1. TECHNICAL FIELD OF THE INVENTION

The invention relates to a centrifugal deaerator for a turbomachine.

2. TECHNOLOGICAL BACKGROUND

The state of the art comprises, in particular, patent applications published under the numbers US-A1-2015/007531, FR-A1-3 007 463 and US-A1-2016/208650, as well as U.S. Pat. No. 5,716,423.

Turbomachines are complex systems which implement a certain number of rotating assemblies (turbines, compressor, etc.) which must be equipped with sealing devices. These sealing devices are generally produced by pressurized air labyrinths arranged in the vicinity of the rotating assembly. To do this, an air is taken directly in the air duct of the turbomachine. This air then transits in the turbomachine by the different labyrinths provided for this purpose, then is evacuated towards the outside of the turbomachine to limit the increase in pressure of the other zones of the turbomachine, in particular the reduction gear, the accessory box, etc. However, this air having passed through different zones of the turbomachine, it is loaded with oil used for the cooling and the lubrication of bearings and pinions of the rotating assemblies. To avoid the oil-loaded air discharge, easing the ecological impact of turbomachines, reducing the oil consumption and limiting the filling operations of the oil reserves, it is important to provide deaerators which allow separating oil from air before evacuating air towards the outside of the turbomachine.

Such a deaerator is generally arranged and driven by a mechanical power take-off at the level of the accessory box or the reduction gear of the turbomachine.

In a known manner, such a centrifugal deaerator comprises one or more housings for centrifugal separation of the air/oil mixture arranged around a hollow shaft and delimited by an outer annular wall and an inner annular wall. The deaerator further comprises an axial inlet for providing the housing with the air/oil mixture, and a peripheral oil outlet arranged in the outer wall. Thus, during the rotating of the deaerator, obtained generally by way of a pinion of the accessory box or of the reduction gear, the oil is naturally driven by centrifugal force towards the oil outlet arranged in the periphery of the deaerator. A de-oiled air outlet is furthermore arranged in the inner wall and connected to the hollow shaft, which enables to evacuate air towards the outside.

Certain deaerators further comprise filters arranged in the housing of the deaerator to improve the capturing of oil drops and to thus favour the de-oiling of the mixture. Indeed, the filters increase the contact surface available and therefore improve the probability that an oil drop transported by the mixture flow is attached to a wall. These filters are generally formed of a metal foam.

One of the disadvantages, however, of these metal form deaerators resides in the fact that at high speed (for example, for speeds of around 6000 revolutions per minutes) and even more so at a very high speed (for example, for speeds of around 25,000 revolutions per minutes), the front surface constituted by the metal foam acts as a wall and the degree of penetration of the air particles in the foam is low. This comes out as substantial load losses at a high speed, that the secondary air system of the turbomachine cannot support with the associate risk of leakage by the sealings of the generator. In order to compensate for load losses, the flow of the secondary air system can be increased in order to guarantee the sealings, with however an increased removal in the duct and therefore an impact on the performance of the generator.

The inventors have therefore sought to improve the performance of known deaerators, in particular reducing load losses of the deaerator, in particular at a high speed. Thus, the secondary air system flow needs are decreased, consequently with an improvement of the engine performance and a decrease of the airflow to be processed. Thus, the oil consumption can be reduced. The consumption of turbomachines remains a major area of improvement. This must allow optimising the quantity of oil on board and therefore to reduce the mass of the turbomachine. This must also allow increasing the duration of the missions. This must also reduce the maintenance operations on the turboshafts. Finally, this must allow improving the ecological impact of the turboshafts.

3. AIMS OF THE INVENTION

The invention aims to provide a deaerator which overcomes at least some of the disadvantages of known deaerators.

The invention aims in particular to provide, in at least an embodiment, a centrifugal deaerator of a turbomachine which presents improved performance with respect to known deaerators.

The invention also aims to provide, in at least an embodiment, a deaerator which conserves good performance (low load losses and low oil consumption) at high or very high speed.

4. SUMMARY OF THE INVENTION

To do this, the invention relates to a centrifugal deaerator for an air/oil mixture of a turbomachine comprising:an annular housing for the centrifugal separation of said mixture arranged around a hollow shaft extending along a direction, so-called axial direction, and delimited by an outer annular wall and an inner annular wall,at least one axial inlet of said air/oil mixture in said housing,a pinion for rotating said housing comprising a web securely connected to said inner and outer annular walls such that a rotation of said pinion drives said housing in rotation,at least one radial oil outlet arranged in said outer wall and configured to be able to evacuate the oil separated from said mixture towards the outside of the deaerator,at least one de-oiled air outlet arranged in said inner wall and configured to be able to evacuate the de-oiled air towards said hollow shaft.

