WO2011151602A1

WO2011151602A1 - Method and system for controlling the clearance at the blade tips of a turbine rotor

Info

Publication number: WO2011151602A1
Application number: PCT/FR2011/051261
Authority: WO
Inventors: Damien Bonneau; Marc Croixmarie; Franck Roger Denis Denece; Bruno Robert Gaully
Original assignee: Snecma
Priority date: 2010-06-03
Filing date: 2011-06-01
Publication date: 2011-12-08
Also published as: FR2960905A1; BR112012030635A2; CN103003529A; EP2576994A1; CA2801193A1; RU2012157775A; CN103003529B; US20130177414A1; FR2960905B1; RU2566510C2

Abstract

The invention relates to a method for controlling the clearance (38) between the tips of mobile blades of a turbine rotor of an aeroplane gas-turbine engine and a turbine shroud of an outer casing surrounding the blades, the method consisting of controlling, according to the operating speed of the engine, a valve arranged in an air conduit opening at a compressor stage of the engine and leading into a control housing arranged around the outer surface of the turbine shroud and supplied with air coming only from said compressor stage. The valve is opened in order to cool the turbine shroud during a high-speed operating phase (TO+CL) which corresponds to the take-off and climb phases of an aeroplane propelled by the engine and during a nominal-speed phase (CR) following the high-speed phase and corresponding to the cruise phase of the aeroplane. The invention also relates to a system for implementing such a method.

Description

Method and system for driving the game at the top of turbine rotor blades

Background of the invention

The present invention relates to the general field of turbomachinery turbines for aeronautical gas turbine engines. It aims more precisely the control of the game between, on the one hand, the tips of moving blades of a turbine rotor and, on the other hand, a turbine ring of an outer casing surrounding the blades.

To increase the performance of a turbine, it is known to minimize as much as possible the clearance between the top of the blades of the turbine and the ring that surrounds them. This game at the top of the blade is dependent on the differences in dimensional variations between the rotating parts (disk and vanes forming the turbine rotor) and the fixed parts (external casing including the turbine ring that it includes). These dimensional variations are both of thermal origin (related to variations in the temperature of the blades, the disk and the casing) and of mechanical origin (in particular related to the effect of the centrifugal force exerted on the rotor of turbine).

To minimize this game, it is known to use active steering systems. These systems generally operate by directing on the outer surface of the turbine ring fresh air taken at a compressor and / or blower of the turbomachine. The fresh air sent to the outer surface of the turbine ring has the effect of cooling the latter and thus limiting its thermal expansion. Such active control is controlled for example by the full authority control system (or FADEC) of the turbomachine and is a function of the various operating modes thereof.

The document EP 1,860,281 describes an example of an active control system in which air taken from the fan of the turbomachine is used to cool the turbine ring during the phases of cruising flight. Such a system however has many drawbacks as its large size in the nacelle of the turbomachine, the strong dependence of its efficiency aerothermal conditions existing in the nacelle, and the performance slopes related to the removal of air flow at the level of the blower that does not participate in the push. Another known active control system consists in taking air at two different stages of the compressor of the turbomachine and modulating the flow rate of each of these samples to adjust the temperature of the mixture to be directed on the external surface of the turbine. turbine ring. Although effective, such a system has the disadvantage of using a complex and cumbersome valve to modulate the flow of cooling air. In particular, in the case of an application to a small turbomachine, the use of such a valve is not optimal in terms of weight and cost.

Object and summary of the invention

The main object of the present invention is thus to overcome such drawbacks by proposing an active control solution that is minimalist in terms of weight and cost.

This object is achieved by means of a game control method between, on the one hand, the tips of moving blades of a turbine rotor of a gas turbine engine, and, on the other hand, a turbine ring of an outer casing surrounding the blades, the method of controlling, according to the operating speed of the engine, a valve disposed in an air duct opening at a compressor stage of the engine and opening into a control box disposed around the outer surface of the turbine ring, said control box being supplied with air from only said compressor stage. According to the invention, the valve is open to cool the turbine ring of the outer casing during a high-speed phase corresponding to the takeoff and ascent of an aircraft propelled by the engine and during a phase nominal speed succeeding the high regime phase and corresponding to the cruising flight of said aircraft.

