system for controlling the pressurization of a downstream cavity of a centrifugal compressor rotor in a turbomachine

Abstract

System for controlling the pressurization of a downstream cavity (Cav) of a rotor (30) of a turbomachine compressor (1), the downstream cavity extending between a downstream face (30a) of the rotor and an annular flange (34). The system comprises: - a ventilation ring (36) pierced with through holes (t1) and arranged against a downstream face (34b) of the annular flange (34) pierced with through holes (t2), - a control member (40) configured to move the ring (36) in rotation relative to the flange (34) between an angular position in which the through holes (t1) and the through holes (t2) are aligned in order to allow passage of a pressurizing air flow from a downstream zone located downstream of the downstream face (34b) of the annular flange (34) towards the downstream cavity (Cav) and a second angular position in which the through holes (t1) and the through holes (t2) are not aligned. Figure for the abstract: Fig. 2.

Description

Title of the invention: system for controlling the pressurization of a downstream cavity of a centrifugal compressor rotor in a turbomachine Technical field

[0001] The present invention relates to a system for controlling the pressurization of a downstream cavity of a centrifugal compressor rotor in a turbomachine. Prior art

[0002] Aircraft turbomachine architectures are known comprising, in the direction of flow of a working fluid (for example air) in the turbomachine, an axial compressor, a centrifugal compressor, a combustion chamber, a first axial turbine and a second axial turbine.

[0003] In the high-pressure part of such a turbomachine, aerodynamic forces exerted on the blades and pressures exerted on the rotor disks are applied to the compressors and the turbines. The resultant of these forces is an axial force which is taken up by a bearing located upstream of the centrifugal compressor. During operation of the turbomachine, the axial force is likely to vary greatly depending on the engine speed, in particular from idle speed to full throttle speed.

[0004] Depending on the turbomachine designs, this force may even be reversed, for a given engine speed, by passing through an operating point where the axial force is zero. Such an operating point may prove problematic for bearings whose ball bearings that take up this axial force deteriorate more quickly when the axial force is zero because the bearing will move back and forth and each movement will cause metal-to-metal contact.

[0005] The inversion of the axial force causes the rotor to move from upstream to downstream and this inversion must therefore be taken into account when sizing the bearings. The bearings must then be oversized in order to be able to support the excess loads which occur during the phenomenon of inversion of the axial force.

[0006] Furthermore, the bearings are conventionally sized according to the maximum axial force which is that reached for an operating point corresponding to the takeoff of the aircraft. With a high axial force, the sizing of the bearings leads to more bulky and therefore heavier bearings, which makes them difficult to integrate into the turbomachine and penalizes fuel consumption.

[0007] In view of the above, it would therefore be useful to provide a solution to the problem of the inversion of the axial force in order to avoid oversizing the bearings with all the consequences described above. Statement of the invention

[0008] The present disclosure is the result of technological research aimed at controlling the pressurization of the area located downstream of the rotor of the centrifugal compressor and therefore at acting on the axial force (piston force) exerted by the fluid pressure on the downstream face of the rotor.

[0009] A first aspect of the present disclosure relates to a system for controlling the pressurization of a downstream cavity Cav of a turbomachine centrifugal compressor rotor in which a fluid flows from upstream to downstream along an axis X, the system comprising an annular flange centered on the axis X and configured to be mounted on the compressor rotor, the annular flange having an upstream face which delimits, with a downstream face of the rotor, the downstream cavity Cav, the system being characterized in that it comprises a ventilation ring which is arranged against a downstream face of the annular flange and is pierced with a first plurality of through holes t1, the annular flange being pierced with a second plurality of through holes t2, the system further comprising at least one member for controlling a pressurization air flow in the downstream cavity Cav which is configured to move the ventilation ring relative to the annular flange around the axis X between, on the one hand,a first angular position around the X axis in which each hole of the first plurality of through holes is aligned with a hole of the second plurality of through holes in order to allow passage of a pressurizing air flow from a downstream zone located downstream of the downstream face of the annular flange to the downstream cavity Cav located upstream of the upstream face of the annular flange and, on the other hand, a second angular position around the X axis in which, around the X axis, each of the holes of the first plurality of through holes is angularly offset with respect to each of the holes of the second plurality of through holes, thus limiting (or even preventing) passage of air from the downstream zone located downstream of the downstream face of the annular flange to the downstream cavity located upstream of the upstream face of the annular flange.

