Patent Publication Number: US-2017370657-A1

Title: Swirl reducing gas turbine engine recuperator

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 13/036,463 filed Feb. 28, 2011, the entire contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The application relates generally to a recuperator for a gas turbine engine and, more particularly, to such a recuperator allowing for reduction of the swirl in the exhaust flow. 
     BACKGROUND OF THE ART 
     Gas turbine engines may include a recuperator, which is a heat exchanger using hot exhaust gas from the engine to heat the compressed air exiting the compressor prior to circulation of the compressed air to the combustion chamber. Preheating the compressed air usually improves fuel efficiency of the engine. In addition, the recuperator reduces the heat of exhaust gas, which helps minimize the infrared signature of the aircraft. 
     Axial or radial air entry swirlers are generally used during combustion in order to stabilize the flame and promote mixing. However, this usually results in a relatively important swirl component in the exhaust flow exiting the turbine section. Typically, deswirling vanes are provided between the turbine section and the exhaust mixer of the engine to reduce the swirl of the exhaust flow, such as to convert the kinetic energy of the flow into increased thrust. 
     SUMMARY 
     In one aspect, there is provided a recuperator configured to extend within an exhaust duct of a gas turbine engine, the recuperator comprising exhaust passages providing fluid flow communication between an exhaust inlet and an exhaust outlet, the exhaust inlet being oriented to receive exhaust flow from a turbine of the engine and the exhaust outlet being oriented to deliver the exhaust flow to atmosphere, the exhaust passages having an arcuate profile in a plane perpendicular to a central axis of the recuperator to reduce a swirl of the exhaust flow, air passages in heat exchange relationship with the exhaust passages and providing fluid flow communication between an air inlet and an air outlet, an inlet connection member defining the air inlet and being designed to sealingly engage a first plenum in fluid flow communication with a compressor discharge of the gas turbine engine, and an outlet connection member defining the air outlet and being designed to sealingly engage a second plenum containing a compressor of the gas turbine engine. 
     In another aspect, there is provided a gas turbine engine comprising a compressor section having a discharge in fluid flow communication with a first plenum, a combustor contained in a second plenum, a turbine section in fluid flow communication with the combustor, an exhaust duct in fluid flow communication with the turbine section, and a recuperator located in the exhaust duct, the recuperator defining: exhaust passages providing fluid flow communication between an exhaust inlet and an exhaust outlet, the exhaust inlet and exhaust outlet extending across the exhaust duct with the exhaust inlet being in fluid flow communication with the turbine section, the exhaust passages having an arcuate profile in a plane perpendicular to a central axis of the recuperator to reduce a swirl of the exhaust flow, air passages in heat exchange relationship with the exhaust passages and providing fluid flow communication between an air inlet and an air outlet, an inlet connection member defining the air inlet and sealingly engaging the first plenum to receive pressurized air from the compressor, and an outlet connection member defining the air outlet and sealingly engaging the second plenum containing the combustor. 
     In a further aspect, there is provided a method of deswirling and cooling an exhaust flow in an exhaust duct of a gas turbine engine, comprising circulating the exhaust flow from a turbine section of the gas turbine engine to a recuperator extending within the exhaust duct, circulating air discharged from a compressor section to a combustor of the gas turbine engine through air passages of the recuperator, and deswirling and diffusing the exhaust flow by circulating the exhaust flow through exhaust passages of the recuperator having an arcuate profile in a plane perpendicular. 
    
    
     
       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. 2  is a partial cross-sectional view of a gas turbine engine, showing a recuperator according to a particular embodiment; 
         FIG. 3  is a schematic tridimensional view of a gas turbine engine including the recuperator of  FIG. 2 , with one segment thereof removed; 
         FIG. 4  is a tridimensional view of the recuperator of  FIG. 2 , with one segment thereof omitted; 
         FIG. 5  is a tridimensional view of a segment of the recuperator of  FIG. 2 ; 
         FIG. 6  is an exploded tridimensional view of the segment of  FIG. 5 ; 
         FIG. 7  is a partial cross-sectional view of a gas turbine engine, showing the recuperator of  FIG. 2  with a diffuser attached thereto; 
         FIG. 8  is a partial cross-sectional view of a gas turbine engine, showing a recuperator according to another embodiment; 
         FIG. 9  is a tridimensional view of the recuperator of  FIG. 8 ; 
         FIG. 10  is a tridimensional view of a segment of the recuperator of  FIG. 8 , with a side plate removed; 
         FIG. 11  is a schematic cross-sectional view of a floating connection between the recuperator of  FIG. 8  and a plenum of the gas turbine engine; 
         FIG. 12A  is a schematic representation of the shape of cold air cells of the recuperator of  FIG. 8 ; and 
         FIG. 12B  is a schematic representation of the shape of the cold air cells of taken along direction B of  FIG. 12A ; and 
         FIG. 13  is a schematic representation of splitters and struts of the recuperator of  FIG. 2  in a plane perpendicular to a central axis of the recuperator. 
