EP0115984A1 - Sealing means for rotor blades of a gas-turbine - Google Patents

Abstract

A seal (86) is mounted on sectors (84) connected by their fallen edge (92) to first hooks (80, 82) carried by an inner ring (44) comprising in its middle part of the elastic tongues ( 72, 74) and to second hooks (32) fixed to an outer ferrule (20) with large inertia, each of the interior (44) and exterior (20) ferrules being ventilated by air taken from a compressor stage, the inner ferrule (44) expanding (or contracting) during the period of mechanical acceleration (or deceleration) and the outer ferrule (20) expanding (or contracting) during the next transitional period of thermal stabilization in order to preserve a minimum operating clearance between the seal (86) and the blade ends.

Description

The invention relates to a sealing device for movable blades of a turbomachine making it possible to limit the clearances at the blade tips to their strict minimum.

We know the importance for the yield on the one hand, but also for obtaining a maximum thrust and for the pumping reserve to reduce leaks due to the games between rotating parts and fixed parts of a turbomachine in particular at the level of the turbine (s).

To reduce these clearances, and correspondingly the leaks, both in stabilized and transient conditions, it is necessary to respect a certain number of conditions, some of which are incompatible with the others or in any case very difficult to achieve well together: concentricity with the axis of rotation of the turbomachine of the blade tips or their peripheral heels and also of the sealing device, non-deformability of the latter (in the light that it must always remain of revolution), increase (respectively decrease) of the radius of the sealing device by following the increase (respectively the decrease) in the radius of the blade tips or their peripheral heels under the effect of both centrifugal and thermal expansions, both in stabilized and transient conditions .

• - soit un jeu supérieur ou égal à "a" dans toute condition de fonctionnement prévue,
• - soit une garniture d'étanchéité d'épaisseur minimale égale à "a", qui sera d'ailleurs en tout cas localement enlevée par abrasion à la première occurence d'ovalisation (ou d'excentrage) maximale "a", formant ainsi au moins une lunule de fuite par un jeu qui localement est égal à "a" et qui, selon toute probabilité, compte-tenu du fait que l'ovalisation (ou l'excentrage) peut se produire suivant des axes différents, sera rapidement égal ou très voisin de "a" sur toute la périphérie de la virole ou de l'ensemble des secteurs d'étanchéité.

If it is relatively easy to ensure that the end of the rotating parts (end of the blades, or peripheral heels) describes well during the rotations a surface of revolution for example by cutting the blades or the heels to length by grinding on disc fineness rotating, it is much more difficult to provide the ferrule surrounding the rotating parts with a form of revolution under the different operating conditions, in particular with regard to the inertial forces which can occur for aeronautical turbomachines (load factors in the z direction or in particular) and especially with regard to deformations of thermal origin. It is necessary, but not sufficient, that the sealing ring (or the elements which carry the seal or which define the position of the sealing sectors) remain perfectly centered on the axis of rotation of the turbomachine, d on the one hand, and does not ovalize, on the other. This requires to provide for this shell, either a monolithic construction of sufficient inertia, or a more complicated system ensuring the concentricity of the sector supports around the axis of the machine on the one hand, and the almost complete absence of ovalization on the other hand. If this condition is not fulfilled and if there is therefore ovalization or eccentricity and if one designates by "a" the maximum distance inwards between the circle of the same developed length and the interior part of the ovalized shell ( or off-center) or segment supports as close to the blade tips as possible as possible (or off-center) under one of the above-mentioned effects, it will be necessary to provide:

• - either a clearance greater than or equal to "a" in any operating condition provided,
• - or a gasket of minimum thickness equal to "a", which will in any case be locally removed by abrasion at the first occurrence of maximum ovalization (or eccentricity) "a", thus forming minus a lunula trailing by a game which locally is equal to "a" and which, in all probability, taking into account the fact that ovalization (or eccentricity) can occur along different axes, will quickly be equal to or very close to "a" over the entire periphery of the shell or of all the sealing sectors.

If it is known in practice practically to obtain, for example by the means described by the Applicant in its patent application 81.20719 filed on November 5, 1981, that the casing supporting the ferrule directly or indirectly carrying the seal is well centered relative to the axis of the turbomachine, and if it is also known to center this ferrule well in the casing, and to give it sufficient inertia so that its deformation by ovalization is practically negligible, it is not possible to ensure all operating modes, and in particular in transitory, a radial dimension of the sealing ferrule or of the sectors reconstituting a ferrule which maintains a positive but very small clearance between the ends of the blades (or their peripheral heels) and sealing ferrule (or sectors) under all operating conditions, including transient conditions.

In what follows, for the sake of simplification, we will describe the case where the movable blades do not have peripheral heels, but it should be understood that the term "blade tip" must be understood "radial end of the peripheral heels blades ", when the blades have such peripheral heels.

If the ferrule carrying the seal is monolithic, the most obvious solution to obtain both in transient and permanent regime that this ferrule provides, to the interior of its trim Ture sealing, a radius which "follows" without delay the variations in radius of the blade tips is, as is well known in the prior art, to supply the periphery by a distributor, in a homogeneous manner of the shell by air taken from one or more compressor stages, said distributor having the function of sending an "adjusted" air flow at any time. This adjustment must in any case be made for the temperature of the air taken off (for example by mixing in suitable proportions of more or less hot air, coming either from different stages of the compressor, or, for at least part of ventilation air, air cooled - or heated - in an exchanger). This makes it possible to precisely adjust the radius of the seal to the radius of the blade tips in steady state. But so that the expansion of the ring "follows" without delay the centrifugal expansion of the disc and the blades, and the thermal expansion of the blade (expansions which are done in a few seconds), then the thermal expansion of the disc (which done in several minutes), this quantity must also be adjusted in quantity. Several patents such as application FR 2 467 292 describe such active control of the games. But in fact the problem is not solved so far, it is only carried over to an air distribution mechanism, adjusted in flow and / or temperature to ensure, not only in steady state, but also in transient state , the suitable instantaneous temperature of the structure of the shell which, by the effect of its coefficient of expansion, will impose on the seal the radius ensuring a positive but very small clearance with respect to the blade tips.

