Patent Publication Number: US-2015075175-A1

Title: Vortex fluid flow device

Description:
The present invention relates to devices for controlling fluid flow. More specifically the invention relates to vortex fluid flow devices and gas turbine engines. The invention may have particular application as part of a fluid flow system in a gas turbine engine. It may for example allow control of fluid flow in forward and reverse directions using a lighter, smaller and/or more efficient device than previously possible. The invention is not however limited to such applications and may for example be used in alternative fluid control systems. 
     Vortex devices use the properties of swirling flows to control various aspects of fluid flow, including direction, pressure and mass flow. Such devices generally rely on boundary conditions between fluid flows and/or between fluid flows and walls. In some cases the arrangement of walls and ports in the device may be sufficient to influence flow in the manner desired, although specifically introduced control flows may also be used to prompt a change. 
     A vortex device designed as a diode permits relatively unobstructed flow in a forward direction (creating little pressure drop) while limiting flow in the reverse direction (creating a relatively large pressure drop). In the forward direction fluid flows relatively unhindered through the device. When however there is flow in the reverse direction, the flow forms a vortex, creating a pressure drop greater than that occurring with forward flow. Such devices may be characterised by a so called turn-down ratio, which for a given pressure ratio applied over the device, is equal to the mass flow that would occur in the forward direction divided by the mass flow that would occur in the reverse direction. Diodicity offers an alternative characterisation of such devices, defined as the pressure drop that would occur in the reverse direction divided by the pressure drop that would occur in the forward direction, at a given mass flow rate. 
     One such vortex diode device is the Zobel diode. This has a disc like chamber. A forward flow inlet is in direct fluid communication with the chamber from a direction substantially perpendicular to the top surface of the disc. A reverse flow inlet is in direct fluid flow communication with the chamber, at the periphery of and substantially tangential to its side wall. When forward flow occurs (entering via the forward flow inlet and leaving via the reverse flow inlet) the flow is relatively unhindered. When reverse flow occurs, fluid entering via the reverse flow inlet forms a vortex guided by the side wall of the chamber. On entry to the chamber, flow in the reverse direction has a total pressure which encompasses both a static and dynamic pressure term. The velocity of the vortex formed in the chamber at any particular point is inversely proportional to the streamline radius within the chamber. Thus at the smallest radius (at the forward flow inlet) the vortex experiences the highest velocity and dynamic pressure, corresponding to a drop in static pressure in this region. Consequently there is a significant pressure drop across the diode in the reverse flow direction. 
     According to a first aspect of the invention there is provided a vortex fluid flow device comprising optionally a vortex chamber, optionally multiple forward flow inlets to the chamber and optionally a reverse flow inlet to the chamber, the vortex fluid flow device being optionally arranged such that in use there is a greater pressure drop across the device when there is reverse fluid flow, in the direction from the reverse flow inlet to the forward flow inlets, than when there is forward fluid flow, in the direction from the forward flow inlets to the reverse flow inlet. 
     In a Zobel diode such as that described in the background section, the turn-down ratio (or performance) is linked to the radius ratio (which may be approximated as the radius of the chamber divided by the radius of the forward flow inlet). With increasing radius ratio the pressure drop in the reverse flow direction will increase due to an increase in the velocity (and corresponding reduction in static pressure) of the flow at the forward flow inlet. 
     In many applications it is desirable to have a relatively large forward mass flow. Where an increase in the forward mass flow is desired, one solution is to increase the radius of the forward flow inlet. This will however result in a reduction in performance (a decrease in turn-down ratio caused by a decrease in the radius ratio). Increasing the radius of the chamber will allow increases in performance once again, but larger chambers are heavier and may be more difficult to physically accommodate in a system. Consequently with the traditional Zobel diode there may be a trade-off between potential forward mass flow and the turn-down ratio. Where size and weight constraints are an important consideration there is therefore a tendency to abandon vortex devices in favour of restrictor valves (despite their performance disadvantages when compared to vortex devices). 
     By increasing the number of forward flow inlets rather than the radius of a single forward flow inlet, the forward mass flow may be increased without reducing the radius ratio. A given reverse flow rate may therefore be maintained despite the increase in forward mass flow. Conversely a performance increase can be obtained for a given forward mass flow. In short the second forward flow inlet may offer a two fold increase in turn-down ratio and forward mass flow without impacting on the absolute reverse mass flow, or for a given forward mass flow provide a reduction in reverse mass flow, and an increase in performance. 
