Device and method for regulating radial clearances at the level of the low pressure turbine

Abstract

The invention relates to a turbomachine (1) comprising a high-pressure turbine (6) and a low-pressure turbine (7), the turbomachine being equipped with an air distribution network on the casing (18) of the low-pressure turbine (7), the turbomachine comprising one or more cooling air ducts (22) and one or more hot air ducts, as well as a selector (30) for choosing the air supplying the distribution network (21). Figure to be published with the abstract: [Fig. 3]

Description

Title of the invention: Device and method for regulating radial clearances at the level of the low pressure turbine Technical field of the invention

[0001] The invention relates to a device and a method for regulating clearances at the low pressure turbine of a turbomachine, in particular the radial clearances between the blades of the low pressure turbine and a casing surrounding said low pressure turbine. State of the prior art

[0002] [Fig.l] represents a double-flow, double-body turbomachine 1. The axis of the turbomachine is referenced X and corresponds to the axis of rotation of the rotating parts.

[0003] The turbomachine 1 comprises, from upstream to downstream in the direction of gas flow, a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6 and a low-pressure turbine 7.

[0004] The air from the blower 2 is divided into a primary flow 8 flowing in a primary annular vein 9, and a secondary flow 10 flowing in a secondary annular vein 11 surrounding the primary annular vein 9.

[0005] The low pressure compressor 3, the high pressure compressor 4, the combustion chamber 5, the high pressure turbine 6 and the low pressure turbine 7 are arranged in the primary vein 9.

[0006] The rotor of the high-pressure turbine 6 and the rotor of the high-pressure compressor 4 are rotationally coupled via a first shaft 12 so as to form a high-pressure body.

[0007] The rotor of the low pressure turbine 7 and the rotor of the low pressure compressor 3 are coupled in rotation by means of a second shaft 13 so as to form a low pressure body, the fan 2 being able to be connected directly to the rotor of the low pressure compressor 3 or else by means of an epicyclic gear train for example.

[0008] As can be better seen in [Fig.2], the low-pressure turbine 7 comprises in particular different successive stages comprising moving wheels 14, or rotor, and fixed parts, also called distributors 19 or stator. The moving wheel comprises a disc 15 at the level of which blades 16 are mounted. The ends of the blades 16 are surrounded by a fixed ring 17 composed of a part made of abradable material, said ring 17 being fixed to the casing 18 of the turbine. The distributors 19, located downstream of the moving wheels 14, and the rings 17 are mounted on the casing by means of flanges or hooks 20 extending from the radially internal surface of the casing 18.

[0009] In order to guarantee a high efficiency of the turbomachine, it is necessary to maximize the air flow passing through the moving wheels 14 of the different stages, that is to say to limit the leaks between the radially external ends of the blades 16 and the ring 17 composed of a part made of abradable material, easily machinable by the tip of the blades. For this, it is necessary to control the clearance (denoted J on an enlarged part of [Fig.2]) at this interface between the blades 16 and the internal surface 17.1 of the ring 17, this clearance J being highly dependent on the temperature of the casing 18. Nevertheless, the primary air flow from the combustion chamber 5 has a very high temperature and heats the parts located downstream, such as the fixed and moving parts of the low pressure turbine 7.In order to control the aforementioned play and to avoid any premature degradation of the various fixed and moving parts of the low pressure turbine 7, it is necessary to provide effective cooling devices which can be easily integrated into the environment of the turbomachine.

[0010] Such a device for cooling the casing 18 of the low-pressure turbine 7 comprises an air distribution network 21 comprising collector boxes extending axially and receiving an air flow and a plurality of tubes opening into one of the collector boxes and extending circumferentially around a part, or all, of the external surface of the casing 18.

[0011] When the turbomachine is operating, a flow of cold air is injected into the cooling device to regulate the expansion of the casing 18 and thus control the clearance J between the radial ends of the blades and the casing 18. However, the turbomachine does not include any means for actively controlling the clearances of the low-pressure turbine when the turbomachine, or engine, is stopped.

[0012] When the engine is stopped, the stator 19 and the casing 18 tend to cool more quickly than the rotor 16, which risks reducing the radial clearances at the low-pressure turbine, up to the contact potential. Generally, the clearances return to their initial position after the engine has completely cooled, i.e. after approximately 6 hours.

[0013] Consequently, in the event of restarting before these 6 hours, the rotation of the engine may be blocked by these potential contacts.