Such a dispenser can obviously be designed, but would be of an extreme complication and of a fairly random reliability (a breakdown of the dispenser being able in certain in case of significant damage to the entire turbine and / or the shell). It should also be noted that the fact that in particular the centrifugal expansion (respectively retraction) of the disc and of the blade occurs in a very short time, of the order of a few seconds, since it is practically equal to the time acceleration (respectively reduction) of the load of the turbomachine, it is necessary that the flow of ventilation air sent to the ferrule is very important to ensure the ferrule carrying the seal a temperature, therefore by the play of its coefficient of expansion PC, a radius which follows without delay the almost instantaneous centrifugal expansion (contraction) of the disc and the blades. Such a distributor must therefore be capable of a high flow rate. It would therefore be heavy, complex, and ultimately very unreliable. In addition, it would be a large consumer of ventilation air to the detriment of the overall efficiency of the turbomachine.

A variant of the invention however provides for the use of a pressure reducer-regulator placed in the air sampling pipe intended for the ventilation of the sealing device, as will be described later. But it will be noted that this regulator is only intended to ensure a pressure, as the operation will be explained later while the mechanisms mentioned above must be adjusted in flow and / or temperature.

Attempts are also known to solve this very delicate problem of making the inner part of a ferrule follow without delay the expansion (respectively the retraction) of the blade tips, that is to say in fact allowing that by example under acceleration, the ferrule carrying the sealing strip responds quickly to centrifugal expansion of the disc and blades, then much more slowly to thermal expansion of the disc, in particular in French patent applications 2,450,344 and 2,450,345. However, the arrangement provided for in these patents, on the one hand, is applicable to turbomachines of low power including return combustion chambers. Those skilled in the art could undoubtedly deduce from the teachings of these patents an equivalent for the chambers, usually with direct flow, of high power turbomachines, but at the expense of a significant and unrealistic complication.

On the other hand, the solution described in one and the other patent uses a so-called elastic "sleeve", that is to say capable of deformation when it is subjected to forces. The elasticity of this sleeve presents the risk and the disadvantage of introducing concentricity and ovalization defects, in particular under the effect of the load factors encountered in flight. It should be remembered as indicated above that compliance with an almost perfect concentricity around the axis of rotation of the mobile and the absence of ovalization of the seal is an imperative necessity to avoid untimely play and these latest patents are far from satisfying these conditions in a satisfactory manner. It is also observed that due to the considerable hyperstatic forces brought into play by bracing in a segmented ring according to patent FR 2 450 345, the slightest heterogeneity of temperature or inertia in the peripheral direction will cause significant deformations of the segmented ring.

It is one of the objectives of the present invention to ensure, for all stabilized speeds and for the transient regime under acceleration, a clearance between the tips of the blades and the seal, which is minimal, but positive in order to avoid the wear of said lining, wear which would cause backlash and therefore leakage in any stabilized or accelerating regimes. For transient conditions during deceleration, the clearance between the blade tips and the seal is positive (so there is no wear), but it is no longer minimal. However, it is at most equal to that obtained by the solutions of the prior art. The specialist also knows that the influence of a significant but not excessive play, for the sole case of transient deceleration, is almost negligible in the general economy of a turbomachine.

It is a second objective of the present invention to achieve this remarkable result without serious disadvan _- tages of complexity and lack of reliability of the machines of the prior art.

It is a third objective of the present invention to obtain this result with a significantly reduced flow compared to the ventilation flows of the prior art.

The sealing device for mobile turbomachine blades of the aforementioned type is characterized according to the present invention by the fact that the sectors carrying said seal are subjected, on the one hand, during a transient phase of mechanical acceleration of the turbomachine to a first servo in the radial position by elements for connection to elastic elements integral with an inner shell which expands in a homogeneous manner during said mechanical acceleration phase by the effect of ventilation over its entire length and its periphery by air taken from a downstream compressor stage, and that said sectors are subjected, on the other hand, during a thermal stabilization phase of the turbomachine succeeding the acceleration phase first, servo-control in radial position by hooks resting on the elastic elements, to an external ring which expands in a homogeneous manner during said thermal stabilization phase also by the effect of ventilation over its entire length and its periphery by air taken from a downstream compressor stage, brought by a multiplicity of pipes opening into holes drilled in the turbine casing.

The ventilation conditions of said inner shroud, its coefficient of thermal expansion o < ₁ and the air intake stage are determined so that during a mechanical acceleration phase of the turbomachine from n ' any speed up to a higher speed, and in particular up to the maximum load of the turbomachine, the thermal expansions of said ferrule "follow" without delay the centrifugal expansion of the disc and of the blades increased, at least in large part, by the thermal expansion of the blades. Similarly, the coefficient of expansion α ₂ , the thermal inertia and the ventilation conditions of the outer ring are determined so that during the phase - which can last several minutes - of thermal stabilization of all the elements of the turbomachine, and in particular of the corresponding disc, the thermal expansions of said ring impose on the sectors carrying the seal which are slaved to it during said phase a radial expansion which "follows" the thermal expansion of said disc.