[0010] By pressurizing the downstream cavity of the rotor of the centrifugal compressor, the system makes it possible to modulate the piston force exerted by the air pressure acting on the downstream face of the rotor and which opposes the aerodynamic forces of the air on the blades of the axial compressor located upstream (e.g.: high pressure compressor), of the centrifugal compressor and of the axial turbine, for example high pressure (this configuration can also be applied to low pressure compressor architectures or intermediate pressure). The resultant of the two forces in opposite directions defines the axial force mentioned above.

[0011] In the prior art, these two forces have opposite directions of action and different values ​​depending on the operating phase of the engine, which explains why the resultant of these two forces influences to the first order the general behavior of the axial force and its possible inversion.

[0012] The controlled increase in the pressurization of the downstream cavity of the rotor of the centrifugal compressor and therefore in the axial pressure (from downstream to upstream) on the downstream face of the rotor makes it possible to increase the axial force towards the upstream and therefore, overall, to reduce the axial force towards the downstream. This thus makes it possible to reduce, or even to overcome, the sizing problems linked to a high value of axial force.

[0013] According to other possible characteristics: -said at least one control member is made of a first material which is different from a second material of the annular flange and which has a coefficient of thermal expansion different from that of the second material; - the system comprises several members for controlling a pressurizing air flow in the downstream cavity, each member for controlling a pressurizing air flow in the downstream cavity Cav comprising two opposite longitudinal ends, a first longitudinal end of which is fixed to the annular flange and a second longitudinal end is fixed to the ventilation ring, each control member being capable of expanding and contracting under the action of a temperature variation, which has the effect of moving the second longitudinal end of the control member relative to its first longitudinal end and therefore moving the ventilation ring from the first to the second angular position around the X axis or conversely from the second to the first angular position around the X axis;- each control member is fixed to a radially external part of the annular flange which is arranged radially outside with respect to the ventilation ring and the second opposite longitudinal end is fixed to the ventilation ring in such a way that each control member extends between its two opposite longitudinal ends and is configured so that an expansion or a contraction of each control member exerts a force causing a rotation of the ventilation ring around the X axis; each control member can extend in a transverse plane perpendicular to the X axis and the preceding configuration is defined according to a view taken in this transverse plane from downstream; ; -the ventilation ring is arranged against a radially internal part of the annular flange which comprises an axially thickened annular portion extending axially in a downstream direction from the downstream face of the annular flange, the second plurality of through holes t2 being arranged in the annular portion axially thickened in order to guide through these holes the pressurizing air flow which flows from downstream to upstream; -the system comprises a plurality of control members distributed circumferentially around the X axis; -each control member of the plurality of control members is a connecting rod; - each of the first longitudinal end and the second longitudinal end of each control member is pierced with a through-hole and two axial holes, which are arranged respectively in a portion of the annular flange and in a portion of the ventilation ring, are each axially aligned with a through-hole of the corresponding end of each control member, an axial fixing member being inserted into each through-hole and into each corresponding axial hole, in order to fix each longitudinal end of each control member to one of the portions of the annular flange and of the ventilation ring; - the portions of the annular flange and of the ventilation ring pierced with an axial hole form radial fixing protrusions for the ends of said at least one control member; - the ventilation ring has a general collar shape.

[0014] A second aspect of the present disclosure relates to a turbomachine, comprising: - a centrifugal compressor having a rotor and a downstream rotor cavity, - a system for controlling the pressurization of the downstream rotor cavity as briefly described above. Brief description of the drawings

[0015] The invention will be better understood and its advantages will appear better, on reading the detailed description which follows, of embodiments represented by way of non-limiting examples. The description refers to the appended drawings which are schematic and aim above all to illustrate the principles of the disclosure.

[0016] In these drawings, from one figure to another, identical or equivalent elements (or parts of elements) are identified by the same reference signs. In these attached drawings:

[0017] [Fig-1] [Fig.l] schematically illustrates a possible architecture of Aircraft turbomachine integrating a system according to one embodiment of the invention.

[0018] [Fig.2] [Fig.2] illustrates in an enlarged schematic manner a detailed view of a part of the downstream zone of the centrifugal compressor rotor of the turbomachine of [Fig.l].

[0019] [Fig.3] [Fig.3] is an enlarged schematic perspective view of the system S of [Fig.2] including an enlarged local part of this system.

[0020] [Fig.4] [Fig.4] is a partial schematic perspective view of an area of ​​the system S mounting an angular position for which the holes tl and t2 are not aligned with each other.