[0014] Furthermore, when the engine has just completed an operating cycle and is still hot and therefore comes to a standstill, the thermal shrinkage times of the rotor part and the stator part differ. Thus, if the engine must be restarted while the initial position of the parts is not in place, a phenomenon known as "rotorlock" or rotor blockage may occur where the rotor part and the stator part are blocked or partially blocked relative to each other. The occurrence of this phenomenon can be detrimental to a company operating the turbomachine. If the rotor is blocked, then it is preferable to wait minutes or even hours in order to be able to restart.

[0015] Furthermore, when designing the turbomachine, this constraint leads to leaving a minimum of radial clearance while the aim is to avoid air flow leaks to maximize the performance of the low pressure turbine.

[0016] In order to overcome this problem, a specific running-in phase has been developed, called "Warm Start". This is a procedure which aims to wear out the radial clearances after having carried out a 45-minute engine stop. This procedure is long and expensive, in addition to being restrictive.

[0017] Furthermore, if the stator cools more quickly radially during the engine stop phase than the rotor, this is also the case axially. A hot restart can therefore lead to rotor / stator contacts which can lead to a breakage of the moving blade in the most extreme cases.

[0018] The invention aims to remedy at least one of these drawbacks. Summary of the invention

[0019] For this purpose, the invention proposes a turbomachine comprising: a primary vein crossed by a primary flow and comprising: a high-pressure compressor; a combustion chamber; a high-pressure turbine; and a low-pressure turbine comprising a moving wheel comprising an annular row of blades and an annular casing comprising an internal surface facing the blades, a radial clearance being defined between the end of the blades and the internal surface; and a device for regulating the radial clearance comprising: at least a first air sampling duct in the primary vein upstream of the combustion chamber; at least a second air sampling duct in the primary vein downstream of the high-pressure compressor; an air distribution network configured to bring the air radially outwardly to the annular casing;a selector configured to select the first conduit(s) and / or alternatively select the second conduit(s) to supply the distribution network.;

[0020] By this system, it is possible to regulate the temperature of the casing and thus obtain a desired and / or sufficient radial clearance to avoid any blockage during a hot restart. The first duct(s) allow cold air to be taken in while the second duct(s) allow hot air to be taken in.

[0021] It is thus possible, in particular by mixing the two air sources and controlling the flow rate of each source, to obtain a desired temperature. Alternatively or in addition, cycles of selection of one source or the other source make it possible to achieve a desired temperature in the distribution network.

[0022] According to another aspect, the at least one first duct takes air upstream of the high-pressure compressor. For example, this cooling air take-off duct may open at the primary annular vein at a low-pressure compressor. This cooling air is used, for example, to supply the air distribution system when the turbomachine is in operation to cool the low-pressure turbine casing. This cooling air is also available to regulate the radial clearance of the turbines during operation or when the turbomachine is stopped.

[0023] According to another aspect, the at least one second conduit draws air downstream of the combustion chamber and upstream of the low-pressure turbine.

[0024] According to another aspect, the turbomachine comprises means for measuring the sampling pressure at the location where the at least one first conduit and where the at least one second conduit take the air, and means for measuring the distribution pressure in the distribution network.

[0025] According to another aspect, the turbomachine comprises a ventilation member arranged in the at least one first duct and / or in the at least one second duct, and configured to actively propel the air into the respective duct when the distribution pressure is higher than the bleed pressure. The control of the ventilation member may be conditioned by the fact that the pressure difference is lower than a threshold: for example, if the distribution pressure is lower than the bleed pressure but the difference is lower than a given threshold, the ventilation member may be made active to guarantee the flow of air.

[0026] The ventilation member may be a fan controlled by a computer, in particular as a function of the temperature of the casing and / or the blades of the low-pressure turbine. The ventilation member may be configured to increase the pressure of the air taken from the upstream part.

[0027] According to another aspect, the air sampling duct(s) comprise(s) a closure member, the closure member being switchable between an “open” position allowing air sampling, and a “closed” position prohibiting air sampling. Advantageously, the closure member can provide intermediate positions, regulating (limiting) the flow rate passing through the ducts.

[0028] According to another aspect, the turbomachine comprises a computer capable of detecting a stopping phase of said turbomachine and controlling the shut-off member and / or the selector and / or the ventilation member.

[0029] According to another aspect, the computer is connected to means for measuring the temperature of the casing of said low-pressure turbine. Thus, the flow rate or pressure of air taken upstream of the low-pressure turbine can be regulated by the computer, by acting on the selector and / or on the opening of the shut-off member and / or on the actuation of the ventilation member, for example as a function of the temperature of the casing.

