Patent Publication Number: US-2022233973-A1

Title: Deaerator for aircraft engine and associated method of operation

Description:
TECHNICAL FIELD 
     The application relates generally to aircraft engine lubrication systems and, more particularly, to deaerators thereof. 
     BACKGROUND OF THE ART 
     Aircraft engines typically have rotating parts held within a casing by bearings. A lubricant, oil, is typically continuously circulated to the bearings to ensure their proper functionality, and scavenged from the bearing cavities for continuous re-use in a cycle. When the oil returns to the pump(s), it can be foamy and have a significant air content. In a static reservoir, the air would eventually separate from the oil over time, its lower density driving it upwardly in reaction to the denser oil&#39;s pull downward due to the action of gravity, but aircraft engines are very dynamic environments, where weight is a constant design concern, in addition to manufacturability, durability, and costs generally, and it may not be practical to base the deaerating strategy solely on the use of a static reservoir. For instance, it can be desired to limit the amount of oil carried by the aircraft. Such considerations can favor the use of a deaerator to actively separate the air from the oil using centrifugal acceleration. While existing deaerators have been satisfactory to a certain degree, there always remains room for improvement, including in optimizing them in a manner to achieve better separation efficiency, require lower maintenance, represent lower cost, achieve lower weight, etc. 
     SUMMARY 
     In one aspect, there is provided a de-aerator for an aircraft engine lubrication system, the de-aerator comprising: a swirler cavity extending circumferentially around axis and axially between a proximal wall and a distal wall, a separation path dividing within the swirler cavity into a radially outer oil segment leading to an oil outlet and a radially inner air segment leading to an air outlet, and a swirling conduit portion having a length turning around the axis upstream of an opening in the proximal wall along the separation path, the opening fluidly connecting the swirling conduit portion to the swirler cavity, the swirling conduit portion oriented both circumferentially and axially immediately upstream of the opening. 
     In another aspect, there is provided a method of separating air from oil in an aircraft engine lubrication system, the method comprising: performing a first separation step including conveying a mixture of said air and oil along a swirling conduit portion including turning a flow of the mixture along an axis while simultaneously advancing the flow of the mixture along the axis, said turning causing the oil to concentrate radially outwardly and said air to migrate radially inwardly; outputting the mixture of air and oil from the swirling conduit portion both circumferentially and axially into a swirler cavity, and performing a second separation step including rotating the mixture of air and oil within the swirler cavity, including directing a radially outward concentration of oil to an oil outlet and a radially inward concentration of air to an air outlet. 
     In a further aspect, there is provided a fluid separator for separating a higher density liquid from a lower density fluid, the separator comprising: a separation path extending sequentially across a swirling conduit portion and a swirler cavity, the swirler cavity having an axis and defined within a radially-outer wall, a proximal wall and a distal wall, the proximal wall and the distal wall extending radially inwardly at axially opposite ends of the radially-outer wall, the separation path dividing within the swirler cavity into a radially outer oil segment leading to an oil outlet and a radially inner air segment leading to an air outlet, the swirling conduit portion turning around the axis upstream of an opening in the proximal wall, the opening fluidly connecting the swirling conduit portion to the swirler cavity, the swirling conduit portion oriented both circumferentially and axially immediately upstream of the opening. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
         FIG. 2A  is a schematic cross-sectional view of a deaerator taken along an axial/radial plane; 
         FIG. 2B  is a proximal elevation view of the deaerator of  FIG. 2A ; 
         FIGS. 3A, 3B and 3C  are corresponding examples of cross-sectional profiles for a swirling conduit portion of a deaerator; 
         FIG. 4  is an oblique view of portions of a deaerator in accordance with another example; 
         FIG. 5  is an oblique view of an opening fluidly connecting a swirling conduit portion to a swirler cavity; 
         FIG. 6A  is an oblique view of another embodiment of a conduit of a deaerator; 
         FIG. 6B  is a schematic view taken along lines  6 B- 6 B of  FIG. 6A ; 
         FIG. 6C  is a schematic view taken along lines  6 C- 6 C of  FIG. 6A ; 
         FIG. 7  is a cross-sectional view of a portion of portions of the deaerator of  FIG. 5 ; 
         FIG. 8  is an oblique view of a swirling conduit portion of the deaerator of  FIG. 5 , schematically representing a lengthwise variation in the cross-sectional profile; 
         FIG. 9  is a cross-sectional view of a deaerator schematizing the effect of the cross-sectional profile adjacent the opening. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a gas turbine engine  10  of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan  12  through which ambient air is propelled, a compressor section  14  for pressurizing the air, a combustor  16  in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases around the engine axis  11 , and a turbine section  18  for extracting energy from the combustion gases. 
