Abstract:
In certain circumstances recovery of a fluid flow presented through a heat exchanger into another flow can create problems with respect to drag and loss of thrust. In gas turbine engines heat exchangers are utilized for providing cooling of other flows such as in relation to compressor air taken from the core of the engine and utilized for cabin ventilation and de-icing functions. By providing an outlet valve through an outlet duct in a wall of a housing the exhaust fluid flow from the heat exchanger can be returned to the by-pass flow with reduced drag effects whilst recovering thrust. The valve may take the form of a flap displaceable into the by-pass flow before an exit plan to create a reduction in static pressure drawing fluid flow through the heat exchanger.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to GB 0607771.3, filed 20 April 2006 and currently issued under United Kingdom Patent No. 2,437,377. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to heat exchanger arrangements and more particularly to heat exchanger arrangements utilised in gas turbine engines for cooling fluid flows such as with respect to ventilation air or oil within the engine or for de-icing. 
     Operation of gas turbine engines is well known and incorporates significant fluid flows including compressed air provided by the compressor fans of that gas turbine engine. This compressed air flow is bled for a number of functional operations and in particular in order to provide through an appropriate heat exchanger cooling of other fluid flows such as the ventilation air in the cabin of an aircraft associated with a gas turbine engine or potentially with respect to fuel or lubricating oil coolers in the engine. The coolant flow, as indicated, is tapped or bled from the engine flows and returned at an appropriate location within the engine to maintain a pressure drop sufficient to provide the necessary cooling function within the heat exchanger with respect to the ventilation air or other fluid flow through that heat exchanger. The ventilation air itself is generally taken from hotter core compressor stages of the engine and so needs cooling at least during certain engine cycles. 
     Prior Art  FIGS. 1 and 2  respectively illustrate a schematic side view of a prior heat exchanger arrangement ( FIG. 1 ) and a plan view ( FIG. 2 ) in the direction of A of the heat exchanger arrangement depicted in Prior Art  FIG. 1 . Thus, the arrangement  1  includes a fluid flow  2  taken from compressor stage  3  air flow generally after a guide vane  4 . The bled fluid flow  2  is regulated by a fan air valve  5  such that the fluid flow passes as a coolant through a heat exchanger  6  which exchanges heat with typically another fluid delivered through ducting  7  (shown in broken line). This other fluid is generally a cooled air flow which may be used as the ventilation air for the cabin of an aircraft associated with a gas turbine engine. The fluid flow  2  having been regulated by the valve  5  and passing through the heat exchanger  6  is exhausted as an exhaust flow  8  out of the heat exchanger  6 . The heat exchanger  6  and valve  5  are located within a wall  15  of a housing  14 , usually known as a splitter fairing, which is generally part of the core nacelle fixing structure of an engine. The exhausted flow  8  mixes with a ventilation flow  13  in a zone  11  that is located radially inwardly of a core cowling  9  and surrounding the engine. In such circumstances the prior heat exchanger arrangement depicted in Prior Art  FIGS. 1 and 2  has a number of disadvantages particularly in relation to increasing the temperature in the zone  11  between the housing incorporated in the heat exchanger  6  and surrounding parts of the engine as well as a necessary large vent exit area  12  to generate the desired pressure drop across the heat exchanger resulting in drag to a main propulsive flow  10  when flow through the heat exchanger  6  is low. 
     In the above circumstances although dumping of the exhaust flow  8  appears to be a relatively simple procedure, there are a number of problems. It will be understood that the exit area  12  has to be sized to cope with the combined ventilation flow  13  and the highest heat exchanger exhaust flow  8  which means that, typically at cruise, when the heat exchanger is operating at low or zero levels it is not possible to recover thrust from this part of the engine as the vent  12  area is effectively oversized. This over sizing also creates a drag penalty as the vent area  12  acts as an aero dynamic step or discontinuity when it is not passing full flow. It will also be understood that extra heat input into the zone  11  requires considerable shielding and heat resistance cabling for the core mounted systems. It will also be understood that by provision of the valve  5  and therefore switchable nature with regard to the flow through the heat exchanger  6  it is difficult to tune the flow regimes in the event of a fire to ensure extinguishants achieve the required density in all parts of zone  11 . 
