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

Abstract

Control system for pressurizing 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) with through holes (t1) and disposed against a downstream face (34b) of the annular flange (34) with through holes (t2), - a control member (40) configured to rotate the ring (36) relative to the flange (34) between an angular position in which the through holes (t1) and through holes (t2) are aligned to allow the passage of pressurized air from a downstream area located downstream of the downstream face (34b) of the annular flange (34) to the downstream cavity (Cav), and a second angular position in which the through holes (t1) and through holes (t2) are misaligned. Figure for the abbreviation: Fig. 2.

Description

Title of the invention: Pressurization control system for a downstream cavity of a centrifugal compressor rotor in a turbomachine technical field

[0001] The present invention relates to a pressurization control system for a downstream cavity of a centrifugal compressor rotor in a turbomachine. Previous technique

[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 section of such a turbomachine, aerodynamic forces exerted on the blades and pressures exerted on the rotor discs are applied to the compressors and turbines. The resultant of these forces is an axial force that is absorbed by a bearing located upstream of the centrifugal compressor. During the operation of the turbomachine, the axial force is likely to vary significantly depending on the engine speed, particularly from idle to full throttle.

[0004] Depending on the turbomachine design, this force may even reverse, for a given engine speed, passing through an operating point where the axial force is zero. Such an operating point can prove problematic for the bearings, whose ball bearings, which absorb this axial force, deteriorate more rapidly when the axial force becomes zero because the bearing will move back and forth, and each movement will result in metal-to-metal contact.

[0005] Reversal of the axial force causes the rotor to move from upstream to downstream, and this reversal must therefore be taken into account when dimensioning the bearings. The bearings must then be oversized to support the additional loads that occur during the axial force reversal phenomenon.

[0006] Furthermore, bearings are conventionally sized according to the maximum axial force, which is that reached at an operating point corresponding to aircraft takeoff. With a high axial force, the sizing of the bearings leads to larger and therefore heavier bearings, making them difficult to integrate into the turbomachine and negatively impacting 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. Description of the invention

[0008] The present presentation 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 pressurization control system for a downstream cavity Cav of a centrifugal turbomachine 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, together with a downstream face of the rotor, delimits the downstream cavity Cav, the system being characterized in that it comprises a venting ring which is disposed 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 control element for a pressurization air flow in the downstream cavity Cav which is configured to move the venting 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 the passage of a pressurization airflow from a downstream area 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) the passage of air from the downstream area 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 centrifugal compressor rotor, the system allows modulation of the piston force exerted by the air pressure acting on the downstream face of the rotor, which opposes the aerodynamic forces of the air on the blades of the upstream axial compressor (e.g., high-pressure compressor), the centrifugal compressor, and the axial turbine, for example, a high-pressure turbine (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 phase of operation of the motor, which explains that the resultant of these two forces influences to the first order the general behavior of the axial force and its possible inversion.

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

[0013] According to other possible characteristics: -the said at least one control element 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 includes several control devices for a pressurization air flow in the downstream cavity, each control device for a pressurization air flow in the downstream cavity Cav having 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 device 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 device relative to its first longitudinal end and thus 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 element is fixed to a radially external part of the annular flange which is arranged radially outside the ventilation ring and the second opposite longitudinal end is fixed to the ventilation ring in such a way that each control element extends between its two opposite longitudinal ends and is configured so that an expansion or contraction of each control element exerts a force causing a rotation of the ventilation ring around the X axis; each control element 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 has an axially thickened annular portion extending axially in projection downstream 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 the pressurization air flow from downstream to upstream through these holes; -the system comprises a plurality of control organs distributed circumferentially around the X axis; -each control element of the plurality of control elements is a connecting rod; - each of the first longitudinal end and the second longitudinal end of each control member is pierced with a through orifice and two axial holes, which are provided respectively in a portion of the annular flange and in a portion of the ventilation ring, are axially aligned each with a through orifice of the corresponding end of each control member, an axial fixing member being inserted into each through orifice 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 the ventilation ring; - the portions of the annular flange and the ventilation ring pierced with an axial hole form radial attachment protrusions for the ends of said at least one control element; - the ventilation ring has a general collar shape.

