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An apparatus for providing propulsive power that utilizes a novel swirl generator for rapidly and efficiently atomizing, vaporizing, as necessary, and mixing a fuel into an oxidant. The swirl generator converts an oxidant flow into a turbulent, three-dimensional flowfield into which the fuel is intr

An apparatus for providing propulsive power that utilizes a novel swirl generator for rapidly and efficiently atomizing, vaporizing, as necessary, and mixing a fuel into an oxidant. The swirl generator converts an oxidant flow into a turbulent, three-dimensional flowfield into which the fuel is introduced. The swirl generator effects a toroidal outer recirculation zone and a central recirculation zone, which is positioned within the outer recirculation zone. These recirculation zones are configured in a backward-flowing manner that carries heat and combustion byproducts upstream where they are employed to continuously ignite a combustible fuel/oxidizer mixture in adjacent shear layers. The swirl generator is compatible with the throttle range of conventional gas turbine engines, provides smooth combustion with no instabilities and minimum total pressure losses, enables significant reductions the in L/D ratio of the combustor and is readily packaged into various applications. Other benefits include simplicity, reliability, wide flammability limits and high combustion efficiency/thrust performance. This concept is applicable to various propulsion systems such as such as ramjet missiles, combine cycle engines, gas turbine afterburners and energy conversion devices.

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1. A fuel/oxidizer mixing and combusting apparatus comprising:a combustor having a combustor inlet; anda swirl generator having:an inlet housing coupled to the combustor inlet, the inlet housing defining a hollow interior volume therein and serving as a conduit through which an oxidizer flow is cond

1. A fuel/oxidizer mixing and combusting apparatus comprising:a combustor having a combustor inlet; anda swirl generator having:an inlet housing coupled to the combustor inlet, the inlet housing defining a hollow interior volume therein and serving as a conduit through which an oxidizer flow is conducted, the oxidizer flow having a velocity that is substantially defined by an axial velocity component, the hollow interior volume intersecting the combustor inlet at a dump step wherein the inlet housing has an inner dimension that is smaller than that of the combustor inlet;a swirl vane pack disposed within the hollow interior volume and having a plurality of vanes, the vanes cooperating to change the velocity of the oxidizer flow so that the velocity includes a substantial tangential velocity component;a centerbody assembly disposed in the hollow interior volume, the centerbody assembly being coupled to the swirl vane pack and extending rearwardly therefrom; the center body assembly including an aft bluff body, an aft-most portion of the aft bluff body being sized relatively larger than an adjacent upstream portion of the centerbody assembly; anda plurality of groups of fuel injectors coupled to at least one of the inlet housing, the swirl vane pack and the centerbody assembly and dispensing a fuel therefrom directly into the oxidizer flow for at least partially mixing the fuel and oxidizer prior to entering the combustor;wherein the swirl generator converts the oxidizer flow received therein into a swirling, three-dimensional flowfield;wherein a first portion of the flowfield flows over the dump step to form an outer recirculation zone;wherein a second portion of the flowfield forms a central recirculation zone that is anchored by an aft end of the centerbody assembly;wherein a first portion of the fuel mixes with the first portion of the flowfield to fuel the outer recirculation zone;wherein a second portion of the fuel mixes with the second portion of the flowfield to fuel the central recirculation zone;and wherein a remaining portion of the fuel enters and fuels a core flow. 2. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the fuel injectors are positioned to inject the fuel downstream of the swirl vane pack. 3. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the fuel injectors include a plurality of circumferentially spaced apart wall injectors that are coupled to the inlet housing and inject fuel therethrough. 4. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein at least one of the fuel injectors is housed in the centerbody assembly. 5. The fuel/oxidizer mixing and combustion apparatus of claim 4, wherein the centerbody assembly includes at least one injection ring, the injection ring including a plurality of fuel injection sites that are spaced apart about a perimeter of the injection ring. 6. The fuel/oxidizer mixing and combustion apparatus of claim 4, wherein the at least one of the fuel injectors is coupled to an aft end of the centerbody assembly and is configured to inject fuel in a direction downstream of the centerbody assembly. 7. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the plurality of fuel injectors include a plurality of fuel injection sites that are formed into at least a portion of the vanes of the swirl vane pack. 8. The fuel/oxidizer mixing and combustion apparatus of claim 7, wherein each vane includes a trailing edge and a lateral surface and wherein the fuel injection sites on a given vane are formed into at least one of the trailing edge and the lateral surface. 9. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the plurality of injectors include a plurality of strut injectors coupled to the inlet housing and the centerbody assembly, each of the strut injectors including a plurality of fuel injection sites. 10. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the a ft bluff body has a boat tail shape that is configured to augment flow separation of the oxidizer flow. 11. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein a plurality of injection sites are formed about a perimeter of the aft bluff body. 12. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the aft bluff body has a shape that is selected from a group consisting of a frusto-conical shape and an ogive shape. 13. The fuel/oxidizer mixing and combustion apparatus of claim 12, wherein a plurality of channels are formed into a perimeter of the aft bluff body. 14. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the swirl generator further comprises at least one igniter, the igniter being coupled to one of the centerbody assembly, the inlet housing and the combustor, the igniter being operable for generating an ignition kernel that ignites the fuel/oxidizer mixture in the central recirculation zone. 15. The fuel/oxidizer mixing and combustion apparatus of claim 14, wherein the igniter is housed in the centerbody assembly. 16. The fuel/oxidizer mixing and combustion apparatus of claim 15, further comprising a second igniter coupled to the combustor at a location downstream of the dump step. 17. The fuel/oxidizer mixing and combustion apparatus of claim 14, wherein the igniter is selected from a group of igniters consisting of spark igniters, plasma jet igniters, laser-based igniters and microwave based igniters. 18. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the combustor has a length-to-diameter ratio that is less than about 2.0. 19. The fuel/oxidizer mixing and combustion apparatus of claim 18, wherein the length-to-diameter ratio is less than about 1.6. 20. The fuel/oxidizer mixing and combustion apparatus of claim 19, wherein the length-to-diameter ratio is about 1.0. 21. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the vanes include a trailing edge, at least a portion of the trailing edge being configured with a plurality of discontinuities. 22. The fuel/oxidizer mixing and combustion apparatus of claim 21, wherein the discontinuities are selected from a group consisting of scallops, ramps and grooves. 23. The fuel/oxidizer mixing and combustion apparatus of claim 21, wherein a plurality of fuel injection sites are formed into each vane proximate the discontinuities, the plurality of fuel injection sites comprising at least a portion of the fuel injectors. 24. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein an inlet ramp is formed onto the inlet housing adjacent the dump step. 25. The fuel/oxidizer mixing and combustion apparatus of claim 24, wherein a plurality of circumferentially spaced apart channels are formed into the inlet ramp, the channels enhancing turbulent transport and fine scale mixing. 26. The fuel/oxidizer mixing and combustion apparatus of claim 24, wherein a plurality of circumferentially spaced apart injection sites are formed into the inlet ramp, the injection sites comprising at least a portion of the fuel injectors. 27. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the inlet of the combustor includes a quarl expansion. 28. The fuel/oxidizer mixing and combustion apparatus of claim 1, wherein the vanes are configured to provide the swirl vane pack with a swirl number that is less than about 2.0. 29. The fuel/oxidizer mixing and combustion apparatus of claim 28, wherein the swirl number of the swirl vane pack is about 0.4 to about 1.2. 30. An apparatus comprising:a combustor having an inlet;a swirl generator that is coupled to the inlet of the combustor, the swirl generator being operable for converting an oxidizer flow with a velocity that is substantially completely defined by an axial velocity component into a three-dimensional flowfield that includes a substantial tangential velocity component, the swirl generator including a flow defining means a nd a fueling means, the flow defining means including swirl vanes and a centerbody with an aft bluff body, at least an aft-most portion of the aft bluff body being sized relatively larger than an adjacent upstream portion of the centerbody, the flow defining means being operable for effecting both an outer recirculation zone and a central recirculation zone in the combustor, the outer recirculation zone being toroidal in shape, the central recirculation zone being disposed inwardly of the outer recirculation zone, the fueling means being operable for fueling the outer and central recirculation zones and including a plurality of groups of fuel injectors for injecting the fuel directly into the oxidizer flow for at least partially mixing the fuel and oxidizer prior to entering the combustor;wherein heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where the heat and combustion by-products are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones. 31. The apparatus of claim 30, further comprising a nozzle coupled to an aft end of the combustor, the nozzle being selected from a group consisting of convergent and convergent/divergent nozzles. 