[0021] [Fig.5] [Fig.5] is an enlarged schematic view in axial section of an area of ​​the system S mounting an angular position for which the holes tl and t2 are aligned with each other.

[0022] [Fig.6] [Fig.6] is a partial schematic view in axial section following a view in perspective of the S system.

[0023] [Fig.7] [Fig.7] is a schematic view of one mode of operation of the turbomachine according to a possible configuration of the S system.

[0024] [Fig.8] [Fig.8] is a schematic view of a mode of operation of the turbomachine according to another possible configuration of the system S.

[0025] [Fig.9] [Fig.9] is a schematic view of one mode of operation of the turbomachine according to another possible configuration of the S system. Description of the embodiments

[0026] In order to make the disclosure more concrete, embodiments are described in detail below, with reference to the accompanying drawings. It is recalled, however, that the invention is not limited to these embodiments.

[0027] [Fig.l] schematically represents the main components of a possible aircraft turbomachine architecture integrating a system according to an embodiment of the invention. The implementation details are omitted in order to highlight the main aspects of this architecture.

[0028] As shown in [Fig.l], a turbomachine such as a turboshaft engine 1, comprises, in the direction of flow of a working fluid, for example here air, an axial compressor 2 (this compressor may be a high pressure compressor, the low pressure compressor not being shown in the figure), a centrifugal compressor 3, a combustion chamber 4, a first axial turbine 5 (for example a high pressure turbine) and a second axial turbine 6 (for example a low pressure turbine).

[0029] The turbine engine 1 also comprises a first rotary shaft 7 and a second rotary shaft 8 mounted coaxially relative to the first rotary shaft 7 and aligned along the longitudinal axis X of the machine. The second rotary shaft 8 connects the axial compressor 2 and the centrifugal compressor 3 to the first axial turbine 5, so that the expansion of the working fluid in this turbine, downstream of the combustion chamber 4, serves to operate the compressors 2 and 3 upstream of the combustion chamber 4. The first rotary shaft 7 connects the second axial turbine 6 to a power outlet 9 positioned downstream and / or upstream of the turbomotor, such that the expansion of the working fluid in the second axial turbine 6 makes it possible to implement the power output 9. Thus, the successive compressions of the working fluid in the compressors 2 and 3, followed by heating of the fluid in the combustion chamber 4, and its expansion in the second axial turbine 6, make it possible to convert part of the thermal energy generated by the combustion phenomenon in the combustion chamber 4 into mechanical work extracted by the power output 9.

[0030] [Fig. 2] is a more detailed and enlarged view of an area of ​​the turbomachine of [Fig. 1] located downstream of the centrifugal compressor 3 and comprising the rotor or impeller 30 of the latter which extends radially relative to the longitudinal axis X around which the rotor is able to rotate. The air compressed by the centrifugal compressor 3 exits radially from the compressor stage at an external radial end 32 towards the combustion chamber not shown.

[0031] The turbomachine comprises an annular flange 34 which extends downstream of the radial downstream face 30a of the rotor 30 and which delimits with this face 30a a downstream cavity Cav. The annular flange 34 is a part fixed to the rotor, comprising a radially external part 34a which extends radially along and at a short distance from the downstream radial face 30a to form a radial annular space Ear. This radial space Ear communicates at its radially external end with the outlet 32 ​​of the stage of the compressor 3 in order to be able to take a fraction of the air leaving this stage and which will ventilate the radial space Ear and the downstream cavity Ca with which it communicates.

[0032] As shown in [Fig.2], the annular flange 34 separates the downstream cavity Cav from a downstream zone or space Eav which is located downstream of the annular flange 34. The annular flange 34 has a structure which depends on the geometry of the zone of the turbomachine in which the flange is integrated and the description of this structure which will be given below is likely to vary according to the turbomachine architectures.

[0033] Generally, the turbomachine comprises a system S for controlling the pressurization of the downstream cavity Cav. This system comprises an annular part 36, called a ventilation ring, which is arranged against a downstream face 34b (this face is directed downstream of the turbomachine, i.e. towards the right of [Fig. 2]) of the annular flange 34 and a device 38 for controlling a pressurizing air flow rate which is configured to move the ventilation ring 36 in rotation around the axis X, relative to the annular flange 34, between two different angular positions around the axis X in order to geometrically match (first position), or not (second position), holes made respectively in the annular flange 34 and in the ventilation ring 36 opposite each other, thus allowing, or not, a passage of air from the downstream space Eav to the downstream cavity Cav (passage of downstream air in upstream). This arrangement makes it possible to control the pressurization in the downstream cavity Cav and therefore to control the piston effect on the downstream face 30a of the rotor.

