FR3069571B1 - FLUID FILM COMPRESSION SYSTEM AND ROTATING MACHINE COMPRISING SUCH A SYSTEM - Google Patents

Abstract

A fluid film compression system (20) for damping the relative movement between two parts (16, 18), the system comprising sealing elements (22, 23, 23a, 23b) to be arranged between the two parts and at least partially defining, between them and with the two parts, an area (24) configured to receive a fluid film, the system further comprising a recovery tank (28) arranged with respect to said area ( 24) so as to recover the fluid that escapes from the zone, and a capillary (32) extending from the recovery tank (28) to said zone (24) for supplying the fluid film.

Description

FIELD OF THE INVENTION

The present disclosure relates to the field of fluid film compression systems. Such systems can be used as dampers, especially in rotating machines.

TECHNOLOGICAL BACKGROUND

In a shaft in rapid rotation, such as, for example, the rotor shaft of a turbomachine such as a turbojet or turboprop aircraft, unbalances tend to cause radial vibration of the shaft. In order to dampen these radial vibrations, and thus to prevent their deleterious effects on the shaft and its environment, it is known to those skilled in the art to use fluid film compression dampers (in English: "squeeze film damper "). For example, the patent application FR 2,845,138 A1 of the Applicant discloses such a damper.

As used herein, the axis of the rotor is called the nominal axis of rotation thereof. The axial direction corresponds to the rotor axis direction and a radial direction is a direction perpendicular to the rotor axis and intersecting this axis. Similarly, an axial plane is a plane containing the rotor axis and a radial plane is a plane perpendicular to this axis.

[0004] A fluid film compression damping system generally comprises a fluid film, typically an oil film, contained in an annular space delimited by two substantially cylindrical surfaces, and by a sealing segment at each of its ends. . The cylindrical surfaces are, most often, an inner surface of a housing and an outer surface of an outer ring of a rotary bearing, in particular a rolling bearing.

Under the effect of imbalance in a rotary shaft housed in such a bearing with fluid film compression damper, the outer ring of the bearing describes an orbital movement relative to the axis of the housing. This orbital motion generates a rotating zone of compression of the fluid film. The rotating movement of this compression zone causes, by the effect of Poiseuille, a damping of the orbital movement of the outer ring of the bearing, and thus of the radial vibrations of the shaft.

This damping, however, generates heat in the liquid film, which it is normally necessary to evacuate in order to prevent the temperature of the liquid film from rising, reducing the viscosity and consequently the damping capacity of the film. liquid. For this, it has been proposed to allow a leakage flow of the liquid in the compression zone.

Thus, a fluid film compression system according to the state of the art requires both a supply circuit and a recovery circuit, to renew the oil of the fluid film.

However, such circuits have drawbacks. On the one hand, the connections and interventions necessary for the maintenance of the oil circuits create risks of leakage and pollution of the oil, which degrades the efficiency of the damping. On the other hand, these circuits are complex, and therefore heavy and bulky, which is particularly detrimental in the case of an aircraft turbine engine where space and mass are critical parameters. There is therefore a need for a new type of fluid film compression system.

PRESENTATION OF THE INVENTION

For this purpose, the present disclosure relates to a fluid film compression system for damping the relative movement between two parts of a turbomachine, the system comprising sealing elements intended to be arranged between the two parts and at least partially defining, between them and with the two parts, a zone configured to receive a fluid film, the system further comprising a recovery tank, arranged with respect to said zone so as to recover the fluid which escapes from the zone, and at least one capillary extending from the recovery tank to said zone for supplying the fluid film.

A seal is said to be partial if it is effective only in a certain range of pressure differences on both sides of the sealing elements. Thus, in the case where the aforementioned sealing elements do not achieve complete sealing of the zone, or space, receiving the fluid film, they still make it possible to ensure, in a manner known per se, that the fluid film is at a minimum pressure guaranteeing its damping function. When the pressure of the fluid film exceeds the design pressure of the sealing members, a fluid leakage rate can be created from the fluid film area to the recovery tank.

The fluid supply circuit serving to feed the fluid film, in particular to compensate for local losses or depressions, comprises at least one capillary (hereinafter used in the singular, without loss of generality) extending from the recovery tank at said area. Due to the fact that the capillary extends from the recovery tank, it is no longer necessary to bring fluid from other more distant places, which significantly reduces the size and complexity of the system. Through the use of a capillary, one can do without actuators or pumps to get the fluid into the area receiving the fluid film. The use of a capillary thus arranged makes it possible to significantly simplify the design of the fluid film compression system, to free up space and to reduce the weight of the system, to simplify the assembly of the system and to reduce the risks of pollution and fluid leakage.