[0014] A second aspect of the present exposition 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 become clearer upon reading the following detailed description of embodiments shown by way of non-limiting examples. The description refers to the accompanying drawings, which are schematic and intended primarily to illustrate the principles presented.

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

[0017] [Fig-1] Fig. 1 schematically illustrates a possible architecture of aircraft turbomachine incorporating a system according to an embodiment of the invention.

[0018] [Fig.2] Fig.2 illustrates schematically, enlarged, a detailed view of a part of the downstream area of ​​the centrifugal compressor rotor of the turbomachine of [Fig.1].

[0019] [Fig.3] Fig.3 is a schematic, enlarged perspective view of 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 t1 and t2 are not aligned with each other.

[0021] [Fig. 5] [Fig. 5] is an enlarged schematic axial cross-sectional view of an area of ​​the system S mounting an angular position for which the holes t1 and t2 are aligned with each other.

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

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

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

[0025] [Fig.9] Fig.9 is a schematic view of one operating mode of the turbomachine following another possible configuration of system S. Description of the implementation methods

[0026] To make the explanation more concrete, embodiments are described in detail below, with reference to the accompanying drawings. It should be noted, however, that the invention is not limited to these embodiments.

[0027] Figure 1 schematically represents the main components of a possible aircraft turbomachine architecture incorporating a system according to an embodiment of the invention. The details of the embodiment are omitted in order to highlight the main aspects of this architecture.

[0028] As shown in [Fig.1], a turbomachine such as a turbomotor 1, comprises, in the direction of flow of a working fluid, for example here air, an axial compressor 2 (this compressor can 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 turboshaft engine 1 also includes a first rotating shaft 7 and a second rotating shaft 8 mounted coaxially with the first rotating shaft 7 and aligned along the longitudinal axis X of the machine. The second rotating shaft 8 connects the axial compressor 2 and the centrifugal compressor 3 to the first axial turbine 5, such that the expansion of the working fluid in this turbine, downstream of the combustion chamber 4, serves to power the compressors 2 and 3 upstream of the combustion chamber 4. The first rotating shaft 7 connects the second axial turbine 6 to a power output 9 positioned downstream and / or upstream of the turbomotor, such that the expansion of the working fluid in the second axial turbine 6 enables the implementation of the power output 9. Thus, the successive compressions of the working fluid in the compressors 2 and 3, followed by a 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] Figure 2 is a more detailed and enlarged view of a region of the turbomachine of Figure 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 in the direction of the combustion chamber (not shown).

[0031] The turbomachine includes an annular flange 34 extending downstream of the radial downstream face 30a of the rotor 30 and defining, together with this face 30a, a downstream cavity Cav. The annular flange 34 is a part fixed to the rotor, comprising a radially external portion 34a extending radially along and a short distance from the radial downstream 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 compressor stage 3 in order to draw a fraction of the air exiting this stage, 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 turbomachine zone 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] In general, the turbomachine includes 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 disposed against a downstream face 34b (this face is directed towards the downstream side of the turbomachine, i.e., to the right of [Fig. 2]) of the annular flange 34, and a pressurization air flow control device 38 configured to rotate the ventilation ring 36, relative to the annular flange 34, between two different angular positions around the X axis in order to geometrically align (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, the passage of air from the downstream space Eav to the downstream cavity Cav (downstream air passage to upstream). This arrangement allows control of the pressurization in the downstream cavity Cav and therefore control of the piston effect on the downstream face 30a of the rotor.

[0034] More particularly, the ventilation ring 36, which is 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 of the arrangement of the ventilation ring 36 against the annular flange 34, the plurality of holes tl 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 a partial enlarged 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 dashed line) of the flange 34. In this second angular position of the ventilation ring 36, no airflow can pass through the assembly.

[0037] Fig. 5 is a partial enlarged axial cross-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 airflow illustrated by the arrow marked by the letter Q can cross axially 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 (motor axis) and axially downstream to a downstream edge 34d forming a shoulder.

[0039] The annular flange 34 further comprises an annular portion 34f extending 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 housing 50 of the turbomachine by means of a screw-nut or similar design. As already mentioned above, the shape of the annular flange can vary depending on the internal configurations of the turbomachine.

[0040] As shown in Figures 2, 3, 5 and 6, the pressurization air flow control device 38 comprises at least one control element 40, and, in particular here, a plurality of control elements 40 ([Fig.3]).

