Abstract:
Embodiments of the present invention include unique gas turbine engines. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines. 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 
       [0001]    The present application claims benefit of U.S. Provisional Patent Application No. 61/581,868 filed Dec. 30, 2011, entitled GAS TURBINE ENGINE WITH VARIABLE SPEED TURBINES, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to gas turbine engines, and more particularly, to gas turbine engines with variable speed turbines. 
       BACKGROUND 
       [0003]    Gas turbine engines that effectively vary the speed of one or more turbines 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 
       [0004]    Embodiments of the present invention include unique gas turbine engines. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for gas turbine engines. 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 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      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. 
           [0007]      FIG. 2  is non-limiting example of a plot depicting turbine efficiency against turbine loading and flow coefficient. 
           [0008]      FIG. 3  schematically illustrates some aspects of a non-limiting example of a portion of a turbine section and shafting system in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    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. 
         [0010]    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 are schematically depicted. In one form, gas turbine engine  10  is an aircraft propulsion power plant. In other embodiments, gas turbine engine  10  may be a land-based or marine engine. In one form, gas turbine engine  10  is a multi-spool turbofan engine. In other embodiments, gas turbine engine  10  may take other forms, and may be, for example, a turboshaft engine, a turbojet engine, a turboprop engine, or a combined cycle engine having a single spool or multiple spools. 
         [0011]    As a turbofan engine, gas turbine engine  10  includes a fan system  12 , a bypass duct  14 , a compressor section  16 , a diffuser  18 , a combustor  20 , a turbine section  22 , a discharge duct  26  and an exhaust nozzle system  28 . Bypass duct  14  and compressor section  16  are in fluid communication with fan system  12 . Diffuser  18  is in fluid communication with compressor section  16 . In some embodiments, compressor section  16  may include a high pressure compressor and a low pressure compressor, each of which may have one or more stages (not shown). In other embodiments, compressor section  16  may include a high pressure compressor, an intermediate pressure compressor and a low pressure compressor, each of which may have one or more stages (not shown). In still other embodiments, compressor section  16  may be a single compressor, which may have one or more stages. Combustor  20  is fluidly disposed between compressor section  16  and turbine section  22 . 
         [0012]    In one form, combustor  20  includes a combustion liner (not shown) that contains a continuous combustion process. In other embodiments, combustor  20  may take other forms, and may be, for example and without limitation, a pressure gain combustion system, or a slinger combustion system, and may employ deflagration and/or detonation combustion processes. In some embodiments, turbine section  22  may include a high pressure turbine and a low pressure turbine, each of which may have one or more stages (not shown). In other embodiments, turbine section  22  may include a high pressure turbine, an intermediate pressure turbine and a low pressure turbine, each of which may have one or more stages (not shown). In still other embodiments, turbine section  22  may be a single turbine, which may have one or more stages. 
         [0013]    Fan system  12  includes a fan rotor system  30 . In various embodiments, fan rotor system  30  includes one or more rotors (not shown) that are powered by turbine section  22 . Bypass duct  14  is operative to transmit a bypass flow generated by fan system  12  to nozzle  28 . Compressor section  16  includes a compressor rotor system  32 . In various embodiments, compressor rotor system  32  includes one or more rotors (not shown) that are powered or driven by turbine section  22 . Each compressor rotor includes a plurality of rows of compressor blades (not shown) that are alternatingly interspersed with rows of compressor vanes (not shown). Turbine section  22  includes a turbine rotor system  34 . In various embodiments, turbine rotor system  34  includes one or more rotors (not shown) operative to separately (or jointly in some embodiments) drive one or more rotors of fan rotor system  30  and one or more rotors of compressor rotor system  32 . Each turbine rotor includes one or more rows of turbine blades (not shown), which are alternatingly interspersed with rows of turbine vanes (not shown). 
         [0014]    Turbine rotor system  34  is drivingly coupled to compressor rotor system  32  and fan rotor system  30  via a shafting system  36 . In various embodiments, shafting system  36  includes a plurality of shafts that may rotate at the same and/or different speeds, and which may rotate in the same and/or different directions. In some embodiments, only a single shaft may be employed. Turbine section  22  is operative to discharge an engine  10  core flow to nozzle  28 . In one form, fan rotor system  30 , compressor rotor system  32 , turbine rotor system  34  and shafting system  36  rotate about an engine centerline  48 . In other embodiments, all or parts of fan rotor system  30 , compressor rotor system  32 , turbine rotor system  34  and shafting system  36  may rotate about one or more other axes of rotation in addition to or in place of engine centerline  48 . 
