FR2747736A1 - IMPROVEMENTS ON GAS TURBINE ENGINES - Google Patents

Abstract

A gas turbine fin tip clearance control device consists of a hollow thermally responsive control ring 24 to which the fin casings 27 are attached. Inside the control ring are arranged a plurality of perforated segments 29 each of which is provided with a separate fluid supply so that certain portions of the control ring can be preferably expanded.

Description

The present invention relates to gas turbine engines

  and more particularly, to engines comprising a turbo rotor

bine of the non-wrapped type.

  It is well known that, to allow a non-enveloped type turbine to operate with good efficiency, the clearance between the ends of the turbine fins and the ring structure

  adjacent envelope must be kept within strict limits

  fiercely defined. The difficulties of maintaining such clearances have been well known for many years and the problem has actually worsened with the increase in both the size and the operating temperature of the engines at

gas turbine.

  One of the main factors that must be taken into consideration

  ration when designing a satisfactory arrangement lies in the adaptation of the respective diameters of the housing and the turbine to the various temperatures and speeds encountered during the engine operating cycle. It is also necessary to take into account the difference in the expansion coefficients of the materials used in conjunction with the different constraints imposed on them as well as their different speeds.

thermal response.

  It is also to be considered that, in addition to aiming to maintain the smallest possible radial clearance between the respective elements, the design must be able to eliminate the appearance of any interference between the different components during the different

  operating cycles to which the engine is subjected.

  Many different designs have been developed in the past to overcome the problems mentioned above. In a large number of designs, the structure of the casing ring has been made radially movable in order to maintain the play of the tips of the turbine blades. Such displacement can be generated by mechanical, electrical or pneumatic means, designed to operate in response to sensors arranged to monitor and detect the play of the tips of the turbine blades. Systems of a different type have also been devised in which the structure of the envelope ring is controlled in accordance with the expansion and thermal contraction of a control ring. All the devices which have just been mentioned suffer from drawbacks, however: they have proved either to be

  unstable, or present an insufficiently rapid response.

  Furthermore, they were not able to maintain an adequate clearance between all the elements of the turbine rotor, that is to say

  that the envelope ring did not remain circular.

  The object of the present invention is to create a device for controlling the radial clearance at the end of the fins of a gas turbine.

  which substantially eliminates the problems mentioned above.

  According to the present invention, a device for controlling the radial clearance between the ends of the fins of a gas turbine engine rotor and a plurality of associated casing segments, comprises a hollow control ring comprising, located in its hollow interior , a plurality of hollow segments which are designed

  to be supplied with a current of fluid, a conduction path

  of the heat between the plurality of hollow segments and the control ring allowing the fluid to control the temperature of the ring, the fluid serving to control the diameter of the control ring by varying its temperature, so that the radial displacement of the hollow control ring

  and associated envelope segments can be kept sensitive-

  equal to that of the tips of the fins for at least one

part of the engine cycle.

  A plurality of sensors, which detect the play of ends

  fins may be provided in the vicinity of the envelope segments

  and the sensors are designed to indicate variations in said clearance so that the flow of fluid in the hollow segments can be adjusted using a valve or the like to move the control ring and the segments

associated envelope.

  As a variant, the flow rate of the fluid in the hollow segments can be modified in accordance with the movement of the shutter.

  engine throttle control or with other engine parameters.

  The fluid supplied to the control ring may include a certain amount of air from the control section.

  high pressure compression of the engine.

  Preferably, each of the plurality of hollow segments is perforated so that the fluid strikes the interior wall of the hollow control ring in order to adjust the temperature of

this one.

  Additionally, each of the plurality of hollow segments is provided with two fluid inlets, each group of adjacent fluid inlets in adjacent segments being adapted to be supplied with fluid from a common power source. Each common power source is provided with a valve or similar means such that the flow of fluid can be controlled as a function of the play of the tips of fins noted in the vicinity of the hollow segments which are supplied by the source of food. Preferably, the fin rotor comprises a

  gas turbine engine high pressure turbine rotor.

  In order to better understand the subject of the invention,

  an embodiment of this will now be more specific.

  fully described, by way of example only and with reference to the accompanying drawings, in which: - Figure i represents a schematic side view of a gas turbine engine implementing a device according to the present invention, which is indicated in this figure of a

schematically.

  - Figure 2 shows a more cross-sectional view

  detailed taken along line 2-2 of Figure 3.

