Abstract:
One embodiment of the present invention is a unique gas turbine engine. Another embodiment of the present invention is a gas turbine engine having a unique secondary air flow circuit. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and secondary air flow circuits. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of U.S. Provisional Patent Application No. 61/428,725, filed Dec. 30, 2010, entitled GAS TURBINE ENGINE WITH SECONDARY AIR FLOW CIRCUIT, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to gas turbine engines, and more particularly, to gas turbine engines having secondary air flow circuits. 
     BACKGROUND 
     Gas turbine engine secondary air flow circuits that effectively transfer secondary air flow across an engine core flowpath remain an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
     SUMMARY 
     One embodiment of the present invention is a unique gas turbine engine. Another embodiment of the present invention is a gas turbine engine having a unique secondary air flow circuit. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines and secondary air flow circuits. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
         FIG. 1  schematically illustrates some aspects of a non-limiting example of a gas turbine engine in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view depicting some aspects of a non-limiting example of a compressor, a diffuser and some surrounding hardware, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
     Referring to the drawings, and in particular  FIG. 1 , some aspects of a non-limiting example of a gas turbine engine  10  in accordance with an embodiment of the present invention is schematically depicted. In one form, gas turbine engine  10  is an axi-centrifugal flow machine, e.g., in the form of an air-vehicle power plant. In other embodiments, gas turbine engine  10  may be a centrifugal flow machine, an axial flow machine, or may be another flow configuration. Embodiments of the present invention include various gas turbine engine configurations, for example, including turbojet engines, turbofan engines, turboprop engines, and turboshaft engines having axial, centrifugal and/or axi-centrifugal compressors and/or turbines. 
     In one form, gas turbine engine  10  includes a compressor  12  having an impeller  14 ; a diffuser  16 ; a combustion system  18 ; a turbine  20  having a turbine rotor  22 ; and a shaft  24  coupling impeller  14  with turbine rotor  22 . Combustion system  18  is in fluid communication with compressor  12  and turbine  20 . Turbine rotor  22  is drivingly coupled to impeller  14  via shaft  24 . Impeller  14 , turbine rotor  22  and shaft  24  form a main engine rotor  26 , which rotates about an engine centerline  28 . Although only a single spool is depicted, it will be understood that embodiments of the present invention include both single-spool and multi-spool engines. The number of blades and vanes, and the number of stages thereof of compressor  12  and turbine  20  may vary with the needs of the application, e.g., the weight, efficiency and power output requirements of a particular application of gas turbine engine  10 . In various embodiments, gas turbine engine  10  may include one or more fans, additional compressors and/or additional turbines. 
     During the operation of gas turbine engine  10 , air is received at the inlet of compressor  12  and compressed. After having been compressed, the air is supplied to diffuser  16 , which reduces the velocity of the pressurized air discharged from compressor  12 . In one form, diffuser  16  is a radial diffuser. In other embodiments, other diffuser arrangements may be employed. The pressurized air exiting diffuser  16  is mixed with fuel and combusted in combustion system  18 . The hot gases exiting combustion system  18  are directed into turbine  20 . Turbine  20  extracts energy from the hot gases to, among other things, generate mechanical shaft power to drive compressor  12  via shaft  24 . In one form, the hot gases exiting turbine  20  are directed into a nozzle (not shown), which provides thrust output for gas turbine engine  10 . In other embodiments, additional compressor and/or turbine stages in one or more additional rotors upstream and/or downstream of compressor  12  and/or turbine  20  may be employed, e.g., in single or multi-spool gas turbine engines. 
     Referring to  FIG. 2 , a cross-sectional view of some aspects of a non-limiting example of compressor  12 , diffuser  16  and some surrounding hardware in accordance with an embodiment of the present invention is depicted. In one form, compressor  12  is a centrifugal compressor. In other embodiments, other compressor types may be employed. Compressor  12  includes a shroud  30  in which impeller  14  is disposed. Diffuser  16  is a flowpath structure configured to form a flowpath  32  downstream of impeller  14  for passing and diffusing the pressurized air flow generated by impeller  14 . In other embodiments, other flowpath structures may be disposed downstream of impeller  14  in addition to or in place of diffuser  16 . 
     The flow pressurized by impeller  14  exits impeller  14  radially outward into flowpath  32  formed by diffuser  16 . The initial flowpath  32  width is defined primarily by the height of impeller blades  33  of impeller  14  within shroud  30 . Compression of the air by operation of blades  33  within shroud  30  results in elevated temperatures in impeller  14 , as well as thermal gradients across impeller  14 . The elevated temperatures and thermal gradients adversely affect the life of impeller  14 . In order to reduce peak temperatures in impeller  14 , and in order to reduce thermal gradients in impeller  14 , secondary air flow AF is provided to a back face  36  of impeller  14  opposite blades  33 . Secondary air flow AF cools a hotter portion of impeller  14 , e.g., a tip portion  38  of impeller  14 , and also transfers heat from tip portion  38  to radially inward portion  40 . Hence, secondary air flow AF reduces peak temperatures in impeller  14 , as well as reduces thermal gradients by increasing temperatures in radially inward portion  40 . The reduction of peak temperatures reduces impeller  14  material requirements by allowing a lower temperature-capable material to be employed in constructing impeller  14  than similar impellers operating under similar circumstances and conditions that to not receive secondary airflow such as secondary airflow AF. The reduced thermal gradients reduce thermally induced stresses, thus further reducing material requirements for impeller  14 . One or both of the reduction in peak temperature and the temperature gradient may allow the use of a lower cost material in the construction of impeller  14 . 
