EP0192556A1 - Turbine cylinder with a device to adjust the tip clearance between the turbine blades and the cylinder - Google Patents

Abstract

The casing (2) of a turbomachine is internally lined with a rigid annular wall (5) consisting of a succession of integral segments alternately of a type (6a) with low thermal inertia and of a type (6b) with thermal inertia high. In contact with the gases from the flow path in the associated rotor stage, the radial movements of said wall (5) automatically reproduce the radial movements of the moving blade heads (1) of said rotor. Said wall (5) is connected to the casing (2) by connecting rods (9) placed in a tangential direction and leaving any freedom of radial movement to the wall (5).

Description

The invention relates to a turbomachine casing associated with a device making it possible to adjust the clearance between said casing and the movable blades of a rotor in operation, automatically.

In a turbomachine, it is necessary to maintain sufficient clearance at all times between the blades of the rotor which are movable and the internal wall of the crankcase which is fixed.

Now the movable blades and the crankcase move radially under the effect of temperature, and also under the effect of centrifugal force for the movable blades, internal and external pressures for the crankcase, which causes significant variations. Game.

To avoid this game being canceled at any time during operation, we are forced to take it large enough, initially. But engine performance is appreciably affected by the presence of this important play and one of the major objectives of engine manufacturers, at these days, is to "drive" this play to reduce it, both in transient and stabilized conditions, while guaranteeing its presence at all times.

Several prior solutions have been proposed in an attempt to resolve this problem. Most use more or less hot air flows, more or less pressurized, taken from particular points of the engine to meet the needs and also use more or less sophisticated regulations, generally comprising a means to measure or calculate the clearance and a means for move the wall elements inside the crankcase and thus act on the clearance. The patent application FR-A-2 540 560 filed by the applicant on February 3, 1983 as well as the documents FR-A-2 485 633, FR-A-2 450 344, GB 2 047 354, GB 2 063 374 illustrate, by describing solutions of this type, the results of this research. These prior solutions have been found to be bulky and cumbersome, complex and therefore unreliable, and above all, by removing the air they need, they make the engine performance lose at least part of what it provides them.

The invention avoids these various drawbacks and in particular makes it possible to obtain a stator wall whose radial evolutions follow exactly the radial evolutions of the movable blades heads without requiring air sampling detrimental to the performance of the turbomachine. Thus, a turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to the invention is characterized in that said casing is internally lined with a rigid annular wall connected to the casing by connecting means which allow said wall completely free to move in the radial direction according to the expansions / contractions in operation and in that said wall consists of a succession of integral segments, each segment being alternately of a type with low thermal inertia and of a type with high thermal inertia so that the radial displacements of the said wall adapt in all operating conditions of the turbomachine to the radial displacements of the moving blade heads.

Advantageously, the inner wall segments with low thermal inertia are thin, their internal surface is directly in contact with the gases of the vein. circulating through the stage of movable blades considered, their external and lateral surfaces are coated with a thermally insulating material and the adjacent segments of inner wall with high thermal inertia are very thick and coated on all their surfaces with material thermally insulating.

• - la figure 1 représente, en coupe transversale par rapport à l'axe de rotation de la turbomachine, une vue simplifiée d'un carter de turbomachine associé à un dispositif pour ajuster le jeu entre aubes mobiles et carter, selon un mode de réalisation de l'invention ;
• - la figure 2 montre un détail agrandi d'une partie de la figure 1 selon II
• - la figure 3 montre un détail agrandi d'une partie de la figure 1 selon III ;
• - les figures 3a et 3b montrent un détail des faces de contact respectivement des deux demi-segments représentés à la figure 3 ;
• - la figure 4 représente, en coupe longitudinale passant par l'axe de rotation de la turbomachine selon IV-IV, une vue partielle du carter et du dispositif associé représentés à la figure 1 ;
• - les figures 5 et 6 représentent dans une vue analogue à la figure 2 deux variantes du détail de la figure 1
• - les figures 6a, 6b, 6c représentent dans une vue selon F trois variantes d'un détail de la figure 6
• - la figure 7 représente dans une vue analogue à la figure 2 une autre variante du détail de la figure 1
• - les figures 8a et 8b représentent dans une vue analogue à la figure 4 deux variantes du détail agrandi de la figure 1 en coupe selon VIII-VIII

Other characteristics and advantages of the invention will be better understood with the aid of the description which follows of an embodiment, with reference to the appended drawings in which:

• FIG. 1 represents, in transverse section with respect to the axis of rotation of the turbomachine, a simplified view of a turbomachine casing associated with a device for adjusting the clearance between movable blades and casing, according to one embodiment of the invention;
• - Figure 2 shows an enlarged detail of part of Figure 1 along II
• - Figure 3 shows an enlarged detail of part of Figure 1 along III;
• - Figures 3a and 3b show a detail of the contact faces respectively of the two half-segments shown in Figure 3;
• - Figure 4 shows, in longitudinal section passing through the axis of rotation of the turbomachine according to IV-IV, a partial view of the housing and the associated device shown in Figure 1;
• - Figures 5 and 6 show in a view similar to Figure 2 two variants of the detail of Figure 1
• - Figures 6a, 6b, 6c show in a view along F three variants of a detail of Figure 6
• - Figure 7 shows in a view similar to Figure 2 another variant of the detail of Figure 1
• - Figures 8a and 8b show in a view similar to Figure 4 two variants of the enlarged detail of Figure 1 in section along VIII-VIII

• - la température T des gaz moteur au niveau de cette aube,
• - la vitesse de rotation N du rotor.

By largely schematizing the phenomena to facilitate understanding, we can say that the radius of gyration R of the head of a moving blade 1 schematically represented in Figure 1 evolves according to two parameters which we consider as independent one of the other, namely:

• - the temperature T of the engine gases at this blade,
• - the rotational speed N of the rotor.

liant R à R_o, rayon giratoire des têtes d'aubes à T_o, température ambiante au sol, K₁ étant le coefficient de dilatation radiale thermique du rotor.The temperature T of the hot engine gases which pass through a grid of blades such as 1 creates a flow of heat which, passing through the blades, spreads as far as the disc which carries them and causes a radial expansion of the assembly, therefore a displacement of the blade heads 1. At stabilized temperature, and the speed N of the rotor being assumed to be zero, the radius of gyration R of the blade heads follows a law which can be represented by the relation:

binding R to R _o , gyratory radius of the blade heads at T _o , ambient temperature on the ground, K ₁ being the coefficient of radial thermal expansion of the rotor.

In temperature transient, that is to say on a change in the temperature T of the hot engine gases, the displacement of the blade heads 1 follows a complex law due to the fact that the blades, which are immersed in the engine gases and are not very thick, heat up or cool down quickly while the discs, which are far from the engine gases and very thick, heat up or cool down more slowly.

The mode of movement of each grid of movable blades such as 1 can however be characterized fairly precisely by means of four parameters.

dans laquelle :

• - K'_l est le coefficient de dilatation radiale thermique des aubes mobiles
• - K"₁ est le coefficient de dilatation radiale thermique du disque
• - e est la constante de Néper
• - θ' est la constante de temps de dilatation radiale thermique des aubes mobiles
• - θ" est la constante de temps de dilatation radiale thermique du disque

et où

• - K'₁ + K"₁ = K₁
• - K'₁ + K"₁ = K₁
• - K'₁ et K"₁ sont voisins de 0,50
• - θ' est de l'ordre de 5 secondes
• - θ" est de l'ordre de 10 minutes.

Indeed, by referring to the case of a "unit scale" of temperature, that is to say to the case of a sudden change in the temperature T of the engine gases from a temperature T stabilized at a new temperature T ₂ stabilized, at speed N of the rotor assumed to be zero, the corresponding change, from R ₁ to R ₂ , of the radius of gyration R of a blade head 1 subjected to this change in temperature is carried out as follows: it is initially rather fast, of the order of 50% of the total displacement carried out in 5 to 10 seconds, then very slow on the remaining 50% of the total displacement carried out in 10 to 20 minutes. Such behavior follows a law which can be represented by the relation as a function of time t:

in which :

• - K ' _l is the coefficient of thermal radial expansion of the movable blades
• - K " ₁ is the coefficient of thermal radial expansion of the disc
• - e is the constant of Neper
• - θ 'is the time constant of thermal radial expansion of the moving blades
• - θ "is the time constant for thermal radial expansion of the disc

and or

• - K ' ₁ + K " ₁ = K ₁
• - K ' ₁ + K " ₁ = K ₁
• - K ' ₁ and K " ₁ are close to 0.50
• - θ 'is around 5 seconds
• - θ "is around 10 minutes.

These four parameters, which we know how to calculate, suffice to determine the response of this system to any change in the temperature T of the engine gases.