[0041] More particularly, each control member 40 extends in a transverse plane perpendicular to the X axis ([Fig.2]) and has two opposite ends 40a, 40b. According to a view taken in this transverse plane from the downstream side 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 disposed 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 by passing in front of a part of the ventilation ring 36 (figs.2, 3 and 6) so that a dilation or contraction of the control member 40 (this ability of the control member to dilate 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 the annular flange 34 and extend across the ventilation ring 36 only over a small portion of its surface (a portion of an arc or a reduced angular segment) in order to remain arranged in a peripheral area of ​​the ring 36. This makes it possible both to exert as tangential a force 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 on the [Fig.6]).In the embodiment shown in the figures, the orientation of the control elements is oblique relative to a radial direction of the ventilation ring and annular flange arrangement 34.

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

[0043] More specifically, the ventilation ring 36 is arranged against the radially internal part 34c of the annular flange 34, which has an axially thickened annular portion 34e extending axially downstream from the downstream face 34b of the annular flange 34 ([Fig. 5]). The flat peripheral area 36c of the ventilation ring 36, which includes the holes t1, rests on this axially thickened annular portion 34e. The second plurality of through holes t2 is provided in the axially thickened annular portion 34e of the annular flange 34 in order to guide the pressurization air flow from downstream to upstream through these holes, 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. We will describe in detail one possible fixing of the The second end 40b of the connecting rods 40 (or of the connecting rod 40 in a single-control-member embodiment) is shown in [Fig. 5], given that the attachment 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 has a through-hole 01 and an axial hole tal is provided in a portion 36b of the ventilation ring 36 opposite it ([Fig. 5]). The axial hole tal is axially aligned with the through-hole 01 of the end 40b. An axial fixing member 42 (pin, screw, etc.) is inserted into the through orifice 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 side of the head 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 attachment protrusions or attachment eyelets for the two opposite ends 40a, 40b of the connecting rod 40.

[0046] In general, 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 (in a circumferential direction) and thus moving the ventilation ring 36 from one angular position to another.

[0047] This relative displacement between parts 36 and 34 is based on the principle of thermomechanical expansion of materials and is made possible by choosing a first material (e.g., a ceramic matrix composite) for the control elements 40 that is different from the second material (e.g., Inconel (registered trademark)) for the annular flange 34. The first material has a different coefficient of thermal expansion than the second material. It should be noted that, to prevent leaks due to 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) allows the holes t1 (ventilation ring 36) and t2 (annular flange 34) to coincide, either at low temperature or at high temperature, and the pressure in the downstream cavity Ca is thus increased (reduction of the axial force at a given operating point of the motor) at either low or high temperature. To switch from one configuration to the other, the holes in the flange 34 or in the ventilation ring 36 are circumferentially offset.

[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 X axis of the motor, the vortex has the effect of reducing the pressure by about 20%.

[0050] When the control system S opens the ventilation holes (alignment of holes t1 and t2 as illustrated in [Fig. 5]), the downstream cavity pressure Cav is still determined by the airflow at the top of the rotor, but the ventilation flow through the holes adds to and modifies the expansion vortex. The ventilation or pressurization flow thus increases 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% in the pressure loss in the radially internal part of the rotor can be expected.

[0051] It should be noted that the dimensioning of the control system S is achieved by determining, on the one hand, the number of holes and their diameter in order to regulate the maximum flow rate to be injected into the downstream cavity Cav and, on the other hand, the length of the control elements 40, the elongation of which 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 should be located in a radial position as close as possible to the engine axis (X-axis) in order to counteract the downstream expansion vortex of the rotor with the greatest efficiency.However, integration constraints within the architecture of the rotor's downstream zone do not always allow for a radially internal position as close as possible to the motor axis. Furthermore, the control elements must be easily fixed and able to move without risk of contacting other parts. For this latter reason, the general shape of the control elements 40, in this case connecting rods, is particularly simple, especially in the central part of the control elements located between the two fixing ends 40, 40b, where the control elements are likely to come into contact with the ventilation ring 36, particularly 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, by at least 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 elements are required. sufficient. For example, for a material such as Inconel (registered trademark) 718, with a temperature of 205°C in one state (open position) and 573°C in the other state (closed position), and a hole diameter of 1.5 mm, the control elements must be 283 mm long. The control system configuration can be achieved by selecting between one and ten holes, with a diameter for each hole between 0.3 and 1 mm, and between three and six control elements. Note that the number of holes is determined by the radius of the ventilation ring and the diameter of the holes. For the control system to be effective, all holes must be covered by the ventilation ring in the closed position. Therefore, in this position, the holes t2 of the annular flange 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, introducing a ventilation / pressurization flow into the downstream cavity Cav increases the pressure in this cavity, particularly 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 pressure increase on the downstream face 30a of the rotor results, by piston effect, in a higher upstream axial force, thus reducing the resulting axial force of the High Pressure (HP) body applied to the entire architecture and directed downstream.

