Abstract:
Gas turbines with multiple gas flow paths are provided. In this regard, a representative gas turbine includes: a spool; a compressor; a turbine mechanically coupled to the spool; the compressor having a first set of blades and a second set of blades, the second set of blades being located downstream of the first set of blades, the first set of blades and the second set of blades being driven by the spool; and means for enabling the first set of blades to rotate at a lower rotational speed than the second set of blades.

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure generally relates to gas turbines. 
     2. Description of the Related Art 
     A typical single-spool gas turbine incorporates an intake that provides a flow of gas, e.g., air, to a compressor, a combustion section and a turbine in sequence. The turbine and the compressor are linked to each other via a spool. In operation, energy generated by combustion of a fuel-air mixture in the combustion section is converted to rotational energy by the turbine. The rotational energy is imparted to the compressor via the spool for compressing additional gas received through the intake. 
     Multi-spool gas turbines also are known, each of which typically includes multiple turbines and multiple compressors. Conventionally, the spools of a multi-spool gas turbine are concentric, with each being linked to a corresponding compressor-turbine pair. 
     SUMMARY 
     An exemplary embodiment of a gas turbine comprises: a high pressure spool; a high pressure compressor; a high pressure turbine mechanically coupled to the high pressure spool, the high pressure compressor having a first set of blades and a second set of blades, the second set of blades being located downstream of the first set of blades and being operative to rotate at a rotational speed corresponding to a rotational speed of the high pressure spool; a lower pressure spool; a lower pressure turbine mechanically coupled to the low pressure spool; and a gear assembly mechanically coupled to the high pressure spool and engaging the first set of blades such that rotation of the high pressure spool rotates the first set of blades at a lower rotational speed than the rotational speed of the second set of blades. 
     Another exemplary embodiment of a gas turbine comprises: a spool; a compressor; a turbine mechanically coupled to the spool; the compressor having a first set of blades and a second set of blades, the second set of blades being located downstream of the first set of blades, the first set of blades and the second set of blades being driven by the spool; and means for enabling the first set of blades to rotate at a lower rotational speed than the second set of blades. 
     An exemplary embodiment of a compressor blade assembly for a gas turbine comprises: an epicyclic gear having a ring gear; and a set of compressor blades mechanically coupled to the ring gear such that the compressor blades are operative to rotate at the rotational speed of the ring gear. 
     Other systems, methods, features and/or advantages of this disclosure will be or may become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features and/or advantages be included within this description and be within the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a schematic diagram depicting an embodiment of a gas turbine. 
         FIG. 2  is a schematic diagram depicting another embodiment of a gas turbine 
         FIG. 3  is schematic diagram depicting another embodiment of a gas turbine. 
         FIG. 4  is a schematic diagram depicting another embodiment of a gas turbine 
         FIG. 5  is schematic diagram depicting another embodiment of a gas turbine. 
         FIG. 6  is schematic diagram depicting still another embodiment of a gas turbine. 
         FIG. 7  is schematic diagram depicting yet another embodiment of a gas turbine. 
     
    
    
     DETAILED DESCRIPTION 
     A representative embodiment of a gas turbine is shown schematically in  FIG. 1 . As shown in  FIG. 1 , gas turbine  100  includes a compressor  102 , a combustion section  104  and a turbine  106 . Thus, the embodiment of  FIG. 1 , the compressor, combustion section and turbine define a gas flow path that has a normal flow direction from the compressor to the turbine. 
     Notably, compressor  102  incorporates a first set of blades  108  and other sets of blades  110 . The first set of blades  108  engages a gear assembly  112 . In this embodiment, the gear assembly is configured such that the first set of blades  108  rotates at a slower rotational speed than that of the other sets of compressor blades  110 . Notably, all of the blades of the compressor and of the turbine are driven by a single spool  114 . 
     With respect to the gear assembly  112 , the embodiment of  FIG. 1  incorporates an epicyclic gear. Although capable of various dimensions and arrangements, in this embodiment, the first set of blades  108  of the compressor is coupled to the ring gear  116  of the epicyclic gear and the spool  114  is coupled to the sun gear  118 . Note also that, in this embodiment, the rotational axes of the planet gears  120  are fixed in position relative to a non-moving portion of the gas turbine. By way of example, in some embodiments, the carrier that mounts the planet gears is mounted to the turbine casing. 