Advantageously, the connecting elements between sectors and elastic elements are constituted upstream and downstream by fallen edges of the sectors inserted in the hooks of the elastic elements.

Preferably, said inner ferrule is in two parts respectively upstream and downstream which are made integral by bolts and nuts fixing edges fallen towards the outside of tongues belonging to one and the other of these two parts, said tongues of joining together being regularly distributed over the periphery and being spaced from one another. Between said spacings of the securing tabs there are elastic tabs for controlling the sectors carrying the seal forming a body integrated alternately with the monolithic part of the upstream part and of the downstream part of said inner ring, said elastic tabs slaving the sectors carrying the gasket to the expansions of said first ferrule without these tabs deforming themselves during the period when the first control is effective, and allowing the control of the sectors carrying the gasket to expansion of said second ferrule, by deformation of these tongues in the elastic domain during the period when the second servo replaces the first.

Preferably, the first ferrule includes heat exchange accelerators (multiple holes through which the ventilation air, fins, pins, etc.) so that its temperature "follows" practically without delay the temperature of the air of the compressor, the density of these exchange accelerators being determined so that the expansion of the first ferrule as a function of the time for acceleration is adjusted to the centrifugal expansion of the disc and of the blades, increased by the thermal expansion of the blades, and their distribution being determined to ensure temperature uniformity at said first shell both longitudinally and peripherally. Preferably the turbine casing comprises means for centering the sealing device according to the invention.

It may also be advantageous to place at least one pressure reducing valve between the air intake pipe to the compressor and a pipe opening into a hole in the turbine casing, comprising an inlet connected by a pipe to a pressure tap located in the downstream part of the external platform of a distributor placed upstream of the movable blading so that a pressure always very slightly greater than the static pressure at the wall of the gas circulation stream of the turbomachine is established from radially outer side of the sectors carrying the seals.

This latter arrangement advantageously makes it possible to eliminate the seals provided upstream and downstream of the sectors carrying the seals and thus to eliminate friction which could in certain cases interfere with optimal operation.

• - la figure 1 représente une coupe longitudinale simplifiée selon I-I de la figure 2 de ce mode de réalisation du dispositif d'étanchéité, conforme à l'invention
• - la figure 2 est une vue développée simplifiée, selon II-II de la figure l ;
• - la figure 3 est une vue analogue à la figure 1 montrant quelques détails de la ventilation qui ne figuraient pas sur les figures 1 et 2 par souci de simplification ;
• - la figure 4 est une vue analogue à la figure 1, en coupe longitudinale simplifiée selon IV-IV de la figure 5 et représentant un dispositif d'étanchéité selon l'invention, qui comporte au moins un réducteur-régulateur de pression ;
• - la figure 5 est une vue développée simplifiée, selon V-V de la figure 4 ;
• - la figure 6 est une vue analogue à la figure 4 montrant quelques détails de la ventilation de manière analogue à la figure 3 ;
• - la figure 7 est une coupe simplifiée d'un réducteur-régulateur de pression conforme à l'invention.

The invention will be better understood from the description of one of the embodiments, with reference to the appended drawings, in which:

• - Figure 1 shows a simplified longitudinal section along II of Figure 2 of this embodiment of the sealing device, according to the invention
• - Figure 2 is a simplified developed view, along II-II of Figure l;
• - Figure 3 is a view similar to Figure 1 showing some details of the ventilation which were not shown in Figures 1 and 2 for simplicity;
• - Figure 4 is a view similar to Figure 1, in simplified longitudinal section along IV-IV of Figure 5 and showing a sealing device according to the invention, which comprises at least one pressure reducer-regulator;
• - Figure 5 is a simplified developed view, along VV of Figure 4;
• - Figure 6 is a view similar to Figure 4 showing some details of the ventilation similar to Figure 3;
• - Figure 7 is a simplified section of a pressure reducer-regulator according to the invention.

In Figure 1, in which we have not shown everything related to ventilation, we can see a turbine housing which in the example shown is in three parts, an upstream part 2, a middle part 4 , a downstream part 6, the three parts being joined by bolts not shown joining together radial flanges 8a, 8b and 8c, 8d, said radial flanges having the role of giving mechanical inertia to the assembly so that it is practically undeformable by ovalization. The upstream part 2 of the casing has a conical extension 10 inwards, in which radial grooves are machined 12. Likewise, the downstream part 6 of the casing has a conical extension 14 inwards, in which grooves are machined radial 16, similar to the grooves 12, but making them opposite.

An outer ring with high inertia 20, comprising for example ribs towards the outside 22, and which can be provided with internal insulation 24, and / or external 26, to give it a suitable response time, also comprises ribs respectively upstream 28 and downstream 30, in which are machined radial grooves 12 'and 16' which cooperate with the radial grooves 12 and 16 to center the ring 20 in the casing. This ring further comprises in its upstream part of the known fixing means for a multiplicity of hooks 32 turned downstream, and in its downstream part of the equivalent fixing means of hooks 34 turned upstream (only the latter elements of attachment being shown). These hooks are used to radially move sectors 84 carrying seals 86 by pressing radially, in the centrifugal direction, directly or by means of shims on longitudinal elements carried by the sectors, as will be described in detail later.