A deaerator according to the invention is characterised in that it comprises a metal foam housed in said housing by partially extending along said axial direction so as to delimit two successive spaces along the axial direction, a foam-free space and a foam-lined space, said foam-free space opening onto said axial inlet(s).

A deaerator equipped with a metal foam, such as a foam commercialised under the name Retimet®, allows forming a potential substantial contact surface with the air/oil mixture which allows improving the probability of capturing an oil particle which is then centrifugated outside of the deaerator. These foams act as a filter. Furthermore, the centrifugal effect allows avoiding the saturation of filters by the continuous evacuation of oil drops attached to the filters.

According to the invention, the metal foam extends along the axial direction, only partially in said housing so as to delimit two separate and attached spaces, a foam-free space and a foam-lined space. The foam-free space extends between the axial inlets and the foam-lined space. The foam-free space favours the suctioning of the air/oil mixture to be separated and contributes to the separation of drops with a large diameter, while the foam-lined space favours the capturing of the remaining oil particles to evacuate through the centrifugal housing. In other words and according to the invention, the metal foam does not fully fill the housing of the deaerator, but only one portion of the housing. A first portion in the vicinity of the axial mixture inlets is left foam-free and a second portion in the vicinity of the bottom of the housing, i.e. arranged axially opposite the inlets, is filled with metal foam.

This specific architecture of the deaerator allows the air/oil mixture to enter into the deaerator through the axial inlets and circulate axially in the foam-free space without notable load losses. In this first space, a first de-oiling phase is carried out by the movement of large-diameter oil drops towards the periphery of the housing under the effect of the centrifugal force. The second space of the housing is lined with metal foams which are axially attacked by air and the remaining oil drops (i.e. of a smaller diameter), thus limiting the load losses. The oil drops captured by the foams are then centrifugated towards the periphery of the housing.

Advantageously and according to the invention, said metal foam presents a variable thickness—for example decreasing—between the inner wall and the outer wall of the housing so as to standardise the load losses between the zones close to the inner wall little subjected to the centrifugal force and the zones close to the outer wall highly subjected to the centrifugal force.

Given the architecture of a deaerator according to the invention, the shortest path for air between the inlet and the de-oiled outlet is that passing through the foam base, i.e. in the vicinity of the hollow shaft. Air therefore tends to pass through this low portion, which is furthermore, less subjected to the centrifugal force than the portions close to the periphery of the housing. To limit this phenomenon, this variant provides a modification of the geometry of the foam between the low portion of the foam (i.e. that in the vicinity of the inner wall) and the low portion of the foam (i.e. that in the vicinity of the outer wall), which allows better distributing the air passage and to standardise the load losses. The flow is thus better distributed and the speeds of the mixture are more homogenous. The oil which rises in the metal foams also tends to form bigger and bigger drops, which increases the oil concentration in the foams in the vicinity of the periphery of the housing. The shape of the filter also allows facilitating the draining of the oil contained in the filter.

Advantageously and according to the invention, each de-oiled air outlet is free of metal foam.

This variant allows avoiding a “bottleneck” effect in the vicinity of the de-oiled air outlets and therefore to avoid an increase of the speeds in the metal foam in the vicinity of the de-oiled air outlets, which would otherwise translate themselves by an increase in load losses.

Advantageously and according to the invention, said housing is formed of a plurality of compartments arranged radially around the hollow shaft, each compartment being supplied in mixture by an axial mixture inlet, being connected to one or more radial oil outlet(s) and to an de-oiled air outlet, each compartment comprising two successive spaces along the axial direction, a foam-free space and a foam-lined space, said foam-free space opening onto said axial inlet.

According to this variant, the housing of the deaerator is divided into a plurality of compartments, each compartment being connected to an axial inlet of the mixture to be able to be provided with mixture, one or several radial oil outlet(s) to be able to evacuate oil outside of the deaerator, and one or several de-oiled air outlet(s) to be able to evacuate de-oiled air towards the hollow shaft. These compartments are evenly distributed around the hollow shaft. This allows improving the de-oiling of the mixture by forming a plurality of centrifugal sub-housings for separating the mixture. Furthermore, each compartment presents the two successive spaces of the housing, namely a foam-free space to favour the suctioning of the air/oil mixture to be separated and a foam-lined space to favour the capturing of oil drops.

Despite these precautions, the use of a filter, typically of the metal foam type, tends to increase the load losses of the deaerator.

