Abstract:
A gas turbine engine combustor swirler has vanes with a spanwise chord length distribution providing a desired swirl distribution.

Description:
BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The invention relates to fuel nozzles for combustors for gas turbine engines. More particularly, the invention relates to the configuration of the vanes of a swirler. 
   (2) Description of the Related Art 
   As is well known in the gas turbine engine technology it is desirable to operate the combustor at a combination of high efficiency, good lean blowout characteristics, good altitude relight characteristics, low smoke and other pollutant output, long life, and low cost. Scientists and engineers have been experimenting with the designs of the fuel nozzles for many years in attempts to maximize the efficacy of the combustor. 
   U.S. Pat. No. 5,966,937 (hereinafter the &#39;937 patent, the disclosure of which is incorporated by reference herein as if set forth at length) discloses a swirler wherein the vanes of the inner duct have a spanwise distributed twist producing a desired swirl angle distribution at the inner duct outlet. The exemplary distribution places the vane chord closer to radial near the outboard/aft wall of the duct than near the inboard/fore wall (in an exemplary implementation, a rearward/aft direction being the downstream flow direction, which may be a rearward direction of the engine). 
   Nevertheless, there remains room for improvements in swirler construction. 
   SUMMARY OF THE INVENTION 
   One aspect of the invention involves a swirler vane pack having an array of vanes and means holding the vanes. Each of the vanes may have first and second ends with a span therebetween and a spanwise changing section. 
   In various implementations, a spacing between adjacent ones of the vanes may be essentially spanwise constant. The spanwise changing section may comprise a spanwise changing chord. The second end may have a chord that is 25%-75% of a chord of the first end. The spanwise changing section may comprise a spanwise monotonically changing chord. The vanes may be unitarily formed with the means. The vane first ends may be proximal of the means and the vane second ends may be distal of the means. The spanwise changing section may comprise a spanwise monotonically distally decreasing chord. The spanwise changing section may be essentially symmetric across a chord (e.g., to not provide airfoil lift). The spanwise changing section may be characterized by first and second flat facets along a major portion of a chordwise length of the vanes. Each of the vanes may be untwisted. 
   Another aspect of the invention involves a method for engineering the vane pack. A target change in swirl angle across a passageway associated with the vane pack is determined. A distribution of the spanwise change in section effective to achieve the target change in swirl angle at a target operating condition is determined. Lean blow out characteristics of a swirler incorporating the vane pack may be measured. 
   Another aspect of the invention involves a swirler assembly including a fuel injector. A bearing is coaxial with the fuel injector and has an outer surface forming a first surface of a first passageway from an inlet to an axial outlet. A prefilmer is coaxial with the fuel injector and has an inner surface forming a second surface of the first passageway and an outer surface forming a first surface of a second passageway from an inlet to an axial outlet. A first array of vanes is in the first passageway, each vane extending from a first end proximate the first passageway first surface to a second end proximate the first passageway second surface and having a section characterized by a spanwise decrease in chord of at least 25% from said first end to said second end. A second array of vanes is in the second passageway. 
   In various implementations, the first and second passageway inlets may be circumferential inlets. The spanwise decrease in chord may be effective to provide, at a target operating condition, a discharge profile characterized by swirl angle of: a peak value located between 0% and 25% of an exit radius; and a swirl angle of between 15° and 25° at a location between 95% and 100% of the exit radius. The spanwise decrease in chord may be effective to provide, at a target operating condition, a discharge profile characterized by a swirl angle of: a peak value located between 15% and 25% of an exit radius; and a swirl angle of between 18° and 21° at a location between 95% and 100% of the exit radius. The peak value may be in excess of 85°. 
   Another aspect of the invention involves a high shear design fuel injector for a combustor of a gas turbine engine. A fuel nozzle is supported at an inlet of the combustor. A first radial inlet swirler is mounted on the fuel nozzle and includes a first passage for flowing air into the combustor and is coaxially disposed relative to the fuel nozzle. A second radial inlet swirler is mounted adjacent to the first radial swirler and includes a second passage for flowing additional air into the combustor and is concentrically disposed relative to the first passage. The first radial inlet swirler has circumferentially disposed vanes. Each of the vanes has a span between first and second ends and has a spanwise change in section effective to change the swirl angle from the first end to the second end to offset the swirl to a higher level than the swirl would be without the change in section so as to produce a Rankine vortex. 
   In various implementations, a majority of the air in the first passage and the second passage may be in the first passage. The amount of air in the first passage may be substantially equal to 50%-95% of the total air flow in the first passage and second passage. A bulk swirl angle of air at a discharge of the second passage may be substantially between 60° and 75°. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view of a swirler. 