As used herein, a capillary may designate both a capillary tube and a structure behaving as a capillary tube in the sense that it gives rise to the capillary phenomenon, for example a porous material.

It is recalled that the capillarity means the ability of a fluid, usually a liquid, to rise naturally along a very thin tube, or equivalent, immersed in this liquid, despite the gravity. The rise is all the stronger as the tube is fine. This phenomenon is due to the surface tension forces of the liquid, the liquid being attracted more by the walls of the tube than by the air above its surface. The tube being very thin, the liquid forms a concave meniscus that can rise, step by step, along the walls, thus overcoming gravity. The forces at the origin of the capillarity thus make it possible to maintain, in the zone receiving the fluid film, a determined pressure.

In some embodiments, the two parts are a support and a bearing, the area receiving the fluid film being located outside the bearing. The support may be a fixed part integral with a stator, for example a housing. The bearing may be a bearing, in particular a ball bearing. Since the fluid film is located outside the bearing, the fluid film compression system is not comparable to a fluid bearing, in which the fluid essentially has a function of lubrication and not radial damping. It is preferable that the support is fixed to the extent that it facilitates the assembly and operation of the fluid film compression system.

In some embodiments, in the use position of the system, the recovery tank is located lower than said zone, to facilitate the recovery of the fluid in said reservoir and better control the capillarity phenomena.

In some embodiments, an enclosure surrounds the sealing elements, the enclosure being configured to conduct the fluid escaping from said zone to the recovery tank. For example, the enclosure may include drains. In these embodiments, the fluid can circulate in a loop between the recovery tank and the zone receiving the fluid film, via the capillary in one direction and via the enclosure in the other direction.

In certain other embodiments, the sealing elements are configured so that the zone is hermetically insulated, whereby the fluid escaping from the zone reaches the recovery tank via the capillary. It is understood that the expression "hermetically isolated" is appreciated excluding the opening formed by the capillary. For example, the aforementioned sealing elements can be resized to ensure complete sealing of the area. Alternatively or in addition, the sealing elements may comprise several sub-elements, the first allowing, in a conventional manner, a leakage flow, and the second surrounding the first and providing a better seal to ensure that the area is hermetically insulated. In all cases, the zone and the recovery tank communicate only through the capillary. When the pressure of the fluid film exceeds the pressure of the capillary, the fluid descends the capillary towards the recovery tank, and vice versa. If necessary, the capillary and / or the recovery tank can be cooled by an air circuit provided for this purpose.

In some embodiments, the recovery tank is defined by a cavity having for single opening the capillary. The cavity may be defined by a plurality of assembled parts, which allows for simplified mounting of the recovery tank and facilitates insertion of the capillary into fluid communication with the recovery tank.

In some embodiments, the system comprises at least two capillaries. A plurality of capillaries makes it possible to increase the capacity of supply of fluid towards the zone and consequently to adapt more easily the characteristics of the fluid film as a function of the needs, in particular of damping. The plurality of capillaries comprises the aforementioned capillary. In addition, each capillary can be arranged similarly to the aforementioned capillary.

In addition to the characteristics that have just been mentioned, the proposed system may have one or more of the following characteristics, considered alone or in technically possible combinations: the fluid may be an oil, for example chosen from oils aeronautical certified synthetic materials such as TURBONYCOIL 13 B (registered trademark) or Exxon Turbo Oil 2380 (registered trademark); the density of the fluid may be between 0.7 g / cm 3 and 1 g / cm 3 (grams per cubic centimeter), preferably between 0.9 g / cm 3 and 1 g / cm 3; the surface tension of the fluid can be between 15 mN / m and 40 mN / m (milliNewton per meter), preferably between 20 mN / m and 32 mN / m; the or each capillary may be a tube whose radius (inside) is less than or equal to 0.5 mm (millimeters), preferably between 0.1 mm and 0.5 mm; the height of the capillary can be between 5 mm and 120 mm. The present disclosure also relates to a rotating machine, in particular for a turbomachine, comprising a rotor and a stator separated by at least one bearing, and a fluid film compression system as previously described for damping the relative movement between the rotor and the stator mainly in a radial direction of the rotor, the zone configured to receive the fluid film being provided between the stator and the bearing.