The upstream part 2 of the turbine casing comprises, further upstream, a radial flange 40, towards the inside, on which is fixed in a known manner a radial flange 42 towards the outside of an internal ferrule 44 (see FIG. 2). This is in two parts for mounting reasons. The upstream part comprises, downstream of the radial flange 42, a cylindrical part 46, and in the example shown another radial flange 48, again towards the inside, then an internal ferrule 50 intended mainly to give it inertia. The inner shroud 50 ends with a radial sealing flange 52. The whole of the upstream part of the shell 44, described above, is monolithic.

Downstream of the radial flange 48 and from a longitudinal position marked 54a, longitudinal cutouts in the cylindrical shell extending part 46 exist which are more visible in FIG. 2 in which only the elements necessary for understanding appear, without in particular the exchange accelerators (holes, ribs and pins).

On the one hand, there are regularly spaced and leaving an interval between them blades 56, terminated by an outer fallen edge 58. Each of these is fixed by a bolt nut assembly 60 to a fallen edge 62 of the downstream part of the inner ring 44, this edge flange 62 ^p ro- along by the blades 64, similar to the blades 56, which connect the downstream part of the monolithic shell 44 to the upstream portion. This monolithic downstream part comprises, from a longitudinal position marked 54b, a cylindrical part 66, similar to the upstream cylindrical part 46 of the ferrule 44, an internal radial flange 68, extended upstream, to give this part downstream monolithic sufficient inertia, by a cylindrical ferrule 70 (similar to 50 but directed upstream), then a radial flange inward 73 (similar to the upstream flange 52), intended to ensure sealing between the sectors and the downstream part of the shell 44.

On the other hand, in the intervals between the tongues 56 and 64 (see FIG. 2) coupled by the fallen edges 58, 62 thanks to the bolts and nuts 60, there are alternately elastically deformable blades, some 72 integral with the upstream part ferrule 44 in two parts and extending downstream, the other 74 soli daires of the downstream part 66 of the shell 44 in two parts, and extending upstream. The blades 72 have, in their downstream part, an edge that falls doubly inward first 76, then upstream 78, thus forming a hook which serves to control the position of the sectors 84 carrying the seal. 86 to the expansions of the inner ferrule 44. Similarly, the blades 74 have in their upstream part an edge which falls doubly inwards firstly 80, then downstream 82, thus forming a hook which serves for servo-control in position of the sectors carrying the seal at the expansion of the inner shell 44.

• - d'une part, vers l'extérieur, des raidisseurs 90 à bord tombé vers l'amont (respectivement aval) 92 qui s'inséreront au montage de la partie aval sur la partie amont de la virole 44, entre les crochets 80, 82 (respectivement 76, 78) ;
• - d'autre part, vers l'intérieur, un flasque comportant un logement 94 pour la mise en place d'un joint d'étanchéité avec les brides radiales 52 (respectivement 73) et un bourrelet 96 de retenue des garnitures d'étanchéité 86.

The sectors 84 carrying the seal have stiffeners 88 preventing their warping but leaving play with the elements 56 and 64 of the ferrule 44. In their upstream (respectively downstream) part the sectors 84 carrying the seal include:

• on the one hand, towards the outside, stiffeners 90 with a fallen edge upstream (respectively downstream) 92 which will be inserted when mounting the downstream part on the upstream part of the shell 44, between the hooks 80, 82 (76, 78 respectively);
• - on the other hand, inwards, a flange comprising a housing 94 for the installation of a seal with the radial flanges 52 (respectively 73) and a bead 96 for retaining the seals 86 .

Referring now to Figure 3, we will explain schematically how ventilation works which has not shown in Figures 1 and 2.

The air taken from one of the downstream compressor stages arrives in a known manner through holes 100 drilled in the upstream part 2 of the turbine casing and regularly distributed along the periphery of this casing. This ventilation air is distributed, according to arrow A, in the enclosure 102 forming a plenum. Part of this air imposes its temperature by a multiplicity of holes 104 in the inner ring 44, both in the most upstream cylindrical part 46, from which it is led downstream of the distributor 106 according to arrows B and C , that in the middle or downstream part where there are securing tabs 56, 64 and / or servo 72 and 74, according to the arrows D (around the hooks 32) and E, through the holes 104 on the tabs integral with the upstream part of the inner shell. In the same way, the downstream part of the ring is ventilated (arrows E ') by a multiplicity of holes also marked 104 drilled in the tongues (of securing or slaving) of the downstream part, in passing, for the part right of Figure 3, around the hooks 34.

The ventilation air having passed through the inner shroud 44 in the part facing the sectors passes through downstream stiffeners 90 (see FIG. 1) of the sectors through holes 108 regularly distributed in the enclosure 108 ′ according to arrow F, d 'where it escapes into a downstream enclosure 118 through holes 110 drilled in the downstream monolithic part 66 of the shell 44, according to the arrows F'.

The part of the air circulating between the ring 20 and the ferrule 44 also ventilates the interior of the ring 20, but with a much longer response time, due to the thermal insulation 24.

Another part of the ventilation air arriving in the enclosure 102 also ventilates the outside of the ring 20, following the following route: through holes 112, regularly distributed over the conical extension 10, it penetrates according to the arrow G in the enclosure 114 between median casing 4 and ring 20, the external part of this ring 20 and in particular its stiffening ribs being suitably insulated; this part of the air escapes from the enclosure 114 by holes 116 drilled in the internal conical extension 14 of the downstream casing 6, along arrow H, and it mixes in the enclosure 118 with the ventilation air ayan-- following the path described above (arrows D, E or E ', F, F').

