Abstract:
A vent for a fluid system includes a chamber through which fluid can flow along either a first flow path or a second flow path, in which the resistance to fluid flow is relatively high when the fluid follows the first flow path and relatively low when the fluid follows the second flow path. In a preferred embodiment the chamber is substantially cylindrical and has two ports, one of which is substantially coaxial with the chamber and the other of which is substantially tangential to the chamber. The fluid flow, at least when flowing the first flow path, may include a component of higher density than the fluid, and the flow of fluid along the first flow path may act to separate the higher density component from the fluid.

Description:
This application is a continuation of National application Ser. No. 11/178,325 filed Jul. 12, 2005, and now abandoned, wherein the aforesaid application is a continuation application of National application Ser. No. 10/619,145 filed Jul. 15, 2003 and now abandoned. 

   FIELD OF THE INVENTION 
   This invention relates to vents for fluid systems. More particularly, but not exclusively, it relates to vents for bearing chambers, for example in gas turbine engines. 
   BACKGROUND OF THE INVENTION 
   Gas turbine engines typically include one or more shafts supported on oil-lubricated bearings. These bearings are housed in bearing chambers, and there are seals between the chamber and the shaft to inhibit the leakage of lubricating oil. It is usually arranged that, under normal operating conditions, the pressure outside a bearing chamber is slightly higher than the pressure within it. This differential pressure ensures that there is a continuous counterflow of air inwards through the seals and oil leakage is avoided. However, under certain transient conditions the pressures may change so that the differential pressure is reversed. In these circumstances, oil will tend to pass through the seals and out of the bearing chamber. 
   Various types of sealing arrangement are known that attempt to prevent oil leakage. Labyrinth seals generally require a large and heavy buffer system to operate properly; some such systems also incorporate drains to dispose of any oil that does leak, adding further weight and complexity. Carbon seals can operate with a smaller counterflow of air, which may save weight in the buffer system, but they are still prone to allow oil to escape if the differential pressure is reversed. 
   A separate vent may be provided for the bearing chamber, to allow an outward flow of air, when required, other than through the bearing chamber seals. Examples of such devices are simple vents, with or without restrictors, and spring-loaded valves; but oil can still escape from the bearing chamber through these devices, and so they do not solve the fundamental problem. 
   Any oil that does leak out of a bearing chamber may contaminate the core air flow of the engine. When gas turbine engines are installed in aircraft, typically a proportion of the core air flow is taken to supply breathable air for the crew and passengers. The “cabin odour” arising out of this sort of contamination has long been recognised as undesirable. However, in recent years it has become increasingly clear that contaminated cabin air may also represent a serious health and safety hazard. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a simple and compact vent, which will allow air to flow both into and out of the bearing chamber, but which will substantially prevent the leakage of oil from the bearing chamber. 
   According to one aspect of this invention, a vent for a fluid system includes a chamber through which fluid can flow along either a first flow path or a second flow path, in which the resistance to fluid flow is relatively high when the fluid follows the first flow path and the resistance to fluid flow is relatively low when the fluid follows the second flow path. 
   Preferably the first flow path is associated with fluid flow in one direction through the chamber, and the second flow path is associated with fluid flow in the opposite direction through the chamber. 
   Preferably the chamber has two ports, the two ports lying in planes substantially perpendicular to each other. 
   In a particular preferred embodiment of this aspect of the invention, the chamber is substantially cylindrical. Preferably, one of the two ports is arranged to be substantially coaxial with the chamber and the other of the two ports is arranged to be substantially tangential to the chamber. 
   The substantially tangential port may have a convergent or convergent-divergent inner profile. 
   An annular wall member may protrude generally axially from the coaxial port into the chamber. 
   The fluid flow, at least when following the first flow path, may include a component of higher density than the fluid, and the flow of the fluid along the first flow path may act to separate the higher density component from the fluid. The chamber may be extended in an axial direction to receive the higher density component separated from the fluid. Means may be provided to carry the higher density component out of the chamber. 
   The higher density component may comprise a lubricant. 
   The vent may be a part of a bearing chamber. The vent may be a part of a gas turbine engine. 