     The compressor  14 , fan  12  and turbine  18  have rotating components which can be mounted on one or more shafts. Bearings  20  are used to provide smooth relative rotation between a shaft and casing (non-rotating component), and/or between two shafts which rotate at different speeds. An oil lubrication system  22  including an oil pump  24 , sometimes referred to as a main pump, and a network of conduits and nozzles  26 , is provided to feed the bearings  20  with oil. Seals  28  are used to delimit bearing cavities  32  and contain the oil. A scavenge system  30  having cavities  32 , conduits  34 , and one or more scavenge pumps  36 , is used to recover the oil from the bearing cavities  32 , which can be in the form of an oil foam at that stage. The oil pump  24  typically draws the oil from an oil reservoir  38 , and an air/oil separating device, which will be referred to simply as a deaerator  40  here, can be used in the return line. 
     The deaerator  40  can allow to achieve a relatively high degree of separation of the air from the oil relatively quickly, at suitable low weight and cost. A motivation to use a deaerator  40  can be associated with a desire to limit the footprint/volume of the oil reservoir, a typical consideration in aviation often put into balance with weight, costs, etc, as a larger oil reservoir could be required to achieve a suitable degree of air-oil separation passively in the reservoir. The deaerator  40  can be active, and be configured for harnessing centrifugal acceleration to accelerate the separation of the oil from the air which tends to arise naturally over time due to the difference in densities between the different fluids. Separation efficiency, a specification which typically refers to the degree at which the fluids are effectively separated from one another in the corresponding outlets in various operating conditions, and which can specify limits of % of oil in air or % air in oil, by volume or by weight, for instance, is typically a significant consideration in aircraft lubrication system deaerator design. 
     An example of a deaerator  40  is presented at  FIG. 2A . The deaerator has a swirler cavity  42 , a cavity shaped in a manner to favor the continuous rotation of the fluid circulating therein around an axis  41 . In this case, the axis is straight and the vortex has a generally solid of revolution in shape. In practice, the cavity  42  is formed within some form of housing  44  which can be made of one or more component and which has an internal surface generally having a surface of revolution shape. In this example, the housing  44 , and can be said to have a radially-outer wall  46  extending along the axis, between a proximal wall  48  and a distal wall  50 . The proximal wall  48  and the distal wall  50  can both extend radially inwardly from corresponding axial ends of the radially-outer wall  46 . In this example, the radially-outer wall  46  is cylindrical tubular and the proximal and distal walls  48 ,  50  are circular discs (except for openings forming inlet and/or outlet). The expression proximal can be used to refer to “closer to the inlet” for instance, in this specification. In one example, the swirler cavity  42  can have a generally cylindrical geometry with the radially-outer wall  46  being tubular in shape and the proximal and distal walls  48 ,  50  being generally disc-shaped, but it will be understood that different, potentially more elaborated or complex geometries can be preferred in alternate embodiments. The swirler cavity  42  is generally solid of revolution shaped and has smooth surfaces to facilitate preservation of fluid rotation around the axis. Maximizing rotation of the fluid in the swirler cavity  42  can be desired as its circumferential momentum can be harnessed to favor separation due to the difference in fluid density and centripetal acceleration. Indeed, the denser oil can be driven radially outwardly and concentrate to form a pool radially outwardly, while the lighter air can migrate radially inwardly. 
     The path followed by the mixture of air and oil can be referred to herein as the separation path  52 . The separation path  52  can be said to separate in the swirler cavity  42  into an oil segment  54  leading to an oil outlet  58 , and an air segment  56  leading to an air outlet  60 . The air segment  56  is typically radially internal to the oil segment  54  past the splitting area. All the walls of the swirler cavity are typically surface of revolution shaped, except for any inlets and outlets, and any inlets and outlets can be configured in a manner to minimize imparting turbulence or pressure losses into the flow. For instance, in a circular disc-shaped proximal wall  48 , an opening  62  can be the only irregularity in an otherwise planar surface. In this embodiment, the opening  62 , acts both as an inlet to the swirler cavity  42 , and as an outlet of an upstream conduit  66 , and fluidly connects the upstream conduit  66  to the swirler cavity  42 . Similarly, outlet openings can be provided. outlet openings can be circular, or be provided in the form of a radially inner edge, for instance, of an annular wall portion centered on the axis. The housing  44  can be housed in another housing, not shown, within which some fluid can be recirculated along the separation path  52  depending on the particulars of the design. Moreover, depending of the design, an impeller may or may not be present within the swirler cavity. If used, the impeller can be driven to introduce circumferential momentum into the vortex, or otherwise simply used as additional partitioning or segmenting of the swirler cavity to favor the efficiency of separation of the oil from the air, and be driven into rotation by the circumferential momentum of the flow. 
