Abstract:
A method of inducing swirl in pressurized air flowing through an air passageway of a fuel nozzle of a gas turbine engine includes inducing swirl in the pressurized air at an exit of the air passageway, by directing the pressurised air through helicoidal grooves formed at a downstream end of the air passageway. The swirling pressurized air exiting the air passageway is then directed into a mixing zone at a downstream end of the fuel nozzle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 14/505,787 filed Oct. 3, 2014, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The application relates generally to gas turbines engines combustors and, more particularly, to fuel nozzles. 
       BACKGROUND 
       [0003]    Gas turbine engine combustors employ a plurality of fuel nozzles to spray fuel into the combustion chamber of the gas turbine engine. The fuel nozzles atomize the fuel and mix it with the air to be combusted in the combustion chamber. The atomization of the fuel and air into finely dispersed particles occurs because the air and fuel are supplied to the nozzle under relatively high pressures. The fuel could be supplied with high pressure for pressure atomizer style or low pressure for air blast style nozzles providing a fine outputted mixture of the air and fuel may help to ensure a more efficient combustion of the mixture. Finer atomization provides better mixing and combustion results, and thus room for improvement exists. 
       SUMMARY 
       [0004]    There is accordingly provided a method of inducing swirl in pressurized air flowing through an air passageway of a fuel nozzle of a gas turbine engine, the fuel nozzle including the air passageway and a fuel passageway extending through the fuel nozzle and meeting in a mixing zone at a downstream end of the fuel nozzle, the method comprising: inducing swirl in the pressurized air at an exit of the air passageway by directing the pressurised air through helicoidal grooves formed at a downstream end of the air passageway; and directing the swirling pressurized air exiting the air passageway into the mixing zone. 
         [0005]    There is also provided a method of manufacturing a fuel nozzle for a gas turbine engine, the method comprising: providing a fuel nozzle body having an air passageway and a fuel passageway extending axially therethough, the air passageway and the fuel passageway meeting in a mixing zone formed at a downstream end of the fuel nozzle, the mixing zone located downstream of the air passageway and upstream of an exit lip of the fuel nozzle; and forming helicoidal grooves in an outer wall of the air passageway at a downstream end thereof that opens into the mixing zone, the helical grooves adapted to induce swirl in pressurized air flowing through the air passageway and into the mixing zone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Reference is now made to the accompanying figures in which: 
           [0007]      FIG. 1  is a schematic cross-sectional view of a gas turbine engine; 
           [0008]      FIG. 2  is a partial schematic cross-sectional view of an embodiment of a nozzle for the combustor of the gas turbine engine of  FIG. 1 ; and 
           [0009]      FIG. 3A and 3B  illustrate alternative designs of swirl-inducing reliefs of the nozzle of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      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 gas turbine engine  10  has one or more fuel nozzles  100  which supply the combustor  16  with the fuel which is combusted with the air in order to generate the hot combustion gases. The fuel nozzle  100  atomizes the fuel and mixes it with the air to be combusted in the combustor  16 . The atomization of the fuel and air into finely dispersed particles occurs because the air and fuel are supplied to the nozzle  100  under relatively high pressures. The fuel could be supplied with high pressure for pressure atomizer style or low pressure for air blast style nozzles providing a fine outputted mixture of the air and fuel may help to ensure a more efficient combustion of the mixture. The nozzle  100  is generally made from a heat resistant metal or alloy because of its position within, or in proximity to, the combustor  16 . 
         [0011]    Turning now to  FIG. 2 , an embodiment of a fuel nozzle  100  will be described. 
         [0012]    The nozzle  100  includes generally a cylindrical body  102  defining an axial direction A and a radial direction R. The body  102  is at least partially hollow and defines in its interior a primary air passageway  103  (a.k.a. core air) and a fuel passageway  106 , all extending axially through the body  102 . 
         [0013]    The air passageway  103  and the fuel passageway  106  are aligned with a central axis  110  of the nozzle  100 . The fuel passageway  106  is disposed concentrically around the air passageway  103 . The fuel passageway  106  is annular. It is contemplated that the nozzle  100  could include more than one air passageway  103  and/or fuel passageway  106 , annular or not. The size, shape, and number of the fuel  106  and air passageway  103  may vary depending on the flow requirements of the nozzle  100 , among other factors. The nozzle  100  could, for example, include a secondary passageway around the fuel passageway  106 . 