32. The apparatus of claim 30, further comprising an inlet structure coupled to the swirl generator opposite the combustor, the inlet structure including a plurality of flow guide vanes for mitigating oxidizer flow distortions and flow separations in the oxidizer flow before the oxidizer flow enters the swirl generator. 33. The apparatus of claim 32, wherein the inlet structure guides the oxidizer flow around a bend. 34. The apparatus of claim 30, wherein the flow defining means includes a swirl vane pack having a plurality of vanes and wherein the vanes are configured to provide the swirl vane pack with a swirl number that is less than about 2.0. 35. The apparatus of claim 34, wherein the swirl number of the swirl vane pack is about 0.4 to about 1.2. 36. The apparatus of claim 30, wherein the combustor has a length-to-diameter ratio that is less than about 2.0. 37. The apparatus of claim 36, wherein the length-to-diameter ratio is less than about 1.6. 38. The apparatus of claim 37, wherein the length-to-diameter ratio is about 1.0. 39. An apparatus comprising:a combustor having an inlet;a swirl generator that is coupled to the inlet of the combustor, the swirl generator being operable for converting an oxidizer flow with a velocity that is substantially completely defined by an axial velocity component into a three-dimensional flowfield that includes a substantial tangential velocity component, the swirl generator including a flow defining means and a fueling means, the flow defining means being operable for effecting both an outer recirculation zone and a central recirculation zone in the combustor, the outer recirculation zone being toroidal in shape, the central recirculation zone being disposed inwardly of the outer recirculation zone, the fueling means being operable for fueling the outer and central recirculation zones; andan inlet structure coupled to the swirl generator apposite the combustor, the inlet structure including a plurality of flow guide vanes for mitigating oxidizer flow distortions and flow separations in the oxidizer flow before the oxidizer flow enters the swirl generator wherein heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where the heat and combustion by-products are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones;wherein the inlet structure guides the oxidizer flow around a bend; andwherein the flow guide vanes are spaced apart so as to define a plurality of flow channels, each of the flow channels having a differently sized cross-s ection such that the flow channels produce a series of inlet flows that are substantially uniform in flow velocity. 40. An apparatus comprising:a combustor having an inlet;a swirl generator that is coupled to the inlet of the combustor, the swirl generator being operable for converting an oxidizer flow with a velocity that is substantially completely defined by an axial velocity component into a three-dimensional flowfield that includes a substantial tangential velocity component, the swirl generator including a flow defining means and a fueling means, the flow defining means being operable for effecting both an outer recirculation zone and a central recirculation zone in the combustor, the outer recirculation zone being toroidal in shape, the central recirculation zone being disposed inwardly of the outer recirculation zone, the fueling means being operable for fueling the outer and central recirculation zones; andan inlet structure coupled to the swill generator opposite the combustor, the inlet structure including a plurality of flow guide vanes for mitigating oxidizer flow distortions and flow separations in the oxidizer flow before the oxidizer flow enters the swirl generator;wherein heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where the heat and combustion by-products are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones;wherein the swirl generator includes a conduit through which is disposed at least one of a fuel conduit and an electrical cable, the conduit extending through at least one of the flow guide vanes, the inlet structure further comprising a fairing member that at least partially surrounds the conduit, the fairing member being operable for reducing flow separations that would otherwise be induced by the conduit. 