FR3081943A1 - COMPRESSOR FOR A TURBOMACHINE - Google Patents

Abstract

The invention relates to a compressor (4) for a turbomachine, the compressor (4) extending along an axis and comprising a flow stream (3) for the flow of an air flow (F) delimited by a radially internal ferrule (20) and a radially outer shell (21), at least one compression stage (E1, E2), the compression stage (E1, E2) comprising at least one row of rotor blades (11) and at least a row of stator blades (17), located downstream of the row of rotor blades (11) relative to the direction of flow of the air flow (F) within the stream (3), characterized in that it comprises at least one movable shutter (24) mounted at the level of the radially external shell (21) or of the radially internal shell (20).

Description

COMPRESSOR FOR A TURBOMACHINE

FIELD [001] The present invention relates to a compressor for a turbomachine, such as for example a turbojet or an airplane turboprop.

BACKGROUND [002] FIG. 1 represents a turbomachine 1 of the prior art, in particular a turbofan engine.

The air or gas flow flowing through the turbomachine 1 is directed from upstream to downstream, that is to say from left to right in Figure 1. [004] The turbomachine 1, of axis X, conventionally comprises a fan 2 downstream of which extends:

a primary stream 3 in which a primary stream flows, said primary stream passing in particular, in the direction of flow of the primary stream, 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, the primary stream being delimited externally at the level of the turbine by a casing 8,

- a secondary vein referenced 9, in which a secondary flow distinct from the primary flow flows.

The secondary stream 9 is surrounded by a nacelle 10 forming a fairing for the turbomachine 1.

FIG. 2 illustrates a low-pressure compressor 4 of the prior art comprising an annular stream 3 for flow of the air flow or primary stream, and three successive compression stages E1, E2, E3. Each compression stage E1, E2, E3 comprises a part forming a stator and a part forming a rotor. Each rotor has a row of blades 11 extending radially in the vein 3. Each blade 11 of the rotor has a blade 12, forming the profiled part extending in the vein 3, said blade 12 having a radially internal end 13 attached to a foot 14 of the blade 11, integral with a disc 15 of the rotor, and a radially external end 16 also called head.

The stator portion of each compression stage comprises a row of stator vanes 17, forming a rectifier stage, that is to say allowing to straighten the air flow F having passed through the rotor wheel located upstream. As before, each stator blade 17 has a radially internal end 18 called the foot, and a radially external end 19 called the head.

The terms upstream and downstream are defined with respect to the direction of circulation of the air flow F. Furthermore, the terms axial and radial are defined with respect to the axis X of the compressor, which is also the axis of the turbomachine 1.

In operation, the turbomachine is subjected to different operating phases, namely in particular starting phases or partial speed, so-called transient phases and cruising speed phases. A partial operating phase is a phase during which the turbomachine operates at a speed equal to a fraction of the nominal speed of the turbomachine. The cruising speed is generally a speed close to the nominal speed. Finally, a transient operating phase is a phase during which a variation in the operating regime occurs.

[010] Whatever the operating phase of the turbomachine, the pumping phenomenon should be avoided. Such a phenomenon can occur when the pressure difference between the inlet and the outlet of the compressor is too high, creating instabilities also called separations, appearing at the blades of the compressor. Such detachments can occur at the foot or at the head of the stator blades.

The aerodynamic stall occurring then no longer makes it possible to direct the air flow from upstream to downstream, causing a reverse flow of at least part of the air from downstream to upstream .

Such a phenomenon appears when the compressor flow rate becomes too low and / or when the compression rate becomes too high. It will be recalled that the compression ratio is the ratio of the pressure downstream of the compressor to the pressure upstream of the compressor.

[013] Such a phenomenon is harmful for the operation and the efficiency of the turbomachine and can cause damage.

In order to avoid such a phenomenon occurring, in particular in the transient regime phases, the compressor must be designed to have a large pumping margin, that is to say have a high tolerance for different variations in speed, in particular during the different operating phases, without generating a pumping phenomenon. Furthermore, the compressor must be designed to maximize its performance, especially during cruising phases.

In general, the design choices tending to maximize the pumping margin generate a deterioration in the efficiency of the compressor, and vice versa.

In order to limit the appearance of the pumping phenomenon, it is possible to have recourse to the use of relief valves, part of the air flow then being extracted from the vein through the valves, thus penalizing the efficiency of the turbomachine.

Another technical solution making it possible to limit the occurrence of the pumping phenomenon is the use of variable pitch vanes on each stage of the compressor. The implementation of such a technical solution is complex and generates a significant additional cost as well as an increase in the mass of the compressor.

SUMMARY OF THE INVENTION [018] The invention aims to respond to the various aforementioned technical constraints, in a simple and reliable manner.