Furthermore, the speed of rotation N of the rotor creates a centrifugal force which acts on the whole of the rotor and causes another radial displacement of the blade heads 1.

At stabilized speed and the temperature T of the engine gases being assumed to be equal to the ambient temperature To, the radius of gyration R of the blade heads 1 follows a law which can be represented by the relation:
R = Ro + K2.N2
K ₂ being the coefficient of centrifugal radial expansion of the rotor.

In speed transient, that is to say on a change in the speed N of the rotor and the temperature T of the engine gases being always assumed to be equal to To, the above relationship remains true. Indeed, the centrifugal force has no delay on the rotational speed N of the rotor and the time t only intervenes through the evolution of speed N.

Under the normal operating conditions of the turbomachine, the speed N and the temperature T both change and their effects on the radius of gyration R of the blade heads 1 add up.

In stabilized regime (constant N and T), in particular, we therefore have an evolution represented by the relation:

où K₃ est le coefficient de proportionnalité entre T et _N2.But the temperature T of the hot engine gases at a given point in the stream is a function of the speed of rotation N of the rotor:

where K ₃ is the coefficient of proportionality between T and _N 2.

This relation can be written in the reverse form:

As a result, the radius of gyration R of the movable blades 1 is linked to the temperature of the hot..engine gases, at a given point in the vein, by a relationship of simultaneity:

cet effet s'ajoutant, comme en régime stabilisé décrit ci-dessus, à celui de la température T des gaz moteur.In transient conditions (N and T not stabilized), a distinction must be made depending on the part of the turbomachine considered, compressor or turbine, the present invention being applicable in either case. For a compressor, located upstream of the combustion chamber, the evolution of the temperature T of the hot engine gases almost instantaneously follows that of the speed N of the rotor, such so that the above relation T = To + K ₃ .N ² is still applicable and that we can still write the effect of the centrifugal force in this way:

this effect adding, as in the stabilized regime described above, to that of the temperature T of the engine gases.

oû Δ T_c est l'écart de température dû à l'excès ou au déficit de carburant brûlé, et T_N est la température qu'auraient les gaz de turbine si la vitesse N était stabilisée.For a turbine, located downstream of the combustion chamber, the evolution of the temperature T of the engine gases is influenced by the fact that the evolution of the speed N is due to a temporary excess or deficit of the flow rate of burned fuel in the combustion chamber in relation to the flow required in stabilized operation. We thus obtain the new relation:

where Δ T _c is the temperature difference due to the excess or deficit of fuel burned, and T _N is the temperature that the turbine gases would have if the speed N were stabilized.

Il n'est pas proportionnel à (T-To) mais à (T_N - To).The effect of centrifugal force is therefore written:

It is not proportional to (T-To) but to (T _N - To).

On the contrary, the temperature difference Δ T _c intervenes directly in the evolution of the radius of gyration R due to the temperature T as before. However, its duration is at most equal to that of the speed transient N, ie 5 to 10 seconds maximum for a simple evolution. His influence is therefore noticeable only on the expansion of the movable blades 1, that is to say, in the case of a "unit step" of temperature as above, in connection only with the gain K'l and the time constant

After having described the radial evolutions of the moving blade heads 1, reference will again be made to FIG. 1 which represents, in transverse section with respect to the axis of rotation of the turbomachine, a simplified view of an embodiment of the invention. Facing the movable blade heads 1, there is a fixed part of a turbomachine constituted by a stator casing 2 which in the example shown is in two parts 2a, 2b, each having a generally semi-cylindrical shape. Each part, respectively 2a and 2b, carries at its ends flanges, respectively 3a and 4a, 3b and 4b which are assembled by any known means, such as bolting. The casing 2 is internally lined with a rigid wall 5, which in the example shown is also in two parts 5a and 5b. This inner wall 5 consists of a succession of integral segments 6 which are of two different types 6a and 6b, more clearly shown in Figure 2, and arranged alternately. A segment such as 6a is thin, its internal surface 6i is directly in contact with the gases of the vein circulating in the stage of movable blades 1 and its external and lateral surfaces are coated with a layer 7a of a material thermally insulating. These segments 6a of the inner wall 5 therefore very quickly take the temperature of the gases of the vein. An adjacent segment such as 6b is very thick and all of its surfaces are coated with a layer 7b of a thermally insulating material. These segments 6b of the inner wall 5 thus have a high thermal inertia and their thermal connection with the outside takes place almost only through their junctions with the adjacent segments 6a. They therefore take the temperature of the vein gases very slowly. The insulating layers 7a and 7b are flexible enough to follow all the thermal expansions / contractions of the interior wall 5. The segments 6a and pb are in sufficient number so that the initially circular shape of the annular wall is sufficiently well preserved during the expansions / thermal contractions occurring during the operation of the turbomachine. The internal surface of the inner wall 5, both for the segments 6a and for the adjacent segments 6b, can be covered with a layer 8 of abradable material constituting a wear and seal lining susceptible during operation of come into contact with the ends of movable blades 1 without causing damage. This material is determined so as not to create a thermal barrier between the internal surface 6i of the segments 6a of the internal wall 5 and the gases of the vein and not to slow down the thermal expansions / contractions of the internal wall 5.