• - d'une part une température homogène aussi bien périphériquement que longitudinalement, cette répartition étant bien entendu fondamentale pour obtenir qu'il n'y ait pas d'ovalisation thermique de l'anneau 44 en deux parties. Mais cette répartition fait partie du savoir-faire de l'homme de métier ;
• - d'autre part une température maximale relativement modérée (celle qui correspond à la température à la sortie de l'étage de compresseur où le prélèvement est effectué), ceci afin que les languettes d'asservissement 72, 74 travaillent dans le domaine élastique lorsque l'on substitue l'asservissement à long temps de réponse par l'anneau 20 dit deuxième asservissement à l'asservissement à court temps de réponse par la virole 44 dit premier asservissement. Le métal de cette virole sera donc préférablement un métal ayant à la fois un coefficient de dilatation relativement élevé et un domaine d'élasticité allant jusqu'à des températures de l'ordre de 450 à 500°C, du type désigné par Z 50 NMC 12 (Norme AFNOR).

It is recalled that FIG. 2 shows only the elements necessary for understanding the invention, and not the detail of the exchange accelerator elements (distribution of the holes, exchange fins, pins, etc.) which allow to ensure:

• - On the one hand a uniform temperature both peripherally and longitudinally, this distribution being of course fundamental to obtain that there is no thermal ovalization of the ring 44 in two parts. But this distribution is part of the skill of the skilled person;
• - on the other hand, a relatively moderate maximum temperature (that which corresponds to the temperature at the outlet of the compressor stage where the sampling is carried out), this so that the control tongues 72, 74 work in the elastic domain when the long response time control is replaced by the ring 20, said second control, for the short response time control by ferrule 44, said first control. The metal of this shell will therefore preferably be a metal having both a relatively high coefficient of expansion and a range of elasticity ranging up to temperatures of the order of 450 to 500 ° C., of the type designated by Z 50 NMC 12 (AFNOR standard).

The substitution action of said second control can be done either directly by pressing the hooks on the end of the fallen edges 92 of the sectors carrying the seals, or, as shown in the accompanying drawings, by indirect support, by l 'Intermediate hooks 78, 82, respectively on the one hand downstream of the tabs 72 and turned upstream and on the other hand upstream of the tabs 74 and turned downstream.

Preferably, the sealing sectors will have a peripheral dimension such that they are controlled both by at least three bearing surfaces of the hooks integral with the inner shell 44 and also by at least three direct or indirect bearing surfaces of the hooks 32 and 34 fixed to the outer shell 20. In Figure 2 there is shown the case where this control is by only three spans.

The boundaries of adjacent sectors are shown in Figure 2 in broken lines. The "bearing surfaces" are shown in cross hatching. We see that the lower sector of Figure 2 is controlled by two upstream supports and a downstream support while the adjacent sectors are controlled by two downstream supports and an upstream support.

These bearing surfaces must take into account the fact that the control tabs 72 and 74 take the end of thermal stabilization, after acceleration, an obliquity, of the rest minimal, relative to their position parallel to the axis shown in the drawings. Those skilled in the art will readily understand that to avoid any risk of jamming, it is necessary to give a very slight "rounding", in particular to the almost cylindrical supports of the hooks 32 and 34 and to the fallen edges 92 upstream and downstream of the - sectors 84. This rounded is also very weak and therefore has not been shown in the drawings, but it should be noted that it avoids giving play between the bearing surfaces, to the benefit of the precision of the radial position of the sectors 84 .

Of course, it would not depart from the scope of the present invention by the use of equivalent means, in particular by a different distribution of the support points of the hooks imposing the position of the sectors carrying the seal successively according to the first mode d 'enslavement then following the second. For example, the hooks 32 (respectively 34) and 82 (respectively 78) can be slightly shifted peripherally which makes it possible to have trapezoidal sectors on four supports close to the four corners of a trapezoid, both when the sectors are slaved to expansion of the ferrule 44 only when they are to that of the ring 20.

• - les joints 94 amont et aval sont supprimés ;
• - il y a un jeu, respectivement j et j', appréciable entre les faces amont (respectivement aval) des secteurs 84 portant les garnitures d'étanchéité 86 et les brides radiales 52 (respectivement 73) et préférablement, le jeu en amont est un peu plus grand qu'à l'aval (par exemple 0,3 à l'amont et 0,1 à l'aval) ;
• - il y a une prise de pression statique de paroi 120, dans la partie aval de la plateforme extérieure du distributeur en amont de la roue mobile, prise de pression qui est raccordée par une canalisation 122 à une "entrée" d'un réducteur-régulateur de pression 124 qui sera décrit plus loin ;
• - ce réducteur-régulateur est relié à un étage aval du compresseur par'une canalisation 126 et à l'enceinte 102 (voir figure 6) par une canalisation 128 ;
• - la virole 46 comporte vers l'aval préférentiellement des accélérateurs d'échange sous forme d'ailettes 130 (voir aussi figure 5) à tout le moins sur leur face extérieure, plutôt que sous forme de multitrous tels que 104, plus nombreux au contraire dans la partie antérieure de ladite virole 46 ;
• - sur les languettes de solidarisation 64 sont fixés vers l'intérieur par un moyen connu (soudage ou brasage) des éléments en forme de cornière 132 (voir aussi figure 5), se recouvrant avec jeu entre eux, en vue de créer une perte de charge entre l'enceinte amont 134 et l'enceinte arrière 136, comprises entre respectivement les éléments de structure 48, 50 ou les secteurs 84 et la virole 46 pour l'enceinte 134 et les éléments de structure 58, 70 et la partie cylindrique aval 66 de la virole 44 pour l'enceinte 136. Bien entendu, ces éléments en forme de cornière 132 laissent également du jeu avec les secteurs 84, et leur longueur radiale est telle que ce jeu s'annule pratiquement lorsque la distance entre secteurs 84 et virole 44 est la plus faible (fin de décélération mécanique comme cela sera expliqué ultérieurement) ;
• - enfin, les trous 110 sont agrandis et/ou augmentés en nombre et les trous 116 sont réduits en section et/ou en nombre en vue d'égaliser les pressions lorsque les débits suivant les flèches F' et H se réunissent, et en vue d'un abaissement de la pression dans l'enceinte 136.