The present disclosure also relates to a turbomachine, including aircraft, comprising such a rotating machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will be better understood on reading the following detailed description of embodiments of the invention given by way of non-limiting examples. This description refers to the accompanying drawings, in which: - Figure 1 shows a schematic axial section of a turbomachine; FIG. 2 represents a diagrammatic view in axial half-section of a fluid film compression system according to a first embodiment; FIG. 3 represents a diagrammatic axial half-section view of a fluid film compression system according to a second embodiment; FIG. 3A partially illustrates, in section, a variant of FIG. 3; FIG. 4 represents a diagrammatic view, in broken section along IV-IV in FIG. 3, of a variant of the fluid film compression system according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates a turbomachine, more precisely a double-body, double-flow turbojet, as an example of a rotary machine comprising a rotor and a stator separated by at least one bearing. In this case, the turbomachine 10 is an aircraft turbomachine comprising a rotor shaft 12, in this case a low pressure shaft, and a stator 14, in this case a housing (hereinafter casing 14). sometimes called intermediate casing. The bearings 16 are here rolling bearings arranged to support the shaft 12 relative to the housing 14. In such a turbine engine 10, the shaft 12 can rotate at very high speeds. Thus, even a slight unbalance of the shaft 12 can cause significant radial vibrations that are transmitted to the turbomachine 10. To dampen such vibrations mainly, the turbomachine 10 is provided with a fluid film compression system, here interposed between the bearing 16 and the casing 14.

A first embodiment of such a fluid film compression system 20 is shown in FIG. 2. As can be seen more clearly in this figure, the rotor shaft 12 has a nominal axis of rotation X which shape the axis of the tree. This shaft 12 is secured to an inner ring 16a of the bearing 16, while the stator, here comprising the housing 14 and a bearing support 18 (also called support 18), is secured to an outer ring 16b of the Bearing 16. The inner ring 16a and the outer ring 16b are rotated relative to each other, in a manner known per se, by means of bearings 16c, in this case balls.

The fluid film compression system 20 comprises sealing elements 22 intended to be arranged between the bearing 16 and the casing 14, more precisely here between the outer ring 16b of the bearing and the support 18, and thus defining at least partially sealing a zone 24 configured to receive a fluid film. The sealing elements 22 being slidably mounted on the bearing 16, so that the bearing 16 can have a radial movement relative to the support 18. As illustrated in FIG. 2, the fluid film occupies the zone 24 delimited by the elements sealing 22, the outer ring 16b and the support 18, thus forming a damping layer to attenuate the radial vibrations of the shaft 12 transmitted by the bearing 16. The zone 24 is outside the bearing 16. The zone 24 can extend, like the bearing 16, annularly around the shaft 12.

As will be detailed later, the pressure of the fluid film in the zone 24 is controlled. When the tightness achieved by the sealing elements 22 is partial, in case of overpressure in the zone 24 at the mercy of the radial movements of the bearing 16, fluid can escape axially. This fluid is recovered in a chamber 26 surrounding the sealing elements 22 and leads, by appropriate means such as drains, to a recovery tank 28.

The recovery tank 28 may be a recess formed in the casing 14. The recovery tank 28 may be located lower than the zone 24 in the use position of the system, so that the gravity naturally leads to the flow rate. leakage of fluid through the chamber 26 to the recovery tank 28. In other words, the chamber 26 is configured to conduct the fluid escaping from the zone 24 to the recovery tank 28. As shown in FIG. 4, the recovery tank 28 may extend in an arc about the X axis, in a lower part of the casing 14.

Referring again to Figure 2, in this embodiment, the recovery tank 28 communicates with the chamber 26. The recovery tank 28 may further be provided with a discharge pipe 30 aiming at evacuating the excess fluid that may come from other systems of the turbomachine 10.

As indicated above, the fluid film compression system 20 comprises a capillary 32 extending from the recovery tank 28 to the zone 24 receiving the fluid film. The capillary 32 allows the supply of the fluid film from the fluid contained in the reservoir 28, according to the principles described above. The capillary 32 can be housed in a bore of the support 18, opening on the one hand on the zone 24, on the other hand on the recovery tank. Alternatively, instead of being an insert, the capillary 32 can be formed by the single drilling of the support 18, by means of the presence of a projection immersed in the recovery tank 28. The characteristics of the capillary 32 determine the pressure of the fluid inside said capillary 32, which also imposes, apart from the variations related to the radial movements of the bearing 16, the pressure of the fluid film in the zone 24.

The capillary is here a tube. In the present embodiment, the fluid is an oil, particularly a synthetic engine oil for aircraft such as Turbonycoil 13B (registered trademark). This oil has a density of 0.942 g / cm 3 and a surface tension of 0.032 N / m, which leads to provide for the capillary 32 a diameter of 0.2 mm and a height less than or equal to 70 mm.

Thus, the fluid film present in the zone 24 is fed automatically by the capillary 32, at a predetermined pressure for good radial damping of the movements of the bearing 26. Such an embodiment eliminates the circuit of conventional fluid supply.

Figures 3 and 4 show the fluid film compression system in other embodiments. In these figures, the elements corresponding or identical to those of the first embodiment will receive the same reference sign and will not be described again.

