EP0192557B1 - Turbine cylinder with a device to adjust the tip clearance between the turbine blades and the cylinder - Google Patents

Description

The invention relates to a turbomachine casing associated with a device making it possible to automatically adjust in operation, the clearance between the ends of movable blades of a turbomachine rotor and the corresponding surface of a stator or fixed part of a turbomachine. , including said housing.

The compressors of modern turbomachinery comprise an axially extending rotor and a stator circumscribed to the rotor.

The compression ratios are high and the temperatures in their last stages can reach 600 to 700 ° C. It is necessary to check the clearances existing between the blades of the blades and the stator casings so that these clearances remain constant and as low as possible, whatever the operating conditions of the machine.

The seal between the end of the blades of the blades and the housing of the rotor or the enclosure of the stator is ensured by friction strips generally comprising a so-called "abradable" wear material. This material allows the adaptation of the joint within the limits of mechanical tolerances or thermal expansions. It is therefore of the greatest importance to be able to control thermal expansions, in particular in the radial direction, so that the clearances between the rotor and the stator are kept at the lowest possible value, and thus make it possible to limit the losses due to the reverse flow of air between the ends of the rotor blades and their envelope.

The blades as well as the rotor discs are generally made of a material resistant to high temperatures and low coefficient of thermal expansion; on the other hand, the stator vanes are generally embedded at one end, in housings provided on the casing of the compressor, which is generally made of steel, a material whose coefficient of thermal expansion is high.

We have therefore sought to control the expansion of the envelope so as to minimize the clearances between rotor and stator.

This is how FR-A-2,535,795 describes a device for suspending blades in a compressor casing characterized by a casing comprising an inner casing and an outer casing. The inner envelope is formed by a set of cylindrical sectors carrying radial grooves in which are maintained friction band supports and sectors of stator blades. The outer casing is cooled by ventilation ramps and cooperates with a system of lugs and pins with the expansions of the inner casing. The sectors have a parallelogram shape and carry two upstream legs and two rear legs capable of receiving a fixing pin so that one pin in two crosses the legs of two consecutive sectors.

The purpose of this device is to allow the clearance between the stator and rotor of an axial compressor to be checked.

FR-A-2 482 661 describes a system for controlling the games of a compressor characterized by a double jacket. The inner casing is made up of sectors carrying the stator vanes and the friction bands of the rotor / stator seals. The segments are kept at a distance from the annular outer casing by rigid radial flanges. To compensate for variations in play between the ends of the rotor blades and the friction bands, the outer casing is ventilated by air jets from ramps surrounding the outer casing, ramps supplied with air taken from the compressor .

Such systems bring an improvement to the operation of the compressors of turbomachines, and in particular in stabilized regime.

However, they fail to present significant leaks at the level of the numerous slots existing between the sectors of the internal envelope. These leaks counterbalance a large part, if not all, of the advantages which one derives from the improved control of the clearances at the tips of the blades.

The invention aims and makes it possible to obtain a significant reduction in these leaks without sacrificing the control of the clearances at the end of the blades.

It is characterized in that the inner casing consists of two deformable half-ferrules comprising on their external face two annular flanges ensuring sealing with the casings situated upstream and downstream, and in that the means of connection between the inner casing and the outer casing are constituted by radial links articulated, on the one hand, on two rows of yokes of the inner casing and, on the other hand, on two rows of internal ears of the outer casing .

• - La figure 1 représente une demi-coupe axiale d'une section de compresseur selon une forme de réalisation de l'invention.
• - La figure 2 est une vue selon une coupe II-II de la figure 1.
• - La figure 1 représente une demi-coupe axiale d'une section de compresseur ou d'un compresseur axial plus particulièrement destiné à équiper une turbomachine.

The explanations and figures given by way of example will make it possible to understand how the invention can be implemented.

• - Figure 1 shows an axial half-section of a compressor section according to an embodiment of the invention.
• - Figure 2 is a view in section II-II of Figure 1.
• - Figure 1 shows an axial half-section of a compressor section or an axial compressor more particularly intended to equip a turbomachine.

According to the example shown, the last four compression stages are arranged in an annular frustoconical channel, the widest section of which receives the air flow to be compressed.

