Abstract:
A flow control system comprises includes a fluidic control device having a main fluid path for a flow of fluid through the device, and a control fluid path for a control flow of fluid through the device. At least part of the control fluid path coincides with at least part of the main fluid path to control the flow of fluid out of the fluidic control device. A valve is associated with the control fluid path. The valve is movable between an open condition to allow fluid to flow along the control fluid path to effect the aforesaid control of the fluid flow out of the fluidic control device, and a closed condition to inhibit or prevent fluid flow along the control fluid path.

Description:
BACKGROUND 
   This invention relates to flow control systems. More particularly, but not exclusively, the invention relates to flow control systems for use in gas turbine engines. Embodiments of the invention relate to flow control systems for modulating secondary flow in a gas turbine engine. 
   In gas turbine engines, it is often necessary to be able to control a secondary fluid flow, for example in cooling air or in the flow of engine oil. 
   SUMMARY 
   According to one aspect of this invention, there is provided a flow control system comprising a fluidic control device having a main fluid path for a main flow of fluid through the device, and a control fluid path for a control flow of fluid through the device, wherein at least part of the control fluid path coincides with at least part of the main fluid path to control the flow of fluid out of the fluidic control device; and a valve associated with the control fluid path, the valve being movable between an open condition to allow fluid to flow along the control fluid path to effect the aforesaid control of the fluid flow out of the fluidic control device, and a closed condition to inhibit or prevent fluid flow along the control fluid path. 
   The fluidic control device may comprise a vortex amplifier. The fluidic control device may include an outlet for the fluid. 
   A first embodiment of the invention comprises a flow control system for use in controlling a fluid flow in a gas turbine engine. 
   The main fluid path of the fluid device may be arranged in fluid communication with relatively low pressure supply of fluid, such as a relatively low pressure compressor stage of a gas turbine engine. The control fluid path may be arranged in fluid communication with a relatively high pressure supply of fluid, such as a higher pressure compressor stage than the compressor stage to which the main fluid path is in fluid communication. 
   The outlet of the fluidic control device may be in fluid communication with a turbine or compressor region of the gas turbine engine to provide cooling air thereto. A first fluidic control device may be provided at the compressor, and a second fluidic control device may be provided at the turbine. The valve may be associated with the first and second fluidic control devices. 
   The flow control system may comprise a plurality of fluidic control devices. The fluidic control devices may be a plurality of the second fluidic control devices, which may be arranged around the turbine. 
   A plurality of the second fluidic control devices may be arranged generally circumferentially around a rotary component of a gas turbine engine, such as a turbine. The second embodiment may include a manifold to supply the control fluid to the second fluidic control devices. 
   The flow control system may be used to control flow in the oil system of a gas turbine engine. The main flow path may be in fluid communication with a bearing chamber of the oil system. The control fluid path may be in fluid communication with a source of gas, for example air from a compressor of the gas turbine engine. 
   Preferably, the main fluid path is in fluid communication with a vent of the bearing chamber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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 diagrammatic sectional side view of the upper half of the gas turbine engine; 
       FIG. 2  is a diagrammatic view of a first embodiment of a flow control system for use in the turbine engine shown in  FIG. 1 ; 
       FIG. 3  is a diagrammatic view of a further embodiment of a flow control system for use in the turbine engine shown in  FIG. 1 ; 
       FIG. 4  is a view of the region marked IV in  FIG. 3 ; 
       FIG. 5  is a partial view along the line V in  FIG. 4 ; and 
       FIG. 6  is a diagrammatic view of a further embodiment of a flow control system. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   Referring to  FIG. 1 , a gas turbine engine is generally indicated at  10  and comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high pressure compressor  14 , combustion equipment  15 , a high pressure turbine  16 , an intermediate pressure turbine  17 , a low pressure turbine  18  and an exhaust nozzle  19 . 
   The gas turbine engine  10  works in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  which produce two air flows: a first air flow into the intermediate pressure compressor  13  and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
   The compressed air exhausted from the high pressure compressor  14  is directed into the combustion equipment  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines  16 ,  17  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbine  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13 , and the fan  12  by suitable interconnecting shafts  20 . 
   At various positions throughout the engine  10 , there are secondary fluid flows, for example in supplying cooling fluid to the turbines  16 ,  17 ,  18  and in oil system flows. These flows of secondary fluid need to be modulated depending upon the operating conditions of the engine  10 . 
     FIG. 2  shows a diagrammatic view of a cooling system supplying cooling air from the compressor stages  13 ,  14  to the turbine stages  16 ,  17 ,  18  in order to cool the components of the turbine stages. The compressor stages  13 ,  14  and the turbine stages  16 ,  17 ,  18  are shown diagrammatically in  FIG. 2 . 
   In order to control the flow of a cooling fluid  22  to the turbines  16 ,  17 ,  18 , a flow control system  24  is provided. The flow control system  24  comprises a fluidic control device in the form of a vortex amplifier  26  and a valve  28  to supply a control fluid via a control conduit  30  to the vortex amplifier  26 . The vortex amplifier  26  includes a main inlet  32  to which air from the compressor stage,  13 ,  14  is supplied by a feed conduit  34 . 