       FIG. 2  is a schematic diagram depicting another embodiment of a gas turbine. As shown in  FIG. 2 , gas turbine  200  incorporates a compressor  202 , a combustion section  204  and a turbine  206 . In this embodiment, the compressor and turbine are coupled to a single spool  208  that engages a gear assembly  210 . Specifically, the gear assembly enables a first set of compressor blades  212  to rotate at a different speed than the speed at which a second set of compressor blades  214  rotate. Notably, compressor blades  214  include one or more set of blades that are located downstream of the first set of blades  212 . 
     In this embodiment, gear assembly  210  incorporates an epicyclic gear that engages the first set of blades via ring gear  216  and engages the spool  208  via sun gear  218 . Note also that the planet gears  220  in this embodiment are held by a carrier  222  that is fixed in position by being mounted to turbine casing  224 . 
     Gas turbine  200  also incorporates two gas flow paths. In particular, the turbine, the combustion section and a portion of the compressor are positioned along a first gas flow path  230 , which is radially located closest to the gas turbine centerline  232 . Radially outboard of the first gas flow path is a second gas flow path  234 . Notably, the first set of blades  212  of the compressor is configured to compress gas travelling along both the first and second gas flow paths. Specifically, each blade of the first set incorporates an inboard portion  236  positioned along the first gas flow path and outboard portion  238  positioned along the second gas flow path. An intermediate shroud  240  or other barrier is located between the two portions  236 ,  238 . Thus, the compressor (e.g., the first set of blades  212 ) mechanically divides the inlet flow of gas into separate inner and outer annular gas flow paths ( 230 ,  234 ). Therefore, only the gas travelling along the inner gas flow path  230  experiences additional stages of the compressor, the combustion section and the turbine. 
       FIG. 3  is a schematic diagram of another embodiment of the gas turbine. As shown in  FIG. 3 , gas turbine  300  includes a compressor  302 , a combustion section  304  and a turbine  306 . Although depicted in proximity to the combustion section, various components such as compressors and/or turbines can be interposed between the compressor  302  and combustion section and/or between combustion section and turbine  306 . This is also the case for other embodiments. 
     Gas turbine  300  also incorporates a multi-stage fan  308  that is driven by a spool  310 . Specifically, a first set of fan blades  312  is driven by the spool via a gear assembly  314  and a second set of blades  316  is driven directly by the spool without any intervening gearing. In this embodiment, the gear assembly comprises an epicyclic gear, of which the ring gear  318  is coupled to the fan blades  312  and the sun gear  320  is coupled to spool  310  for driving the fan blades  316 . In operation, rotation of the spool causes the fan blades  316  to rotate at a corresponding speed, while the gear assembly  314  causes the fan blades  312  to rotate at a different speed, which is typically slower. Note also that, in this embodiment, the axes of rotation of the planet gears  322  are held by a carrier  324  that is fixed in position relative to a non-moving portion of the gas turbine such as a case or other stationary support. 
     Another embodiment of gas turbine is depicted schematically in  FIG. 4 . As shown in  FIG. 4 , gas turbine  400  incorporates a high pressure compressor  402 , a combustion section  404  and a high pressure turbine  406 . The high pressure compressor and high pressure turbine are interconnected with and driven by a high spool  410 . Spool  410  also drives a first set of blades  414  of the high pressure compressor via an interposed gear assembly  412 . 
     Gas turbine  400  also incorporates a lower pressure turbine  420  (e.g., a low pressure turbine) that is interconnected with and drives a low spool  422 . Spool  422  drives at least some of the blades of a multi-stage fan  424 . In particular, the multi-stage fan incorporates a first set of blades  426 , which is driven by spool  422  via an intervening gear assembly  428 , and a second set of blades  430 , which is driven at a speed directly corresponding to the rotational speed of the spool  422 . In this embodiment, the gear assembly incorporates an epicyclic gear, the ring gear  432  of which is coupled to the blades  426  and the sun gear  434  of which is coupled to spool  422 . Note also that, in this embodiment, the axes of rotation of the planet gears  436  are held by a carrier  438  that is fixed in position relative to a non-moving portion of the gas turbine. 