41. An apparatus for providing propulsive power comprising:an inlet structure for conducting an oxidizer flow therethrough, the inlet structure including a plurality of flow guiding vanes that cooperate to affect the oxidizer flow such that it is substantially uniform and axial;a swirl generator coupled to an aft end of the inlet structure, the swirl generator including a flow affecting means and a fueling means, the flow affecting means including a plurality of vanes, a centerbody having an aft end that terminates rearwardly of a root of the vanes and a dump step, the flow affecting means being operable for converting the uniform and axial oxidizer flow into a three dimensional flowfield that includes a substantial tangential velocity component, the flow affecting means being further operable for effecting both a toroidal outer recirculation zone, which is anchored by the dump step, and a central recirculation zone that is disposed inwardly of the outer recirculation zone and anchored by the aft end of the centerbody, the fueling means being operable for fueling the outer and central recirculation zones and a core flow; anda combustor coupled to an aft end of the swirl generator, the combustor including a nozzle;wherein heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where the heat and combustion by-products are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones; and wherein combustion by-products from the core flow are expelled through the nozzle to produce thrust. 42. The apparatus for providing propulsive power of claim 41, wherein the fueling means injects a fuel down stream of an aft end of the vanes of the flow affecting means. 43. The apparatus for providing propulsive power of claim 42, wherein the fueling means includes a plurality of circumferentially spaced apart wall injections that are coupled to the inlet structure and which inject the fuel through the inlet structure. 44. The apparatus for providing propulsive power of claim 42, wherein the fueling means includes at least one fuel injector that is housed in the centerbody. 45. The apparatus for providing propulsive power of claim 44, wherein the centerbody includes at least one injection ring, the injection ring including a plurality of fuel injection sites that are spaced apart about a perimeter of the injection ring. 46. The apparatus for providing propulsive power of claim 44, wherein at least one of the fuel injectors is coupled to an aft end of the centerbody and is configured to inject the fuel in a direction downstream of the centerbody. 47. The apparatus for providing propulsive power of claim 41, wherein the fueling means includes a plurality of fuel injection sites that are formed into at least a portion of the vanes of the flow affecting means. 48. The apparatus for providing propulsive power of claim 47, wherein each of the vanes of the flow affecting means includes a trailing edge and a lateral surface and wherein the fuel injection sites on a given vane are formed into at least one of the trailing edge and the lateral surface. 49. The apparatus for providing propulsive power of claim 41, wherein the centerbody terminates at an aft bluff boat tail-body, the aft bluff boat-tail body being configured to augment flow separation of the oxidizer flow. 50. The apparatus for providing propulsive power of claim 49, wherein the fueling means includes a plurality of injection sites that are formed about a perimeter of the aft bluff boat-tail body. 51. The apparatus for producing propulsive power of claim 49, wherein the aft bluff boat-tail body has a shape that is selected from a group consisting of a frusto-conical shape and an ogive shape. 52. The apparatus for providing propulsive power of claim 51, wherein a plurality of channels are formed into a perimeter of the aft bluff boat-tail body. 53. The apparatus for providing propulsive power of claim 41, further comprising at least one igniter that is coupled to one of the centerbody, the inlet structure and combustor. 54. The apparatus for providing propulsive power of claim 53, wherein a first igniter is housed in the centerbody and a second igniter is coupled to the combustor downstream of the dump step. 55. The apparatus for providing propulsive power of claim 53, wherein the igniter is selected from a group of igniters consisting of spark igniters, plasma jet igniters, laser-based igniter end microwave based igniters. 56. The apparatus for providing propulsive power of claim 41, wherein the combustor has a length-to-diameter ratio that is less than about 2.0. 57. The apparatus for providing propulsive power of claim 56, wherein the length-to-diameter ratio is less than about 1.6. 58. The apparatus for providing propulsive power of claim 57, wherein the length-to-diameter ratio is about 1.0. 59. The apparatus for providing propulsive power of claim 41, wherein a plurality of discontinuities are formed into a trailing edge of at least a portion of the vanes of the flow affecting means. 60. The apparatus for providing propulsive power at claim 59, wherein the discontinuities are selected from a group consisting of scallops, ramps and grooves. 