[0034] More particularly, the ventilation ring 36 movable in rotation around the axis X relative to the annular flange 34 is pierced with a first plurality of axial through holes t1 and the annular flange 34 is pierced, for its part, with a second plurality of axial through holes t2.

[0035] [Fig. 3] shows, in a perspective view, the arrangement of the ventilation ring 36 against the annular flange 34, the plurality of holes t1 distributed circumferentially on the part 36 and which is even more visible on the enlarged area of ​​the rectangle shown in the lower part of [Fig. 3].

[0036] [Fig.4] is an enlarged partial view of the downstream side of the arrangement of the ventilation ring 36 against the annular flange 34 which shows a relative angular position between these two parts in which the hole t1 of the part 36 is not aligned (in geometric correspondence) with the hole t2 (in dotted lines) of the flange 34. In this second angular position of the ventilation ring 36, no air flow can pass through the assembly.

[0037] [Fig. 5] is an enlarged partial axial sectional view of the arrangement of the ventilation ring 36 against the annular flange 34 which shows another relative angular position (first position) between these two parts in which the hole t1 of the part 36 is aligned (in geometric correspondence) with the hole t2 of the flange 34. In this other angular position of the ventilation ring 36, an air flow illustrated by the arrow marked with the letter Q can axially pass through the assembly from downstream to upstream to pressurize the downstream cavity Cav from the downstream space Eav.

[0038] More particularly, in the example shown, the ventilation ring 36 has a general collar shape. The annular flange 34, for its part, comprises the aforementioned radially external part 34a which is extended radially by a part 34c which extends both radially towards the longitudinal axis X (engine axis) and axially downstream to a downstream edge 34d forming a shoulder.

[0039] The annular flange 34 further comprises an annular portion 34f which extends axially downstream from the aforementioned radially external portion 34a to a downstream annular end forming a downstream flange 34g which is fixed to an internal casing 50 of the turbomachine by screw-nut type means or the like. As already mentioned above, the shape of the annular flange can vary according to the internal configurations of the turbomachine.

[0040] As shown in Figures 2, 3, 5 and 6, the device 38 for controlling a pressurizing air flow rate comprises at least one control member 40, and, in particular here, a plurality of control members 40 ([Fig.3]).

[0041] More particularly, each control member 40 extends in a transverse plane perpendicular to the axis X ([Fig.2]) and has two opposite ends 40a, 40b. According to a view taken in this transverse plane from downstream of the architecture (view taken from the right of [Fig.2], 5 or 6 and looking towards the left of the figure), a first end 40a of each control member 40 is fixed to a radially external part 34f of the annular flange 34 which is arranged externally to the circumference of the ventilation ring 36 (figs. 2 and 6). A second opposite end 40b is fixed to the ventilation ring 36 (figs. 2, 3, 5 and 6) in such a way that each control member 40 extends between its two opposite ends 40a, 40b passing in front of a part of the ventilation ring 36 (figs.2, 3 and 6) so that an expansion or contraction of the control member 40 (this ability of the control member to expand and contract under the action of a temperature variation will be described later) exerts a tangential rotational force on the ventilation ring 36. As shown in [Fig. 3], the control members 40 are distributed circumferentially relative to the ventilation ring 36 and to the annular flange 34 and extend across the ventilation ring 36 only over a small portion of surface (arc portion or reduced angular segment) in order to remain arranged in a peripheral zone of the ring 36. This makes it possible both to exert a force as tangential as possible relative to the circumference of the ring and not to interfere with a radially internal portion of the annular flange 34 which extends axially (portion 34d in [Fig.6]).In the embodiment shown in the figures, the orientation of the control members is oblique relative to a radial direction of the ventilation ring and annular flange arrangement 34.

[0042] The distribution of the control members 40 is here regular and there are three members 40 although in other configurations a different number of members can be envisaged. In the example shown the control members are elongated parts which here take, for example, the form of connecting rods.