To this end, the invention relates to a compressor for a turbomachine, the compressor extending along an axis and comprising a flow stream of an air flow delimited by a radially internal ferrule and a radially external ferrule , and at least one compression stage, the compression stage comprising at least one row of rotor blades and at least one row of stator blades, located downstream of the row of rotor blades relative to the direction flow of air flow within the vein, characterized in that it comprises at least one obturator mounted at the level of the radially external shell or of the radially internal ferrule of the vein, said obturator being movable between at least a first position in which said obturator does not extend inside the vein and is flush with the surface facing the vein of the ferrule in which it is mounted, and a second position in which said obturator s extends at least partially within the vein so as to obstruct partially the stopper being pivotally mounted on a fixed part of the compressor.

The shutter, when it is moved to its second position, displaces part of the air flow in the direction of the dawn area in which there is a risk of detachment. Such displacement allows the air flow to be picked up in sensitive areas and thus delays the appearance of the pumping phenomenon. In other words, the displacement of the shutter member for a short period of operation makes it possible to shift the pumping limit favorably and thus increases the pumping margin. It will be noted that, during a period of transient or partial speed, the efficiency of the compressor can be degraded in favor of an increase in the pumping margin.

[021] The compressor may include several shutters regularly distributed over the circumference of the radially internal or external shell.

[022] The or each shutter is mounted at the level of the radially outer shell.

[023] In this case, the shutter allows the air flow to be re-bonded at the level of the root zones of the blade, that is to say at the level of the radially internal ends of the blades. Such a solution can be chosen when the zone generating a risk of pumping, or limiting zone, is the zone located at the foot of the blade.

Each shutter can be mounted at the level of the radially internal ferrule.

[025] In this case, the shutter allows the air flow to be re-bonded at the level of the head zones of the blade, that is to say at the level of the radially outer ends of the blades.

[026] The or each shutter can extend circumferentially over an angular range of between 4 and 90 °.

[027] The minimum value of the above-mentioned angular range can correspond substantially to an inter-blade pitch.

[028] Each obturator can be mounted at the level of the radially outer ferrule, the axis of rotation of each obturator being offset radially relative to the internal surface of the outer ferrule, opposite the vein.

The shutter can be located axially downstream of a first compression stage, and upstream of a second compression stage.

The shutter can also be located between the rotor and the stator of the same compression stage.

It will be noted that, in a compressor, the section of the vein at the first compression stage is greater than the section of the vein at the second compression stage.

At least one obturator can also be movable in a third position in which said obturator is spaced from the vein and does not lie flush with the corresponding ferrule of the vein.

The third position corresponds to the case where the obturator is in the retracted position in the corresponding ferrule, so as to locally increase the section of the vein, by comparison with the first position. The movement of the shutter in this third position allows the air flow to be picked up on the blades located upstream. This increases the pumping margin at the level of the stage directly upstream of the shutter, when this stage is the critical stage concerning the pumping phenomenon. [034] As a reminder, the first position corresponds to the case where the shutter has no influence on the pumping margin or on the efficiency of the compressor.

The second position corresponds to the case where the obturator reduces the section of the vein in the plane passing through the obturator. In this second position, the air flow is glued to the base of the blades located downstream. This increases the pumping margin at the level of the stage directly downstream of the shutter, when this stage is the critical stage concerning the pumping phenomenon.

The invention also relates to a turbomachine comprising at least one compressor of the aforementioned type.

[037] The turbomachine is for example a turbojet or an airplane turboprop.

The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of nonlimiting example with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic view in axial section of a turbomachine of the prior art;

Figure 2 is a half view in axial section of a low pressure compressor of the prior art;

Figure 3 is a schematic half-view of a part of a compressor according to an embodiment of the invention;

Figures 4 and 5 are views of a detail of Figure 3, showing a shutter respectively in the first position and in the second position;

FIG. 6 is a diagram representing the characteristic curve of the evolution of the compression ratio as a function of the flow rate passing through the compressor, for the compression stage situated directly downstream of the shutter;

Figure 7 is a sectional view of a portion of a compressor according to an alternative embodiment of the invention;

Figure 8 is a view along a radial plane illustrating an embodiment of the invention;

Figure 9 is a view corresponding to Figure 8, illustrating another embodiment of the invention;

Figures 10 to 12 are views illustrating a part of a compressor according to another embodiment, respectively in the first position, the second position and the third position of the shutter.

DETAILED DESCRIPTION [039] FIG. 3 represents a part of a high-pressure compressor 4 of a turbomachine 1, such as for example a turbojet or an airplane turboprop. The compressor 4 comprises an air flow stream 3 or primary stream, of generally annular shape and of which only a part is shown here. Said vein 3 has a radially internal annular wall or ferrule 20, a radially external annular wall or ferrule 21, said ferrules 20, 21 being coaxial. As illustrated in FIG. 7, each annular wall or ferrule 20, 21 may consist of several adjacent elements or adjacent ferrules 21a, and delimiting the vein 3, as is known per se.