     
    
    
     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, and a turbine section  18  for extracting energy from the combustion gases. The compressor section  14  and combustor  16  are typically in serial flow communication with one another through a gas generator case  22  which contains the combustor  16  and which receives the flow from the compressor discharge, which in the embodiment shown is in the form of diffuser pipes  20 . The combustion gases flowing out of the combustor  16  circulate through the turbine section  18  and are then expelled through an exhaust duct  24 . 
     Although illustrated as a turbofan engine, the gas turbine engine  10  may alternately be another type of engine, for example a turboshaft engine, also generally comprising in serial flow communication a compressor section, a combustor, and a turbine section, and a propeller shaft supporting a propeller and rotated by a low pressure portion of the turbine section through a reduction gearbox. 
     Referring to  FIG. 2 , in the present embodiment, the gas generator case  22  is separated in at least two plenums, including a plenum  26  containing the combustor  16 , and another plenum  28  in fluid flow communication with the diffuser pipes  20  of the compressor section  14 . 
     A recuperator  30  extends across the exhaust duct  24 , such that the exhaust gas from the turbine section  18  circulates therethrough. The recuperator  30  also provides the fluid flow communication between the combustor plenum  26  and the compressor plenum  28 , as will be further detailed below. 
     Referring to  FIG. 3-6 , the recuperator  30  includes a plurality of arcuate segments  32 , which function independently from one another and are connected to the engine  10  independently from one another, and which together define the annular shape of the recuperator  30 . A controlled gap  34  (see  FIG. 4 ) is provided between adjacent ones of the segments  32  to allow for thermal expansion without interference. In a particular embodiment, the segments  32  are sized to extend between adjacent structural struts  36  (see  FIG. 3 ) of the engine  10 , and as such the gap  34  is sized to allow for thermal expansion of each segment  32  without major interference with the strut  36  extending in the gap  34 . A compressible side plate  46  at the side of the segment  32  provides sealing with the strut  36  and vibrational damping during engine operation. In the embodiment shown, each segment  32  is sized and located such as to be removable from the outside of the engine  10  through an opening accessible when the exhaust scroll  38  (see  FIG. 2 ) is removed. With an exhaust scroll  38  that is removable on the wing, such a configuration allows for the recuperator segments  32  to be removed and replaced if necessary with the engine  10  remaining on the wing. 
     Referring particularly to  FIGS. 5-6 , each segment  32  defines a plate heat exchanger, with a first group of fluid passages  40  for circulating the compressed air, and a second group of fluid passages  42  for circulating the exhaust gas. The air and exhaust passages  40 ,  42  alternate and are in heat transfer relationship with one another. In the embodiment shown, the air and exhaust passages  40 ,  42  are relatively oriented such as to define a mixed counter flow and double pass cross flow heat exchanger. A panel assembly  44  thus defines the alternating U-shaped first fluid passages  40  and curved second fluid passages  42 . In a particular embodiment, the panels  44  are made of a nickel alloy and are brazed to one another. The side plates  46  and a rear bulkhead  48  respectively seal the opposed side ends and the rear end of the panel assembly  44 . The bulkhead  48  also provides vibrational damping of the segment  32  during engine operation. 
     The exhaust fluid passages  42  communicate with a same exhaust inlet  50  defined by the radially inward end of the segment  32  and with a same exhaust outlet  52  defined by the radially outward end of the segment  32 . The exhaust inlet and outlet  50 ,  52  extend across the exhaust duct  24 , with the exhaust inlet  50  located in proximity of the turbine section  18 . 