     As presented in the example deaerator  40  presented in  FIGS. 2A and 2B , it was found that introducing a swirling conduit portion  64  immediately upstream of the swirler cavity  42  could be beneficial to separation efficiency. In particular, it was found that curvature in a conduit  66  upstream of the swirler cavity  42 , such as a swirling conduit portion  64  or even an elbow  68  can be beneficial to begin separating the oil from the air, with the oil migrating radially outward of the curvature radius and the air “floating” above it radially inwardly relative to the curvature radius, within the conduit. Moreover, it was found that the geometry of the conduit  66 , and particularly the portion immediately upstream of the swirler cavity  42 , can contribute to the strength of the vortex. Indeed, purposeful orientation of the fluid as it enters the swirler cavity  42 , in a manner to cross the opening with a significant amount of tangential momentum, and in a manner to avoid generating unnecessary turbulence, can favor the strength of the vortex and thus the centrifugal acceleration within the swirler cavity and the separation efficiency. Finally, it was also found that by using a swirling conduit portion  64  which turned around the axis  41 , in a somewhat helical manner as perhaps best seen by looking both to  FIGS. 2A and 2B , before reaching the opening  62  and the swirler cavity  42 , can further predispose an area of higher oil concentration in a manner to be positioned and directed radially outwardly nearing the outlet  62  of the inlet conduit  66 , which can direct it specifically towards the radially-outer oil segment  54  of the separation path, and can simultaneously predispose an area of higher air concentration radially inwardly, which can direct air specifically towards the radially-inner air segment, and be further beneficial to separation efficiency. Further explanation and example concerning the latter will be presented below. 
     In the embodiment presented in  FIGS. 2A and 2B , the swirling conduit portion  64  is oriented both circumferentially and axially immediately upstream of the opening  62  due to the combination of the turning around the axis  41  (as best seen in  FIG. 2B ) and of the pitch P of the swirling conduit portion (best seen in  FIG. 2A ), which takes the form of a progression in the orientation of the axis  41  along the turning length of the conduit. This circumferential and axial momentum enters the swirler cavity  42  with the fluid and contributes to sustaining the vortex. Any turbulence or restriction to fluid flow can break or slow down this momentum, but turbulences can be minimized with smooth surfaces and restrictions can be minimized by streamlining the structure as a function of the engineered vortex flow geometry. 
     The conduit  66  upstream of the swirler cavity  42  can have different cross-sectional profiles, depending on the embodiment, and the cross-sectional profile can be constant along a portion or the entirety of the length, or vary along a portion or the entirety of the length.  FIG. 3A  schematizes a possible circular cross-sectional profile in the swirling conduit portion  64  of the conduit  66 .  FIG. 3B  schematizes a possible obround cross-sectional profile, and  FIG. 3C  schematizes a possible elliptic cross-sectional profile. The latter cross-section profiles can be said to be symmetrically concave parabolic. Other cross-sectional profiles are possible and the cross-sectional profile can even be intentionally modified along the length of the conduit, an example of which will be presented below. 
     In the swirling conduit portion  64 , the cross-sectional shape of the profile can be said to have an axial dimension  70 , extending in the orientation of the axis  41 , and a radial dimension  72 , extending radially relative to the axis  41 . In the case of the obround and elliptic cross-sectional profiles, shown respectively in  FIGS. 3B and 3C , the axial orientation can be greater than the radial orientation, for instance. Moreover, the cross-sectional shape of the profile can be said to have a radially inner side  74  or surface, relative to the axis  41 , and a radially outer side  76  or surface, diametrically opposite the radially inner side  74 . Further, the cross-sectional shape of the profile can be said to have a first side  78  proximate the swirler cavity  42 , and a second side  80  diametrically opposite the first side  78 , away from the swirler cavity  42 . We will get back to these notions for characterizing possible shapes and configurations further below. 
     The shape of the opening  62  in the proximal wall  48  of the housing  44 , which fluidly connects the conduit to the swirler cavity, can depend on a number of factors such as the geometry of the proximal wall  48 , the cross-sectional profile of the conduit  66  along the opening, immediately upstream of the opening, and the particularities of the swirling path in the opening region, such as the turning radius (particularly relative to the dimensions of the proximal wall) and pitch for a helical swirling conduit portion for instance. 