[0030] The invention also relates to a method for implementing a turbomachine. as described above, the method comprising regulating, while the turbine engine is stopped, the radial clearance between the blade tips of the low-pressure turbine and the annular casing by controlling the selector in order to select the air source for supplying the distribution network with air at the desired temperature.

[0031] By "operating state", it is meant that the rotors of the turbomachine are in motion. By "stopped state", it is meant that the rotors are stationary.

[0032] According to another aspect, the method comprises activating a ventilation member in the conduit(s) to ensure a flow of air from the sample to the distribution network.

[0033] When the turbomachine is stopped, the selector and / or the ventilation members and / or the shutters can be controlled to obtain a target radial clearance. This clearance can be obtained by regulating the temperature of the casing. The temperature can be detected or estimated empirically, the cooling curves of each of the elements of the turbomachine being able to be known by experiments. Brief description of the figures

[0034] [Fig-1] represents an axial sectional view of a dual-flow turbomachine of the art prior,

[0035] [Fig.2] represents an axial sectional view of a part of the turbomachine of the prior art, illustrating in particular the low pressure turbine,

[0036] [Fig.3] represents an axial sectional view of a turbomachine. Detailed description of the invention

[0037] Figures 1 and 2 have been discussed above.

[0038] With reference to [Fig. 3], the turbomachine 1 is equipped with an air distribution system in order to maintain the temperature of the casing 18 and to reduce its cooling compared to the cooling of the blades 16 of the moving wheel, in particular when the turbomachine is stopped.

[0039] The distribution system comprises one or more air cooling sampling duct(s) 22 fluidly connecting the secondary annular vein 11 to the distribution network 21. When the turbomachine 1 is in operation, the air is sampled from the primary air flow 9, in particular circulating at the low-pressure compressor 3 and is conveyed to the distribution network 21. The air sampled from the primary air flow 9 circulates in the tubes surrounding the casing 18. This air is injected onto the external surface of the casing 18 through orifices provided in the tubes and directed towards the casing 18. Thus, when the temperature of the moving wheels and the distributors increases, which reduces the radial clearances between the casing 18 and the blades of the moving wheels and the distributors, the distribution network 21 makes it possible to regulate the di rotation of the casing 18 and thus control the clearance between the radial ends of the blades and the casing 18.

[0040] The duct 22 also comprises a ventilation member 26 for extracting air from the low-pressure compressor stream 3 and directing it towards the distribution network 21, in particular when the pressure difference between the sampling at the low-pressure compressor 3 and the air distribution network 21 is less than a threshold. The threshold may correspond to the pressure difference between the upstream part and the air distribution system which reduces or no longer allows the sampling of air from the upstream part towards the air distribution system.

[0041] When the turbomachine 1 stops, the stator 19 tends to cool more quickly than the rotor 16, which risks reducing the radial clearances at the level of the low pressure turbine, up to the contact potential.

[0042] In order to regulate the radial clearances and avoid blocking of the low-pressure turbine 7, the turbomachine is configured to send hot air in a controlled manner in order to keep the casing 18 at temperature. This makes it possible to keep the non-contact clearances and the radial clearances at engine stop unchanged throughout the engine stop phase.

[0043] For this, the turbomachine comprises an air heating sampling duct 24 sampling air from the primary vein 9 at the level of the high pressure turbine 6.

[0044] A selector 30 can be controlled to select the air flow (cold or hot, coming from the pipe 22 or the pipe 24) intended to supply the distribution network 21.

[0045] The selector 30 is here schematically represented as a collector interposed between the pipes 22, 24 and the distribution network 21. Other designs are possible. The pipes 22, 24 form inputs of the selector 30 and one or more outputs of the selector 30 supply the distribution network 21.

[0046] The selector 30 may consist of a set of valves or flow limiters, controlled by a computer. The computer can control the selector so that one or more pipes 22, and / or so that one or more pipes 24 deliver air to the distribution network 21. Depending on the temperature and pressure, measured or estimated empirically, at the air sampling level, and at the casing level, the computer can control flow rates and closing / opening of pipes. The control may be dynamic over time. Cycles of opening or closing of the selector or the shutters may be provided.

[0047] For a given turbomachine design, it is possible to know by experimentation the cooling law of each of the elements of the turbomachine and it is therefore not essential to link the control of the selector 30 to a dynamic measurement of the temperatures to obtain a target value of air temperature in the distribution network.

[0048] In addition to the selector 30, the distribution system may comprise a member 23 for closing the air heating sampling duct 24, such as a valve. The closing member 23 may have an “open” position in which the closing member 23 allows air to flow between the high-pressure turbine 6 and the selector or the distribution network 21. The closing member 23 may have a “closed” position in which air is prevented from circulating in the air heating sampling duct 24. The shutter 23 may also assume intermediate positions in which a flow is permitted but limited.