The compressor housing has two envelopes: an inner envelope 1 and an outer envelope 2.

The inner envelope 1 is fixed to the outer envelope 2 by means of radial links 3; it carries the stator vanes 11 and between the crowns of blades, friction strips 12, made of a wear material, called "abradable", and on which the blade ends of the rotor blades are likely to rub. r.

The stator vanes 11 carry at their end closest to the axis, means (not shown) ensuring sealing with the rotor.

The inner envelope 1 consists of two identical half-ferrules 1a and 1b.

Each half-ferrule is limited upstream and downstream by a radial flange 1c and 1d respectively. These flanges cooperate respectively with flanges 42a of the low pressure casing 4 upstream and 51a of the diffuser casing 5 downstream. The flanges 42a and 51a have an annular groove 42b and 51b respectively which receive a seal 42c and 51c respectively, ensuring the tightness of the gas circulation stream.

The external face of each half-ferrule 1a 1b comprises two rows of yokes respectively 1i and 1j regularly spaced apart peripherally and on which the feet of the links 3 are articulated by means of pins 6.

The outer casing 2 consists of a cylindrical ferrule comprising on its internal face two rows of ears respectively 2a and 2b, regularly spaced and on which the heads of the rods 3 are articulated by means of another series of pins 6.

The yokes 1i, 1j and the ears 2a, 2b, are arranged so that there is in the same plane passing through the axis of the machine: a yoke 1 a yoke 1j, an ear 2a, and an ear 2b .

Thus, the yokes of the same pair 1 i, 1j can be crossed by the same pin 6a. Similarly, the ears of the same pair 2a, 2b can be crossed by the same pin 6b.

The outer casing 2 has on its outer face, in line with the rows of ears 2a, 2b, an upstream flange 2c and a downstream flange 2d comprising holes 2 and 2 f respectively.

These flanges are fixed by bolts 2e, 2f respectively to the downstream flange 4a of the low pressure compressor casing 4 and to the upstream flange 5a of the diffuser casing 5.

The low pressure compressor casing 4 is a double skin casing, 41 and 42.

The external skin 41 comprises, in addition to the flange 4a, an internal flange 4b which axially locks the hinge pins 6b.

The internal skin 42 has a flange 42a which comes to bear by its seal 42c on the flange 1c of the internal half-ferrule.

It also comprises a row of bores 43 arranged between the stator vanes through which the air samples intended for supplying the heating ramps 7a, 7b are taken. 7c and 7d of the outer envelope 2.

The heads of the links 3 are articulated on the ears 2a-2b by means of the pins 6b. The holes made in the heads or feet of the connecting rods, in the yokes 1i, 1j or in the ears 2a 2b, can receive eccentric sockets 6c and 6d respectively, in order to facilitate the mounting of the pins and compensate for the misalignment of the drilling in the event of stacking out of tolerance for manufacturing defects.

The two links 31, 32 located on either side of the 12 o'clock position of the half-ferrule 1a (see FIG. 2) and on both sides of the 6-hour position of the half-ferrule 1b are larger than the others and oriented on converging directions; this arrangement constitutes for each half-ferrule a fixed point from which the peripheral expansions develop.

The two converging links, on each half-ferrule, can be replaced by a system of mechanical stops not shown in the drawing, playing the same role as the links.

The operation of the mechanical structure which has just been described is established in the manner developed below.

The compressor casing according to the invention is in the form of two concentric cylindrical casings 1 and 2 linked to each other by radial rods 3 articulated at their two ends; the inner casing 1 consists of two half-ferrules 1a and 1 linked by their respective lateral edges forming planes of sliding but watertight joints.

Under the adaptation conditions, for example when cruising, the two cylindrical envelopes 1 and 2 expand by an equal radial value which is a function of their diameters and of their respective expansion coefficients. The connecting rods 3 themselves expand by the same amount.

The radial expansion of the envelopes 1 and 2 and of the links 3 has been calculated so that in steady state it equals the sum of thermal or centrifugal expansions affecting the blades and the compressor discs. The clearances between the ends of the rotor blades and the friction bands are thus maintained at their optimum value without it being necessary to maintain the rate of heating of the outer casing 2 in the ramps 7a to 7d.