The internal ferrule 20 is connected to a hub 23, the external ferrule 21 being connected to an external casing 8. Two compression stages E1, E2 of the high-pressure compressor 4 are shown here. The first compression stage E1 is located upstream of the second compression stage E2.

The terms upstream and downstream are defined relative to the direction of circulation of the air flow F within the vein 3.

[041] Each compression stage E1, E2 comprises a movable part forming a rotor and a fixed part forming a stator. The rotor of each stage E1, E2 conventionally comprises a row of rotor blades 11. Each rotor blade 11 comprises a blade 12 and a blade root, separated by a platform. Said platforms internally delimit the air circulation stream 3. The radially inner end 13 of the blade 12 is called the foot area and the radially outer end 16 of the blade 12 is called the head area. The rotor blades 11 are mounted around a disc which is capable of being rotated.

[042] The stator of each compression stage comprises a row of stator blades 17, located downstream of the row of rotor blades. The stator blades form a rectifier capable of straightening the air flow from the row of rotor blades located upstream. Each stator blade 17 has a radially internal end or foot region 18, and a radially external end or head region 19.

[043] In the embodiment shown in Figure 3, it is assumed that the critical area concerning the pumping phenomenon is the foot area of the stator vanes 17 of the first stage E1, detachments of the air flow may appear at level of this area. The dimensioning of the compressor can be carried out so that the limiting zone is the foot zone.

[044] In order to avoid such detachment as well as the appearance of the pumping phenomenon, shutters 24 are mounted at the level of the outer shell 21, axially between the row of rotor blades 11 and the row of blades stator 17. As is better visible in Figures 4 and 5, each shutter 24 is pivotally mounted about an axis 25 extending circumferentially. Said axis 25 is for example located in an upstream and radially internal zone of the obturator 24. Said axis 25 is offset with respect to the radially internal surface 26 of the external shell 21, opposite to the vein 3, c ' that is to say offset towards the outside with respect to said surface 26.

Each shutter 24 is actuated by an actuator illustrated here schematically by a slide link 27 oriented radially. Each shutter 24 can be actuated between a first position (FIG. 4) in which said shutter 24 does not extend inside the vein 3 and is flush with the radially outer shell 21, and a second position (FIG. 5) in which said shutter 24 extends, at least in part, inside the vein 3 so as to partially obstruct it.

[046] The number of shutters 24 may vary depending on the applications. FIG. 8 illustrates for example the case where the compressor 4 comprises four shutters 24 regularly distributed over the circumference of the outer shell

21. FIG. 9 illustrates the case where the compressor 4 has eight shutters regularly distributed around the circumference of the outer shell 21.

[047] Each shutter 24 can extend circumferentially over an angular range of between 4 °, in the case of a shutter 24 located opposite each blade 17, and 90 °, in the case of four shutters 24. The value 4 ° is of the same order of magnitude as an inter-blade pitch.

[048] The length of the pivot axis 25 and the radial position of the axis relative to the outer shell 21 are adapted to the circumferential extension of each obturator 24.

[049] The shutter 24 is preferably devoid of opening and seals the vein 3 whatever its position in operation.

[050] The effect of such a shutter 24 will now be explained with reference to the diagram in FIG. 6.

[051] This diagram represents the characteristic curve of the evolution of the compression ratio Te as a function of the reduced air flow D passing through the compression stage situated directly downstream of the shutter 24, that is to say for the second stage E2.

[052] During the operation of the turbomachine 1, the operating point of this stage E2 moves along the curve C as a function in particular of the reduced speed of this stage E2. The left end of curve C is the pumping limit Lp. The pumping limit Lp has the coordinates (Tcmax, Dmin). In other words, if the compression ratio Te reaches the value Tcmax, or if the air flow rate within the compressor 4 is reduced to the value Dmin, then a pumping phenomenon appears. [053] It is assumed that the point Po, of coordinates (Tco, Do) represents any point of operation of the compressor 4, in which each shutter 24 is in its first position illustrated in FIG. 4. The margin on pumping is the distance separating point Po from the pumping limit Lp. [054] If each shutter 24 is moved to its second position, illustrated in FIG. 5, the operating point is moved to the point Pi, with coordinates (Ti, Di). It can be seen that the distance between Lp and Pi, in other words the pumping margin, is then increased by the displacement of the shutters 24.