       FIG. 2  is an end view of a swirler vane array of the swirler of  FIG. 1 . 
       FIG. 3  is an enlarged view of two vanes of the array of  FIG. 2 . 
       FIG. 4  is a medial sectional view of a vane of  FIG. 3 , taken along line  4 - 4 . 
       FIG. 5  is a leading edge view of a vane of  FIG. 3 , taken along line  5 - 5 . 
   

   Like reference numbers and designations in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
     FIG. 1  shows a combination of a swirler assembly  20  and a fuel injector nozzle  22 . The nozzle has a distal end outlet  24  discharging a fuel spray  26  into an inner duct or passageway  28  of the swirler. The swirler and injector nozzle share a central longitudinal axis  500 . The fore end of the swirler is formed by a bearing  30  having a cylindrical interior surface  32  that closely accommodates the injector nozzle allowing relative longitudinal movement of the nozzle and swirler. The exemplary bearing has generally aft and fore surfaces  34 ,  36 ,  38  and  40 ,  42 . The aft and fore surfaces extend between a circumferential perimeter rim surface  44  and the cylindrical interior surface  32 . In the exemplary embodiment, the aft surface has a radially-extending outboard portion  34  extending inward from the perimeter rim surface  44 , a curved portion  36  transitioning therefrom to near longitudinal, and an inboard radial rim portion  38  extending to the cylindrical interior surface  32 . The fore surface has a radially-extending outboard portion  40  and a rearwardly/inwardly tapering portion  42  extending to the cylindrical interior surface  32 . Spaced rearwardly of the bearing is a prefilmer  50  having generally aft and fore surfaces  52 ,  54 ,  56  and  58 ,  60 . The aft surface includes a radially-extending outboard portion  52  extending inward from a perimeter rim surface  62 , a longitudinally concavely curved, rearwardly converging, transition portion  54 , and an aft rim portion  56  extending radially inward at the end of the curved portion. The fore surface includes a stepped radially-extending outboard portion  52  extending inward from the rim  62  and a longitudinally convexly curved, rearwardly converging, transition portion  60  extending therefrom to the rim  56 . The bearing aft surface and prefilmer fore surface generally cooperate to define the inner passageway  28  and an inner flowpath  202  extending radially inward from an inlet  64  and curving aft to an outlet  66  at the rim surface  56 . Air  70  entering the inlet  64  mixes with the fuel  26  in a downstream central portion of the inner passageway  28  to be expelled as a mixture from the outlet  66 . 
   An outer passageway  72  is formed between the prefilmer aft surface and the fore surface  74 ,  76  and divergent rim surface  78  of an outer wall  80 . The outer wall  80  has an aft surface  82 ,  84 . The outer wall aft and fore surfaces have radial portions  82  and  74  extending inward from a circumferential outer rim  86  and respectively transitioning to longitudinally concave and convex portions  84  and  76  meeting at the aft rim  78 . The second passageway defines a flowpath  204  from an inlet  90  between the prefilmer and outer wall outer rims  62  and  86  to an outlet  92  at the junction of the outer wall aft surface  84  and rim surface  78 . In the exemplary embodiment, the inner passageway outlet is recessed slightly behind the second passageway outlet so that the two passageways begin to merge at that point. 
   Inlet portions of the first and second passageways carry first and second circumferential arrays of vanes  100  and  102  so as to impart swirl to the air flowing therethrough. General operation may be as described in the &#39;937 patent. Whereas the &#39;937 patent discloses achieving a desired swirl profile by an appropriately distributed twist of vanes having otherwise constant section, the exemplary embodiment achieves this by varying blade section without such twist. In the exemplary embodiment, the bearing is formed with a main piece  101  and a vane pack  103  including the vanes  100 . A base portion  104  of the vane pack rides in a rebate  105  in the main piece and has exposed perimeter and aft surfaces respectively forming portions of the perimeter  44  and surface  34 . 
     FIG. 2  shows each vane  100  as extending between leading and trailing edges  110  and  112  from a proximal end at the platform  104  to a distal end  114 . The exemplary vanes have first and second side surfaces  116  and  118  having major flat portions converging radially inward at an angle θ 1 . Exemplary θ 1  may be between 0.5° and 5°, more narrowly, 0.5° and 2°. In the exemplary embodiment, the first surface  116  of one vane is nearly parallel to the adjacent second surface  118  of the next vane. With major lengths of these surfaces being straight, a major portion of the space  119  therebetween will have nearly constant width.  FIG. 2  further shows a line (or longitudinal plane)  502  extending substantially medially through one of the spaces  119 . A radial line (longitudinal radial plane)  504  intersects the line/plane  502  at a center  506  of the space  119  and is at an angle θ 2  thereto. Non-zero θ 2  is effective to impart swirl. Exemplary θ 2  may be between 5° and 45°, more narrowly, 15° and 30°. 