  - Figure 3 shows a schematic view further enlarged,

  taken in the direction of arrow A in Figure 1.

  According to Figure 1 of the drawings, a gas turbine engine, generally designated by the reference 10, comprises in series in the direction of flow, a blower 12, a medium pressure compressor 13, a high pressure compressor 14 , combustion equipment 15, a high pressure turbine 16, a medium pressure turbine 17 and a low pressure turbine 18, the engine ending in an outlet nozzle 19. The low pressure rotary system, the rotary pressure system medium pressure and the high pressure rotary system are each mounted respectively on the main shafts of the low, medium and high pressure motor 20, 21, 22, each of them rotating in support bearings. A device according to the present invention is indicated diagrammatically at 23, in a position located radially

  the exterior of the high pressure turbine 16.

  The device shown schematically in Figure 1 is shown in detail in Figure 2. It includes a ring

  hollow control 24 which is connected by means of a relative element 25

  flexible hose extending axially, at part 26 of the main motor casing. It will be observed that the use of such a mounting method ensures that the control ring 24 is relatively unaffected either by a displacement or by a change in temperature of the part 26 of the casing, being partly mechanically isolated from that -this. The radially innermost portion of the control ring carries the envelope-carrying segments which serve to carry the envelope segments, one of which is shown at 27. The envelope segments 27 are arranged in the vicinity of the ends of the turbine blades, one of which is shown

  at 28, and define a sealing clearance in the meantime.

  The envelope-carrying segments, one of which is shown at 27a, serve to isolate the control ring 24 from the hot turbine gases. The control ring and the associated structure are bathed in a continuous stream of relatively cold air from the section

engine compression.

  Inside the hollow control ring 24 is arranged

  a plurality of hollow segments, one of which is shown at 29.

  The segments 29 are dimensioned so as to define a gap between their own external surface and the surface of the hollow interior of the control ring 24. The segments 29 are positioned inside the hollow control ring 24 at way of projections

  31, 32 etc ... formed on their outer face.

  Figure 3 of the drawings shows other details of the hollow segments, etc .; however, for reasons of clarity, the ring

  command 24 has been omitted from this figure.

  Two fluid supply tubes 33 are arranged so as to communicate with each of the hollow segments. The tubes of each pair of these fluid supply tubes are arranged to be in communication with a common fluid supply source 34 each of which is supplied with air under high pressure from the high pressure compression section 14 of the engine. The flow rate of each fluid supply source 34 can be individually adjusted by a valve or the like.

not visible in the drawings.

  Between the adjacent ends of each pair of contiguous hollow segments 29 are provided sensors 35 which pass through

  through openings in the control ring 24.

  The sensors are arranged to detect the sealing clearance between

  the turbine fins 28 and the casing segments 27 adjacent.

  The sensors 35 can comprise electrical, optical or pneumatic devices, designed to deliver an electrical signal when a variation in the value of the play of the tips of the fins appears. The electrical signals can therefore be used to adjust the valve controlling the flow of fluid in the elements 34, so that the flow rates can be modified in accordance with the different conditions of play of the fins in order to vary the dimensions of the ring. 24 and as a result of

  move the envelope segments 27.

  Alternatively, the fluid flow rate in the control ring 24 can be changed using control means designed to react in accordance with the settings of the engine gas shutter; However, it is considered that it may also be necessary to provide the fin tip sensors 35 in order to ensure

  adequate play under all operating conditions.

  As previously indicated, during the operating cycle of a gas turbine engine, the components thereof are subjected to variations both in temperature and in mechanical stress, these two types of variations modifying the clearance between the turbine fins 28 and the adjacent casing segments 27. However, it appears that, by precise control of the degree of expansion or contraction to which the control ring 24 is subjected, it is possible to maintain said play within reasonable limits during critical periods of the engine cycle. The engine is obviously designed so that the play of the tips of the fins is at their minimum value when it is in cruising speed. However, it is also important that the engine runs as efficiently as possible,

  especially during "take off" and "climb" periods.

  During periods of "start-up" and subsequent periods of "inactivity on the ground", the turbine blades become elongated due to both thermal expansion and centrifugal force, and this tends to reduce the radial clearances between the ends of fins 28 and the envelope segments 27; However, such a reduction in clearance can be taken into account in a simple manner in the design of the engine by appropriate dimensioning of the parts in relation and by a selection of compatible materials, since it is relatively unimportant that 'there are quite large games

  when the engine is cold and stationary.