[0043] More particularly, the ventilation ring 36 is arranged against the radially internal part 34c of the annular flange 34 which comprises an axially thickened annular portion 34e extending axially downstream from the downstream face 34b of the annular flange 34 ([Fig.5]). The flat peripheral zone 36c of the ventilation ring 36 comprising the holes t1 rests on this axially thickened annular portion 34e. The second plurality of through holes t2 is arranged in the axially thickened annular portion 34e of the annular flange 34 in order to guide through these holes the pressurizing air flow which flows from downstream to upstream, into the downstream cavity Cav.

[0044] The possible fixings of each end of the connecting rods 40 are for example of the type shown in figures 2, 3, 5 and 6. A possible fixing of the second end 40b of the connecting rods 40 (or of the connecting rod 40 in an embodiment with a single control member) with reference to [Fig. 5], knowing that the fixing of the first end 40a (on a portion of the annular flange 34) visible in Figures 2, 3 and 6 is identical. Thus, for example, the end 40b is pierced with a through orifice 01 and an axial hole tal is arranged in a portion 36b of the ventilation ring 36 opposite ([Fig. 5]). The axial hole tal is axially aligned with the through orifice 01 of the end 40b. An axial fixing member 42 (pin, screw, etc.) is inserted into the through-hole and the axial hole aligned with each other, in order to fix the end 40b to the portion of the ventilation ring 36. A washer 44 and an annular ring 46 are mounted on the head side of the axial fixing member 42 (downstream side) and with a support (not shown) on the upstream side to lock the assembly.

[0045] As shown in Figures 2, 3 and 6, the portions 34h of the annular flange 34 and 36b of the ventilation ring 36 pierced with an axial hole tal form radial fixing protrusions or fixing eyelets for the two opposite ends 40a, 40b of the connecting rod 40.

[0046] Generally, each control member 40 is capable of expanding and contracting under the action of a temperature variation: it expands under the effect of a temperature variation (increase in temperature) and contracts under the effect of an inverse temperature variation (decrease in temperature), which has the effect of moving the second end 40b of the control member 40 relative to its first fixed end 40a (along a circumferential direction) and therefore of moving the ventilation ring 36 from one angular position to the other.

[0047] This relative movement between the parts 36 and 34 is based on the principle of thermomechanical expansion of the materials and is made possible by choosing for the control members 40 a first material (e.g., for example, a ceramic matrix composite) which is different from the second material (e.g., Inconel (registered trademark)) of the annular flange 34. The first material has a coefficient of thermal expansion different from that of the second material. It will be noted that, to avoid leaks by radial displacement, the same material is used for the ventilation ring 36 and the annular flange 34.

[0048] Depending on the requirements, the control system S (passive linkage system) makes it possible to make the holes t1 (ventilation ring 36) and t2 (annular flange 34) coincide, either at low temperature or at high temperature and the pressure in the downstream cavity Ca is therefore increased (reduction of the axial force on a given operating point of the engine) either at low temperature or at high temperature. To switch from one configuration to the other, the holes in the flange 34 or in the ventilation ring 36 are offset circumferentially.

[0049] When the control system closes the ventilation holes (misalignment between holes t1 and t2 as illustrated in [Fig.4]), the pressure of the downstream cavity Cav is given by the air stream at the top of the rotor and, by approaching radially the axis X of the motor, the vortex has the effect of reducing the pressure by around 20%.

[0050] When the control system S opens the ventilation holes (alignment of the holes t1 and t2 as illustrated in [Fig.5]), the pressure of the downstream cavity Cav is still given by the air stream at the top of the rotor but the ventilation flow passing through the holes will be added and modify the expansion vortex. The ventilation or pressurization flow will thus increase the pressure in the radially internal part of the rotor and, consequently, the pressure on the downstream face of the rotor. In this open position, a gain of approximately 50% on the pressure loss in the radially internal part of the rotor can be envisaged.

[0051] It will be noted that the dimensioning of the control system S is carried out by dimensioning, on the one hand, the number of holes and their diameter in order to adjust the maximum flow rate that one wishes to inject into the downstream cavity Cav and, on the other hand, the length of the control members 40 whose elongation is managed through the temperature variation between the state where the system is in an open position and that where it is in a closed position. This dimensioning makes it possible to obtain the maximum ventilation / pressurization flow rate at a given temperature and therefore for a given flight phase. In general, the holes must be located in a radial position as close as possible to the engine axis (axis X) in order to be able to counter the downstream expansion vortex of the rotor with the greatest efficiency.However, the constraints of integration into the architecture of the downstream zone of the rotor do not always allow a radially internal position to be adopted as close as possible to the engine axis. Furthermore, the control members must be able to be easily fixed and move without risking coming into contact with other parts. For this last reason, the general shape of the control members 40, in this case the connecting rods, is particularly simple, in particular in the central part of the control members located between the two fixing ends 40, 40b, where the control members are likely to come into contact with the ventilation ring 36, in particular with its annular edge 36a ([Fig.6]).