         [0015]    Discharge duct  26  extends between a discharge portion  40  of turbine section  22  and engine nozzle  28 . Discharge duct  26  is operative to direct bypass flow and core flow from a bypass duct discharge portion  38  and turbine discharge portion  40 , respectively, into nozzle system  28 . In some embodiments, discharge duct  26  may be considered a part of nozzle  28 . Nozzle  28  is in fluid communication with fan system  12  and turbine section  22 . Nozzle  28  is operative to receive the bypass flow from fan system  12  via bypass duct  14 , and to receive the core flow from turbine section  22 , and to discharge both as an engine exhaust flow, e.g., a thrust-producing flow. In other embodiments, other nozzle arrangements may be employed, including separate nozzles for each of the core flow and the bypass flow. 
         [0016]    During the operation of gas turbine engine  10 , air is drawn into the inlet of fan  12  and pressurized by fan  12 . In one form, some of the air pressurized by fan  12  is directed into compressor section  16  as core flow, and some of the pressurized air is directed into bypass duct  14  as bypass flow, and is discharged into nozzle  28  via discharge duct  26 . In other embodiments, other flow arrangements may be utilized. Compressor section  16  further pressurizes the portion of the air received therein from fan  12 , which is then discharged into diffuser  18 . Diffuser  18  reduces the velocity of the pressurized air, and directs the diffused core airflow into combustor  20 . Fuel is mixed with the pressurized air in combustor  20 , which is then combusted. The hot gases exiting combustor  20  are directed into turbine section  22 , which extracts energy in the form of mechanical shaft power sufficient to drive fan system  12  and compressor section  16  via shafting system  36 . The core flow exiting turbine section  22  is directed along an engine tail cone  42  and into discharge duct  26 , along with the bypass flow from bypass duct  14 . Discharge duct  26  is configured to receive the bypass flow and the core flow, and to discharge both as an engine exhaust flow, e.g., for providing thrust, such as for aircraft propulsion. 
         [0017]    In certain applications, it is desirable to operate a turbine, for example and without limitation, a low pressure turbine or power turbine, at more than one speed, e.g., depending upon the engine  10  operating condition, with the power output or turbine enthalpy extraction remaining at either maximum power rating or at apart power rating. Although this may be accomplished by using gearing, e.g., reduction gearing, gearing can be heavy. The inventors have determined that a valve between two turbine stages may be employed to accomplish the same or a similar goal (for example and without limitation, an embodiment of which is schematically illustrated in  FIG. 3  and subsequently described). For higher speed operation, the valve is opened to a desired degree, permitting the gases exiting the higher pressure stage(s) to exit the engine and bypass the lower pressure stage(s), hence reducing the amount of energy delivered to the lower pressure stage(s) or not energizing the lower pressure stage(s). This increases the expansion ratio across the higher pressure stage(s), resulting in an increased rotational speed of the higher pressure stage(s). With increased speed, the higher pressure stage(s) may operate more optimally, as illustrated in  FIG. 2 .  FIG. 2  illustrates a plot  44  of turbine efficiency against turbine loading, ΔH/U 2 , and flow coefficient, VA/U, where H is enthalpy, U is a blade loading coefficient, V is gas velocity, and A is turbine flow area. Since delta enthalpy is the same, the turbine loading, ΔH/U 2 , becomes lower, with the efficiency of the high pressure stage(s) becoming more favorable to maintain the higher speed, as indicated by arrow  46 , which shows increasing efficiency at constant flow coefficient with decreasing turbine loading. Arrow  46  also reflects the direction of power turbine front section operating point migration with increased speed resulting from increased expansion ratio due to bypassing the 2 nd  power turbine section. The expansion ratio across the lower pressure stage(s) becomes closes to unity, consequently producing reduced torque or no torque. In some embodiments, a clutch is included, disposed between the higher pressure stage(s) and the lower pressure stage(s), and is operative to allow the lower pressure stage(s) to slow down. 
         [0018]    With the valve closed, the exhaust from the higher pressure stage(s) is directed into the lower pressure stage(s), the higher pressure stage(s) operate at a lower speed, and the lower pressure stage(s) produce torque as in a conventional turbine. When the valve closed, the clutch is operative to combine the torque output of the lower pressure stage(s) with the torque of the higher pressure stage(s). In some embodiments, variable geometry turbine vanes (nozzles) may be incorporated to further optimize performance in both operating modes (high and low speed). 