     In one form, secondary air flow is supplied to impeller  14  from a cavity  42  formed by a structure  44 , a structure  46  and a structure  48 . Cavity  42  is positioned on the opposite side of flowpath  32  from back face  36 . In other embodiments, the secondary air flow may be supplied from another location. In one form, structures  44 ,  46  and  48  are static load bearing structures. In other embodiments, one or more of structures  44 ,  46  and  48  may not be load bearing structures. In still other embodiments, one or more of structures  44 ,  46  and  48  may not be static structures. Secondary air flow AF is supplied to cavity  42  defined by structures  44 ,  46  and  48  by means not shown. In one form, structure  48  is an engine case structure. In other embodiments, structure  48  may be another engine structure. Structures  44  and  46  are coupled to structure  48 , and are configured to support diffuser  16  loads. In one form, structures  44  and  46  are coupled to diffuser  16  via a threaded fastener system  50 . In other embodiments, structures  44  and  46  may be coupled to diffuser  16  via other means, e.g., including pins, cross-key arrangements or other threaded and/or non-threaded fastener types. 
     Diffuser  16  includes a plurality of vanes  34  that extend across flowpath  32 , and are configured to guide the flow exiting impeller  14 . In one form, each vane  34  includes a transfer opening  52  therein that extends through diffuser  16  and across flowpath  32 . In other embodiments, fewer than all of vanes  34  may include transfer openings  52 . Structure  44  includes a plurality of supply openings  54  in fluid communication with transfer openings  52  and with cavity  42 . Supply openings  54  are configured to transmit secondary air flow from cavity  42  into transfer openings  52 . In one form, transfer openings  52  are sized to control the flow rate of secondary air flow AF. In other embodiments, the flow rate of secondary air flow AF may be controlled by the size of openings  54 . In still other embodiments, the flow rate of secondary air flow AF may be controlled by other effective areas or control means. 
     In one form, disposed between transfer openings  52  and supply openings  54  is a distribution channel  56 . Distribution channel  56  fluidly couples transfer openings  52  and supply openings  54 . Distribution channel  56  is operative to enhance the transition flow area between supply openings  54  and transfer openings  52 , which assists the entry of the secondary air flow into transfer openings  52  from supply openings  54 , and also reduces the need for precision indexing of structure  44  with respect to diffuser  16  to enhance alignment of openings  52  and  54 . In one form, distribution channel  56  is an annular channel extending circumferentially around structure  44 . In other embodiments, distribution channel  56  may take the form of discreet cavities. In one form, distribution channel  56  is formed in structure  44 . In other embodiments, distribution channel  56  may be formed in diffuser  16  in addition to or in place of structure  44 . 
     Disposed opposite diffuser  16  and back face  36  of impeller  14  is a static structure in the form of a cover plate  58 . In one form, cover plate  58  includes a plurality of openings  60  that are configured to direct the secondary air flow from transfer openings  52  to tip portion  38  of impeller  14 . In one form, openings  60  are configured to induce preswirl in secondary airflow AF in the direction of rotation of impeller  14 , e.g., in order to reduce losses. In other embodiments, openings  60  may not be configured to induce preswirl. In one form, openings  60  are slots formed in cover plate  58 . In other embodiments, a single opening  60 , e.g., in the form of an annular cavity, may be employed. In still other embodiments, cover plate  58  or another component may simply be spaced apart from diffuser  16  by some desired amount. Cover plate  58  is spaced apart from back face  36  of impeller  14 , and is operative to direct the secondary air flow from tip portion  38  of impeller  14 , radially inward along the back face of impeller  14 . 
     Openings  54 ,  52  and  60 , as well as a cavity  66  defined between impeller  14  and cover plate  58 , form a cooling circuit  62 . Cooling circuit  62  is operative to deliver secondary air flow  64  to impeller  14  for controlling the temperature of a portion of impeller  14 , e.g., back face  36  in the present embodiment, wherein secondary air flow AF is delivered to back face  36  of impeller  14  from across flowpath  32  through transfer openings  52 . Secondary air flow AF is supplied from cavity  42  at a pressure sufficient to overcome pressure gradients, and centrifugal loading imposed by back face  36 , resulting in a net positive flow radially inward from tip portion  38 . A flow discourager  64  is positioned at the end of cooling circuit  62  to reduce the secondary air flow rate exiting back face  36  of impeller  14 , and to prevent ingress of other gases into the cavity  66  defined between cover plate  58  and impeller  14  back face  36 . In one form flow discourager  64  is a labyrinth seal. In other embodiments, flow discourager  64  may take other forms, and may be, for example and without limitation, a carbon seal system or other type of sealing or flow discouraging system. In one form, secondary air flow AF exiting flow discourager  64  is supplied to turbine  20  as cooling air. In other embodiments, secondary air flow AF may be, for example, supplied to other components, or may be supplied to the engine core flowpath, or may be dumped overboard. 