Each part, respectively 5a and 5b, of the inner wall 5 is fixed inside the corresponding part of the casing 2, respectively 2a and 2b, by means of connecting rods 9. For this purpose, a yoke 10 is fixed, for example by screwing, on at least some of the segments 6b of the inner wall 5, at a 7th end of these segments in a radially external zone. Similarly, a yoke 11 is also fixed, for example by screwing, on the internal surface of the casing 2, in a position circumferentially offset with respect to the associated yoke 10. Each link 9 is provided at its ends with yokes, respectively 9a and 9b which cooperate by means of axes of rotation 10a and lla with said yokes 10 and 11. These links 9 are thus placed in a direction substantially tangential to the inner wall 5 and thus leave the wall 5 free to move radially under the influence of thermal expansion / contraction. To allow the attachment of the rods 9 to the casing 2, an access hole 5c can be made in the interior wall 5, preferably at the level of a thin segment 6a.

The two parts 5a and 5b of the interior wall 5 are assembled in such a way that they bear on one another and that, during any radial displacement originating from thermal expansion / contraction during operation, their longitudinal axis remains in coincidence with the longitudinal axis of rotation of the turbomachine. For this purpose, each end of the inner wall part, respectively 5a and 5b, comprises a half-segment respectively 6c or 6d of the very thick type. As shown in more detail in FIGS. 3, 3a and 3b, these half-segments 6c and 6d are joined by their respective end faces by means, for example, of a bolt 12. In addition, each of these faces comprises by example a tenon 13 and a mortise 14 arranged in two perpendicular directions and cooperating respectively with a mortise 14a and a tenon 13a of the face of the associated half-segment to very precisely join the two parts 5a and 5b of the inner wall 5. A passage access 15 is provided through the casing 2 to allow the establishment of the bolting 12.

As shown in FIG. 4, the internal wall 5 is placed in a housing constituted by an annular recess 16 formed on the internal face of the casing 2. Under the action of the pressure P of the gases, the internal wall 5 thus comes to be pressed laterally on the surface 16a of the recess 16 where the pressure P is the lowest. The corresponding lateral surface of the wall 5 is coated with a layer 7b of thermally insulating material, as previously described, which in this zone prevents gas leaks, reduces contact friction and reduces heat exchange between the interior wall 5 and the casing 2. In the example shown in FIG. 4, it is a stage of movable blades 1 of the turbine and in this case the internal wall 5 is pressed against a surface 16a of the recess 16 located downstream with respect to the direction of gas flow in the stream of the turbomachine. In the case of a stage of compressor blades, conversely, the inner wall 5 would be pressed against an upstream surface. Note that in the example shown the inner wall 5 like the casing 2 have a generally cylindrical shape which corresponds to the outer shape of the gas stream of the turbomachine in the area considered. But of course, the invention applies in the same way in the case where this shape of vein is conical and in this case the inner wall 5 also has a generally conical shape adapted to the vein.

After having previously described the radial evolutions of the moving blade heads 1, it is advisable to specify, according to the objectives targeted by the invention, the modes of implementation making it possible to obtain, under the different operating conditions of the turbomachine, in regimes stabilized and transient, the desired clearance between the vanes 1 and the inner wall 5 associated with the casing 2.

The solution proposed by the invention consists in producing a "thermal model" of the rotor on the stator. In other words, an interior wall 5 is produced which, in regimes transient as well as in stabilized regimes, very precisely follows the radial movements of the blades of the rotor, and this by the only thermal effect on this inner wall 5 of the hot gases which lick it. Because this interior wall 5 is a complete circumference, any peripheral expansion results in a radial expansion of the interior wall 5. This is the principle used.