[0052] It should be noted that, in order for two holes t1 and t2 to coincide with each other (axial alignment of the two holes), these holes must be spaced laterally (circumferentially), in the non-aligned position, at least by a distance corresponding to their diameter. To obtain a displacement between an angular position where the holes coincide (first position) and an angular position where the holes are angularly offset (second position), a temperature difference between the two operating points and a length of control members are required. sufficient. For example, for a material such as Inconel (registered trademark) 718, with a temperature of 205°C for one state (open position) and 573°C for the other state (closed position) and a hole diameter of 1.5 mm, the control members must have a length of 283 mm. The configuration of the control system can be achieved by choosing a number of holes between one and ten holes with a diameter for each hole between 0.3 and 1 mm and a number of control members 40 ranging from three to six. It will be noted that the number of holes is conditioned by the radius of the ventilation ring 36 and by the diameter of the holes. For the control system to be effective, all the holes must be plugged by the ventilation ring in the closed position and, thus, in this position, the holes t2 of the annular flange 34 must be positioned opposite the solid material of the ventilation ring.Therefore, the maximum number of holes allowed corresponds to the staggered configuration of the holes in the annular flange with those in the ventilation ring.

[0053] Generally speaking, the introduction of a ventilation / pressurization flow into the downstream cavity Cav makes it possible to increase the pressure in this cavity, in particular in the lowest radially internal part of the configuration (i.e. below the radially internal space Ear of the downstream space of the impeller or rotor 30), and increases the downstream pressure of the rotor by vortex effect. This increase in pressure on the downstream face 30a of the rotor causes, by piston effect, a higher axial force towards the upstream, thus reducing the resulting axial force of the High Pressure (HP) body applied to the entire architecture and which is directed towards the downstream.

[0054] Figures 7 to 9 schematically illustrate different possible operating modes depending on a number of holes and a diameter of holes sized appropriately.

[0055] [Fig.7] represents an operating mode for a configuration where the number of holes is low. The ventilation flow Q1 which passes through the ventilation ring 36 and the annular flange 34 when the holes t1 and t2 coincide geometrically (first angular position), pressurizes the downstream cavity Cav. The flow q1 taken from the compressor outlet is added with the flow Q1 passing through the holes t1 and t2 to obtain a flow q2 (q1+Q1) going towards the high pressure turbine. The introduction into the downstream cavity of the flow Q1 reduces the vortex expansion factor from 20% to 10%. Thus, the pressure increases over the entire downstream face 30a, which also increases the axial force towards the upstream.

[0056] [Fig.8] represents an operating mode for a configuration where the number of holes is higher than in [Fig.7]. The ventilation flow Q2 which passes through the ventilation ring 36 and the annular flange 34 when the holes t1 and t2 coincide geometrically (first position), further pressurizes the downstream cavity Cav than in the configuration of [Fig.7]. The flow Q2 being greater than the flow taken from the compressor outlet, it reverses this flow which is therefore reintroduced at the compressor outlet. The rest of the ventilation flow always circulates towards the axial turbine in the form of a flow q3 (Q2-ql). The pressure introduced into the downstream cavity Cav being higher than in the configuration of [Fig.7], the resulting local axial force is also greater. The axial force towards the upstream is thus increased and, overall, the axial force towards the downstream is reduced.

[0057] [Fig.9] represents an operating mode for a configuration where a pressure balance is established between the ventilation or pressurization flow rate Q3 ensured by the alignment of the holes tl and t2 and the flow rate ql' taken from the compressor outlet. The pressure in the downstream cavity Cav is at an intermediate pressure between the pressure of the downstream cavity of [Fig.7] and that of [Fig.8].