   According to an alternative aspect of the invention, a venting arrangement for a fluid system comprises a first vent and a second vent, the first and second vents being arranged in flow series, in which the first and second vents are so arranged that when fluid flows through the venting arrangement in one direction it follows the first flow path through the chamber of the first vent, and when fluid flows through the venting arrangement in the other, opposite direction it follows the first flow path through the chamber of the second vent. 
   According to a further alternative aspect of the invention, a venting arrangement for a fluid system comprises a plurality of vents, the vents being arranged in flow series, in which the vents are so arranged that when fluid flows through the venting arrangement in one direction it follows the first flow path through the chamber of each vent in succession, and when fluid flows through the venting arrangement in the other, opposite direction it follows the second flow path through the chamber of each vent in succession. 
   The venting arrangement may be a part of a bearing chamber. The venting arrangement may be a part of a gas turbine engine. 
   The preferred embodiments of all the aspects of the invention described in this specification use a device, known as a vortex throttle or vortex diode, which is well known in the art of fluidics. This device will be described in more detail later in the specification. Those skilled in the art of fluidics will be aware of the distinctions between a vortex throttle and a vortex diode; for the purposes of this specification such distinctions are generally unimportant and for the sake of clarity the term “vortex diode” will be used throughout. 
   Fluidics is a discipline whose origins lie in attempts to overcome the susceptibility of electronic circuits to interference from electromagnetic radiation. It teaches the construction of circuits, analogous to electrical or electronic circuits, in which a flow of fluid, rather than a flow of electrons, performs the work. Devices such as switches, diodes, amplifiers and so on, familiar in an electrical context, can also be made to work satisfactorily in fluidic circuits. Fluidics has received relatively little attention in recent years, although its principles have been applied (on a larger scale) in fields such as sewage flow control, where the absence of moving parts in fluidic components permits the construction of reliable valves that are not prone to blockage. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  is a schematic sectional view of a vortex diode of known type, showing the air flows in the “low resistance” direction; 
       FIG. 2  is a schematic sectional view taken on the line A-A in  FIG. 1 ; 
       FIG. 3  is a schematic sectional view of a vortex diode of known type, showing the air flows in the “high resistance” direction; 
       FIG. 4  is a schematic sectional view taken on the line B-B in  FIG. 3 ; 
       FIG. 5  is a schematic representation of a bearing chamber having a vent according to one aspect of the invention; 
       FIGS. 6 and 7  are schematic sectional views of two alternative embodiments of a bearing chamber vent according to one aspect of the invention; 
       FIG. 8  is a schematic sectional view of a further alternative embodiment of a bearing chamber vent according to one aspect of the invention; 
       FIG. 9  is a schematic representation of a bearing chamber having a venting arrangement according to an alternative aspect of the invention; 
       FIG. 10  is a schematic representation of a bearing chamber having a venting arrangement according to a further alternative aspect of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIGS. 1 and 2 , a vortex diode  20  of known type comprises structure  22  defining a cylindrical volume  24 . Two ducts of circular cross-section are in fluid communication with the cylindrical volume  24 . Duct  26  is coaxial with the cylindrical volume  24  and duct  28  is tangential to the cylindrical volume  24 . 
   When fluid flows into the cylindrical volume  24  through the duct  26 , as shown by the arrow  30  in  FIG. 2 , it will tend to flow substantially in the manner indicated by the arrows  32  so as to exit the cylindrical volume  24  via the duct  28 , and the resistance to flow will be relatively low. 
   Referring now to  FIGS. 3 and 4 , the arrangement of the vortex diode  20  is exactly as in  FIGS. 1 and 2 . When fluid flows into the cylindrical volume  24  through the duct  28 , as shown by the arrows  40 , the geometry of the cylindrical volume  24  will tend to urge the fluid into vortical flow, as shown by the arrow  42  in  FIG. 3 . The fluid will then exit the cylindrical volume  24  via the duct  26  (as shown by the arrow  44  in  FIG. 4 ), but because of the swirling motion imparted to the flowing fluid the resistance to flow will be relatively high. Furthermore, any higher density component entrained in the fluid will tend to be urged outwards by centrifugal force, and will tend to be separated from the fluid. 
   The duct  28  may have an inner profile that converges towards the cylindrical volume  24 , or may have an inner profile that is convergent-divergent. When fluid flows into the cylindrical volume  24  through the duct  28 , as shown in  FIGS. 3 and 4 , such an inner profile will increase the velocity of the fluid flowing into the cylindrical volume  24 , for a given pressure drop, and thus increase the efficiency of the separation. 