Correlatively, the subject of the invention is a game control system between, on the one hand, vertices of moving blades of a turbine rotor of a gas turbine engine and on the other hand , a turbine ring of an outer casing surrounding the blades, the system comprising an air duct intended to open at a compressor stage of the engine and to open into a control box disposed around the surface external of the turbine ring and intended to be supplied with air coming solely from said compressor stage, a valve arranged in the air duct, and a circuit adapted to control the valve to open during a high-speed phase corresponding to the takeoff and ascent of an aircraft propelled by the engine and during a phase of nominal speed following the high speed phase and corresponding to the cruising flight of said aircraft.

High speed means here a higher speed than the rated operating speed of the turbomachine. In a gas turbine engine, the rated speed is the airborne cruising speed adopted during most of the flight, and the high speed is a higher speed than the flight cruising point used in particular during the take-off and climb phase of the aircraft.

The invention is remarkable in that it uses a single air intake at the compressor that ensures a pressure differential sufficient to ensure a fresh air flow to the turbine ring (the control box does not present only one air source). In addition, this air taken from the compressor is discharged only in the control box and does not supply other engine components. Also, when the valve is closed, no air is actually drawn into the compressor which limits the pressure losses within it. In this way, it is possible to minimize the air ducts and air intakes in the engine, and to use a valve as simple as possible (in terms of structure and control). This results in a low cost and low mass control system.

Preferably, the valve is closed during a phase of idling in flight succeeding the phase of nominal speed and corresponding to the approach phase of the aircraft before landing.

Still preferably, the valve is closed during an idling phase on the ground preceding the phase rated speed and corresponding to the taxi phase of the aircraft before takeoff.

The idling speed is a lower speed than the rated operating speed of the turbomachine. In a gas turbine engine, the idle speed is therefore a lower speed than the cruising point in flight.

Advantageously, the flow of air opening towards the outer surface of the turbine ring is progressively decreased during a transition between the high-speed phase and the nominal-speed phase. In the case of a valve with a controlled position, such a gradual decrease in the air flow rate can be obtained by progressively closing the valve. In the case of an on-off valve, the progressive decrease of the air flow can be obtained by alternating the opening and closing phases of the valve.

The invention further relates to a gas turbine engine comprising a gaming control system as defined above.

Brief description of the drawings

Other features and advantages of the present invention will emerge from the description given below, with reference to the accompanying drawings which illustrate an embodiment having no limiting character. In the figures:

- Figure 1 is a schematic view in longitudinal section of a gas turbine engine engine equipped with a control system according to the invention;

FIG. 2 is an enlarged view of the engine of FIG. 1 showing in particular the high-pressure turbine thereof;

FIG. 3 shows curves illustrating a variation in the operating speed and the corresponding radial-dimensional variations of the rotor and the stator in a gas turbine engine; and

FIGS. 4A to 4C show representative curves of examples of control of an on-off valve used in an exemplary embodiment of the control system according to the invention.

Detailed description of an embodiment

FIG. 1 schematically represents a turbojet engine 10 of the double-flow, double-body type to which the invention applies in particular. Of course, the invention is not limited to this particular type of gas turbine engine.

In a well known manner, the turbojet engine 10 of longitudinal axis XX comprises in particular a fan 12 which delivers a flow of air into a primary flow stream 14 and into a secondary flow stream 16 coaxial with the vein primary flow. Upstream downstream in the direction of flow of the gaseous flow therethrough, the primary flow flow channel 14 comprises a low-pressure compressor 18, a high-pressure compressor 20, a combustion chamber 22, a high-pressure turbine 24 and a low pressure turbine 26.

As shown more specifically in FIG. 2, the high-pressure turbine 24 of the turbojet comprises a rotor formed of a disk 28 on which a plurality of blades 30 arranged in the flow vein of the primary stream 14 are mounted. rotor is surrounded by a turbine casing 32 comprising a turbine ring 34 carried by an outer turbine casing 36 by means of fixing struts 37.

The turbine ring 34 may be formed of a plurality of adjacent sectors or segments. On the inner side, it is provided with a layer 34a of abradable material and surrounds the vanes 30 of the rotor, making with the apices 30a thereof a clearance 38.