   Under normal operating conditions, the air passing into the fluidic control device  26  passes out of an outlet  36  and along a main conduit  38  to the turbine stages  16 ,  17 ,  18 . 
   The air supplied to the feed conduit  34  is supplied from a lower pressure region of the compressor stages  13 ,  14  than the air supplied to the value  28 . The control conduit  30  is connected to the high pressure compressor stage  14  via the valve  28 . 
   As can be seen, the control fluid conduit  30  extends to a control inlet  40  of the fluidic control device  26 . When the value  28  is opened, air from the high pressure compressor stage  14  enters the fluidic control device  26  generally tangentially thereto, and impinges upon the main flow of fluid entering the vortex amplifier  26  via the main inlet  32 . 
   As the valve  28  is further opened, the flow of air from the high pressure compressor stage  14  into the vortex amplifier  26  via the control fluid conduit  30  increases in pressure until the pressure of the fluid along the control fluid conduit  30  exceeds the pressure of the air entering the vortex amplifier  26  via the main inlet  32 . As a result, the flow of air through the vortex amplifier  26  starts to form a vortex. This results in the rate of flow of the air out of the vortex  36  reducing. As the pressure of the flow of air through the control conduit  30  increases, the formation of the vortex also increases until, with a high enough pressure of air flowing along the control conduit  30 , the flow of air through the main inlet  32  is cut off. 
   A further embodiment is shown in  FIG. 3  which comprises first and second vortex amplifiers  26 A,  26 B. The first vortex amplifier  26 A is arranged in or on a casing  35  surrounding the high pressure compressor stage  14 . The second vortex amplifier  26 B is provided at the high pressure turbine stage  16 . The second vortex amplifier  26 B comprises a plurality of vortex amplifiers arranged around the turbine casing in a circumferentially spaced relationship (see  FIG. 5 ). Each of the circumferentially spaced second vortex amplifiers  26 B is in fluid communication with a circumferentially extending manifold  42  to receive the control fluid therefrom. The control conduit  30  extends to the manifold  42 . 
   The arrangement shown in  FIG. 3  comprises an upstream pipe  30 A of the control conduit  30 . The upstream pipe  30 A is arranged upstream of the valve  28  and extends from the compressor  14  to the valve  28 . The control conduit  30  also includes first and second downstream pipes  30 B,  30 C extending respectively from the valve  28  to the first vortex amplifier  26 A and to the second vortex amplifiers  26 B. Thus the control fluid is fed from the compressor  14  to the first vortex amplifier  26 A integral with the casing of the compressor  14  and to the second vortex amplifiers  26 B on the turbine  16 . 
   The first vortex amplifier  26 A in the embodiment shown in  FIG. 3  also receives fluid from the high pressure compressor  14 , but from a stage that is at a lower pressure than the stage feeding compressed air to the control conduit  30 . Under normal operating conditions, the fluid flows from the first fluid control device  26 A via the main conduit  38  to the manifold  42  to be fed to the second fluid control device  26 B. The flow of cooling fluid  22  from the compressor  14  to the turbine  16  is controlled at two regions, the first being at the compressor  14  and the second being at the turbine  16 . 
   A further embodiment is shown in  FIG. 6  in which the fluid flow control system  24  is mounted on a bearing chamber  44  of the oil system of the gas turbine engine  10 . The bearing chamber  44  has a vent conduit  45  upon which the flow control system  24  is mounted. 
   The control conduit  30  feeding the control fluid to the vortex amplifier  26  is in fluid communication with a source of air, such as the high pressure compressor  14 . A mixture of air and oil from the bearing chamber at  44  passes along the vent conduit  45  to the vortex amplifier  26 , as shown by the arrow  46 . This mixture enters the vortex amplifier  26  via the main inlet  32 . In normal operation, the mixture of oil and air then passes out of the outlet aperture  36  and along the outlet conduit  38 . This condition is generally obtained when the engine  10  is operating at low power, thereby maximising the pressure drop across the bearing chamber seals. 
   When the engine is running at high power, the valve  28  is moved to its open condition. Compressed air from the high pressure compressor  14  flows along the control flow conduit  30  into the vortex amplifier  26  via the control flow inlet  40  to impinge upon the mixture of air and oil entering via the main inlet  32 . A vortex within the vortex amplifier  26  starts to form. The flow of the air and oil mixture into the vortex amplifier  26  along the vent conduit  45  is thus stopped. 
   As the power of the engine increases, the valve  28  is opened further to increase the pressure of the flow along the control conduit  30  thereby increasing the vortex within the vortex amplifier  26  until none of the oil and air mixture passes out of the vortex amplifier  26  along the outlet conduit  38 . 
   In this condition, there is no further flow of air and oil along the vent conduit  45  which restricts the flow of air leaking into the bearing chamber, as shown by the arrows A. 
   Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the invention can be made without departing from the scope of the invention. 
   Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.