[0049] In a variant not illustrated, the selector 30 is replaced by a set of shutters 23 arranged on each of the conduits 22, 24 and coordinated to deliver an air flow at a target temperature to the distribution network 21.

[0050] A ventilation member 25 may also be arranged at the level of the air heating sampling duct making it possible to extract air from the primary annular vein 9 at the level of the high-pressure turbine 6 and to direct it towards the cooling device 21, in particular when the pressure difference between at the level of the high-pressure turbine 6 and the air distribution system 21 is less than a threshold.

[0051] The computer controlling the selector 30 can also be configured to control the ventilation member 25 and / or the closure member 23.

[0052] In particular, the computer is able to detect a stop phase of the turbomachine 1. The computer then controls the passage of the shutter member 23 to the “open” position and the possible activation of the ventilation member 25. Thus, in the stop phase of the turbomachine, the relatively hot air around the high-pressure turbine 6 makes it possible to regulate the clearances J between the radial ends of the blades and the casing 18. The computer can be connected to means for measuring the temperature of the casing 18 of the low-pressure turbine 7. The flow rate, or the pressure, of air taken from the high-pressure turbine 6 can be regulated by the computer, by acting on the opening of the shutter member 23, as a function of the temperature of the casing 18.

[0053] Furthermore, when the computer detects an operating phase of the turbomachine 1, it can be configured to control the passage of the shut-off member 23 to the “closed” position. The pressurized and relatively cold air at the primary annular vein is taken, in the air cooling take-off duct 22, by pressure difference and feeds the distribution network 21. In particular, the air can be taken at the low-pressure compressor 3. The air taken from the low-pressure compressor 3 makes it possible to accelerate the cooling kinetics d of the casing 18.

Claims

Claims

1. Turbomachine (1) comprising: a primary vein (3, 4, 5, 6, 7) crossed by a primary flow (8) and comprising: a high-pressure compressor (4); a combustion chamber (5); a high-pressure turbine (6); and a low-pressure turbine (7) comprising a mobile wheel (14) comprising an annular row of blades (16) and an annular casing (18) comprising an internal surface (17.1) facing the blades (16), a radial clearance (J) being defined between the end of the blades (16) and the internal surface (17.1); and a radial clearance regulation device comprising: at least one first duct (22) for sampling air in the primary stream upstream of the combustion chamber (5); at least one second duct (24) for sampling air in the primary stream downstream of the high-pressure compressor (4); an air distribution network (21) configured to bring the air radially outwardly to the annular casing; a selector (30) configured to select the first duct(s) (22) and / or alternatively select the second duct(s) (24) to supply the distribution network (21).

2. Turbomachine according to claim 1, in which the at least one first conduit takes air upstream of the high pressure compressor (4).

3. Turbomachine according to claim 1 or 2, in which the at least one second duct takes air downstream of the combustion chamber (5) and upstream of the low-pressure turbine (7).

4. Turbomachine according to one of the preceding claims, comprising means for measuring the sampling pressure at the location where the at least one first conduit (22) and where the at least one second conduit (24) take the air, and means for measuring the distribution pressure in the distribution network (21).

5. Turbomachine according to the preceding claim, comprising a ventilation member (25, 26) arranged in the at least one first duct (22) and / or in the at least one second duct (24), and configured to actively propel the air into the respective duct (22, 24) when the distribution pressure is higher than the sampling pressure.

6. Turbomachine (1) according to the preceding claim, in which the air sampling duct(s) (22, 24) comprise(s) a closure member (23), the closure member being switchable between an “open” position allowing air sampling, and a “closed” position prohibiting air sampling.

7. Turbomachine (1) according to the preceding claim, comprising a computer capable of detecting a stopping phase of said turbomachine (1) and controlling the shut-off member (23) and / or the selector (30) and / or the ventilation member (25, 26).

8. Turbomachine (1) according to the preceding claim, characterized in that the computer is connected to means for measuring the temperature of the casing (18) of said low pressure turbine (7).

9. Method for implementing a turbomachine according to one of the preceding claims, the method comprising regulating, while the turbomachine (1) is stopped, the radial clearance (J) between the blade tips (16) of the low-pressure turbine (7) and the annular casing (18) by controlling the selector in order to select the air source for supplying the distribution network (21) with air at the desired temperature.

10. A method according to claim 9, comprising activating a ventilation member (25, 26) in the conduit(s) (22, 24) to ensure a flow of air from the sample to the distribution network (21).

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