The second embodiment, illustrated in FIG. 3, differs from the first embodiment essentially as regards the evacuation of the fluid under pressure in the zone 24. More particularly, in this embodiment, the elements sealing are configured so that the zone 24 is hermetically insulated. To do this, in addition to first sealing elements 22 similar to those of the first embodiment, the system may comprise second sealing elements 23, placed on either side of the zone 24, around the first elements 22. The second sealing elements completely isolate the zone 24 and prevent the passage of fluid to the chamber 26. In case of overpressure of the fluid film, a leakage rate is installed in the direction of a space 25 provided between the first and second sealing elements, but this flow rate is confined to the space 25. Unlike the first sealing elements 22, the second sealing elements 23 are not slippery with respect to the bearing 16 or the support 18. According to an example, the second sealing elements 23 may comprise a deformable membrane in at least the radial direction. Alternatively, as illustrated in FIG. 3A, each of the second sealing elements 23 may comprise an annular flat gasket 23a mounted in axial abutment against the bearing 16 and against a shoulder of the support 18. The seals 23a can be kept compressed by holding members 23b, such as nuts, here assembled to the support 18.

Moreover, as is also apparent from Figure 3, the recovery tank 28 can be closed. In this case, the recovery tank 28 may take the form of a closed cavity, for example provided in the housing 14. The closed cavity may be obtained by assembling two parts sealingly, typically by welding or screwing with presence of seals. The cavity has, as single opening or single fluid passage, the capillary 32. There may be provided a plug 34 to close the recovery tank 28 after its initial filling fluid.

Thus, in this embodiment, the fluid circulates in closed circuit between the zone 24 and the recovery tank 28. The capillary 32 serves both to drive the fluid from the recovery tank 28 to the zone 24, in case of fluid supply need, that to drive the fluid from the zone 24 to the recovery tank 28, in case of overpressure of the fluid film. Such an embodiment makes it possible to limit the fluid losses as well as the pollution of the fluid that may occur, for example, in the enclosure 26.

It is preferable, in this embodiment, to assemble the support 18 to the housing 14 before performing the drilling receiving the capillary 32, to ensure proper alignment for the passage of the capillary.

Alternatively, as shown in Figure 4, it is possible to provide a plurality of capillaries 32, for example angularly distributed about the axis X, to increase the fluid supply capacity to the zone 24. This variant could also be implemented for the first embodiment.

Although the present invention has been described with reference to specific embodiments, modifications can be made to these examples without departing from the general scope of the invention as defined by the claims. For example, instead of being a tube, the capillary 32 may be formed of a porous material having open porosities. More generally, individual features of the various embodiments illustrated / mentioned may be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

Claims (10)

A fluid film compression system (20) for damping the relative movement between two parts (16, 18) of a turbomachine, the system comprising sealing elements (22, 23, 23a, 23b) for disposed between the two parts and defining at least partially, between them and with the two parts, an area (24) configured to receive a fluid film, the system further comprising a recovery tank (28) arranged with respect to said zone (24) to recover fluid that escapes from the zone, and at least one capillary (32) extending from the recovery tank (28) to said zone (24) for feeding fluid film. 2. System according to claim 1, wherein the two parts are a support (18) and a bearing (16), the zone (24) receiving the fluid film being located outside the bearing (16). 3. System according to claim 1 or 2, wherein, in the use position, the recovery tank (28) is located lower than said zone (24). 4. System according to any one of claims 1 to 3, wherein an enclosure (26) surrounds the sealing elements (22), the enclosure (26) being configured to conduct the fluid escaping from said zone ( 24) to the recovery tank (28). 5. System according to any one of claims 1 to 3, wherein the sealing elements (22, 23, 23a, 23b) are configured so that the zone (24) is hermetically insulated, whereby the fluid s escaping from the zone (24) reaches the recovery tank via the capillary (32). 6. System according to any one of claims 1 to 5, comprising at least two capillaries. 7. System according to any one of claims 1 to 6, wherein each capillary (32) is a tube whose radius is less than or equal to 0.5 mm. 8. System according to any one of claims 1 to 7, wherein the height of the capillary (32) is between 5 mm and 120 mm. 9. System according to any one of claims 1 to 8, wherein the recovery tank (28) is defined by a cavity having for single opening the capillary (32). Rotary machine for a turbomachine, comprising a rotor (12) and a stator (14) separated by at least one bearing (16), and a fluid film compression system (20) according to any one of claims 1 to 9 for the damping of the relative movement between the rotor (12) and the stator (14) mainly in a radial direction of the rotor (12), the zone (24) configured to receive the fluid film being provided between the stator (14) and the bearing (16).