  Various variations in the diameter of the turbine blades also appear during other phases of engine operation, such as during acceleration to "take-off" power, acceleration between the "cruising" period and the "climb" and, on landing, between the period

  "approach" and the "reverse thrust" period.

  During these phases, the casing segments 27 and the motor housing undergo a certain expansion due to the thermal effects and to the pressure. However, this expansion does not appear to be sufficient to maintain adequate clearance at the ends of the fins.

  in the absence of the annular control device.

  Harmonization of the respective growth rates of the casing segments 27 of the turbine and of the fins 28 of the turbine, so as to maintain an acceptable clearance during the "take-off" and "climb" periods of the engine cycle is achieved. by harmonizing the rate of expansion of the control ring 24 and that of the structure of the disc and the fins

of the turbine rotor.

  Such harmonization is achieved by providing relatively hot pressurized air from the high pressure compressor 14 via the power sources 34 so that this air passes through the hollow segments 29 and through the perforations 36 to strike the internal wall of the hollow control ring 24, out of making it expand substantially at the same rate as the turbine 28 and its associated disc, etc ...; the clearance at the ends of the fins therefore remains substantially constant by virtue of the fact that the segments

  envelope 27 move in accordance with the control ring 34.

  When the engine finally takes its cruising speed, the air flow through the conduits 33 can be notably reduced and it is considered that certain power sources 34 can

be completely closed.

  It will be observed that, during the operation of the engine, each play sensor 35 constantly detects the play of the ends of the fins in its immediate vicinity and, by means of a control system not shown in the drawings, requires a constant adjustment of the flow rate of fluid through the conduits 33 to maintain the above clearance substantially constant. By varying the fluid flow rates through the different pairs of conduits 33, it is

  thus possible to move a portion of the control ring 24.

  This can have particular advantages in that, under certain operating conditions, slight eccentricities of the turbine relative to the casing or an ovalization may appear. Obviously, this problem is significantly avoided by

  the use of the device according to the present invention.

  It will be observed that this presentation does not give a description

  complete neither the necessary control systems nor the game sensors; However, such devices are readily available, and their realization does not exceed the possibilities of

one skilled in the art.

9 2747736

Claims (8)

Claims:   1.- Device for controlling the radial clearance between the ends of the fins (28) of a gas turbine engine rotor (10) and a plurality of associated envelope segments (27), comprising a hollow control ring ( 24) comprising, situated in its hollow interior, a plurality of hollow segments (29) which are designed to be supplied with a stream of fluid, a heat conducting path (30) between the plurality of hollow segments (29) and the control ring (24) allowing the fluid to control the temperature of the ring, the fluid serving to control the diameter of the control ring by varying its temperature, so that the radial displacement of the control ring hollow (24) and its associated envelope segments (27) can be kept substantially equal to that of the ends of the fins (28) during at least part of the engine cycle.  2. Device according to claim 1, in which a plurality of sensors (35), which detect the play of the ends of the fins (28), are provided in the vicinity of the envelope segments (28), and the sensors (35) are designed to indicate variations in said clearance so that the flow of fluid in the hollow segments (29) can be adjusted by means of a valve or the like to move the control ring and the segments envelope associated.   3.- Device according to claim 1, wherein the fluid flow rate in the hollow segments (29) is modified in accordance with the movement of the gas control flap of the   engine or with other engine parameters.   4.- Device according to any one of claims   previous, wherein the fluid supplied to the control ring (24) includes a certain amount of air from the high pressure compression section of the motor (14). .10 2747736   5.- Device according to claim 1, wherein the plurality of hollow segments (29) are perforated (36) so that the fluid strikes the inner wall of the hollow control ring (24) in order to adjust the temperature of this one. 6.- Device according to claim 1, wherein each of the plurality of hollow segments (29) is provided with two fluid inlets (33), each group of adjacent fluid inlets in adjacent segments being designed to be supplied with fluid from a source common supply (34).   7.- Device according to claim 6, wherein each common power source (34) is provided with a valve or similar means such that the flow of fluid can be controlled according to the play of the tips of fins (28) noted in the vicinity of the hollow segments (24) which are   powered by the common power source (34).   8.- Device according to claim 1, wherein the finned rotor comprises a high turbine rotor   gas turbine engine pressure.