         [0019]    Referring to  FIG. 3 , some aspects of a non-limiting example of a portion  50  of turbine section  22  in accordance with an embodiment of the present invention are schematically illustrated. In one form, portion  50  is a low pressure turbine or power turbine, and will be referred to as turbine  50 . Turbine section  22  also includes a high pressure turbine (not shown) upstream of turbine  50 . In other embodiments, portion  50  may be an intermediate pressure turbine or a high pressure turbine. In one form, turbine  50  is a three stage turbine, and includes three rotating blade stages  52 ,  54  and  56 , which are first, second and third stage blades, respectively; three vane stages  62 ,  64  and  66 , which are first, second and third stage vanes, respectively; an exhaust guide vane stage  68 ; a valve  70 ; a second stage exhaust  72  and a third stage exhaust  74 . In various other embodiments, turbine  50  may include only two turbine blade stages, or may include any number of turbine blade stages beyond three. Valve  70  is in fluid communication with second stage exhaust  72 . In one form, valve  70  is fluidly disposed between blade stages  54  and  56 . In other embodiments, valve  70  may be fluidly disposed between any two turbine stages. In still other embodiments, a plurality of valves  70  may be employed between any two stages in multiple sets of two turbine stages, e.g., between a first stage and a second stage, and between a second stage and a third stage. Second stage exhaust  72  and third stage exhaust  74  are in fluid communication with engine exhaust nozzle  28 . 
         [0020]    In one form, turbine  50  is coupled to fan rotor  30  via a shafting subsystem  76  of shafting system  36 . In other embodiments, turbine  50  may be coupled to a compressor rotor or another power absorber, including and without limitation, a gearbox, a generator or other electrical power producing machine, a pump and/or any other type of machine in addition to or in place of fan rotor  30 . 
         [0021]    Shafting subsystem  76  includes a shaft  80 , a shaft  82  and a clutch  84 . Turbine  50  is drivingly coupled to fan rotor  30  via shafting subsystem  76 . In some embodiments, turbine  50  may be drivingly coupled to a compressor rotor via shafting subsystem  76 , e.g., a low pressure compressor, in addition to or in place of fan rotor  30 . In other embodiments, turbine  50  may be drivingly coupled to one or more other load absorbers, e.g., via shafting subsystem  76  or another shafting system, in addition to or in place of fan rotor  30 . Shaft  80  is coupled to the load absorber (e.g., fan  30 ), and is operable to transmit power from rotating turbine blade stages  52  and  54  to the load absorber. Shaft  82  is coupled to shaft  80  via clutch  84 , and is operable to transmit power from rotating turbine blade stage  56  to shaft  80 , and hence, to the power absorber (e.g., fan rotor  30 ) via clutch  84  and shaft  80 . In one form, clutch  84  is disposed between blade stages  54  and  56 . In other embodiments, clutch  84  may be disposed between any two turbine stages. In still other embodiments, a plurality of clutches  84  may be employed between any two stages in multiple sets of two turbine stages, e.g., between a first stage and a second stage, and between a second stage and a third stage. 
         [0022]    Clutch  84  is configured to allow rotating turbine blade stages  52  and  54  to rotate at a faster speed than rotating turbine blade stage  56 . Clutch  84  is also configured to prevent rotating turbine blade stage  56  from rotating faster than rotating turbine blade stages  52  and  54 . In one form, clutch  84  is an overrunning clutch, for example and without limitation, a sprag clutch. In other embodiments, one or more of other types of clutches may be employed in addition to or in place of an overrunning clutch. 
         [0023]    Valve  70  is configured to selectively vent the output of the second stage turbine blades  54  to second stage exhaust  72  and into nozzle  28  or to supply the output of second stage turbine blades into the third turbine stage (e.g., vanes  66  and blades  56 ). In one form, valve  70  is a variable position valve. As a variable position valve, valve  70  may be configured to move or operate, in incremental and/or continuous fashion, between a fully or partially closed position and a fully or partially opened position. In other embodiments, valve  70  may be an on/off valve, i.e., configured to be selectively positioned at either a fully or partially closed position or at a fully or partially opened position. In one form, valve  70  is a rotating sleeve valve. In other embodiments, valve  70  may take other forms, for example and without limitation, louvers that are pivotable to open or close a flow area therebetween. In one form, valve  70  is formed of a rotatable sleeve  86  and a turbine case structure  88 . Sleeve  86  includes a plurality of openings  90 . Case structure  88  includes a plurality of openings  92 . For clarity of illustration, only two each of openings  90  and  92  are shown. However, it will be understood that any number of openings  90  and  92  may be employed, e.g., commensurate with flow requirements. Sleeve  86  is configured to be rotated by an actuation mechanism (not shown) to selectively align and misalign openings  90  and  92  in order to selectively vent the output of turbine blade stage  54  into nozzle  28  via second stage exhaust  72  or supply the output of turbine blade stage  54  into third stage turbine vanes and blades  66  and  56 , respectively. It will be understood that the distance “D” between blades  54  and vanes  66  may vary with the needs of the application, and may be, for example, any suitable length that promotes flow exiting blades  54  to turn into valve  70 . 