[0058] Although the present invention has been described with reference to specific exemplary embodiments, it is obvious that various modifications and changes may be made to these examples without departing from the general scope of the invention as defined by the claims. Furthermore, individual features of the various embodiments discussed may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Claims

1. System (S) for controlling the pressurization of a downstream cavity (Cav) of a rotor (30) of a centrifugal compressor of a turbomachine (1) in which a fluid flows from upstream to downstream along an axis (X), the system comprising an annular flange (34) centered on the axis (X) and configured to be mounted on the compressor rotor (30), the annular flange (34) having an upstream face (34am) which delimits, with a downstream face (30a) of the rotor (30), the downstream cavity (Cav), the system being characterized in that it comprises a ventilation ring (36) which is arranged against a downstream face (34b) of the annular flange (34) and which is pierced with a first plurality of through holes (tl), the annular flange (34) being pierced with a second plurality of through holes (t2),the system further comprising at least one control member (40) for controlling a pressurizing air flow in the downstream cavity (Cav) which is configured to move the ventilation ring (36) relative to the annular flange (34) around the axis (X) between, on the one hand, a first angular position around the axis (X) in which each hole of the first plurality of through holes (t1) is aligned with a hole of the second plurality of through holes (t2) in order to allow passage of a pressurizing air flow from a downstream zone located downstream of the downstream face (34b) of the annular flange (34) to the downstream cavity (Cav) located upstream of the upstream face (34am) of the annular flange (34) and, on the other hand, a second angular position around the axis (X) in which, around the axis (X), each of the holes of the first plurality of through holes (t1) is angularly offset from each of the holes of the second plurality of through holes (t2),thus limiting a passage of air from the downstream zone located downstream of the downstream face (34b) of the annular flange (34) to the downstream cavity (Cav) located upstream of the upstream face (34am) of the annular flange (34).,

2. System according to claim 1, wherein said at least one control member (40) is made of a first material which is different from a second material of the annular flange (34) and which has a coefficient of thermal expansion different from that of the second material.

3. System according to claim 1 or 2, comprising several members for controlling a pressurizing air flow in the downstream cavity (Cav), each control member (40) comprising two opposite longitudinal ends, including a first longitudinal end (40a) which is fixed to the annular flange (34) and a second longitudinal end (40b) which is fixed to the ventilation ring (36), each control member (40) being capable of expanding and contracting under the action of a temperature variation, which has the effect of moving the second longitudinal end (40b) of the control member relative to its first longitudinal end (40a) and therefore of moving the ventilation ring (36) from the first to the second angular position around the axis (X), or conversely from the second to the first angular position around the axis (X).

4. System according to claim 3, in which each control member (40) is fixed to a radially external part of the annular flange (34) which is arranged radially outside with respect to the ventilation ring (36) and the second opposite longitudinal end (40b) is fixed to the ventilation ring (36) in such a way that each control member (40) extends between its two opposite longitudinal ends (40a, 40b) and is configured so that an expansion or a contraction of each control member (40) exerts a force causing a rotation of the ventilation ring (36) around the axis (X).

5. The system of claim 4, wherein the ventilation ring (36) is arranged against a radially inner portion (34c) of the annular flange (34) which comprises an axially thickened annular portion (34e) extending axially in a downstream direction from the downstream face (34b) of the annular flange (34), the second plurality of through holes (t2) being arranged in the axially thickened annular portion (34e) in order to guide through these holes the pressurizing air flow which flows from downstream to upstream.

6. System according to one of claims 3 to 5, in which the system comprises a plurality of control members (40) distributed circumferentially around the axis (X).

7. System according to the preceding claim, in which each control member of the plurality of control members (40) is a connecting rod.

8. System according to one of claims 3 to 7, in which each of the first longitudinal end (40a) and the second longitudinal end (40b) of each control member (40) is pierced of a through-orifice and two axial holes, which are arranged respectively in a portion of the annular flange (34) and in a portion of the ventilation ring (36), are each axially aligned with a through-orifice of the corresponding end of each control member (40), an axial fixing member being inserted into each through-orifice and into each corresponding axial hole, in order to fix each longitudinal end (40a, 40b) of each control member (40) to one of the portions of the annular flange (34) and of the ventilation ring (36).

9. System according to the preceding claim, in which the portions of the annular flange (34) and of the ventilation ring (36) pierced with an axial hole form radial fixing protrusions for the longitudinal ends (40a, 40b) of each control member (40).

10. System according to one of the preceding claims, in which the ventilation ring (36) has a general collar shape.

11. Turbomachine (1), comprising: - a centrifugal compressor (3) having a rotor (30) and a downstream rotor cavity (Cav), - a system (S) for controlling the pressurization of the downstream rotor cavity (Cav) according to one of the preceding claims.

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