     SUMMARY OF THE INVENTION 
     In accordance with aspects of the present invention there is provided a heat exchanger arrangement for a gas turbine engine, the arrangement comprising a fluid flow presented to a heat exchanger at an inlet and the heat exchanger incorporated within a housing over which in use the fluid flow passes, the arrangement characterised in that the heat exchanger has a duct to an outlet valve and the outlet valve is displaceable into the fluid flow to generate a reduction in static pressure in use to draw fluid flow through the heat exchanger. 
     Generally, the outlet valve is upstream of a fan nozzle exit plane. 
     Typically, the outlet valve is in a wall of the housing. 
     Advantageously, the outlet valve comprises a hinged flap. 
     Generally, the static pressure is variable by specific displacement of the valve. 
     Generally, the valve is opposite a shroud wall providing a fixed cross-sectional area within which the valve is operable. 
     Generally, the heat exchanger is for cooling an other fluid flow. Typically, the other fluid flow is ventilation air or oil. 
     Typically, the housing comprises a mounting nacelle for a gas turbine engine. 
     The invention also includes a gas turbine engine including an arrangement as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: 
         FIG. 1  is a schematic side view of a prior art heat exchanger arrangement; 
         FIG. 2  is a plan view in the direction of A of the prior art heat exchanger arrangement depicted in  FIG. 1 ; 
         FIG. 3  is a schematic side view of a first embodiment of a heat exchanger arrangement in accordance with aspects of the present invention; 
         FIG. 4  is a schematic plan view in the direction B of the arrangement depicted in  FIG. 3  with an outlet valve in an open configuration; 
         FIG. 4   a  is a section X-X in  FIG. 5  of the outlet valve; 
         FIG. 5  is a schematic plan view in the direction B of the arrangement depicted in  FIG. 3  with an outlet valve in a closed configuration; 
         FIG. 6  is a schematic side view of a second embodiment of a heat exchanger arrangement in accordance with aspects of the present invention; 
         FIG. 7  is a schematic plan view in the direction of arrowhead C of the heat exchanger arrangement depicted in  FIG. 6 ; 
         FIG. 7   a  is a section X-X in  FIG. 7  of the outlet valve; 
         FIG. 8  is a schematic side view of the second embodiment of the heat exchanger depicted in  FIGS. 6 and 7  in an open configuration; and, 
         FIG. 9  is a schematic plan view of the heat exchanger depicted in  FIGS. 6 to 8  in a closed configuration. 
         FIG. 9   a  is a section X-X in  FIG. 9  of the outlet valve. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with aspects of the present invention a heat exchanger  26  acting as a pre-cooler system for a gas turbine engine is arranged such that the coolant fluid flow exhaust is kept separate from the zone  11 . Nevertheless, an important factor to achieve appropriate heat exchanger operation is to provide an adequate pressure drop across the heat exchanger, that is to say from the coolant inlet to the coolant outlet sides. Previously such a pressure drop necessitated the exhausts of the coolant to be ducted downstream of the nozzle exit plane ( 45 ) where the adequate reduction in static pressure can be achieved. It will be understood that through the various compressor stages of a gas turbine engine compressed air flows increase and therefore by appropriate ducting to higher flow rates the coolant flow can be sucked through the heat exchanger. 
     By aspects of the present invention a reduction in static pressure is achieved without requiring considerable ducting which would otherwise introduce problems with respect to weight and flow losses. In accordance with aspects of the present invention the coolant fluid flow from the heat exchanger is injected into a fan by-pass flow relatively close to the heat exchanger through an outlet valve. This outlet valve is configured through its geometry to generate a reduction in static pressure at the exhaust side to create the required pressure drop through the heat exchanger. 