     FIG. 4  shows the vane as tapering in chord length from its proximal end  120  toward its distal end  114 . In the exemplary embodiment, the chord length near the proximal end is shown as S 1ROOT  and the chord length at the distal end is shown as S 1TIP  with a height from the proximal end to the distal end shown as H.  FIG. 5  further shows an exemplary blending or filleting  122  along the vane sides. If such filleting is present along the leading and trailing edge portions, it may affect actual chord length.  FIG. 4  further shows the exemplary trailing edge  112  as extending longitudinally. The leading edge  110  is inclined to provide the taper. In the exemplary embodiment, the leading edge (or a major portion thereof) is inclined at an angle θ 3  off vertical as measured in the section of  FIG. 4 . In the exemplary embodiments, S 1TIP  is ≦75% of S 1ROOT  and ≧25%. Exemplary θ 3  may be between 10° and 40°, more narrowly, 15° and 30°.  FIG. 3  shows a line (longitudinal plane)  510  extending through the space  119  from the intersection of the flat trailing edge  112  and the adjacent vane second side surface  118  of one adjacent vane and intersecting along the first side  116  of the other adjacent vane.  FIG. 3  further shows a line  512  extending normal to that first side surface  116  from the beginning of the flat portion thereof and intersecting the second side  118  of the first vane (at the distal end  114  thereof).  FIG. 3  further shows a similar line  514  at the proximal end. A separation (length) between the line/plane  510  and the second line  512 ,  514  will progressively vary along the span of the vanes. The separation is shown as S 2  with specific lengths S 2TIP  and S 2ROOT  shown.  FIG. 3  further shows S 3  as the width of the space  119  at the line/plane  510 . 
   The effect of the tapering vanes is to reduce the imparted swirl along the reduced chordline length. Such tapering may be used to achieve the same or similar flow properties as are identified in the &#39;937 patent. It is noted that the exemplary embodiment of the &#39;937 patent places the proximal ends of its vanes on the prefilmer whereas the present exemplary embodiment places the proximal ends on or near the bearing for ease of manufacturability. Accordingly, this factor should be remembered to avoid confusion. Thus, whereas the aft (proximal) ends of the &#39;937 patent vanes are at lower angle than the fore (distal) ends the presently-illustrated embodiment has an aft (distal) chord length smaller than a fore (proximal) chord length to achieve a similar fore-to-aft swirl reduction. This, in turn, produces in a downstream portion of the first duct a tailored profile that has both a relatively low swirl value (e.g., less than 25°) near the prefilmer and a peak swirl value at a relatively high radial location inboard thereof (e.g., at least 20% of an exit radius). In the exemplary resulting stretched Rankine vortex, the peak swirl angle (90°) marks the transition between the inboard recirculation zone solid body rotation and the outboard free vortex. An exemplary range for the radius of this transition is 0-25% of the exit radius (e.g., of the surface  60  at the outlet  66 ). As the higher numbers may be more advantageous, narrower ranges of 15-25% or 20-25% may be appropriate. The swirl angle at the prefilmer may best be characterized as just outside of any boundary layer. Typically, this will fall at a radius of at least 95% of the exit radius. This swirl angle may typically be at least 15° (e.g., 15-25° or, more narrowly, 18-21°). 
   The local degree of turning of the flow may be less than θ 2  if, locally, the space  119  does not have sufficient length. For the exemplary vane configuration, the turning has been observed to be substantially θ 2  where the ratio of the length S 2  to the separation S 3  is greater than approximately 0.5. Where less than this value, the turning will be incomplete and only a portion of θ 2 . In exemplary implementations, essentially full turning is desired near the front (proximal) ends of the vanes and, less than full turning is desired near the aft (distal) ends. An exemplary S 2ROOT  may be greater than 0.5 and an exemplary S 2TIP  may be ≦0.25. An exemplary amount of turning provided at the tip is 35%-60% of θ 2 . For other vane configurations, appropriate relationships may be determined by modeling or measurement. 
   One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when the invention is applied to the reengineering of an existing swirler, details of the existing swirler and/or associated manufacturing techniques may influence details of any associated implementation. Additionally, the invention may be combined with other modifications either presently known or to be developed. Accordingly, other embodiments are within the scope of the following claims.