     The provision of additional forward flow inlets may also offer additional fluid system architecture options. By way of example, multiple flows arriving in the forward direction may be combined by the device, and a single flow arriving in the reverse direction may be split by the device. 
     In some embodiments there is at least one pair of forward flow inlets with each of the forward flow inlets in the pair on opposite walls of the chamber. 
     In some embodiments the forward flow inlets in at least one of the pairs have a circular cross-section. In other embodiments at least one of the forward flow inlets may have a non-circular cross-section. 
     In some embodiments the forward flow inlets in at least one of the pairs are coaxial. This may allow for the same pressure drop across all forward flow inlets. In other embodiments the forward flow inlets in at least one of the pairs are not coaxial. This may be desirable where different pressure drops across different forward flow inlets are required. 
     In some embodiments the forward flow inlets in at least one of the pairs are at the centre of their respective walls. This may allow for an increased turn-down ratio for a chamber of a particular size. 
     In some embodiments the forward flow inlets in at least one of the pairs have the same diameter. This may mean that the same mass flow occurs via each of the forward flow inlets in the pair and may also allow for an increased turn-down ratio. Where however it is desirable for there to be different mass flows through each forward flow inlet, the forward flow inlets in the pair may have different diameters. 
     In some embodiments there are exactly two forward flow inlets. This may allow for an increased turn-down ratio for a chamber of a particular size. This configuration may also mean that the vortex fluid flow device has a T-junction configuration, such that two flows are combined in the forward direction and a single flow is split in the reverse direction. 
     In some embodiments the device further comprises a single forward flow fluid source which when there is a forward flow supplies at least two of the forward flow inlets with fluid and when there is a reverse flow recombines fluid from at least two of the forward flow inlets. 
     In some embodiments the chamber is substantially cylindrical in shape, having top, bottom and side walls. The diameter of the cylinder may be greater than its height. The ratio of cylinder diameter to cylinder height may be between 4:1 and 7:1 and preferably between 5:1 and 6:1. The edges of the cylinder may be curved. The chamber may therefore be considered annular (where the centre of the annulus is occupied by forward flow inlets) or disc like. In alterative embodiments the chamber may be shaped differently; it may for example be substantially rhombohedral or biconic in shape. The shape may be selected to aid with flow from the forward flow inlets to the reverse flow inlet when there is forward flow. 
     In some embodiments the forward flow inlets enter from the top and/or bottom walls of the disc like chamber. 
     In some embodiments one or more of the forward flow inlets enters from a substantially perpendicular direction to the wall at the point from which it enters. Alternatively however one or more of the forward flow inlets may not be perpendicular and may for example be angled towards the reverse flow inlet. This may reduce the pressure drop in the forward flow direction. 
     In some embodiments the reverse flow inlet enters from the side wall of the disc like chamber. 
     In some embodiments the reverse flow inlet is angled so as to be substantially tangential with the side wall at the point from which it enters. 
     In some embodiments the vortex fluid flow device is arranged for use in a gas turbine engine in the control of fluid. The fluid may for example be gas such as air (which may be used for cooling and/or sealing and/or may be exhaust gas), oil, fuel, water or glycol mix. 
     According to a second aspect of the invention there is provided a fluid system comprising a vortex fluid flow device according to the first aspect of the invention. 
     In some embodiments the fluid system is arranged to supply air bled from a compressor system of a gas turbine engine to seal one or more bearing chambers in the gas turbine engine. 
     In some embodiments the fluid system is arranged so that air is bled from a later stage of the compressor system when the engine is running slower and from an earlier stage of the compressor system when the engine is running faster. 
     In some embodiments the forward flow inlets of the vortex fluid flow device are connected to a bleed from the earlier stage of the compressor system and the reverse flow inlet is connected to the areas surrounding the bearing chambers such that the forward flow direction is from the bleed to the areas surrounding the bearing chambers and the reverse flow direction is from the areas surrounding the bearing chambers to the bleed. 
     In some embodiments the bleed comprises a pair of bleed off-takes, each connected to one of two forward flow inlets of the vortex fluid flow device. 
     According to a third aspect of the invention there is provided a gas turbine engine comprising a vortex fluid flow device according to the first aspect of the invention. 
     The skilled person will appreciate that a feature described in relation to any one of the above aspects of the invention may be applied mutatis mutandis to any other aspect of the invention. 
