annular element and the outer platform 18 is possible in the radial direction. This relative radial displacement between these parts takes place in the presence of a dilation of the platforms 18, 20 of the distributor according to a procedure described in connection with the Figures 4A and 4B .

The Figure 4A represents the distributor in the absence of expansion of its platforms 18, 20. This state corresponds for example to an idling operation of the turbomachine.

The Figure 4B represents the same distributor in the presence of a dilation of its platforms. This state corresponds to the operating states of the turbomachine other than idling (for example full throttle).

In the position corresponding to the idling operation of the turbomachine ( Figure 4A ), the temperature of the flue gas flowing in the flow line 22 (of the order of about 750 ° K) is not high enough to expand the external platform 18 and internal 20 of the distributor. The annular element 24 then remains hidden in the groove 26 of the outer platform 18. It partially reconstitutes the flow stream 22 and therefore does not interfere with the flow of gas flowing in this vein. The height of the vein 22 at the section of the neck of the dispenser is symbolized by the coast H0.

In the position corresponding to the other operating states of the turbomachine ( Figure 4B ), the external platforms 18 and internal 20 of the dispenser which are made of metal tend to expand under the effect of the significant heat generated by the combustion gases flowing in the flow path 22 (temperature of the about 1400 ° K). The dilation of the platforms, which is a phenomenon known in the field of turbomachine distributors, is represented by the arrows of the Figure 4B .

On the other hand, since the annular element 24 has a coefficient of expansion less than that of the platforms, it expands little or not at all (and in any case less than the platforms). As there is a possibility of relative radial displacement between the outer platform 18 and the annular element 24, the latter then becomes salient in the flow path 22 thus causing a reduction in the cross section of the distributor neck. In this state, the height of the vein 22 at the distributor neck which is symbolized by the H1 coast is less than H0.

According to an advantageous characteristic of the invention, the annular element 24 has, at an upstream portion, a cross section which decreases downstream upstream. This characteristic, which is particularly visible on Figures 4A and 4B , is intended to prevent the annular element to form a too abrupt step in the flow vein during the expansion of the platforms of the distributor which would have the effect of reducing the performance of the dispenser.

The present invention thus takes advantage of the known phenomenon of the expansion of a distributor between the different operating phases of the turbomachine to achieve the variation of the neck section of the distributor. The reduction of the neck section during the operating phases of the turbomachine other than idling can for example be of the order of 4%, this value depending on the type of turbine on which is mounted the device for varying the section of the turbine. collar.

The present invention has many advantages. It has a very simple and reliable mode of operation since it relies only on the phenomenon of the expansion of the dispenser. In addition, the device for varying the neck section has only very few parts and does not rely on any articulation, which facilitates its assembly and maintenance and reduces its cost.

Other variants may be added to the embodiment described above. In particular, it may be envisaged to control the variation of the neck section according to the different operating phases of the turbomachine other than idling. For this purpose he may for example be provided to control a flow of air from cooling the external platform of the dispenser to reduce expansion and thus limit the relative movement between this platform and the annular element of the device.

Claims (9)

1. A device for varying the section of the throat of a turbine nozzle, the nozzle (10) being made up of a plurality of stationary vanes (16) extending radially between outer (18) and inner (20) annular platforms spaced apart from each other so as to define a flow passage (22) for combustion gas passing through the turbine, the vanes (16) being spaced apart from one another in order to define a throat presenting a minimum flow section, the device being characterised in that it comprises an annular element (24) having a coefficient of expansion that is less than that of the platforms (18, 20) of the nozzle, said annular element (24) being secured to the outer platform (18) and being suitable for occupying two positions: one position corresponding to no expansion of the platforms (18, 20) in which the element provides continuity for the profile of the flow passage (22), and another position corresponding to the platforms (18, 20) being expanded, in which position the element projects into the flow passage (22) in such a manner as to reduce its section.
2. A device according to claim 1, characterised in that the annular element (24) is held axially in an annular groove (26) of the outer platform (18) of the nozzle in the absence of the nozzle platforms (18, 20) expanding, and is suitable for moving radially relative to the nozzle in the event of the platforms expanding.
3. A device according to claim 1 or claim 2, characterised in that the annular element (24) includes at least one radial tab (28) that is received in a notch (30) in the outer platform (18) so as to prevent the annular element (24) from becoming eccentric relative to said outer platform.
4. A device according to claim 3, characterised in that it further includes at least one member (32) for axially retaining the tab (28) of the annular element (24) relative to the outer platform (18).
5. A device according to any one of claims 1 to 4, characterised in that the annular element (24) presents an upstream portion of right section that tapers from downstream to upstream.
6. A device according to any one of claims 1 to 5, characterised in that the annular element (24) extends axially over the entire length of the nozzle throat.
7. A device according to any one of claims 1 to 6, characterised in that the annular element (24) is made of a composite material.
8. A device according to any one of claims 1 to 6, characterised in that the annular element (24) is made of a ceramic material.
9. A turbine nozzle, characterised in that it includes a device according to any one of claims 1 to 8 for varying the section of its throat.

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