     In operation, intake gas is acted upon by the first set of blades  426  of the multi-stage fan and then by the second set of blades  430 , which rotates at a faster speed than the first set of blades  426 . Thereafter, the gas is diverted to flow either along a first gas flow path  440  or a second gas flow path  442 . Along the first gas flow path, the gas interacts with inboard portions  444  of a first set of compressor blades  414  that rotate at a speed that is slower than a subsequent set of blades of the compressor  402 . This speed differential is facilitated by the gear assembly  412 . 
     Gear assembly  412  incorporates another epicyclic gear, the ring gear  450  of which is coupled to the compressor blades  414  and the sun gear  452  of which is coupled to spool  410 . Note also that, in this embodiment, the axes of rotation of the planet gears  454  are held by a carrier  456  that is fixed in position relative to a non-moving portion of the gas turbine. Additionally, the sun gear  452  includes a central aperture  458  through which spool  422  extends. 
     After passing through the compressor  402 , gas flowing along the first gas flow path travels through the combustion section  404 , the high pressure turbine  406  and the lower pressure turbine  420  in sequence. In contrast, downstream of the multi-stage fan  424 , gas flowing along the second gas flow path is acted upon by outboard portions  446  of the first set of compressor blades  414 . Thereafter, the gas does not pass through additional stages of the compressor, the combustion section, the high pressure turbine or the lower pressure turbine. 
       FIG. 5  schematically depicts another embodiment of the gas turbine. As shown in  FIG. 5 , gas turbine  500  incorporates various components that will be described generally in sequential order starting from the upstream or inlet side. In this regard, gas entering inlet  502  encounters a strut assembly  504 , an inboard portion of which is configured as a strut  506  that mounts an adjustable inlet guide vane  508 . The vane  508  is positioned between an outer shroud  510  and an inner shroud  512 , a portion of which divides the strut assembly into inboard (strut) and outboard (vane) portions. Notably, the inner shroud divides the flow of gas such that an outer annular gas flow path  520  is created that surrounds an inner annular gas flow path  540 . 
     After passing the strut assembly, gas travelling along the gas flow path  520  interacts with tip rotor blades  522  of an outboard, auxiliary fan  524 . In this embodiment, the tip rotor blades are mounted to distal ends of radially extending spokes  526  of a rotor wheel with faired spokes such as a Cortland Burge Wheel (CBW), that is driven by a spool  538 . The spokes of this embodiment are not aerodynamic bodies, in that the spokes are designed not to impact flow characteristics of the gas travelling through the spokes substantially. 
     Downstream of the tip rotor blades  522  of the auxiliary fan, gas travelling along the gas flow path  520  encounters an adjustable exit guide vane  528 . Thereafter, the gas is directed through the annular path between adjacent shrouds  510 ,  512  before exiting as exhaust. 
     Along the gas flow path  540  downstream of the spokes  526  of the CBW, the gas encounters an adjustable inlet guide vane  542  that, in this embodiment, incorporates a fixed leading edge portion  544  and a variable trailing edge portion  546 . Downstream of the vane  542 , a multi-stage fan  550  is positioned. In this embodiment, the multi-stage fan incorporates a first set of blades  552  and a second set of blades  554  between which is interposed a set of adjustable stator vanes  556 . Notably, the second set of fan blades  554  is driven by a spool  558  at a higher rotational speed than the rotational speed of the first set of blades  552 . In this regard, a gear assembly  560  is mechanically coupled between the first set of fan blades and the spool  558  so that the blades of the first set exhibit a slower rotational speed. 
     In the embodiment of  FIG. 5 , the gear assembly  560  incorporates an epicyclic gear, the ring  562  of which is coupled to the first set of fan blades and the sun gear  564  of which is coupled to the spool  558  for driving the second set of fan blades. Note that the planet gears  566  are held by a carrier  568  that is fixed in position by mounting to a non-moving portion of the gas turbine. In this embodiment, the carrier is attached to the fixed leading edge portion  544  of the vane  542 . Note also that the sun gear  564  includes an aperture through which spool  538  passes. 