     Referring to  FIGS. 5-6 , the air passages  40  communicate with a same air inlet  56  defined at one end thereof and with a same air outlet  72  defined at the opposed end thereof. The air inlet  56  is defined by an inlet connection member  58  which is designed to sealingly engage the compressor plenum  28  for receiving the compressed air. The air inlet  56  is oriented such that the compressed air flows axially or approximately axially therethrough. The inlet connection member  58  includes a duct  60  having one end connected to an inlet bulkhead  62  attached to the panel assembly  44 , and an opposed end having a flange  64  extending outwardly therearound. Referring to  FIG. 2 , the inlet connection member  58  also includes a flexible duct member  66  having a first end rigidly connected to the flange  64 , for example through an appropriate type of fasteners with a compressible seal ring or a gasket (not shown) therebetween. A second end of the flexible duct member  66  is rigidly connected to the compressor plenum  28 . In the embodiment shown, the flexible duct member  66  includes two rigid duct portions  68  interconnected by a diaphragm  70 , which allows relative movement between the two duct portions  68 ; alternately, the entire flexible duct member  66  may be made of flexible material. Accordingly, “flexible duct member” is intended herein to designate a duct member which includes at least a flexible portion such as to allow for relative movement between its opposed ends. The inlet connection member  58  thus defines a floating connection with the compressor plenum  28 , such that some amount of axial and radial relative motion is allowed therebetween. 
     Referring back to  FIGS. 5-6 , the air outlet  72  is defined by an outlet connection member  74  which is designed to sealingly engage the combustor plenum  26  for delivering the heated compressed air to the combustor  16 . The air outlet  72  is oriented such that the heated compressed air flows axially or approximately axially therethrough. The outlet connection member  74  includes a duct  76  having one end connected to an outlet bulkhead  78  attached to the panel assembly  44 , and an opposed end having a flange  80  extending outwardly therearound. Referring to  FIG. 2 , the flange  80  is rigidly connected to the combustor plenum  26 , for example through an appropriate type of fasteners. A compressible seal ring or a gasket (not shown) is received between the flanged  80  and the plenum  26  to form a sealed connection. The outlet connection member  74  thus defines a rigid connection with the combustor plenum  26 . 
     Alternately, the inlet connection member  58  may define a rigid connection with the compressor plenum  28 , with the outlet connection member  74  defining a floating connection with the combustor plenum  26 . 
     Referring back to  FIG. 2 , in the embodiment shown, the rear bulkhead  48  includes a protrusion  82  which is designed to be the contact point between the segment  32  and the wall  84  of the exhaust duct  24 , in order to stabilize the position of the segment  32  within the exhaust duct  24 . The protrusion  82  facilitates the relative sliding motion between the rear bulkhead  48  and the exhaust duct wall  84  when relative movement due to the floating connection occurs, and acts as a control surface maintaining contact between the segment  32  and the exhaust duct wall  84 . 
     In a particular embodiment, the exhaust passages  42  have a flaring shape, i.e. the cross-sectional area of each exhaust passage  42  increases from the exhaust inlet  50  to the exhaust outlet  52 , such as to diffuse the exhaust flow. The exhaust inlet  50  thus has a smaller cross-sectional area than that of the exhaust outlet  52 . Referring particularly to  FIG. 2 , a concentric split diffuser  53  is provided in the exhaust duct  24  upstream of the exhaust inlet  50 . The diffuser  53  includes circumferential splitters  54  which are supported by radial struts  55 . The splitters  54  progressively curve from the axial direction at the upstream end toward the radial direction. The splitters  54  define passages having a flaring shape, i.e. with an upstream end having a smaller cross-sectional area than the downstream end, to diffuse of the exhaust flow further diffused within the recuperator  30 . Diffuser vanes  51  may also be provided at the exit of the power turbine, upstream of the split diffuser  53 . The diffusion of the exhaust flow allows for an improved heat exchange within the recuperator  30 . 
     In the alternate embodiment shown in  FIG. 7 , the concentric split diffuser  53 ′ including splitters  53 ′ and radial struts  55 ′ forms part of the recuperator  30 , and extends from the exhaust inlet  50 . 
     In a particular embodiment, the recuperator  30  also reduces the swirl of the exhaust flow. As can be seen from  FIG. 4 , the exhaust passages  42  have an arcuate profile in a plane perpendicular to a central axis C of the recuperator to reduce the exhaust flow swirl. The splitters  54  ( FIGS. 2 and 13 ) may also be curved in the plane perpendicular to the central axis of the recuperator. The radial struts  55 ,  55 ′ which are structural members supporting the splitters  54 ,  54 ′ ( FIGS. 2, 7 and 13 ) have an asymmetrical airfoil shape twisted to allow a progressively increased swirl with increasing radius, optimised to reduce the turning losses as the flow turns from the axial to the radial direction within the diffuser  53 ,  53 ′. The vanes  51  may also have an asymmetrical airfoil shape similar to the struts  55 ,  55 ′. The swirl, i.e. the circumferential component of the flow velocity at the power turbine exit, is thus first slowed in the diffuser vanes  51 . The flow exiting the vanes  51  enter the split diffuser  53 ,  53 ′. The flow in the split diffuser  53 ,  53 ′ slows down both in the axial direction due to the splitters  54 ,  54 ′ as well as in circumferential direction, i.e. the swirl, due to the increased radius of the swirling shape of the radial struts  55 ,  55 ′. 