The inner envelope 1 has expanded under the influence of the temperature of the vein on the one hand and on the other hand under the influence of the tensile forces exerted by the outer envelope 2 by means of the rods 3 ; But. at equilibrium, the expansions of the two envelopes 1 and 2 are equal, the links 3 are not subjected to any tensile force, the clearances are kept at their optimum value without it being necessary to maintain the heating of the envelope exterior 2;

There is thus obtained a noticeable improvement in the efficiency of the machine on the one hand, by a reduction in aerodynamic losses at the ends of the blades and on the other hand by a reduction in compressor levies, from which an improvement in specific consumption results.

Control of games under transient conditions roofs are obtained in the manner described below. In the acceleration condition (take-off for example) air is taken at 300 ° C, upstream of the HP compressor and this air is directed into the ramps 7a to 7d, from where it is injected over all the periphery of the outer envelope 2.

This expands more quickly and exerts on the inner envelope 1, via the connecting rods 3 as many tensile forces which act as as many jacks and accelerate the expansion of the inner envelope 1.

• Cette hétérogénéité des dilatations entraîne deux sortes de défauts :
  • - ouverture des plans de joint
  • - déformation en polygone des demi-viroles du fait qu'elles présentent entre les chapes des zones de moindre résistance.

In fact, due to the presence of two mechanical stops or two converging links 31-32, located at 12 o'clock on the half-ferrule 1a and at 6 o'clock on the half-ferrule 1 b the dilations of the half-ferrules are not not homogeneous and cross as one moves away from these stops;

• This heterogeneity of dilations leads to two kinds of defects:
  • - opening of the joint planes
  • - deformation in polygon of the half-ferrules due to the fact that they present zones of least resistance between the yokes.

The inner envelope 1 takes the form of a polygon circumscribed to the initial perfect circle.

It should be noted, however, that these deformations are extremely reduced due to the fact that the amplitude of the expansions is small (of the order of a few tenths of a millimeter) and that consequently the oligocyclic stresses to which the non-negligible envelopes are subjected.

In the deceleration condition, it suffices to partially restore the power supply to the ramps 7a to 7d so that the outer casing 2 follows the rapid retraction of the rotor with a certain delay. The resulting increase in play affects the performance only in a negligible way but above all, it constitutes a safety reserve against the destruction of the abradable in the event of a sudden re-acceleration.

Claims (4)

1. Turbo-engine housing associated with a device for adjusting the clearance between rotor and stator as a result of the thermomechanical action of the casing of the stator, comprising an outer casing (2) consisting of a cylindrical ring and an inner casing (1) to which the stator blades are fastened, the said inner and outer casings (1, 2) respectively having fastening means (1 i, 1j, 2a, 2b) which interact via connection means (3), ventilation means (7), on the other hand, being provided round the outer casing (2) in order to ensure the thermal control of the latter, characterized in that the inner casing (1) consists of two deformable half-rings (ia-ib) having, on their outer face, two annular flanges (1c-1d) ensuring sealing rotative to the housings located upstream (4) and downstream (5), and in that the connection means (3) between the inner casing (1) and the outer casing (2) consist of radial links (3) articulated, on the one hand, on two rows of forks (1 i, 1j) of the inner casing (1) and, on the other hand, on two rows of inner lugs (2a, 2b) of the outer casing (2).

2. Turbo-engine housing according to Claim 1, characterized in that the connecting links (3) are articulated on the forks (1 i. 1 and on the lugs (2a. 2b) via pins (6a. 6b) and eccentric bushes (6c. 6d).

3. Turbo-engine housing according to one of Claims 1 or 2, characterized in that the pairs of links (31-32) arranged in the 12 o'clock positions of the first half-ring (1a) and in the 6 o'clock positions of the second half-ring (1 b) are oriented in converging directions.

4. Turbo-engine housing associated vith a device for adjusting the clearance between rotor and stator, according to any one of the preceding claims, characterized in that the ventilation means consist partially of orifices (43) made between. the straightening blades of a stage of the highpressure compressor, the said orifices (43) communicating with a chamber formed between the two casings (41-42) of the compressor and, from there, towards at least one toroidal ramp (7a, 7b, 7c, 7d) arranged round the outer casing.

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