According to the invention, there is provided a system for controlling the clearance 38 by decreasing, in a controlled manner, the internal diameter of the outer turbine casing 36.

For this purpose, a control box 40 is arranged around the outer turbine casing 36. This housing receives fresh air by means of an air duct 42 opening at its upstream end in the flow duct. primary flow at one of the stages of the high pressure compressor 20 (for example by means of a scoop known per se and not shown in the figures). In particular, the control unit is supplied with air only by this single sampling at the compressor (there is no other source of air supplying the housing).

The fresh air circulating in the air duct 42 is completely discharged on the outer casing of turbine 36 (for example by means of a multiperforation of the walls of the control box 40) causing a cooling thereof and therefore a decrease in its internal diameter. In particular, the air taken from the stage of the high-pressure compressor does not supply other organs than the control box. As shown in FIG. 1, a valve 44 is disposed in the air duct 42. This valve is controlled by the full authority regulation system (or FADEC) 46 of the turbojet engine as a function of the operating speeds of the turbojet engine.

By controlling the valve 44 according to the different flight phases of the aircraft, it is thus possible to vary during a mission the internal diameter of the outer casing of turbine 36 - and therefore the internal diameter of the ring of turbine 34 - and therefore to control the clearance 38 existing between the turbine ring and the top of the blades 30 of the rotor of the high-pressure turbine.

FIG. 3 represents the variation of this game 38 during a typical mission of the airplane as it is obtained by the system and the control method according to the invention.

In this figure are represented various curves, namely: a curve 100 illustrating the rotational speed of the high-pressure body of the turbojet, a curve 200 illustrating the external diameter of the rotor of the high-pressure turbine (disk 28 and blades 30), a curve 300 illustrating the internal diameter of the stator of the high-pressure turbine (outer casing of turbine 36 and turbine ring 34) as controlled by the control system according to the invention, and a curve 300a (in dotted lines) illustrating the internal diameter of the stator as it would be in the absence of control.

These different curves are represented as a function of the different operating phases of the turbojet representative of a typical mission, namely: an idling phase GI ground (corresponding to the taxi phase of the aircraft before takeoff), followed by a high-speed TO + CL phase (corresponding to the take-off and ascent of the aircraft), followed by a nominal CR phase (corresponding to the flight cruising point regime), followed by an IF phase idle flight (corresponding to the approach of the aircraft before landing), followed by a REV phase of thrust reversal (corresponding to the braking of the aircraft on the ground), followed by a new phase of idling GI on the ground.

As represented by the curve 100, it will be noted that the high-speed phase TO + CL occurs at a higher speed than the nominal speed of the turbojet engine (CR phase). The idling phases (on the ground and in flight) take place at speeds below the rated speed of turbojet engine, the idling phase IF flight having a regime also lower than that of the phase id id on the ground. It should also be noted that the nominal CR phase is adopted during most of the mission.

The control of the valve 44 according to the invention is as follows:

- During phase GI ground idle, the valve is closed and the internal diameter of the stator remains substantially unchanged. During the transition phase between the GI phase and the TO + CL phase, the valve is always closed and the stator is free to expand under the effect of hot air in the primary flow flow vein. During this same transition phase, it will be noted that the rotor begins to expand mechanically under the effect of the centrifugal force.

- During high-speed phase TO + CL phase, the valve 44 is open, which cools the stator and, consequently, decreases its internal diameter. The game is weak and greatly reduced compared to what it would be in the absence of steering. This results in a strong performance gain during this phase. Note that the opening of the valve occurs more precisely once the pinch point has passed, that is to say once reached the transition point between the mechanical expansion phase of the rotor and the thermal expansion phase of the rotor .

- During the phase CR nominal speed, the valve 44 is kept open to cool the stator and thus obtain a small clearance, which is beneficial to the performance of the engine.

It will be noted that at the end of the TO + CL phase, during the transition to the nominal phase CR, the air flow directed towards the stator is progressively reduced. It will also be noted that during the CR phase, this same airflow may be greater or less depending on the flight altitude. Different ways of achieving a decrease in air flow will be detailed later in connection with Figure 4.