     Downstream of the multi-stage fan, the gas flow diverges again. This time, the inner annular gas flow path  540  is separated into a gas flow path  570  and a gas flow path  572 . Each of these gas flow paths incorporates an adjustable inlet guide vane ( 574 ,  576 ) at its respective inlet. In this embodiment, the vanes  574 ,  576  are separately controllable to provide highly adjustable flow controllability. 
     A set of blades  578  of a high pressure compressor  580  is located downstream of the vanes  574 ,  576  along each of the gas flow paths  570 ,  572 . Specifically, in this embodiment, the set of blades  578  forms a first stage of the high pressure compressor, with outboard portions  579  being located along the path  572  and inboard portions  581  being located along the path  570 . Others of the sets of blades of the high pressure compressor (in this case, all of the subsequent sets of blades) are located only along the innermost gas flow path  570 . Despite being driven by the same spool  582 , the first set of blades is driven at a slower rotational speed than at least some of the other blades of the high pressure compressor. This is accomplished by mechanically coupling a gear assembly  584  between the first set of blades and the spool  582 . 
     In this embodiment, the gear assembly includes an epicyclic gear, the ring gear  586  of which is coupled to the first set of blades and the sun gear  588  of which is coupled to the spool. Note that, in this embodiment, carrier  590  that holds the planet gears  592  is fixed in position relative to the gas turbine by attachment to the turbine casing  594 . Note also that the sun gear  588  includes an aperture through which spools  558  and  538  pass. 
     Returning briefly to the radially central gas flow path  572 , downstream of the outboard portions of the first set of compressor blades, gas encounters an adjustable guide vane  596 . Thereafter, the gas travels the remainder of the gas flow path  572  as defined by the turbine casing  594  and the inner shroud  512 . In contrast, after departing the high pressure compressor, gas travelling along the gas flow path  570  is directed through a combustion section  598  and thereafter through an adjustable inlet guide vane  602  prior to entering a high pressure turbine  604 . Note that the high pressure turbine is used to drive spool  582 . 
     An adjustable exit guide vane  606  is positioned downstream of the high pressure turbine. The vane  606  also functions as an adjustable inlet guide vane for an intermediate pressure turbine  608 . The intermediate pressure turbine drives spool  558 , which powers the multi-stage fan  550 . 
     An adjustable exit guide vane  610  is located downstream of the intermediate pressure turbine that also functions as an adjustable inlet guide vane for a low pressure turbine  612 . The low pressure turbine drives the spool  558 , which powers the auxiliary fan  524 . An adjustable exit guide vane  614  is located downstream of the low pressure turbine. 
     In the embodiment of  FIG. 5 , a mixer  620  is used to mix gas exiting from the gas flow paths  570 ,  572 . Additionally or alternatively, fan air from the gas flow path  520  can exit through a separate nozzle, which may or may not be variable in exit area (not shown). 
     In operation, an embodiment of a gas turbine such as that depicted in  FIG. 5  can potentially provide enhanced flow controllability and corresponding improvements in performance at various power and operating conditions. By way of example, allowing the low pressure turbine to drive the auxiliary fan can potentially enable improved matching of the flow and power requirements of the auxiliary fan with the flow and power output of the low power turbine. In some embodiments, this matching can be enhanced by the use of adjustable geometry inlet and exit guide vanes associated with the auxiliary fan, as well as adjustable geometry inlet and exit guide vanes of the low pressure turbine. 
     Additionally or alternately, adjustable geometry inlet and exit vanes affecting the outboard portions of the blades of the high pressure compressor can enable an improved matching of the flow and pressure of the gas flow path  570  with the exit flow and pressure of the gas flow path  572 . Such improved matching can potentially reduce turbine screech, for example. 
     Additionally, or alternatively, improved matching of the speed, flow and power of each spool can be achieved by the adjustable geometry inlet and exit vanes of each of the turbines. 
     Additionally or alternatively, use of a gear assembly can enable slower rotor tip speeds of at least some of the upstream blades of the high pressure compressor and higher rotor tip speeds of at least some of the downstream blades of the high pressure compressor. Similarly, use of a gear assembly can enable at least one upstream stage of a multi-stage fan to exhibit a slower rotor tip speed than the rotor tip speed at least one downstream stage. 