    
    
     
       Embodiments of the invention will now be described, by way of example only, with reference to the accompanying Figures, in which: 
         FIG. 1  is a sectional side view of a gas turbine engine; 
         FIG. 2  is a side view of a vortex fluid flow device according to an embodiment of the invention; 
         FIG. 3  is top view of the vortex fluid flow device shown in  FIG. 2 ; 
         FIG. 4  is a schematic diagram showing a mode of operation of the vortex fluid flow device shown in  FIGS. 2 and 3 ; 
         FIG. 5  is a schematic diagram showing a mode of operation of the vortex fluid flow device shown in  FIGS. 2 and 3 ; 
         FIG. 6  is a schematic diagram showing a mode of operation of an alternative vortex fluid flow device embodiment; 
         FIG. 7  is a schematic diagram showing another mode of operation of an alternative vortex fluid flow device embodiment; 
         FIG. 8  is a cross-sectional side view of a vortex fluid flow device according to an embodiment of the invention; 
         FIG. 9  is a top view of a vortex fluid flow device shown in  FIG. 8 ; 
         FIG. 10  is a cross-sectional side view of a vortex fluid flow device according to an embodiment of the invention; 
         FIG. 11  is a top view of a vortex fluid flow device shown in  FIG. 10 ; 
         FIG. 12  is a cross-sectional side view of a vortex fluid flow device according to an embodiment of the invention. 
     
    
    
     A gas turbine engine  10  is shown in  FIG. 1  and comprises an air intake  12  and a propulsive fan  14  which generates two airflows A and B. The gas turbine engine  10  comprises, in axial flow A, an intermediate pressure compressor  16 , a high pressure compressor  18 , a combustor  20 , a high pressure turbine  22 , an intermediate pressure turbine  24 , a low pressure turbine  26  and an exhaust nozzle  28 . A nacelle  30  surrounds the gas turbine engine  10  and defines, in axial flow B, a bypass duct  32 . 
     Referring now to  FIGS. 2 and 3 , a vortex fluid flow device is generally shown at  40  as may for example be used in control of air, oil or fuel flow in the gas turbine engine  10  of  FIG. 1 . The vortex fluid flow device  40  comprises a vortex chamber  42 . The vortex chamber  42  is of substantially disc like shape, having parallel and opposed top  44  and bottom  46  walls and a curved side wall  48  spanning the gap between the top  44  and bottom  46  walls and joining them at their perimeters. The vortex chamber  42  defined by the top  44  bottom  46  and side  48  walls is fluid tight with the exception of multiple forward flow inlets  50  (in this case two) and a reverse flow inlet  52 . 
     The two forward flow inlets  50  form a pair, one entering the vortex chamber  42  from the top wall  44  and one entering the vortex chamber  42  from the bottom wall  46 . Each of the pair of forward flow inlets  50  extends towards and enters its respective wall  44 ,  46  from a direction perpendicular to that wall  44 ,  46  at the point of entry. As will be appreciated the pair of forward flow inlets  50  are provided on opposite walls  44 ,  46 . Further the pair of forward flow inlets  50  have the same cross-sectional shape (circular) and diameter. The pair of forward flow inlets  50  are also coaxial, each being positioned at the centre of its respective wall  44 ,  46 . 
     The reverse flow inlet  52  enters the vortex chamber  42  from the side wall  48 . The reverse flow inlet  52  extends towards and enters the side wall  48  from a direction tangential to that side wall  48  at the point of entry. 
     With reference to  FIGS. 2-5  it can be seen that the vortex fluid flow device  40  has a T-junction configuration and acts as a vortex diode arranged to produce different pressure drops between forward and reverse fluid flows through the device. 
     When there is forward flow (as shown in  FIG. 4 ), fluid is supplied to the vortex chamber  42  by the forward flow inlets  50 . The fluid entering the chamber  42  travels relatively unhindered through the chamber  42  and out of the reverse flow inlet  52 , thereafter supplying a component, system, exhaust or similar connected to the reverse flow inlet  52 . 
     If however the fluid flow direction is reversed (as shown in  FIG. 5 ), such that fluid is supplied to the vortex chamber  42  by the reverse flow inlet  52 , fluid entering the chamber  42  is guided by the side wall  48  into forming a vortex. This occurs in view of the reverse flow inlet  52  being positioned and angled to present the flow of fluid substantially tangentially to the side wall  48 . The formation of the vortex causes a substantial pressure drop in the reverse direction. On entry to the chamber  42 , flow in the reverse direction has a total pressure which encompasses both a static and dynamic pressure term. The velocity of the vortex formed in the chamber  42  at any particular point is inversely proportional to the streamline radius within the chamber  42 . Thus at the smallest radius (at one of the forward flow inlets  50 ) the vortex experiences the highest velocity and dynamic pressure, corresponding to a drop in static pressure in this region. Having passed into one of the forward flow inlets  50 , the fluid passes onward to supply a component, system, exhaust or similar connected to one, other or both of the forward flow inlets  50 . 