During the flight idling phase FI, the valve 44 is closed again so that the stator is free to expand under the effect of the hot air flowing in the primary flow flow vein. The game opens during this phase of approaching the aircraft before landing in order to avoid an unforeseen situation requiring a relaunch (and therefore a high reversion). Finally, during the phases of thrust reversal REV and ground idling GI, the valve 44 is kept closed.

Different valve structures can be used for the implementation of such play control. The valve 44 can be of the regulated flow type (by FADEC control), which facilitates the control of the air flow directed towards the valve. stator notably at the end of the TO + CL phase and in the CR phase.

However, for reasons of cost and reliability, it is advantageous to use an all-or-nothing valve. To obtain a modulation of the flow of air directed towards the stator with this type of valve, it is possible to alternate the phases of opening and closing of the valve.

FIGS. 4A to 4C represent different rates that can be obtained with such an on-off valve control. In these figures are represented crenellated signals illustrating, on the ordinate, the position of the valve (0 = open valve and 1 = closed valve), and on the abscissa, the time t. The curves Ca to Ce illustrate the average air flow delivered by the valve according to the different opening times thereof: the longer the valve is open (at each opening cycle), the higher the average air flow rate. delivered by the valve is high (and vice versa).

In this way, it is understood that by playing on the one hand on the opening frequency and on the other hand, on the opening / closing duty cycle of the valve, it is possible to obtain a variation of the average flow rate of the valve. the air directed towards the stator.

Different all-or-nothing valve architectures are well known to those skilled in the art and will not be described here. Preferably, one will choose an electrically controlled valve which would remain in closed position in the absence of power supply (thus, it is ensured that the valve remains closed in the event of a control fault).

Claims

1. Game control method (38) between, on the one hand, tips of blades (30) of a turbine rotor of a gas turbine engine and on the other hand, a turbine ring (34) of an outer casing (36) surrounding the blades, the method of controlling, depending on the operating speed of the motor, a valve (44) disposed in an air duct (42); opening at a compressor stage (20) of the motor and opening into a control box (40) disposed around the outer surface of the turbine ring, said control box being supplied with air coming solely from said stage compressor, characterized in that the valve is open to cool the turbine ring (34) of the outer casing (36) during a high-speed phase corresponding to the take-off and ascent of an aircraft propelled by the engine and during a nominal regime phase succeeding the high-speed phase and corresponding to the cruising flight of udit plane.

2. The method of claim 1, wherein the valve is closed during a phase of idling in flight succeeding the phase of nominal speed and corresponding to the approach phase of the aircraft before landing.

3. Method according to one of claims 1 and 2, wherein the valve is closed during a ground idling phase preceding the phase rated speed and corresponding to the taxi phase of the aircraft before takeoff .

4. Method according to any one of claims 1 to 3, wherein the flow of air opening to the outer surface of the turbine ring is gradually decreased during a transition between the high speed phase and the phase of rated speed.

5. The method of claim 4, wherein the valve is a controlled position valve, the gradual decrease in the air flow opening to the outer surface of the turbine ring during the transition being obtained by closing the valve gradually.

6. The method of claim 4, wherein the valve is an on-off valve, the progressive decrease of the air flow opening to the outer surface of the turbine ring during the transition being obtained by alternating the phases of opening and closing of the valve.

7. Game control system (38) between, on the one hand, blade tips (30) of a turbine rotor of a gas turbine engine and on the other hand, a turbine ring (34) of an outer casing (36) surrounding the vanes, the system comprising:

an air duct (42) for opening at a compressor stage (20) of the engine and opening into a pilot housing (40) disposed around the outer surface of the turbine ring and for supplying air from only said compressor stage;

a valve (44) disposed in the air duct; and

a circuit capable of controlling the valve to open it during a high-speed phase corresponding to the takeoff and ascent of an aircraft propelled by the engine and during a nominal speed phase following the engine phase high and corresponding to the cruise flight of said aircraft.

The system of claim 7, wherein the valve is a regulating valve.

The system of claim 7, wherein the valve is an all-or-nothing valve.

A gas turbine engine engine comprising a game control system according to any one of claims 7 to 9.