• - le coefficient de dilatation thermique du matériau qui les constitue,
• - et leur longueur périphérique totale, sont choisis pour que leur allongement thermique donne à la paroi intérieure 5 une dilatation radiale égale au déplacement de la tête des aubes dû à leur propre allongement thermique et à la force centrifuge ( coefficient K'_l + K₂ ) , en régime stabilisé, et ^K ₃

les autres paramètres :

• - la capacité calorifique du matériau qui les constitue,
• - leur épaisseur,
• - et les coefficients d'échange thermique des revêtements, sont choisis pour que les segments 6a aient une constante de temps thermique égale à celle des aubes 1 seules (θ).

To define the so-called "low thermal inertia" segments 6a, two parameters

• - the coefficient of thermal expansion of the material from which they are made,
• - And their total peripheral length, are chosen so that their thermal elongation gives the inner wall 5 a radial expansion equal to the displacement of the head of the blades due to their own thermal elongation and to the centrifugal force (coefficient K ' _l + K ₂ ), in steady state, and ^K ₃

the other parameters:

• - the heat capacity of the material from which they are made,
• - their thickness,
• - And the heat exchange coefficients of the coatings, are chosen so that the segments 6a have a thermal time constant equal to that of the blades 1 alone (θ).

• - le coefficient de dilation thermique du matériau qui les constitue,
• - et leur longueur périphérique totale,

sont choisis pour que leur allongement thermique donne à la paroi intérieure 5 une dilatation radiale égale à celle que subit la tète des aubes 1 du fait de l'allongement thermique des disques qui les supportent (coefficient K₁" ), et les autres paramètres :

• - la capacité calorifique du matériau qui constitue les segments 6b,
• - leur masse,
• - leur forme,
• - la section des liaisons entre segments 6a et 6b,
• - et les coefficients d'échange thermique des revêtements,

sont choisis pour que les segments 6b aient une constante de temps thermique égale à celle des disques seuls (θ").Similarly, to define the segments 6b called "with high thermal inertia", two parameters:

• - the coefficient of thermal expansion of the material from which they are made,
• - and their total peripheral length,

are chosen so that their thermal elongation gives the inner wall 5 a radial expansion equal to that that undergoes the head of the blades 1 due to the thermal elongation of the discs which support them (coefficient K ₁ "), and the other parameters:

• - the heat capacity of the material which constitutes the segments 6b,
• - their mass,
• - their shape,
• - the section of the connections between segments 6a and 6b,
• - and the heat exchange coefficients of the coatings,

are chosen so that the segments 6b have a thermal time constant equal to that of the discs alone (θ ").

Certain possible adaptations are shown in FIG. 5 for a segment 106b equivalent to a segment 6b.

Close and long connections such as 23 with the neighboring segments 6a and internal partitions such as 24 slow down the entry and the flow of heat in the segment 106b. The mass of segment 106b is increased by a longer hammer shape by adding end portions such as 22. Zones of thermal radiation, which are not covered with a layer of insulating material, on the outer wall of these segments, such as 17, and cooling fins produced in these zones, such as 18, make it possible to radiate heat towards the stator casing 2, therefore to decrease the temperature of the segments 106b. If necessary, it is also possible to add spacers with a low or zero coefficient of thermal expansion (not shown) in the middle of the segments 6b. These devices make it possible, when necessary, to obtain exactly the characteristics required for the interior wall 5.

It is also possible, as shown in FIG. 6, to have segments 206b with high thermal inertia radially spaced apart towards the outside. In this case, the adjacent segments 206a with low thermal inertia each extend respectively by a portion 25. These portions 25 remain without influence on the changes in diameter of the interior wall 5 because they are separated by a slot 26 which can have different shapes , as shown in FIGS. 6a, right, 6b, oblique, or 6c, with a balonette. The ends of the parts 25 are covered by a part 27 which covers the slot 26.

In the particular case of transient regimes for a turbine, it is necessary to take into account the fact already mentioned that the momentary excess or deficit of fuel burned instantly results in a higher or lower gas temperature T than at the same speed N stabilized. Because of this, the clearance between the vanes 1 and the inner wall 5 increases or decreases momentarily. This does not bring any noticeable discomfort during acceleration, but imposes a slightly larger clearance in stabilized regime so that it is still sufficient in deceleration.