     The vortex fluid flow device  40  is therefore arranged such that in use there is a greater pressure drop across the device when there is reverse fluid flow than when there is forward fluid flow. The difference in the respective pressure drops is characterised by the diodicity. This in turn is determined by the arrangement of the forward flow inlets  50  and the radius at which the reverse flow inlet  52  is positioned. In this case, the forward flow inlets  50  are coaxial, have a circular cross-section, have the same diameter and are at the centre of their respective opposed walls  44 ,  46  of a disc shaped vortex chamber  42 . Consequently the vortex fluid flow device  40  has the maximum possible turn-down ratio for a disc-shaped chamber  42  of its particular diameter. Specifically the radius ratio between the streamline at which the flow enters for fluid travelling in the reverse flow direction to the radius of either of the forward flow inlets  50  is maximised. 
     An example application of the vortex fluid flow device  40  as shown in  FIGS. 2-5  is as part of a bearing chamber sealing system in a gas turbine engine. Bearing chambers in gas turbine engines contain bearings used to allow support of rotating components (such as engine shafts) by static parts of the engine. The bearings are lubricated by oil. The oil is contained by the bearing chamber before it is scavenged and ultimately returned to the oil tank. With a view to preventing the leakage of oil from the bearing chamber into the surrounding engine, the area around the bearing chamber is pressurised with air from a compressor of the gas turbine. In this way any passage of air across seals of the bearing chamber tends to be into rather than out of the bearing chamber, thereby reducing oil leakage. 
     A complication concerns the different speeds at which the engine may be operated. Alterations in this speed tend to impact on the pressure inside the bearing chamber. The oil scavenge system is powered by rotation of the engine, scavenging more oil (and air) from the bearing chamber when the engine is running at high speed and vice versa. Consequently it is desirable to tailor the pressure outside of the bearing chamber to the engine speed. Without such tailoring the pressure differential across the bearing chamber seals might reverse (encouraging oil leakage) or may become too great in magnitude (potentially damaging the seals and/or other components). 
     The compressor air used to pressurise the area around the bearing chamber may therefore be taken from different compressor stages as the speed of the engine alters. It may be for example that when the engine is running at high speed, sealing air is taken from an earlier compressor stage (e.g. the second high pressure compressor stage), and when it is running at low speed, sealing air is taken from a later compressor stage (e.g. a fourth high pressure compressor stage). In a system such as this the vortex fluid flow device  40  may be positioned between the second high pressure compressor stage and the area surrounding the bearing chamber. The vortex fluid flow device  40  is arranged such that in the forward flow direction, the forward flow inlets are supplied with air from the second high pressure compressor stage, and the reverse flow inlet supplies the air to the area surrounding the bearing chamber. 
     With the arrangement described above there would be little pressure drop across the vortex fluid flow device  40  in the forward flow direction (that is when the second high pressure compressor stage is supplying air to the area surrounding the bearing chamber). When however the area surrounding the bearing chamber is supplied with air from the fourth high pressure compressor stage the vortex fluid flow device  40  would provide significant resistance to flow of that air to the second high pressure compressor stage. 
     The vortex fluid flow device  40  may be particularly advantageous in use as described above because: 
     a) Air is typically bled from the second high pressure compressor stage at two off-takes. Therefore in prior art systems it has been necessary to provide separate T-junction and flow diode components. The present device combines the functionality of these two components, reducing size and weight of the components. 
     b) As previously discussed the vortex fluid flow device  40  offers an improved turn-down ratio for a vortex chamber of a given size. The vortex fluid flow device  40  may for example therefore decrease pressure loss from the area surrounding the bearing chamber to the second high pressure compressor stage when it is being supplied from the fourth high pressure compressor stage. This may improve the sealing of the bearing chamber without the need to increase the size of the flow diode (which would incur weight and size penalties). The reduction in leakage of air from the fourth high pressure compressor stage to the second high pressure compressor stage via the area surrounding the bearing chamber and vortex fluid flow device  40  may also reduce spoiling of the flow through the compressor. 
     c) The vortex fluid flow device has no moving parts and is not therefore susceptible to damage resulting from degradation of abradable materials (in contrast to a check valve solution). 