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

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

[0056] Figure 8 represents an operating mode for a configuration where the number of holes is higher than in Figure 7. The ventilation flow Q2 passing through the ventilation ring 36 and the annular flange 34 when holes t1 and t2 coincide geometrically (first position) further pressurizes the downstream cavity Cav is similar to the configuration in [Fig. 7]. Since the flow rate Q2 is greater than the flow rate drawn from the compressor outlet, it reverses this flow, which is then reintroduced into the compressor outlet. The remaining ventilation flow continues to circulate towards the axial turbine as a flow rate q3 (Q2-q1). Because the pressure introduced into the downstream cavity Cav is higher than in the configuration of [Fig. 7], the resulting local axial force is also greater. The upstream axial force is thus increased, and overall, the downstream axial force is reduced.

[0057] Figure 9 represents an operating mode for a configuration where a pressure equilibrium is established between the ventilation or pressurization flow rate Q3 ensured by the alignment of holes t1 and t2 and the flow rate ql' taken from the compressor outlet. The pressure in the downstream cavity Cav is at a pressure intermediate between the pressure in the downstream cavity of Figure 7 and that of Figure 8.

[0058] Although the present invention has been described with reference to specific embodiments, it is evident that various modifications and changes can 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 mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims

Demands

1. System (S) for pressurizing a downstream cavity (Cav) of a centrifugal turbomachine (1) compressor rotor (30) 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 venting ring (36) which is disposed against a downstream face (34b) of the annular flange (34) and which is pierced with a first plurality of through holes (t1), the annular flange (34) being pierced with a second plurality of through holes (t2),the system further comprising at least one control element (40) for a pressurization air flow in the downstream cavity (Cav) which is configured to move the vent ring (36) relative to the annular flange (34) about the axis (X) between, on the one hand, a first angular position about 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 a passage of pressurization air flow from a downstream area 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 about the axis (X) in which, about the axis (X), each of the holes of the first plurality of through holes (t1) is angularly offset with respect to each of the holes in the second plurality of through holes (t2),thus limiting the 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. A system according to claim 1 or 2, comprising several control elements for a pressurization air flow in the downstream cavity (Cav), each control member (40) having two opposite longitudinal ends, of which a first longitudinal end (40a) is fixed to the annular flange (34) and a second longitudinal end (40b) is fixed to the ventilation ring (36), each control member (40) being able to expand and contract 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 thus 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, wherein each control member (40) is fixed to a radially external part of the annular flange (34) which is arranged radially outside opposite the ventilation ring (36) and the second opposite longitudinal end (40b) is fixed to the ventilation ring (36) such that each control member (40) extends between its two opposite longitudinal ends (40a, 40b) and is configured so that a dilation or contraction of each control member (40) exerts a force causing a rotation of the ventilation ring (36) about the axis (X).

5. System according to claim 4, wherein the ventilation ring (36) is arranged against a radially internal part (34c) of the annular flange (34) which has an axially thickened annular portion (34e) extending axially in projection downstream 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 pressurization air flow which flows from downstream to upstream.

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

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

8. A system according to any one of claims 3 to 7, wherein each of the first longitudinal end (40a) and the second longitudinal end (40b) of each control member (40) is drilled of a through orifice and two axial holes, which are provided respectively in a portion of the annular flange (34) and in a portion of the ventilation ring (36), are axially aligned each 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, wherein the portions of the annular flange (34) and the ventilation ring (36) pierced with an axial hole form radial attachment protrusions for the longitudinal ends (40a, 40b) of each control member (40).

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

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