In the embodiment of the invention represented in FIGS. 4 to 7, the following differences are noted according to FIG. 4 compared to the embodiment represented in FIG. 1:

• - Upstream and downstream seals 94 are removed;
• - there is a play, respectively j and j ', appreciable between the upstream (respectively downstream) faces of the sectors 84 carrying the seals 86 and the radial flanges 52 (respectively 73) and preferably, the upstream clearance is slightly greater than downstream (for example 0, 3 upstream and 0.1 downstream);
• - there is a static pressure tap on the wall 120, in the downstream part of the external platform of the distributor upstream of the moving wheel, pressure tap which is connected by a pipe 122 to an "inlet" of a reducer - pressure regulator 124 which will be described later;
• - This reducer-regulator is connected to a downstream stage of the compressor by a pipe 126 and to the enclosure 102 (see FIG. 6) by a pipe 128;
• - the shell 46 preferably comprises downstream exchange accelerators in the form of fins 130 (see also FIG. 5) at least on their external face, rather than in the form of multi-holes such as 104, more numerous on the contrary in the front part of said shell 46;
• - On the securing tabs 64 are fixed inward by known means (welding or soldering) of the elements in the form of angle iron 132 (see also Figure 5), overlapping with play between them, in order to create a loss of load between the upstream enclosure 134 and the rear enclosure 136, comprised respectively between the structural elements 48, 50 or the sectors 84 and the shell 46 for the enclosure 134 and the structural elements 58, 70 and the downstream cylindrical part 66 of the ferrule 44 for the enclosure 136. Of course, these angle-shaped elements 132 also leave play with the sectors 84, and their radial length is such that this play is practically canceled when the distance between sectors 84 and ferrule 44 is the smallest (end of mechanical deceleration as will be explained later);
• - Finally, the holes 110 are enlarged and / or increased in number and the holes 116 are reduced in section and / or in number in order to equalize the pressures when the flows according to the arrows F 'and H meet, and in view a reduction in the pressure in the enclosure 136.

It should be noted that with this arrangement, at full stabilized gas, the radial clearance between the sectors 84 and the internal edge of the angle elements 132 is smaller than under the conditions of stabilized partial speed, which increases the pressure drop between enclosures 134 and 136 when the engine is under heavy load. This corresponds to the direction of variation of the pressure in the vein, since the pressure drop in the moving wheel is greater the greater the engine load, although this favorable effect is partially offset by the leak rate may exist between the angle elements 132 and the elastic elements 72, 74 when these are moved outward during the phases where the second control comes into action.

For FIG. 6, reference will be made to the description which is given above, the differences compared to the previously described breakdown being explained below.

The ventilation air flow coming from a downstream stage of the compressor, via the reducing-regulator pressure 124, having passed through the ferrule 46, through the holes 104 opening into the enclosure 134, is partly sent by the clearance j upstream of the sectors carrying the seal according to arrow K. As will be explained below , the pressure reducing regulator 124 ensures in the enclosure 134 an extremely reduced overpressure compared to the static pressure at the wall, measured by the pressure tap 120. As a result, the flow rate according to the arrow K by the play j is minimized.

Another part of the flow arriving in the enclosure 134 bypasses the angle elements 132, either by the slight clearance between each angle 132 and its neighbors (arrow L also see FIG. 5) or by the clearance between the angles 132 and the bearing sectors the seal (arrow M), or even in certain cases by the clearance between the angles 132 and the elastic elements 72 and 74. Due to these bypasses and the weakness of these clearances, the air flow arriving in the enclosure 136 is at a pressure lower than that existing in the enclosure 134. Part of this flow passes through the slot j 'along arrow N, the other part following the circuit described in the basic patent (arrows F and F').

In FIG. 7 is shown a pressure reducer-regulator 124. It comprises a casing 138 provided with a boss 140 (on the left side of the figure) connected to the static wall pressure tap 120 by the pipe 122 ( see figure 4). It further comprises an air intake boss 142 taken from a downstream stage of the compressor by the pipe 126 (see FIG. 4), for example the last one, and a local expansion 144, terminated by a boss 146, delivering the air at reduced pressure and regulated via a pipe 128 (see FIG. 4) at enclosure 102.

Inside the reducer-regulator 124 is fixed, by known means not shown, a jacket 148 which comprises, opposite the boss 142, a hole 150 communicating with an annular enclosure 152 around the drawer 154 whose function will be described later. The shirt 148 has, in line with the local development 144, a slot 156 intended to regulate the pressure supplying the enclosure 102. The drawer 154 has at its two ends cylindrical surfaces 155 cooperating with the internal part of the shirt 148 for example by carbon segments or seals 158. In addition, an oblique hole 160 places the annular enclosure 152 in communication with the enclosure 162 of the reduction-regulator opposite the boss 140. The casing 138 is closed by a cover 164, fixed by known means (for example by screwing) to the casing 138, the seal between the casing 138 and the cover 164 being ensured by a seal 166.