       FIGS. 3 to 5  illustrate a first embodiment of a heat exchanger arrangement  21  in accordance with aspects of the present invention. Thus, the arrangement  21  has a heat exchanger  26  to act as a pre-cooler for another fluid such as the ventilation air for the cabin of an aircraft. Conduits for that other cooled fluid are shown by broken lines  27   a  ,  27   b  in  FIG. 3 . The heat exchanger  26  receives a coolant fluid flow  22  through an inlet  25 . The regulating fan air valve, as with the previous arrangement depicted in prior art  FIGS. 1 and 2  is not required and therefore removed. The heat exchanger  26  receives the coolant fluid flow  22  and exhausts that flow through ducting  35  to an outlet valve  36 . This valve  36  is shown schematically in  FIG. 3  and as more closely depicted in  FIGS. 4 to 5  and extends into a by-pass fluid flow  32  in order to generate a reduction of static pressure and so suck coolant flow  22   b  through the heat exchanger  26 . 
     By provision of a heat exchanger geometry and particularly in respect of the exhaust duct  35  with a variable flap valve  40  acting as the outlet valve  36  it will be understood that the efficiency of the heat exchanger  26  can be maintained by the pressure drop across that heat exchanger  26  between the inlet duct  25  and the outlet duct  35  without the necessity of long conduits to downstream by-pass flow areas of an engine. 
     The coolant flow  22  is generally generated by a compressor fan  23  and is part of the propulsive fan flow  32 . The heat exchanger  26  as well as the ducting  35  and outlet valve  36  are generally mounted within the wall structure  15  of an inner nacelle housing  14  (splitter fairing) or mounting structure or pylon  84 , as shown in  FIG. 1 , for an engine. The wall structure  15  is a bifurcation structure, commonly located at top and/or bottom of the engine when wing mounted, and which spans the bypass duct  80 . 
     The outlet valve  36  extends radially between the bypass duct&#39;s radially inner and outer walls  82 ,  81  respectively. The outlet valve  36  may extend the complete radial height of between walls  81 ,  82 , but in this example the valve  36  extends over part of the radial height. 
     During heat exchanger operation, the variable flap  40  of the outlet valve  36  protrudes into the fan by-pass flow  32 . In the first embodiment depicted in  FIGS. 3 to 5 , a portion  32   a  of this by-pass flow  32  is enclosed between the housing wall  15  and a shroud wall  39 . The velocity of the portion of flow  32   a  increases as the variable flap  40  protrudes and reduces the flow area, particularly at the valve&#39;s outlet. Increasing speed of the by-pass fan flow  32  adjacent to the valve  36  drops the static pressure at an exhaust plane of the valve  36  creating a suction effect which increases the pressure drop across the heat exchanger  26  so driving coolant fluid flow through that heat exchanger  26 . It will be understood that in a preferred embodiment the outlet valve comprises a flap hinged to one side and displaceable to vary the degree of protrusion into the by-pass flow  32  and so allows alterations with respect to the suction effect as a result of the pressure drop across the heat exchanger  26 . This variation in the valve  26  will allow optimisation with respect to cooling requirements. 
     It will also be understood as the exhaust flow  22   b  from the heat exchanger  26  does not interfere with the ventilation zone flows (zone  11  in prior art  FIG. 1 ). Thus for the arrangement of the present invention, over-sizing of the vent outlet  12  is not required and a suitably sized outlet  12  is used for maximum thrust recovery and/or flow disturbance from the ventilation air flow. 
     It will be noted that the outlet valve  36  is located upstream of a fan nozzle exit plane  45  ( FIGS. 3 and 4 ). Such position ensures that there is thrust recovery if required. 
       FIG. 4  and  FIG. 5  illustrate respectively open and closed configurations with regard to heat exchanger arrangements in accordance with the first embodiment of the present invention. As described previously, a fluid flow  22  acts as a coolant for the heat exchanger  26  and this is exhausted through a duct  35  such that an outlet valve  36  including the variable flap  40  can create variation in the static pressure, at the duct&#39;s outlet, to suck fluid flow  22  through the heat exchanger  26 . 
     In  FIG. 4  the flap  40  is in an open configuration such that fluid flow  22   b  is drawn through an aperture  41  between the flap  40  and parts of the duct  35  or housing  15 . This flow through the heat exchanger  36  will provide a cooling effect with regard to another flow such as compressor air from the turbine stages of an engine to be used for cabin ventilation or de-icing. The flap  40  position creates a low static pressure, local to and importantly immediately downstream of the flap  40 , in a by-pass duct  80  created between the housing  15  and a shroud wall  39  as described previously. This variation in static pressure will act to regulate the fluid flow  22  instead or as well as of the previous fan air valve ( 5  in prior art  FIG. 1  and prior art  FIG. 2 ). 