         [0014]    The body  102  includes an upstream end (not shown) connected to sources of pressurised fuel and air and a downstream end  114  at which the air and fuel exit. The terms “upstream” and “downstream” refer to the direction along which fuel flows through the body  102 . Therefore, the upstream end of the body  102  corresponds to the portion where fuel/air enters the body  102 , and the downstream end  114  corresponds to the portion of the body  102  where fuel/air exits. 
         [0015]    The primary air passageway  103  is defined by outer wall  103   b.  The outer wall  103   b  ends at exit end  115 . The primary air passageway  103  carries pressurised air illustrated by arrow  116 . The air  116  will be referred interchangeably herein to as “air”, “jet of air”, or “core flow of air”. 
         [0016]    The fuel passageway  106  is defined by inner wall  106   a  and outer wall  106   b  and carries a fuel film illustrated by arrow  117 . The fuel  117  will be referred interchangeably herein to as “fuel” or “fuel film”. In the embodiment shown in the Figures, the inner wall  106   a  has a helicoidal relief to induce swirl in the fuel film  117 . By “swirl”, one should understand any non-streamlined motion of the fluid, e.g. chaotic behavior or turbulence. It is contemplated that the inner wall  106   a  could be straight and/or could have grooves/ridges to induce swirl in the fuel film  117 . It is also contemplated that the outer wall  106   b  could have grooves/ridges or that the inner wall  106   a  could be straight. 
         [0017]    The fuel passage  106  is typically convergent (i.e. its cross-sectional area) may decrease along its length, from inlet to outlet) in the downstream direction at the downstream end  114 . The outer wall  106   b  of the fuel passageway  106  converging at the downstream end  114  forces the annular fuel film  117  expelled by the fuel passageways  106  onto a jet of air  116  from the primary air passageway  103 . The outer wall  106   b  of the fuel passageway  106  includes a first straight portion  120 , a second converging portion  122  extending from a downstream end  126  of the straight portion  120 , and a third straight portion  124  extending from a downstream end  128  of the converging portion  122 . The third straight portion  124  forms an exit lip  127  of the nozzle  100 . The lip exit  127  is disposed downstream relative to the exit end  115  of the primary air passageway  103 . A diameter D 1  of the outer wall  106   b  at the third straight portion  124  is slightly bigger than a diameter D 2  of the outer wall  103   b  at the first straight portion  120 . 
         [0018]    A downstream end portion (or exit lip)  132  of the outer wall  103   b  of the air passageway  103  includes a surface treatment or swirl-inducing relief in the form of a plurality of grooves  130 . The grooves  130  define a plurality of ridges  131  between them. The ridges  131  form abrupt transitions in the outer wall  103   b  and induce swirl in the core flow of air  116  as it exits the air passageway  103 . By inducing swirl to the core air, shearing forces between the fuel film  117  and the air  116  may be increased. The shearing induces better mixing between the air and the fuel, better breakdown of the fuel. In turn, a size of the fuel droplets created may be reduced. 
         [0019]    The grooves  130  in the illustrated embodiment are disposed up to the exit end  115  of the air passageway  103  in order to ensure that the air swirling is sustained to a fuel breakdown region FB, right after the exit of the air passageway  103  at about the third straight portion  124 . 
         [0020]    In the embodiment shown in the Figures, the grooves  130  are circumferential, helicoidal and of round cross-section. It is contemplated that the grooves  130  could have various shapes, for example, the grooves  130  could be axial, circular, of a rectangular cross-section, or of a triangular cross-section. The grooves  130  could be continuous or discontinuous. 
         [0021]      FIGS. 3A and 3B  show examples of alternative of designs of the relief of the downstream end portion  132  of the air passageway  130 . Grooves  130   a  in  FIG. 3A  have a sawtooth cross-section, and the grooves in  FIG. 3B  are replaced by protrusion  130   b  extending inwardly from the outer wall  103   b.  The protrusions  130   b  could also be substitute by vanes, which may be disposed circumferentially along the outer wall  103   b.    
         [0022]    The relief of the outer wall  103   b  may have various aspects, as long as it induces some sort of non-streamline behavior, e.g. turbulence, swirl or chaotic behavior in the air  116 . The relief could be right at the exit end  115  of the air passageway  103 , as shown in the Figures, or slightly upstream of the exit end  115 . 
         [0023]    The nozzle  100  may include one or more secondary air passageway(s) sandwiching the fuel film  117  with the core flow of air  116 . The secondary air passageway(s) may include grooves similar to the grooves  130  or protrusion/ridges to induce swirl in the secondary stream of air. The grooves may be of the same type (e.g. helicoid) with the same characteristics (e.g. angle of the helix) as the grooves  130  or could be different. 
         [0024]    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. Other 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.