     Embodiments of the present invention include a gas turbine engine, comprising: a compressor having an impeller; a diffuser having a plurality of diffuser vanes; wherein the diffuser forms a flowpath downstream of the impeller; wherein the diffuser vanes extend across the flowpath; and wherein at least one of the diffuser vanes has a first opening extending through the diffuser vanes and across the flowpath; a combustor in fluid communication with the compressor; a turbine in fluid communication with the combustor; and a secondary flow circuit operative to deliver secondary air flow to the impeller for controlling a temperature of a portion of the impeller, wherein the secondary air flow is delivered to the impeller from across the flowpath through the first opening. 
     In a refinement, the impeller is a centrifugal impeller, and wherein the diffuser is a radial diffuser. 
     In another refinement, the impeller includes a plurality of blades and a back face opposite the plurality of blades, further comprising a static structure spaced apart from the back face and configured to direct the secondary air flow from the first opening to the back face of the impeller. 
     In yet another refinement, the static structure is configured to direct the secondary air flow from a tip portion of the impeller radially inward along the back face of the impeller. 
     In still another refinement, the static structure includes a second opening configured to direct the secondary air flow from the first opening to the tip portion of the impeller. 
     In yet still another refinement, the gas turbine engine further comprises a first static structure coupled to the diffuser and having an opening therein configured to supply the secondary air flow to at least one diffuser vane from a cavity adjacent to the first static structure. 
     In a further refinement, the first static structure is a load bearing structure of the gas turbine engine. 
     In a yet further refinement, the gas turbine engine further comprises a second static structure operative to form the cavity in conjunction with the first static structure, wherein the first static structure and the second static structure are configured to support diffuser loads. 
     In a still further refinement, the gas turbine engine further comprises an engine case, wherein the first static structure and the second static structure are coupled to the engine case; and wherein the engine case, the first static structure and the second static structure form the cavity. 
     Embodiments of the present invention include a gas turbine engine, comprising: a compressor having an impeller and an impeller configured to generate a pressurized air flow; a flowpath structure configured to form a flowpath downstream of the compressor and receive the pressurized air flow, wherein the flowpath structure includes a stationary structure extending across the flowpath and having a transfer opening extending therethrough and across the flowpath; a source of secondary air flow disposed on one side of the flowpath; and a secondary flow circuit operative to deliver a secondary air flow to the impeller for controlling a temperature of a portion of the impeller, wherein the secondary air flow is delivered to the impeller across the flowpath through the transfer opening. 
     In a refinement, the impeller includes a plurality of blades and a back face opposite the plurality of blades, further comprising a static structure configured to direct the secondary air flow from the transfer opening to the back face of the impeller. 
     In another refinement, the gas turbine engine further comprises a flow discourager between the static structure and the impeller, wherein the flow discourager is configured to reduce a flow rate of the secondary air flow exiting the back face of the impeller. 
     In another refinement, the flow discourager is a labyrinth seal. 
     In yet another refinement, the static structure is configured to direct the secondary air flow from a tip portion of the impeller radially inward along the back face of the impeller. 
     In still another refinement, the gas turbine engine further comprises a static structure coupled to the stationary structure and having a supply opening therein configured to supply the secondary air flow to the transfer opening. 
     In yet still another refinement, the gas turbine engine further comprises a distribution channel fluidly coupling the supply opening with the transfer opening. 
     In a further refinement, the gas turbine engine further comprises a turbine, wherein the secondary air flow is delivered to the turbine after acting on the impeller. 
     Embodiments of the present invention include a gas turbine engine, comprising: a compressor having an impeller and an impeller configured to generate a pressurized air flow; a flowpath structure configured to form a flowpath downstream of the compressor and receive the pressurized air flow; a source of secondary air flow disposed on one side of the flowpath; and means for conducting the secondary air flow across the flowpath to an opposite side of the flowpath for controlling a temperature of a portion of the impeller. 
     In a refinement, the impeller includes a back face, further comprising means for directing the secondary air flow radially inward along the back face of the impeller. 
     In another refinement, the gas turbine engine further comprises means for controlling a flow rate of the secondary air flow. 
     In yet another refinement, the means for conducting includes a diffuser having a plurality of diffuser vanes; wherein the diffuser forms a flowpath downstream of the impeller; wherein the diffuser vanes extend across the flowpath; wherein at least some of the diffuser vanes each have an opening extending through the diffuser vanes and across the flowpath, and wherein the openings are configured to transfer the secondary air flow across the flowpath. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.