       FIG. 4   a  shows the outlet valve  36  in the direction X-X. Thus, as can be seen, the flap  40  protrudes into the gap between the shroud  39  and parts of the housing wall  15  in order to present the aperture  41  through which flow  22   b  passes when drawn as a result of the reduced static pressure. 
     By having a fixed shroud wall  39  and wall  15  it will be understood that a well-defined flow  32  conduit is created local to the flap  40  giving greater control of the flow conditions adjacent to the duct  35  exhaust. In such circumstances the disturbance as a result of the flap  40  protruding into that conduit will create the desired variations in static pressure and therefore flow rate through the heat exchanger  26 . When the flap is forced into a closed configuration as depicted in  FIG. 5 , it will be understood that there will be no fluid flow  22  through the duct  25  to the heat exchanger  26 . The flap is closed, therefore there will be no flow  22   b  through the conduit  35  and in such circumstances normal fan flow  32  can be presented without any drag or impingement as a result of the exhaust flow  22   b  from the heat exchanger  26  as described previously. By such an approach the prior necessity of having an outlet vent which is appropriately sized for highest expected conditions is avoided. Fluid flow  22  through the heat exchanger  26  can be adjusted dependent upon actual requirements and this flow recovered in combination with the by-pass flow  32  for greater engine efficiency. By providing a fixed shroud wall  39  it will be understood that an accentuation of the static pressure reduction effects of flap  40  can be achieved. 
     The variable flap  40  is rotatable about its upstream edge  40   a  and in an open position defines a converging passage  86 . Fluid flow  32   a  therefore accelerates and creates a low static pressure local to the outlet plane  41 . The variable flap  40  is moveable between a closed position ( FIG. 5 ) and an open position ( FIG. 4 ) via an actuation mechanism. One such actuation mechanism comprising a motor  90  having a drive arm  92  connected to the flap  40 . The motor  90  is mounted to a wall of the duct  35 . The motor  90  is operable via electronics as would be understood by the skilled person. The motor  90  is operable to vary the amount of flow  22   b  through the valve  36  to maximise thrust recovery. As the flap  40  may be closed completely, the flap and drive mechanism  90 ,  92  is capable of operating as the inlet valve  5 , which in this case is omitted. 
     Alternatively, a second embodiment in accordance with aspects of the present invention is depicted in  FIGS. 6 to 9 . In this embodiment, an elongated flap is utilised in order to again create a static pressure reduction to stimulate and regulate fluid flow through the heat exchanger. As previously, a compressor fan  53  provides a bypass fluid flow  52 , part of which fluid flow  52   a  is presented to a heat exchanger  56  which in the embodiment depicted in  FIGS. 6 to 9  also includes a fan air valve  55 . As previously, the heat exchanger  56  exhausts an exhaust fluid flow  58  through a conduit  65  to a valve  66 . The fluid flow through the heat exchanger  56  cools another flow generally comprising compressed air in a conduit  57  in order to act as cabin ventilation or de-icer flows for operations within an aircraft associated with an engine incorporating a heat exchanger arrangement  51  in accordance with aspects of the present invention. The outlet valve  66  is schematically depicted in  FIG. 6  but as can be seen in more detail in  FIG. 7  this valve comprises a hinged flap  70  secured about a hinge  71 . 
     As described previously with regard to the flap  40  in  FIGS. 3 to 5 , the flap  70  is displaceable in order to vary a gap between the exhaust conduit  65  and parts of a housing  14  within which the heat exchanger  56  is located. In such circumstances there is a reduction in the static pressure as a result of fluid flow  78  moving past the flap  70 . This reduction in static pressure will suck fluid flow  52  as a coolant through the heat exchanger  56  for appropriate operation. 
     Generally, the flap  70  will be displaceable about the hinge  71  and come into a kiss seal engagement with parts of the housing  14  and the duct  65 . 