       FIG. 6  is a schematic diagram of another embodiment of the gas turbine. As shown in  FIG. 6 , gas turbine  600  includes a compressor  602 , a combustion section  604  and a turbine  606 . Although depicted in proximity to the combustion section, various components such as compressors and/or turbines can be interposed between the compressor  602  and combustion section and/or between combustion section and turbine  606 . This is also the case for other embodiments. 
     Gas turbine  600  also incorporates a multi-stage fan  608  that is driven by a single spool  610 . Specifically, a first set of fan blades  612  is driven by the spool via a gear assembly  614  and a second set of blades  616  is driven directly by the spool without any intervening gearing. In this embodiment, the gear assembly comprises an epicyclic gear, of which the planet carrier  624  is coupled to the fan blades  612  and the sun gear  620  is coupled to spool  610  for driving the fan blades  616 . In operation, rotation of the spool causes the fan blades  616  to rotate at a corresponding speed, while the gear assembly  614  causes the fan blades  612  to rotate at a different, typically slower, speed. Note also that, in this embodiment, the axes of rotation of the planet gears  622  are held by a ring gear  618  that is fixed in position relative to a non-moving portion of the gas turbine. 
     Another embodiment of gas turbine is depicted schematically in  FIG. 7 . As shown in  FIG. 7 , gas turbine  700  incorporates a high pressure compressor  702 , a combustion section  704  and a high pressure turbine  706 . The high pressure compressor and high pressure turbine are interconnected with and driven by a spool  710 . Spool  710  also drives a first set of blades  714  of the high pressure compressor via an interposed gear assembly  712 . 
     Gas turbine  700  also incorporates a lower pressure turbine  720  (e.g., a low pressure turbine) that is interconnected with and drives a spool  722 . Spool  722  drives at least some of the blades of a multi-stage fan  724 . In particular, the multi-stage fan incorporates a first set of blades  726 , which is driven by spool  722  via an intervening gear assembly  728 , and a second set of blades  730 , which is driven at a speed directly corresponding to the rotational speed of the spool  722 . In this embodiment, the gear assembly incorporates an epicyclic gear, the ring gear  732  of which is coupled to the blades  726  and the sun gear  734  of which is coupled to spool  722 . Note also that, in this embodiment, the axes of rotation of the planet gears  736  are held by a carrier  738  that is fixed in position relative to a non-moving portion of the gas turbine. 
     In operation, intake gas is acted upon by the first set of blades  726  of the multi-stage fan and then by the second set of blades  730 , which rotates at a different, e.g., faster, speed than the first set of blades  726 . Thereafter, the gas is diverted to flow either along a first gas flow path  740  or a second gas flow path  742 . Along the first gas flow path, the gas interacts with inboard portions  744  of a first set of compressor blades  714  that rotate at a speed that is typically slower than a subsequent set of blades of the compressor  702 . This speed differential is facilitated by the gear assembly  712  which incorporates another epicyclic gear, the ring gear  750  of which is coupled to the compressor blades  702  and the planet carrier  752  which is coupled to compressor blades  714 . Note also that, in this embodiment, the axes of rotation of the planet carrier  752  and ring gear  750  are held by a sun gear  754  that is fixed in position relative to a non-moving portion of the gas turbine. Additionally, the sun gear  754  includes a central aperture  756  through which spool  722  extends. 
     After passing through the compressor  702 , gas flowing along the first gas flow path travels through the combustion section  704 , the high pressure turbine  706  and the lower pressure turbine  720  in sequence. In contrast, downstream of the multi-stage fan  724 , gas flowing along the second gas flow path is acted upon by outboard portions  746  of the first set of compressor blades  714 . Thereafter, the gas does not pass through additional stages of the compressor, the combustion section, the high pressure turbine or the lower pressure turbine. 
     It should be emphasized that the above-described embodiments are merely possible examples of implementations set forth for a clear understanding of the principles of this disclosure. Many variations and modifications may be made to the above-described embodiments without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the accompanying claims.