         [0024]    By venting the output of turbine blade stage  54  into second stage exhaust  72 , thereby bypassing third stage turbine vanes and blades  66  and  56 , respectively, the rotational speed of the first and second stages  52  and  54  increases, which increases the efficiency of the first and second stage turbines, as set forth above with respect to  FIG. 2 . Clutch  84  allows the third stage blades  56  to slow down. The expansion ratio across blades  56  decreases, and the torque output though shaft  82  decreases. When valve  70  is in the closed position, thereby directing the output of turbine blade stage  54  into third stage turbine vanes and blades  66  and  56 , respectively, the rotational speed of the first and second stages  52  and  54  decreases, and the rotational speed of blades  56  increases until the speed of shaft  82  reaches the speed of shaft  80 , at which point clutch  84  engages. The expansion ratio across blades  56  increases with the gas flow therethrough, hence increasing the torque transmitted through shaft  82  and into shaft  80  via clutch  84 . 
         [0025]    Embodiments of the present invention include a gas turbine engine, comprising: a fan; a compressor in fluid communication with the fan; a combustor in fluid communication with the compressor; a first turbine in fluid communication with the combustor and operative to drive the compressor; a second turbine in fluid communication with the first turbine and operative to drive the fan, wherein the second turbine includes at least a first stage and a second stage downstream of the first stage; and a clutch configured to allow the first stage to rotate at a faster speed than the second stage. 
         [0026]    In a refinement, the gas turbine engine further comprises a valve fluidly disposed between the first stage and the second stage, wherein the valve is configured to vent the output of the first stage. 
         [0027]    In another refinement, the valve is configured as a sleeve valve. 
         [0028]    In yet another refinement, the valve is configured as a rotating sleeve valve. 
         [0029]    In still another refinement, the output of the first stage is vented to an engine exhaust when the valve is in an opened position. 
         [0030]    In yet still another refinement, the gas turbine engine is configured to rotate the first stage at a faster speed than the second stage when the valve is in an opened position. 
         [0031]    In a further refinement, the gas turbine engine is configured to rotate the first stage at the same speed as the second stage when the valve is closed. 
         [0032]    In a yet further refinement, the clutch is configured to prevent the second stage from rotating faster than the first stage. 
         [0033]    In a still further refinement, the clutch is an over-running clutch. 
         [0034]    Embodiments of the present invention include a gas turbine engine, comprising: a compressor; a combustor in fluid communication with the compressor; a first turbine in fluid communication with the combustor and operative to drive the compressor; a second turbine in fluid communication with the first turbine and operative to drive a load absorber, wherein the second turbine includes at least a first stage and a second stage downstream of the first stage; and a valve fluidly disposed between the first stage and the second stage, wherein the valve is configured to vent the output of the first stage. 
         [0035]    In a refinement, the valve is configured as a sleeve valve. 
         [0036]    In another refinement, the valve is configured as a rotating sleeve valve. 
         [0037]    In yet another refinement, the output of the first stage is vented to an engine exhaust when the valve is opened. 
         [0038]    In still another refinement, the gas turbine engine is configured to rotate the first stage at a faster speed than the second stage when the valve is in an opened position. 
         [0039]    In yet still another refinement, the gas turbine engine is configured to rotate the first stage at the same speed as the second stage when the valve is closed. 
         [0040]    In a further refinement, the gas turbine engine further comprises a clutch configured to allow the first stage to rotate at a faster speed than the second stage. 
         [0041]    In a yet further refinement, the clutch is configured to prevent the second stage from rotating faster than the first stage. 
         [0042]    In a still further refinement, the clutch is an over-running clutch. 
         [0043]    Embodiments of the present invention include a gas turbine engine, comprising: a compressor; a combustor in fluid communication with the compressor; a first turbine in fluid communication with the combustor and operative to drive the compressor; a second turbine in fluid communication with the first turbine and operative to drive a load absorber, wherein the second turbine includes at least a first stage and a second stage downstream of the first stage; and means for selectively increasing the speed of the first stage and decreasing the speed of the second stage or selectively operating both the first stage and the second stage at the same speed during operation of the gas turbine engine. 
         [0044]    In a refinement, the means includes a valve fluidly disposed between the first stage and the second stage and operative to selectively vent the output of the first stage, and a clutch configured to allow the first stage to rotate at a faster speed than the second stage. 
         [0045]    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.