     The T-junction configuration of the vortex fluid flow device  40  (as discussed with respect to  FIGS. 2-5 ) may be convenient where it is desirable for the flow in the forward direction to be combined and the flow in the reverse direction to be split (as per the example above). With reference to  FIGS. 6 and 7 , where however a single flow is ultimately desired to and from a vortex fluid flow device  60  in both forward and reverse directions, a single forward flow fluid source  62  can be connected to forward flow inlets  64 . As shown in  FIG. 6 , where then there is forward flow, both forward flow inlets  64  are supplied by the forward flow fluid source  62 . Fluid then enters a vortex chamber  66 , before leaving the vortex chamber  66  via a reverse flow inlet  68 . Similarly, as shown in  FIG. 7 , when there is reverse flow from the reverse flow inlet  68 , both forward flow inlets  64  supply the forward flow fluid source  62 . 
     It is possible to make various alterations to the configurations shown in  FIGS. 1-7 . By way of example different numbers of forward and reverse flow inlets may be provided. The diameters, cross-sectional shapes, cross-sectional radii and radial positions with respect to the vortex chamber may all also all be varied for each inlet. Altering the shape of the vortex chamber is also possible. Further inlets may be paired and positioned coaxially (or not) and/or enter from opposing walls (or not). These possible variations allow for an appropriate arrangement to be selected according to the particular requirements of the application. Each inlet may be thought of as a source and/or recipient of fluid for which there is a desired pressure and mass flow given particular conditions. By making arrangement selections as discussed above, that mass flow and pressure may be selected for each inlet for both forward and reverse flow directions. Additionally or alternatively the turn-down ratio may be determined in this way. 
     Examples of the alterations discussed above are briefly discussed with reference to  FIGS. 8-12 . 
     Referring to  FIGS. 8 and 9  a vortex fluid flow device  70  is shown having three forward flow inlets  72  and a reverse flow inlet  74 . In this case two of the forward flow inlets  72  enter a disc-shaped vortex chamber  76  of the vortex fluid flow device  70  from a top wall  78  and one enters from a bottom wall  80 . The reverse flow inlet  74  is arranged as in the embodiments of  FIGS. 1-7 . Each of the forward flow inlets  72  have different radial positions with respect to the vortex chamber  76  radius. The forward flow inlets  72  entering away from the centre of the bottom wall  80  (i.e. with increased radial position with respect to the chamber  76 ) will reduce the turn-down ratio by comparison with the embodiments of  FIGS. 1-7 . Nonetheless fluid flow in the reverse direction will be split three ways, and fluid flow in the forward direction will be combined from three flows to one. This may be advantageous in certain arrangements, allbeit at the expense of turn-down ratio. Further, the mass flow in the forward direction may be increased due to the provision of the additional forward flow inlet  72  and where there is fluid flow in the reverse direction the pressure drop will be different across each forward flow inlet  72 . 
       FIGS. 10 and 11  show a vortex fluid flow device  81  where the angle at which a pair of forward flow inlets  82  approach and enter a vortex chamber  84  is shifted away from perpendicular with respect to the point of entry on the respective top  86  or bottom  88  wall of the chamber  84 . Each of the forward flow inlets  82  is angled so as fluid travelling in the forward direction and entering through one or other of the forward flow inlets  82  is incident substantially in the direction of a reverse flow inlet  90 . This may reduce the pressure drop in the forward flow direction without impacting on the pressure drop in the reverse flow direction. Furthermore, design freedom in determining the angle of the forward flow inlets  82  may be advantageous in facilitating alternative system architectures (e.g. pipe layouts). 
     Referring now to  FIG. 12  a vortex fluid flow device  100  is shown having an alternative vortex chamber  102  shape. In this case the vortex chamber  102  has a biconic shape, there being opposed forward flow inlets  104  entering at top  106  and bottom  108  vertices of the chamber  102  and a reverse flow inlet  110  entering at and substantially tangential to a side wall  112  of the chamber  102 . As will be appreciated many alternative regular or irregular chamber shapes may be used (e.g. rhombohedral, ellipsoid, spherical or disc-like). Different chamber shapes may impact on the pressure drop in forward and reverse flow directions as well as offering different architecture options particularly with regard to arranging coaxial forward flow inlets. 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the various concepts described herein. Except where mutually exclusive any of the features may be employed separately or in combination with any other features and the invention extends to and includes all combinations and sub-combinations of one or more features described herein in any form of vortex fluid flow device.