[055] The invention illustrates the case where the shutters 24 are arranged at the level of the outer shell 21. It is also possible to arrange the shutters 24 at the level of the inner shell 20, in the case where the separation of the flow of air at the origin of a pumping phenomenon is located in the head zones 19 of the blades 17 concerned.

[056] Furthermore, the means for actuating the shutters 24 may be a system composed of a movable ring around the ferrule, connected by connecting rods to the shutters 24, in the manner of the means for actuating blades to variable timing.

[057] Figures 10 to 12 illustrate another embodiment of the invention. In this embodiment, the shutters 24 are arranged axially between the stator vanes 17 of the first stage E1 and the rotor vanes 11 of the second stage E2. The vein 3 has a generally angled shape. The section S1 of the vein 3 at the level of the first stage E1 is greater than the section S2 of the vein 3 at the level of the second stage E2. S designates the section at the radial plane passing through the shutters 24. The radially internal surface 29 of each shutter 24, that is to say the surface facing the vein 3, has an upstream portion 29a plane s' extending in the extension of the internal surface 26 of the external shell 21 at the level of the first stage E1. Said radially internal surface 29 of each obturator 24 further comprises a flat downstream portion 29b extending in the extension of the internal surface 26 of the external shell 21 at the second stage E2.

[058] The two flat portions 29a, 29b form an angle with respect to each other, for example an angle between -30 and 30 °.

[059] In this embodiment, the shutter 24 is movable between the first position, illustrated in FIG. 10, the second position, illustrated in FIG. 11, and a third position, illustrated in FIG. 12.

In the first position, as before, the internal surface 29 of the shutter 24 is flush with the internal surface 26 of the outer shell 21. In the first position, the shutter 24 has no influence on the margin pumping.

[061] In the second position, as before, the shutter 24 extends at least in part in the vein 3, so as to reduce the section

S. In this second position, the air flow F is glued to the base areas 18 of the blades 11 located directly downstream. This increases the pumping margin at the level of the stage E2 located directly downstream of the shutters 24.

[062] In the third position, said shutter 24 is spaced from the vein 3 and does not lie flush with the corresponding ferrule 21 of the vein 3. It will be noted that each shutter 24 is designed to seal the vein 3 in this third position. In this third position, the section S of the vein 3 is increased, by comparison with the first position. The movement of the shutter 24 in this third position allows the air flow F to be picked up on the blades 17 of the stage E1 located upstream. This increases the pumping margin at the level of the stage E1 located directly upstream of the shutter 24.

[063] The invention is applicable to a high-pressure compressor or to a low-pressure compressor. It should also be noted that the presence of shutters can also make it possible to limit the number of rows of blades with variable setting.

Claims (8)

1. Compressor (4) for a turbomachine (1), the compressor (4) extending along an axis (X) and comprising a flow stream (3) for the flow of an air flow (F) delimited by a radially internal ferrule (20) and a radially external ferrule (21), and at least one compression stage (E1, E2), the compression stage (E1, E2) comprising at least one row of rotor blades (11 ) and at least one row of stator blades (17), located downstream of the row of rotor blades (11) relative to the direction of flow of the air flow (F) within the stream ( 3), characterized in that it comprises at least one shutter (24) mounted at the level of the radially outer shell (21) or of the radially inner shell (20), said shutter (24) being movable between at least a first position in which said shutter (24) does not extend inside the vein (3) and is flush with the facing surface of the vein (3) of the ferrule (20, 21) in which it is my tee, and a second position in which said shutter (24) extends, at least in part, inside the vein (3) so as to partially obstruct it, the shutter (24) being pivotally mounted on a fixed part of the compressor (4). 2. Compressor (4) according to claim 1, characterized in that it comprises several shutters (24) regularly distributed around the circumference of the radially internal (20) or external (21) shell. 3. Compressor (4) according to claim 1 or 2, characterized in that the or each shutter (24) is mounted at the level of the radially outer shell (21) of the vein (3). 4. Compressor (4) according to one of claims 1 to 3, characterized in that the or each shutter (24) extends circumferentially over an angular range between 4 and 90 °. 5. Compressor (4) according to one of claims 1 to 4, characterized in that each shutter (24) is mounted at the level of the radially outer shell (21), the axis of rotation (25) of each shutter ( 24) being offset radially with respect to the internal surface (26) of the external shell (21), opposite the vein (3). 6. Compressor (4) according to one of claims 1 to 5, characterized in that the shutter (24) is located axially downstream of a 5 first compression stage (E1), and upstream of a second compression stage (E2). 7. Compressor (4) according to claim 6, characterized in that at least one shutter (24) is also movable in a third position in which said shutter (24) is spaced from the vein (3) and 10 does not appear on the corresponding ferrule (21). 8. Turbomachine (1) comprising at least one compressor (4) according to one of claims 1 to 7.