     In an effort to harness circumferential momentum in the swirling conduit portion  64 , the pitch P can be limited. However, a certain amount of pitch may be required to allow a suitable shape and size of the opening  62 . Independently of the cross-sectional profile, the cross-sectional profile can have an axially oriented dimension  70  and a transversally oriented dimension  72 . The pitch, can be defined as the amount of axial progression of the conduit  66  for a complete turn thereof around the axis (including possibly a projection of such an axial progression should the swirling continue for a full turn in cases such as the one illustrated where it does not). The pitch can be of a size comparable to the axially oriented dimension  70  of the profile, for instance. The pitch P can be between 0.5 and 1.5 of the axial dimension  70 , for instance, or perhaps preferably of between 0.8 and 1.2 of the axial dimension  70 . Sizes lower than the axial dimension  70  are possible when the swirling does not make a full turn, for instance. 
       FIG. 4 , presents portions of a deaerator  140  having another possible geometry, and in which the swirling conduit portion  164  has a continuous, obround, cross-sectional profile. The turning of the conduit can continue along the circumferential length of the opening, which can give the opening  162  a shape reminiscent of a crescent or banana, with profiles and pitches such as presented above, and a generally planar, disc-shaped proximal swirler cavity wall  148 . The shape of the opening can progressively increase in radial width and then progressively decrease in radial width as its center progresses circumferentially in the orientation of the swirl, and as the axial thickness of the conduit diminishes as a function of the pitch and turning. 
       FIG. 5  shows a computer fluid mechanics simulation of the relative concentration of oil and air which can occur at the opening  162  based on the use of a swirling conduit portion  164  upstream thereof, showing that the oil can be significantly more concentrated radially outwardly  180  relative to the axis and the air can be significantly more concentrated radially inwardly  182  relative to the axis, another color or tone being used to depict regions of intermediate concentration  184 . 
       FIGS. 6A-6C  present another embodiment of a conduit  266  having a swirling conduit portion  264  turning around an axis  241  upstream of an opening  262 . In this embodiment, the conduit  266  has an obround-shaped cross-section such as illustrated in  FIG. 3B , which tapers off due to the pitch along the circumferential length of the opening, i.e. from an upstream end  288 , or beginning, of the opening  262 , to a downstream end  289  of the opening  262 . To better illustrate the tapering, additional views  6 B and  6 C are presented, taken from corresponding lines  6 C- 6 C and  6 B- 6 B of  FIG. 6A , and where the intersection of a virtual cylindrical surface  299  and the inside of the conduit  266  is shown relative to the structure of the conduit  266  which is otherwise made translucent to allow seeing the intersection for the purpose of illustration and understanding. The view of  FIG. 6C  is taken roughly radially inwardly in alignment with the beginning  288  of the opening, showing the beginning of the circumferentially oriented tapering, whereas the view of  FIG. 6B  is taken roughly radially inwardly in alignment with the downstream end  289  of the opening  262 , showing the termination of the circumferentially oriented tapering as the swirling conduit portion feathers into the swirler cavity. The interface between the edges of the opening and the swirling conduit portion can be rounded to a certain extent to provide a smooth transition between the two flow environments. 
     The turning of the conduit  166 ,  66 ,  266  can preferably extend upstream of the circumferential length  186  of the opening  162 . For instance, the swirling conduit portion can extend along an angle of at least 10°, preferably at least 25°, more preferably at least 40°, more preferably at least 55°, before the circumferential position of the beginning  188  of the opening  162 . It was found that in some embodiments, the advantages associated to extending the length of the swirling conduit portion  164 ,  64  began to fade when extending the length to above about 90°, 75°, or even 60° upstream of the opening  162 ,  62 , at which point other considerations such as additional weight associated to additional conduit length can begin to take precedence over any advantages associated to further extending the length of the swirling conduit portion  64 . This being said, in some embodiments, using an additional curve higher upstream of the conduit  66  can be useful. In the embodiment presented in  FIGS. 2A and 2B , it was found useful to introduce an elbow  68  upstream of a straight portion  69  connecting the elbow portion  68  to the swirling conduit portion  64 . 
     The radius of curvature r at which the center of the swirling conduit portion  64 ,  164  turns around the axis  41  can be roughly the same as the radial position R of the center of the opening relative to the axis  41 . In some cases there can be some degree of axial misalignment between the radius of curvature and the axis  41 . Moreover, in some cases, it can be preferred for the radial position of the center of the opening  62  to be somewhat greater than the radius of curvature of the swirling conduit portion  64  upstream of the opening  62 . For instance, in some embodiments, the radial distance between a center of the opening and the axis can be of between 115% and 100% of a radius of curvature of the swirling conduit portion upstream of the opening, preferably of between 105 and 110%. 