When the rotational speeds are substantial, the mixture acquires, in the air cells of the foam, substantial kinetic momentum. By orienting towards the outlet, the de-oiled air orients itself centripetally and the angular speed increases to conserve this kinetic momentum. This results in angular speeds, and therefore very substantial flow speeds in the hollow shaft of the deaerator. This significantly affects the load losses, in particular in high-speed applications.

Advantageously, to compensate the load losses connected to the use of filters or to reduce the load losses of a simple centrifugal deaerator, a vortex inhibitor is housed in the hollow shaft. This inhibitor can be added by gluing, screwing or interference fitting in particular, and constitutes a simple and easily integrable part in the hollow shaft. This variant thus allows reducing the load losses of a centrifugal deaerator with or without Retimet®, and therefore improving the performance of it. The vortex inhibitor can comprise flow recovery blades.

Advantageously according to the invention, said axial mixture inlet(s) and said radial oil outlet(s) are arranged axially on either side of said web of said pinion so as to prevent any reintroduction of oil evacuated by said radial oil outlet(s) in the housing through said axial mixture inlet(s).

A deaerator according to this variant of the invention allows segregating the air/oil mixture inlet flows of the oil evacuation flows by cleverly arranging the mixture inlets and the oil outlets with respect to the web of the pinion for rotating the deaerator. This arrangement provides that the mixture inlets and the oil outlets are axially arranged on either side of the web of the pinion. This therefore allows limiting, to the maximum, the reintroduction of oil evacuated through the radial oil outlets directly in the mixture present at the inlet of the deaerator. In other words, the web of the pinion acts as a separation wall between the mixture at the inlet of the deaerator and the oil evacuated through the radial oil outlets. Furthermore, when functioning, the pinion being in rotation, the teeth of the pinion generate, through air mixing, an air wall which surrounds the pinion and which therefore contributes also to limit the passage of the oil evacuated by the radial outlets towards the axial mixture inlets arranged on either side of the pinion. The pinion can be arranged axially at any point between the mixture inlets and the oil outlets. In particular, it can be arranged in the proximity of the mixture inlets or in the proximity of the oil outlets, centred or not.

This specific arrangement of the mixture inlets and of the oil outlets allows limiting the phenomenon of re-introducing oil into the mixture, which improves the de-oiling performance of the air/oil mixture. This improvement of performance allows optimising the quantity of oil embedded in the turbomachines and therefore reducing the mass of the turbomachine. This consequently allows improving the ecological impact of a turboshaft equipped with a deaerator according to the invention.

Advantageously, a deaerator according to the invention further comprises at least one anti-return disc extending perpendicularly to the outer wall and partially blocking said axial mixture inlet(s) in the housing so as to prevent an oil outlet in the vicinity of said outer wall through said axial mixture inlet(s).

According to this variant, the housing comprises an anti-return disc which acts as a wall preventing the oil outlet through the inlet of the mixture. In particular, when functioning, the housing is rotated by way of the pinion. The oil is thus driven by the centrifugal acceleration towards the outer wall of the housing. In the vicinity of the outer wall, before the evacuation of oil through the radial outlets, the oil forms an oil film which extends over the inside of the outer wall. To avoid this film sliding over the inside of the outer wall and emerging through the axial mixture inlets, the invention according to this variant provides a disc which blocks at the level of the outer wall of the oil passage. This therefore allows avoiding the mixture at the inlet of the housing being enriched by the oil extracted from the mixture during the processing by the deaerator.

Advantageously and according to this variant, the anti-return disc is formed by a portion of the web of the pinion arranged upstream of said housing and surrounding the axial mixture inlets.

According to this variant, the web of the pinion is arranged upstream of said housing. Furthermore, it is contributed to form the anti-return disc.

Advantageously and according to this variant, said web of said pinion comprises access openings to said axial inlet(s) of the mixture in the housing.

The pinion being arranged upstream of the housing, the web comprises advantageously openings allowing the mixture accessing the housing.

The invention also relates to a turboshaft comprising a mechanical member of the accessory box or reduction gear type, characterised in that it comprises a deaerator according to the invention adapted to be driven in rotation by said mechanical member.

A turboshaft according to the invention equipped with a deaerator according to the invention therefore consumes less oil than a turboshaft of the prior art by an improved oil recovery. A turboshaft according to the invention presents a lighter weight than a turboshaft of the prior art. The duration of a mission of a helicopter equipped with turboshafts according to the invention is therefore longer. Furthermore, the maintenance operations are less frequent. Finally, the ecological impact of a turboshaft according to the invention is better than that of the turboshafts of the prior art.

The invention also relates to a deaerator and a turboshaft characterised in combination by all or some of the features mentioned above or below.