Because of the hole 160, the pressure prevailing at 162 on the right side of the slide in the figure is equal to the pressure taken from a downstream stage of the compressor, for example the last one. It is therefore higher than the pressure prevailing in the enclosure 168 on the side of the inlet of static wall pressure 120 through the pipe 122 connected to the boss 140. In fact, the static pressure at the wall downstream of the distributor corresponds to the downstream pressure of the compressor, reduced by the pressure drop in the chamber and by the static pressure drop in the upstream distributor of the impeller (or even by the pressure losses of one or more turbine stages upstream if the device is used for one of the turbine wheels BP). The force exerted on the slide 154 to the left equal to the pressure difference between the enclosures 162 and 168 multiplied by the internal section of the jacket is balanced by a spring 170.

The operation of the reducer-regulator is as follows. For determined operating conditions (engine load, altitude, flight speed, etc.), the various parameters are determined, in particular the dimensions of the reducer-regulator 124, the dimensions of the slot 156, the diameter and the number of turns of the spring 170, and the pressure drop in the multi-holes 104 so that the pressure prevailing in the enclosure 134 is very slightly greater than the static pressure at the wall upstream of the moving wheel. The corresponding calculation obviously depends on each turbomachine and is within the reach of those skilled in the art. If the operating conditions (engine load, altitude, flight speed, etc.) change, for example causing an increase in static pressure at the wall upstream of the moving wheel, the pressure taken from the compressor is generally itself increased, which is a step in the right direction. It will be assumed in what follows that this increase in pressure is insufficient to completely compensate, taking into account the pressure drops in multi-holes 104, the increase in pressure at the wall of the hot gas stream upstream of the moving wheel. , which is generally the case (in the opposite case, several means can be used: diaphragm on the line 126, change of the sampling stage, modification of the reduction-regulator, in particular of the position of its slot). Under these conditions, the reducing-regulator will make it possible to adjust the pressure in the enclosure 134 by the following mechanism: the increase in static pressure at the wall upstream of the moving wheel is detected by the static pressure tap at the wall 120, and is sent to the left face (in FIG. 7) of the drawer 154 of the reduction-regulator 124. As a result, the drawer 154 will move to the right, revealing an additional section of the slot 156 of the jacket 148. The pressure drop in this slot will decrease due to the increase in cross-section and there will follow an increase in pressure in the enclosure 102 which will be reflected after deduction of the pressure losses by the multi-holes 104, in the enclosure 134. By playing on the form of the slot 156, the pressure in the enclosure 134 "will follow" the pressure 120, that is to say that it will always remain higher, but by a small amount at the static pressure measured by the pressure tap 120. Again, it is the know-how of a person skilled in the art which will make it possible to give the slot 156 the shape making it possible to ensure that the pressure in the enclosure 134 "follows" the pressure at the wall of the vein of hot gases, but always remaining slightly higher than the pressure at the wall of the vein.

As mentioned above, the pressure drop which occurs during the bypassing of the angle elements 132 has the consequence that the pressure in the enclosure 136 is lower than the pressure in the enclosure 134. This pressure drop is in common sense to ensure in the enclosure 134 a pressure not too much higher than the pressure in the stream downstream of the turbine wheel. However, the pressure drop in the vein is generally greater than the pressure drop between the enclosure 134 and the enclosure 136. It is for this reason that it is preferable to have a clearance i downstream positive but less than clearance j.

It is to increase the pressure drop between enclosure 134 and enclosure 136 that, as mentioned above, the holes 110 are in this version increased in number and / or in section relative to the holes 110 of the basic patent. This leads, if we want to collect the flows according to the arrows F 'and H, for example to be used for cooling a downstream low-pressure distributor, to decrease in number and / or in section the holes 116, in order to equalize the pressures in the enclosure 118 at a lower level, practically equal to that prevailing in the enclosure 136, this in order to decrease the flow rate according to arrow N, going through the game i.

It would not be departing, of course, from the scope of the present invention by using two reduction-regulators 124, one supplying the upstream space 134, via the enclosure 102, the other supplying the downstream space 136 (by a pipe not shown analogous to pipe 128 but opening directly into enclosure 136), the latter reducing-regulator being governed by a pipe similar to pipe 122 by a static pressure tap of the wall not shown, analogous to the taking of wall 120, and mounted at the front of the external platform of the downstream distributor 107 of the turbine wheel. It would not be departing from the scope of the present invention to use a single reducer-regulator 124, but the latter comprising 2 slots 156, shifted peripherally with, of course, a local expansion 144 and a connection boss 146 opposite each slot, the first connection boss 146 supplying the enclosure 134 via the enclosure 102 and the multi-holes 104, the second directly supplying the enclosure 136, by a pipe not shown, the cross section of the slot supplying the enclosure 136 being, for each position of the drawer, lower than that of the slot supplying the enclosure 102, in order to take account of the static pressure drop in the stream of hot gases, when the moving wheel passes.