     Referring now to  FIGS. 8-12 , a recuperator  130  according to an alternate embodiment is shown. The recuperator  130  includes a plurality of independent arcuate segments  132 , with a controlled gap  134  being defined between adjacent segments  132  for thermal expansion. Each segment  132  defines a plate heat exchanger, with a first group of fluid passages  140  for circulating the compressed air, and a second group  142  of fluid passages for circulating the exhaust gas, alternating and in heat transfer relationship with one another. 
     The recuperator  130  extends within the exhaust duct  24  closer to the turbine section  18  than the previously described embodiment. Each segment  132  includes an exhaust inlet  150  defined by a radially extending end of the segment  132  located in proximity of the turbine section  18  and in communication with the exhaust passages  142 . The exhaust inlet  150  is oriented such that the exhaust gas flows axially or approximately axially therethrough. Each segment  132  also includes an exhaust outlet  152  in communication with exhaust passages  142 , and oriented such that the exhaust gas flows outwardly radially or approximately outwardly radially therethrough. 
     The air passages  140  communicate with a same air inlet  156  defined at one end thereof and with a same air outlet  172  defined at the opposed end thereof. The air inlet  156  is defined by an inlet connection member  158  which is designed to sealingly engage the compressor plenum  28  for circulating the compressed air. The air inlet  156  is oriented such that the compressed air flows axially or approximately axially therethrough. The inlet connection member  158  includes a support  164  surrounding the inlet  156  which is rigidly connected to the compressor plenum  28 , for example through an appropriate type of fasteners with a compressible seal ring or a gasket (not shown) therebetween. The inlet connection member  158  thus defines a rigid connection with the compressor plenum  28 . 
     The air outlet  172  is defined by an outlet connection member  174  which is designed to sealingly engage the combustor plenum  26  for delivering the heated compressed air to the combustor  16 . The air outlet  172  is oriented such that the heated compressed air flows radially outwardly or approximately radially outwardly therethrough. The outlet connection member  174  includes a duct  176  which is engaged in a corresponding opening of the combustor plenum  26 . Referring to  FIG. 11 , a flexible and compressible circular seal  94 , for example having a C-shaped cross-section, surrounds the duct  176  and abuts the wall  98  of the plenum  26  around the opening where the duct  176  is received. A collar  92 , sandwiched between retaining rings  90 , is received between the seal  94  and an outwardly extending flange  96  of the duct  176 , and compresses the seal  94 . The connection member  174  thus defines a floating connection with the combustor plenum  26 , as some amount of axial and tangential relative motion is allowed between the connection member  174  and the support opening of the plenum  26  to compensate for thermal mismatch. The circular seal  94  seals the connection. 
     As can be seen in  FIG. 8  and  FIG. 12B , the exhaust passages  142 , defined between the air cells  141  forming the air passages  140 , have a flaring shape such as to diffuse the exhaust flow. The exhaust inlet  150  thus has a smaller cross-sectional area than that of the exhaust outlet  152 . The diffusion of the exhaust flow allows for an improved heat exchange within the recuperator  130 . In the embodiment shown, the recuperator  130  has a shape substantially confirming to that of the exhaust duct  24 , with a controlled gap  134  (see  FIG. 11 ) being provided between the recuperator  130  and exhaust duct wall to prevent restriction of the relative movement allowed by the floating connection. 
     In a particular embodiment, the recuperator  130  also reduces the swirl of the exhaust flow. As can be seen from  FIGS. 9 and 12B , the air cells  141  forming the exhaust passages  142  act as vanes, and have an arcuate profile in a plane perpendicular to a central axis C of the recuperator to reduce the exhaust flow swirl. The air cells  141  thus define a diffusion area  99  and a deswirling and diffusion area  100 , which act to slow down the exhaust flow both in the axial direction as well as in circumferential direction. 
     In the above described embodiments, each segment  32 ,  132  of the recuperator  30 ,  130  is only connected to the engine  10  through the inlet and outlet connection members  58 ,  158 ,  74 ,  174 , and the segments  32 ,  132  are independent from each other. Since one of these connection members defines a floating connection, some relative movement is allowed between each segment  32 ,  132  of the recuperator  30 ,  130  and the remainder of the gas turbine engine  10 , such as to accommodate some amount of thermal expansion without impeding the seal of the connections. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.