       FIG. 7  presents a possible example geometry of a swirler cavity  142  for the deaerator  140  shown in  FIG. 4 . As shown, in this example, the housing forming the swirler cavity  142  has a rotor  190  in the form of one or more component configured to rotate around the axis  141 , in the circumferential direction of the flow, relative to other components such as the swirling conduit portion  164  which can remain fixed relative to the axis  141 . In this example, the rotor  190  has as impeller blades  192 . The proximal wall can be formed by a combination of a static portion  148 , and an annular, radially outward portion  194  of the rotor  190 . The rotor  190  can have a circumferentially outwardly oriented pool area  196  where a given oil level can be sustained during operation of the deaerator, and a disc-like partition  198  can partially, radially-outwardly, penetrate into the pool  196 , around the entire circumference, and at an intermediate axial location, so as to further favor separation efficiency. The air segment can penetrate radially inwardly upstream of the partition  198 , into an axially oriented conduit portion  160  formed in the rotor. The rotor can be externally driven into rotation. A distal “gate” portion  199  of the rotor  190  forms the opposite axial end of the pool  196 . 
     During standard operation, oil can be fed into the swirler cavity  142 ,  42  at a tangential, angular velocity of between 95% and 110% of the angular velocity or the rotating impeller  192 , preferably between 100 and 105%, and the deaerator  140  can be configured specifically with this in mind. For instance, in one embodiment, the impeller  192  can be driven entirely by the momentum of the oil/air mixture and naturally reach a speed of between 95 and 100% of the speed of the oil/air mixture through the opening, or the scavenge pump and any drive motor can be configured, taking into consideration the context of fluid circulation in primary operating conditions, in a manner for such relative speeds to be sustained. 
     As evoked above, the cross-sectional profile of the conduit, and in particular of the swirling conduit portion  164 , can evolve along its length for various reasons. In the embodiment presented in  FIG. 4 , it was preferred to vary the cross-sectional profile of the conduit  166  in the swirling conduit portion  164  as it reaches, and along the circumferential length of the opening, from a symmetrically concave parabolic cross-section to a progressively more and more unsymmetrically-concave parabolic cross section having gradually diffusing and enlarging exit area to minimize the axial discharge velocity of the working fluid and direct a concentration of oil more specifically towards the pool  196  and otherwise the oil segment of the separation path, so as to avoid and/or limit any remixing of oil and air in the swirler cavity. 
       FIG. 8  illustrates the evolution of the cross-sectional profile of the swirling conduit portion  164  in the vicinity of the opening  162 . More specifically, as the swirling conduit portion  164  reaches the opening  162 , the radially outer surface or side  176  begins to slope towards the radially inner surface  174  towards the second side  180 . 
     As shown in  FIG. 9 , the resulting cross-sectional profile at the outlet section of the conduit which is open due to the presence of the opening  162 , can have a radially inner side  174  which is generally axially oriented, and a radially outer side  176  which fans the concentration of oil radially outwardly towards the pool  196   
     Generally, in accordance with the above, it was found possible to shape a swirling conduit portion in a manner to increase gas-liquid mixture separation before entering the swirler cavity. The mixture can follow a longer and smoother path from the exit of the scavenge pumps towards the rotating impeller. The helical path of the swirling conduit portion can push the denser oil to the outer surface of the passage due to its higher inertia. As a result, most of the denser liquid can enter the impeller at the largest diameter of its inlet. This can help to reduce the impeller&#39;s burden on separation as it receives a flow already stratified improving separation efficiency while minimizing heat generation. 
     Moreover, the cross section of the swirling conduit portion can be sized sized so that the mixture enters the rotational impeller domain with a similar circumferential velocity. This can reduces the amount of energy necessary to drive the impeller to separate the oil as the impeller does not have to increase the circumferential speed of the denser liquid. 
     The embodiments described in this document provide non-limiting examples of possible implementations of the present technology. Upon review of the present disclosure, a person of ordinary skill in the art will recognize that changes may be made to the embodiments described herein without departing from the scope of the present technology. For example, although referred to herein as a deaerator for simplicity, it will be understood that the deaerator is a separator which can be used to separate other fluids than air from oil in different applications. Moreover, in the embodiments presented above, it will be noted that the swirling conduit portion does not penetrate into the swirler cavity, and rather connects and terminates with the proximal wall, this can be preferred in some embodiments to avoid a re-entrant edge affecting the swirling momentum of the flow within the cavity. Yet further modifications could be implemented by a person of ordinary skill in the art in view of the present disclosure, which modifications would be within the scope of the present technology.