     FIG. 5  shows a schematic sectional view of a bearing chamber  50  of a gas turbine engine (not shown having a vent according to one aspect of the invention. Conduit  52  links the bearing chamber  50  to the tangential port  54  of a vortex diode  56  of known type. Conduit  58  links the coaxial port  60  of the vortex diode  56  to a region  62  outside the bearing chamber  50 . 
   The vent is shown attached to the side of the bearing chamber. However, it is envisaged that it could equally well be integrated into the structure of the bearing chamber, or alternatively be entirely separate from the bearing chamber and mounted separately within the engine. 
   In normal operation, the pressure in the bearing chamber  50  will be lower than the pressure in the region  62  outside the bearing chamber  50 , and so there will be a flow of air from the region  62  into the bearing chamber  50 . Air will therefore flow into the vortex diode  56  through the coaxial port  60 , and out through the tangential port  54 . The air flow through the vortex diode  56  will therefore be substantially as shown by the arrows  30  and  32  in  FIGS. 1 and 2 , and the resistance to flow will be relatively low. 
   It is possible, under certain operating conditions of the gas turbine engine, that the relative pressures in the engine may change such that the pressure in the bearing chamber  50  is higher than the pressure in the region  62 . There will then be a flow of air from the bearing chamber  50  into the region  62 . Air will therefore flow into the vortex diode  56  through the tangential port  54 , and out through the coaxial port  60 . The air flow through the vortex diode  56  will therefore be substantially as shown by the arrows  40 ,  42  and  44  in  FIGS. 3 and 4 , and the resistance to flow will be relatively high. It is likely that some oil or similar lubricant will be entrained in the air flow, and (as explained in the discussion of  FIGS. 3 and 4 ) the swirling motion imparted to the air will tend to urge any such component outwards by centrifugal force, and will thus tend to separate it from the air. 
     FIGS. 6 and 7  show two alternative embodiments of the vortex diode used in the vent of  FIG. 5 , in which provision is made to collect oil separated out from the air flow. In the embodiment of  FIG. 6  the cylindrical volume  24  is extended downward by the addition of an annular volume  64 . In  FIG. 7 , the whole of the cylindrical volume  24  is enlarged downward. In use, under the abnormal conditions described earlier when the air flow is as shown in  FIGS. 3 and 4 , any oil separated out from the air flow will collect in the annular volume  64  (of  FIG. 6 ) or in the lower part of the enlarged cylindrical volume  24  (of  FIG. 7 ). Subsequently, when the air flow returns to normal, as shown in  FIGS. 1 and 2 , the separated oil can flow through the conduit  66  back into the duct  28  and subsequently back to the bearing chamber, impelled by the normal flow of air out of the vortex diode  20  through the duct  28  (as shown by arrow  32  in  FIG. 1 ). The conduits  66  and  28  may be arranged so that the separated oil will tend to flow back to the bearing chamber under the action of gravity. 
     FIG. 8  shows an alternative embodiment of a vortex diode having a higher resistance to flow in the “low resistance” direction. An annular collar  68  protrudes into the cylindrical volume  24 . In addition, the duct  28  is of smaller diameter than in the vortex diode of  FIG. 1 . It will be appreciated, by one skilled in the art, that changes may be made to the protrusion of the collar  68 , and to the diameters of the two ducts  26  and  28 , so as to tailor the flow resistance of the vortex diode in both directions to suit particular applications. 
     FIG. 9  shows a bearing chamber having a venting arrangement, according to an alternative aspect of the invention, which comprises two vortex diodes in flow series. Conduit  52  links the bearing chamber  50  to the tangential port  70  of a first vortex diode  72 . Conduit  74  links the coaxial port  76  of the first vortex diode  72  to the coaxial port  78  of a second vortex diode  80 . Conduit  82  links the tangential port  84  of the second vortex diode  80  to a region  62  outside the bearing chamber  50 . 