     In the second embodiment there is no provision of an opposed shroud wall  39  as depicted in  FIGS. 3 to 5  and so the embodiment depicted in  FIGS. 6 to 9  is dependent upon the combination of the fan by-pass fluid flow  78  and the flap  70  creating sufficient suction through a static pressure drop without the constraint of a conduit formed between the housing  14  and an opposed shroud wall such as wall  39  in  FIGS. 3 to 5 . In such circumstances as described above, typically the flap  70  will be more elongate than the flap  40  depicted in  FIGS. 3 to 5  in order to take the exhaust flow  58  further downstream to generate sufficient static pressure reduction. However, the particular advantage of such an arrangement is that there is less drag/blockage due to deletion of the fixed shroud wall  39  and housing wall  14  in the first embodiment depicted in  FIGS. 3 to 6 . The second embodiment depicted in  FIGS. 6 to 9  will require more space for accommodation but as indicated may have less detrimental effects with regard to drag and blockage. The particular embodiment utilised for the outlet valve in accordance with aspects of the present invention will be dependent upon particular requirements within a gas turbine engine. 
       FIG. 8  and  FIG. 9  respectively show the heat exchanger arrangement  51  as depicted in  FIG. 6  and  FIG. 7  in an open configuration ( FIG. 8 ) and in a closed configuration ( FIG. 9 ). 
     In  FIG. 8  the fluid flow  52  acts as a coolant for a heat exchanger  56  and is regulated by a fan air valve  55 . The exhaust fluid flow  52   a  is drawn by a pressure differential created by displacement of the flap  70  about the hinge  71 . An end  74  of the flap  70  will be positioned such that a static pressure reduction is created. Typically, the end  74  will be arranged to extend towards a fan nozzle. In such circumstances, fluid flow for cooling effect in the heat exchanger  56  will be enhanced without providing a blockage to the by-pass duct in an engine. 
       FIG. 9  illustrates the heat exchanger arrangement depicted in  FIGS. 6 to 8  and, in particular, the arrangement depicted in  FIG. 8  in a closed configuration. Thus, the flap  70  generally lies upon the housing  14  in order that there is no flow  52   a . The flap  70  is in kiss seal engagement with the wall  15  and possibly an end part  65   a  of the outlet ducting  65 . In such circumstances between the open configuration depicted in  FIG. 8  and the closed configuration depicted in  FIG. 9  it will be understood that regulation of the fluid flow for cooling effect within the heat exchanger  56  can be adjusted with less detrimental effect upon by-pass flow rate in terms of drag whilst the exhaust flow  22   b,    52   a  can be recovered in terms of adding to the thrust provided through the by-pass as it is located before the fan nozzle exit plane  60 . It will also be understood that the fan air valve  55  in the second embodiment depicted in  FIGS. 6 to 9  may be deleted such that fluid flow for cooling effect in the heat exchanger  56  is achieved generally through displacing the valve flap or door  70  about the hinge  71 . 
     It will be understood that in accordance with aspects of the present invention there is a separation between the fluid flow exhausted from the heat exchanger from the ventilation zone within the housing for the heat exchanger which is typically the central nacelle mountings for that engine. This will reduce heating within the vent zone of that housing, will allow independent optimisation of vent and heat exchanger exhaust to maximise thrust recovery whilst minimising drag. Furthermore, for a given by-pass flow rate, aspects of the present invention will reduce the exhaust static pressure to increase the pressure drop across the heat exchanger which in turn should create an improved cooling efficiency within that heat exchanger. It will also be understood in view of the selectivity with regard to positioning the outlet valve arrangement in accordance with the present invention a further means for controlling flow rate through the heat exchangers is provided in addition to or in replacement of a fan air inlet valve as utilised with previous heat exchanger arrangements. Removal of the fan air inlet valve will enable a more compact design to be achieved with less blockage and a lighter weight penalty. 
     As indicated above, aspects of the present invention relate to a heat exchanger which can be applied to a situation where a coolant medium, that is to say a fluid flow, is ejected into a moving flow to minimise drag and constriction whilst facilitating thrust recovery.