61. The apparatus for providing propulsive power of claim 59, wherein the fueling means includes a plurality of injection sites that are formed into the vanes of the flow affecting means, each of the injection sites being proximate an associated one of the discontinuities. 62. The apparatus for providing propulsive power of claim 41, wherein the flow affecting means includes an inlet ramp that is coupled to the inlet structure adjacent the dump step. 63. The apparatus for providing propulsive power of claim 62, wherein a plurality of circumferentially spaced apart channels are formed into the inlet ramp. 64. The apparatus for providing propulsive power of claim 63, wherein the fueling means includes a plurality of circumferen tially spaced apart injection sites that are formed into the inlet ramp. 65. The apparatus for providing propulsive power of claim 41, wherein the combustor includes a quarl expansion. 66. The apparatus for providing propulsive power of claim 41, wherein the vanes of the flow affecting means provide a swirl number that is less than about 2.0. 67. The apparatus for providing propulsive power of claim 66, wherein the swirl number is about 0.4 to about 1.2. 68. An apparatus for providing propulsive power comprising:a combustor having a combustor inlet, the combustor including a nozzle; anda swirl generator having:an inlet housing coupled to the combustor inlet, the inlet housing defining a hollow interior volume therein and serving as a conduit through which an oxidizer flow is conducted, the oxidizer flow having a velocity that is substantially defined by an axial velocity component, the hollow interior volume interjecting the combustor inlet at a dump step wherein the inlet housing has an inner dimension that is smaller than that of the combustor inlet;a swirl vane pack disposed within the hollow interior volume and having a plurality of vanes, the vanes cooperating to change the velocity of the oxidizer flow so that the velocity includes a substantial tangential velocity component;a centerbody assembly disposed in the hollow interior volume, the centerbody assembly being coupled to the swirl vane pack and extending rearwardly therefrom, the centerbody assembly including an aft bluff body, an aft-most portion of the aft bluff body being sized relatively larger than an adjacent upstream portion of the centerbody assembly; anda plurality of groups of fuel injectors coupled to at least one of the inlet housing, the swirl vane pack and the centerbody assembly anddispensing a fuel therefrom directly into the oxidizer flow for at least partially mixing the fuel and oxidizer prior to entering the combustor;wherein the swirl generator converts the oxidizer flow received therein into a swirling, three-dimensional flowfield, wherein a first portion of the flowfield flows over the dump step to form an outer recirculation zone, wherein a second portion of the flowfield forms a central recirculation zone that is anchored by an aft end of the centerbody assembly, wherein a first portion of the fuel mixes with the first portion of the flowfield to fuel the outer recirculation zone, wherein a second portion of the fuel mixes with the second portion of the flowfield to fuel the central recirculation zone, and wherein a remaining portion of the fuel enters and fuels a care flow; andwherein combustion by-products from the core flow are expelled through the nozzle to produce thrust. 69. The apparatus for providing propulsive power of claim 68, wherein the fuel injectors are positioned to inject the fuel downstream of the swirl vane pack. 70. The apparatus for providing propulsive power of claim 68, wherein the fuel injectors include a plurality of circumferentially spaced apart wall injectors that are coupled to the inlet housing and inject fuel therethrough. 71. The apparatus for providing propulsive power of claim 68, wherein at least one of the fuel injectors is housed in the centerbody assembly. 72. The apparatus for providing propulsive power of claim 71, wherein the centerbody assembly includes at least one injection ring, the injection ring including a plurality of fuel injection sites that are spaced apart about a perimeter of the injection ring. 73. The apparatus for providing propulsive power of claim 68, wherein the aft bluff body has a boat tail shape that is configured to augment flow separation of the oxidizer flow. 74. The apparatus for providing propulsive power of claim 68, wherein a plurality of injection sites are formed about a perimeter of the aft bluff body. 75. The apparatus for providing propulsive power of claim 68, wherein the aft bluff body has a shape that is selected from a group consisting at a frusto-conical shape an d an ogive shape. 76. The apparatus for providing propulsive power of claim 75, wherein a plurality of channels are formed into a perimeter of the aft bluff body. 77. The apparatus for providing propulsive power of claim 68, wherein the swirl generator further comprises at least one igniter, the igniter being coupled to one of the centerbody assembly, the inlet housing and the combustor, the igniter being operable for generating an ignition kernel that ignites the fuel/oxidizer mixture in the central recirculation zone. 78. The apparatus for providing propulsive power of claim 77, wherein the igniter is housed in the centerbody assembly. 