Claims (14)

1. Sealing device for movable blades of a turbomachine, of the type comprising sectors carrying a gasket made of material capable of wearing out in the event of contact between the blade ends and this gasket, characterized in that said sectors (84) are subjected, on the one hand, during a transient phase of mechanical acceleration of the turbomachine, to a first servo in radial position by connecting elements (76, 78, 80, 82, 92) to elements elastic (72, 74) integral with an inner ferrule (44) which expands during said mechanical acceleration phase by the effect of ventilation over its entire length and its periphery by air taken from a stage downstream of compressor, in a homogeneous manner, and that said sectors (84) are subjected, on the other hand, during a thermal stabilization phase of the turbomachine succeeding the mechanical acceleration phase, to a second servo-control replacing the first, servo in rad position ial by hooks (34, 32) resting on the elastic elements (72, 74) to an outer ring (20) which expands during said thermal stabilization phase also by the effect of ventilation over its entire length and periphery by air taken from a downstream compressor stage, in a homogeneous manner, brought by a multiplicity of pipes opening into holes (100) drilled in the turbine casing. 2. Sealing device according to claim 1, characterized in that the connecting elements between the sectors (84) and the elastic elements (72 ₎ 74) are formed upstream and downstream by fallen edges (92) of the sectors (84) inserted in hooks (76, 78, 80, 82) of the elastic elements (72, 74). 3. Sealing device according to one of claims 1 and 2, characterized in that said inner ferrule (44) is in two parts respectively upstream and downstream, linked by fallen edges (58, 62) of securing tabs ( 56, 64) respectively secured to the upstream (46) and downstream (66) monolithic parts of the ferrule (44), said securing tabs (56, 64) being regularly distributed over the periphery and spaced apart. 4. Sealing device according to any one of claims 1 to 3, characterized in that in each interval between the securing tabs (56, 64) there is an elastic tongue (72, 74) respectively connected alternately to the upstream part (46) and downstream part (66) monolithic of the inner shell (44). 5. Sealing device according to any one of the preceding claims, characterized in that the inner shroud (44) comprises a multiplicity of heat exchange accelerators (104) distributed to ensure the uniformity of the temperatures of said inner shroud (44) both in the longitudinal direction and in the peripheral direction, for all operating conditions. 6. Sealing device according to claim 1, characterized in that the outer ring (20) comprises radial stiffening elements (22) and inner (24) and outer (26) insulation, the latter notably insulating the stiffening elements (22) and in that this outer ring is centered in the middle casing (4) in line with the device by radial elements (12) belonging to the casing and (12 ') belonging to a radial flange (28) of the ring (20), cooperating with each other, and by radial elements (16) belonging to the casing and (16 ') belonging to a radial flange (30) of the outer ring (20) and cooperating with each other. 7. Sealing device according to the preceding claim, characterized in that the hooks (34, 32) fixed on the outer ring (20) bear on the fallen edges (92) of the sectors (84) via hooks (78, 82) of the elastic tongues (72, 74) of the ferrule (44) thus substituting the servo action for the expansions of the ring (20) by means of the hooks (34, 32) to the action of slaving to the expansions of the shell (44), by means of the tongues (72, 74). 8. Sealing device according to one of the preceding claims, characterized in that the quick-response ferrule (44) is made of a metal having both a high coefficient of expansion and a range of elasticity up to temperatures in the range of 450 ° C to 500 ° C. 9. Sealing device according to one of the preceding claims, characterized in that the air flow rates sampled to ventilate the inner shell (44) and to ventilate the outer ring (20), come from the same compressor stage, and are collected in an enclosure (102) serving as a plenum located upstream of the sealing device. 10. Sealing device according to any one of claims 1 to 9 characterized in that at least one pressure reducer-regulator (124) is placed between the pipe (126) for extracting air from the compressor and a pipe. (128) opening into a hole (100) in the turbine casing and has an inlet connected by a pipe (122) to a pressure tap (120) located in the downstream part of the external platform of a distributor (100) placed upstream of the movable blading so that a pressure always very slightly greater than the static pressure at the wall of the gas circulation stream of the turbomachine is established from radially outer side of the sectors (84) carrying the seals (86). 11. Sealing device according to claim 10, characterized in that the pressure reducing regulator (124) consists of: - A casing (138) closed by a cover (164) and doubled by an internal jacket (148) comprising a slot (156) opposite the outlet of the reduction-regulator (124); - A drawer (154) loaded by a spring (170) and providing between its two ends (155) cooperating with the jacket (148) an annular enclosure (152) which communicates by an oblique hole (160) with the enclosure closed (162) of the reduction-regulator (124). 12. Sealing device according to claim 10 characterized in that angle-shaped elements (132) overlapping with each other with play are fixed inwardly on the connecting tabs (64). 13. Sealing device according to any one of claims 10 to 12, characterized in that two pressure reducing regulators (124) respectively supply, the first, an upstream space (134) located on the radially inner side of the ferrule interior (44) upstream and in line with the sectors (84) and the second, a downstream space (136) located downstream of the sectors (84) between the two radially offset ferrules (66, 70) belonging to the inner ferrule (44). 14. Sealing device according to claim 10, characterized in that the pressure reducing regulator (124) consists - a casing (138) closed by a cover (164) and doubled by an internal jacket (148) comprising two slots (156) offset peripherally each corresponding to an output of the reduction-regulator (124), the first output being connected to an upstream space (134) located on the radially inner side of the inner shell (44) upstream and in line with the sectors (84) and the second outlet being connected to a downstream space (136) located downstream from the sectors (84) between the two radially offset ferrules (66, 70) belonging to the inner ferrule (44), - A drawer (154) loaded by a spring (170) and providing between its two ends (155) cooperating with the jacket (148) an annular enclosure (152) which communicates by an oblique hole (160) with the enclosure closed (162) of the reduction-regulator (124),
the cross section of the first slot (156) corresponding to the first outlet always being greater than the cross section of the second slot (156) corresponding to the second outlet of the reducing-regulator (124).

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