In addition to the embodiment which has been described, the invention is susceptible of other embodiments, a few variants of which will be indicated. Thus to facilitate the manufacture and repair of the inner wall 5, it may be convenient to divide it into several elements. An example of this embodiment is shown in FIG. 7. Each element 105 of internal wall 5 is terminated by two half-segments 306c and 306d of the type with high thermal inertia to facilitate the attachment of the elements to each other. We can go so far as to have as many elements 105 as segments with low thermal inertia 306a. Snap elements between them can for example be produced as described above between the two parts 5a and 5b of the inner wall 5, with reference to Figures 3, 3a and 3b.

Due to the small thickness of the segments with low thermal inertia, the rigidity of the interior wall 5 may be insufficient despite its pressing on a lateral surface 16a of the recess 16 of the casing 2 (see FIG. 4). To remedy this, it is possible to equip the thin segments with stiffeners. Thus, as shown in Figure 8a, are placed on the upstream and downstream side edges of the segments 406a of the inner wall 5, two ribs 19 thin enough to maintain the thermal performance of the two types of segments. The requested lateral seal can then be produced on one of these ribs, bearing on the lateral surface 16a of the recess 16 of the casing 2 (see FIG. 4). As shown in FIG. 8b, it is possible, as an alternative, to provide on each lateral edge of a thin segment 506a stiffening elements 20 and 21 attached and fixed to the external wall of the segments 506a.

Claims (10)

1. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing, characterized in that said casing (2) is internally lined with a rigid annular wall (5) connected to the casing (2) by means of connection (9 to 11) which leave to said wall (5) any freedom of movement in the radial direction according to the expansions / contractions in operation, and in that said wall (5) consists of a succession of segments (6a, 6b) integral and subjected to the sole influence of the hot air of the turbomachine passing through the state of the moving blades, each segment being alternately of a type with low thermal inertia and of a type with high thermal inertia so that the radial movements of said wall (5) automatically undergo, in all operating conditions of the turbomachine, the same radial movements as the movable blade heads (1). 2. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to claim 1, characterized in that the segments (6a) of inner wall (5) with low thermal inertia are thin, in that their internal surface is directly in contact with the gases of the vein circulating through the stage of movable blades (1) considered and that their external and lateral surfaces are coated with a material (7a) thermally insulating and in that the segments adjacent (6b) inner wall (5) with high thermal inertia are very thick and coated on all their surfaces with a thermally insulating material (7b), and mechanically and thermally connected by a small surface to the adjacent segments (6a). 3. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of claims 1 and 2, characterized in that the inner wall (5) is fixed inside the casing (2) by means of support rods (9) placed in a tangential direction and one end (9b) of which is fixed inside the casing and the other end (9a) is fixed to at least some of the very thick segments (6b ) of inner wall (5). 4. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of the preceding claims, characterized in that the casing (2) is in two parts (2a, 2b) semi-cylindrical assembled by bolting and that the inner wall (5) is in at least two parts (5a, 5b), the connection between the two parts (5a, 5b) taking place between two very thick half-segments (6c, 6d) whose contact faces have cooperating tenons and mortises (13, 13a, 14, 14a) for centering and which are assembled by means of bolts (12). 5. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of the preceding claims, characterized in that the internal wall (5) is placed in a housing constituted by an annular recess (16) formed on the internal face of the casing (2) and at least one of the lateral surfaces of said wall (5) capable of pressing against the cooperating surface (16a) of the recess (16) is coated with a layer of insulating material (7b) constituting a seal. 6. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to one any one of the preceding claims, characterized in that the radially internal surface of the interior wall (5) is coated with a layer (8) of abradable material constituting a wear and sealing lining. 7. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of the preceding claims, characterized in that the thin segments (206a) entering the inner wall (5) have on their lateral edges respectively upstream and downstream, with respect to the axial direction of circulation of the gases of the turbomachine, stiffening elements consisting for example of ribs (19). 8. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of the preceding claims, characterized in that the very thick segments (106b) of the internal wall (5) have internal partitions (24), hammer ends (22), areas (17) not covered with thermal insulation and fins (18) of energy dissipation, narrow and long connections (23) being formed between these segments (106b ) and their adjacent segments (6a) of small thickness. 9. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of the preceding claims, characterized in that the very thick segments (206b) of the interior wall (5) are radially spaced from the movable blade ends (1) and the continuity of the internal surface of said wall (5) is ensured by parts (25) of thin segments (406a) separated by a median slot (26). 10. Turbomachine casing associated with a device for adjusting the clearance between movable blades and casing according to any one of the preceding claims, characterized in that the thin segments (6a) of the interior wall (5) have a hole ( 5c) allowing access for fixing the support rods (9) to the housing (2).

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