79. The apparatus for providing propulsive power of claim 78, further comprising a second igniter coupled to the combustor at a location downstream of the dump step. 80. The apparatus for providing propulsive power of claim 77, wherein the igniter is selected from a group of igniters consisting of spark igniters, plasma jet igniters, laser-based igniters and microwave based igniters. 81. The apparatus for providing propulsive power of claim 68, wherein the combustor has a length-to-diameter ratio that is less than about 2.0. 82. The apparatus for providing propulsive power of claim 81, wherein the length-to-diameter ratio is less than about 1.6. 83. The apparatus for providing propulsive power of claim 82, wherein the length-to-diameter ratio is about 1.0. 84. The apparatus for providing propulsive power of claim 68, wherein an inlet ramp is formed onto the inlet housing adjacent the dump step. 85. The apparatus for providing propulsive power of claim 68, wherein the vanes are configured to provide the swirl vane pack with a swirl number that is less than about 2.0. 86. The apparatus for providing propulsive power of claim 85, wherein the swirl number of the swirl vane pack is about 0.4 to about 1.2. 87. An apparatus for providing propulsive power comprising:a combustor having an inlet and a nozzle;a swirl generator that is coupled to the inlet of the combustor, the swirl generator being operable for converting an oxidizer flow with a velocity that is substantially completely defined by an axial velocity component into a three-dimensional flowfield that includes a substantial tangential velocity component, the swirl generator including a flow defining means and a fueling means, the flow defining means including swirl vanes and a centerbody with an aft bluff body, at least an aft-most portion of the aft bluff body being sized relatively larger than an adjacent upstream portion of the centerbody, the flow defining means being operable for effecting both an outer recirculation zone and a central recirculation zone in the combustor, the outer recirculation zone being toroidal in shape, the central recirculation zone being disposed inwardly of the outer recirculation zone, the fueling means being operable for fueling the outer and central recirculation zones and including a plurality of groups of fuel injectors for injecting the fuel directly into the oxidizer flow for at least partially mixing the fuel and oxidizer prior to entering the combustor;wherein heat and combustion by-products produced during combustion are carried upstream by the outer and central recirculation zones where the heat and combustion by-products are employed to continuously ignite a combustible fuel/oxidizer mixture in a shear layer adjacent each of the outer and central recirculation zones; andwherein combustion by-products are expelled through the nozzle to produce thrust. 88. The apparatus of claim 87, further comprising a nozzle coupled to an aft end of the combustor, the nozzle being selected from a group consisting of convergent and convergent/divergent nozzles. 89. The apparatus of claim 87, further comprising an inlet structure coupled to the swirl generator opposite the combustor, the inlet structure including a plurality of flow guide vanes for mitigating oxidizer flow distortions and flow separations in the oxidiz er flow before the oxidizer flow enters the swirl generator. 90. The apparatus of claim 89, wherein the inlet structure guides the oxidizer flow around a bend. 91. The apparatus of claim 90, wherein the flow guide vanes are spaced apart so as to define a plurality of flow channels, each of the flow channels having a differently sized cross-section such that the flow channels produce a series of inlet flows that are substantially uniform in flow velocity. 92. The apparatus of claim 89, wherein the swirl generator includes a conduit through which is disposed at least one of a fuel conduit and an electrical cable, the conduit extending through at least one of the flow guide vanes, the inlet structure further comprising a fairing member that at least partially surrounds the conduit, the fairing member being operable for reducing flow separations that would otherwise be induced by the conduit. 93. The apparatus of claim 87, wherein the flow defining means includes a swirl vane pack having a plurality of vanes and wherein the vanes are configured to provide the swirl vane pack with a swirl number that is less than about 2.0. 94. The apparatus of claim 93, wherein the swirl number of the swirl vane pack is about 0.4 to about 1.2. 95. The apparatus of claim 87, wherein the combustor has a length-to-diameter ratio that is less than about 2.0. 96. The apparatus of claim 95, wherein the length-to-diameter ratio is less than about 1.6. 97. The apparatus of claim 96, wherein the length-to-diameter ratio is about 1.0.