   In normal operation, when the pressure in the bearing chamber  50  is lower than the pressure in the region  62 , there will be a flow of air from the region  62  into the bearing chamber  50 . Air will therefore flow into the second vortex diode  80  via its tangential port  84 , and out through its coaxial port  78 . It will be apparent that the air flow through the second vortex diode  80  will therefore be substantially as shown by the arrows  40 ,  42  and  44  in  FIGS. 3 and 4 , and that the resistance to flow will be relatively high. Furthermore, any oil entrained in the air flow will tend to be separated out by centrifugal force. The air will subsequently flow through the conduit  74  and through the first vortex diode  72 , entering through the coaxial port  76  and exiting through the tangential port  70 . The air flow through the first vortex diode  72  will therefore be substantially as shown by arrows  30  and  32  in  FIGS. 1 and 2 , and the resistance to flow will be relatively low. 
   In the converse case, where the pressure in the bearing chamber  50  is higher than the pressure in the region  62 , the flow of air will be from the bearing chamber  50  into the region  62 . It will be apparent that the flow of air through each of the first and second vortex diodes will be reversed. Consequently the first vortex diode  72  will now offer a relatively high resistance to flow, and any oil entrained in the air flow will tend to be separated out by centrifugal force; the second vortex diode  80  will offer a relatively low resistance to flow. Thus, this venting arrangement will offer a relatively high resistance to flow in both directions, while still permitting the centrifugal separation of any oil entrained in the air flow. 
   It will be appreciated, by one skilled in the art, that this arrangement could be further refined by tailoring the flow characteristics of the first and second vortex diodes (as discussed with reference to  FIG. 8 ) to obtain various combinations of flow characteristics in the two directions 
   The venting arrangement is shown attached to the side of the bearing chamber. However, it is envisaged that it could equally well be integrated into the structure of the bearing chamber, or alternatively be entirely separate from the bearing chamber and mounted elsewhere within the engine. 
   It will be appreciated that the two vortex diodes may be arranged differently in relation to each other, provided that their coaxial ports are always linked together, without affecting the operation of the venting arrangement. 
     FIG. 10  shows a bearing chamber having a venting arrangement according to a further aspect of the invention, comprising three vortex diodes arranged in flow series. 
   Conduit  52  links the bearing chamber  50  to the tangential port  54  of a first vortex diode  56 . A conduit  57  links the coaxial port  60  of the first vortex diode  56  to the tangential port  54  of a second vortex diode  56 . A further conduit  57  links the coaxial port  60  of the second vortex diode to the tangential port  54  of a third vortex diode  56 , in like manner. Conduit  58  links the coaxial port  60  of the third vortex diode  56  to a region  62  outside the bearing chamber  50 . 
   Under normal operating conditions, when the pressure within the bearing chamber  50  is less than the pressure in the region  62  outside the bearing chamber  50 , air will flow from the region  62 , through the conduit  58 , then successively through the three vortex diodes  56 , entering each in turn through its coaxial port  60  and exiting through its tangential port  54 . Within each vortex diode  56 , then, the flow of air will be substantially as shown by the arrows  30  and  32  in  FIGS. 1 and 2 , and the resistance to flow through each vortex diode  56  will be relatively low. 
   In the converse case, when the pressure within the bearing chamber  50  is greater than the pressure in the region  62 , air will flow out of the bearing chamber  50 , through the conduit  52 , then successively through the three vortex diodes  56 , entering each in turn through its tangential port  54  and exiting through its coaxial port  60 . Within each vortex diode  56 , then, the flow of air will be substantially as shown by the arrows  40 ,  42  and  44  in  FIGS. 3 and 4 , and the resistance to flow will be relatively high. In addition, any oil entrained in the air flow can be separated out by centrifugal force in any of the three vortex diodes, thus giving a more effective separation than in the embodiment having only one vortex diode. 
   The venting arrangement is shown attached to the side of the bearing chamber. However, it is envisaged that it could equally well be integrated into the structure of the bearing chamber, or alternatively be entirely separate from the bearing chamber and mounted elsewhere within the engine. 
   It will be appreciated that the three vortex diodes may be arranged differently in relation to each other, provided that the ports of the successive vortex diodes are always connected in the manner shown in  FIG. 10 , without affecting the operation of the venting arrangement. 
   Although this aspect of the invention has been described with reference to three vortex diodes, it will be appreciated by those skilled in the art that other numbers of vortex diodes could equally well be used. 
   It will be appreciated that it would also be possible for each of the vortex diodes to have different flow characteristics (as discussed in connection with  FIG. 8 ), for example to optimize the oil separation.