Abstract:
An apparatus and method for controlling rotating bladed machinery by using a source of pressurized gas is disclosed. The source of pressurized gas, such as air, imparts braking torque on a turbomachinery component through the use of one or more impinging orifices or jets. The orientation of the jets is such that the transfer of momentum from the pressurized gas results in a force substantially opposite the direction of rotation of the turbomachinery component. This transfer of momentum from the pressurized gas allows for a controlling torque to be applied to the turbomachinery component without the need of mechanical and/or electrical devices applying torque to the rotating shaft.

Description:
BACKGROUND 
       [0001]    The invention relates generally to a rotary machine, and in particular to an apparatus and method for controlling rotational speed of a component of the rotary machine by using pressurized gas. 
         [0002]    Rotary machines include, without limitation, turbines for steam turbines, compressors and turbines for gas turbines and turbines for hybrid fuel cells. A steam turbine has a steam path that typically includes, in serial-flow relationship, a steam inlet, a steam generating device, a turbine and a steam outlet. A gas turbine has a gas path that typically includes, in serial-flow relationship, an air intake (also known as an inlet), a compressor, a combustor, a turbine, and a gas outlet. A hybrid fuel cell has a gas path that typically includes, in serial-flow relationship, an air intake, a compressor, a fuel cell, a turbine and a gas outlet. In the abovementioned turbines, the gases (steam or gas) flow to a turbine that extracts energy for driving a turbine shaft to produce output power for powering an electrical generator. A turbine is typically operated for extended periods of time at a relatively high base load for powering the electrical generator to produce electrical power in a utility grid, for example. In some cases, the rotary machine is subject to a grid transient or load interruption that causes the output breakers of the electrical generator to open thereby resulting in a sudden loss of load that can cause an overspeed condition. The loss of load, in addition to a response time of the rotary machine to the load interruption, may cause an acceleration effect to the rotary components and, at times, result in mechanical damage therein. 
         [0003]    In the case of a free-spinning turbomachinery component, such as an unloaded turbine, rotational speed control requires application of torque to the shaft of the turbomachinery component. Previous methods of rotational speed control include the use of a relatively complex mechanical and/or electrical system to provide a load to the shaft. Although such systems are acceptable for most applications, there is a need to provide a simple, reliable, repeatable, lightweight, and inexpensive apparatus and method to impart a torque to a rotating shaft of turbomachinery component without the use of a relatively complex mechanical and/or electrical system. 
       BRIEF DESCRIPTION 
       [0004]    Briefly, an apparatus for controlling a rotational speed of a rotary machine comprises a source of pressurized gas; and one or more orifices in fluid communication with the source of pressurized gas for allowing the source of pressurized gas to pass therethrough, wherein the pressurized gas impinges on a surface of a rotating blade of the rotary machine to impart an implied torque thereto, thereby controlling the rotational speed of the rotary machine. 
         [0005]    In another aspect of the invention, an apparatus for controlling a rotational speed of an air turbine comprises a source of pressurized air; and one or more jets in fluid communication with the source of pressurized air for allowing the source of pressurized air to pass therethrough, wherein the pressurized air impinges on a surface of a rotating blade of the air turbine to impart an implied torque thereto, thereby controlling the rotational speed of the air turbine. 
         [0006]    In yet another aspect of the invention, a method of controlling a rotational speed of a rotary machine comprises the step of providing a source of pressurized gas through one or more orifices in fluid communication with the source of pressurized gas, whereby the pressurized gas impinges on a surface of a rotating blade of the rotary machine to impart an implied torque thereto, thereby controlling the rotational speed of the rotary machine. 
     
    
     
       DRAWINGS 
         [0007]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0008]      FIG. 1  is a cross-sectional view illustration of a variable cycle turbofan-ramjet engine and a schematically illustrated direct air turbine with orifice(s) for controlling the rotational speed by using pressurized gas according to an embodiment of the invention. 
           [0009]      FIG. 2  is a perspective view of an apparatus for controlling a rotational speed of a rotary machine, such as an air turbine, according to an embodiment of the invention. 
           [0010]      FIG. 3  is a velocity diagram of the blade and gas in the x-y plane of the blade. 
           [0011]      FIG. 4  is a velocity diagram of the blade and gas in the y-z plane of the blade. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  is a schematic illustration of an apparatus, shown generally at  10  for controlling a rotary machine  94 , and a variable cycle turbofan-ramjet engine, shown generally at  12  for providing pressurized gas  95 , such as pressurized air, to the rotary machine  94 .  FIG. 2  shows the apparatus  10  for controlling the rotary machine, such as an air turbine  94 , according to an embodiment of the invention. 
         [0013]    The engine  12  includes a single annular engine inlet duct  16  for receiving ambient air (not illustrated in  FIG. 1 ) from outside the aircraft and conveying inlet duct air  15  from the aircraft inlet  14  and ducting it to an engine inlet  17  of the engine  12 . A fan duct  19  extends downstream from the engine inlet  17  and is defined between an outer casing  20  and an inner conical hub  22  both disposed concentrically about a longitudinal centerline axis  24  of the engine  12 . 
         [0014]    A fan section  25  illustrated as split fan assembly  26  including a forward fan  28  disposed in the fan duct  19  and an aft fan  30  is disposed downstream from the forward fan  28  in flow communication therewith. The forward and aft fans  28  and  30  each include a single row of circumferentially spaced apart forward and aft fan blades  32  and  34 , respectively. Inlet guide vanes  36  are disposed in the fan duct  19  upstream of the forward fan  28  and extend between the casing  20  and the hub  22 , and variable outlet guide vanes  38  are disposed in the fan duct  19  immediately downstream of the forward fan  28  and extending between the hub  22  and the casing  20 . The aft fan  30  includes an outer casing  40  defining a flow splitter  42  at an upstream end thereof, and an inner casing  44  spaced radially inwardly from the outer casing  40 . 
         [0015]    The engine  12  further includes a core engine  50  disposed downstream from the aft fan  30  and in flow communication therewith. The core engine  50  includes in turn a high pressure compressor (HPC)  52 , combustor  54 , and a high pressure turbine (HPT)  56 . Downstream of the HPT  56  is a low pressure turbine (LPT)  58 . The exemplary embodiment of the core engine  50  illustrated herein includes a single row of circumferentially spaced HPT turbine blades  55  in the HPT  56  and a single row of circumferentially spaced LPT turbine blades  57  in the LPT  58 . The HPT  56  is drivingly connected to the aft fan  30  and the compressor  52  by first rotor shaft  84 . The LPT  58  is drivingly connected to the forward fan  28  by a second rotor shaft  86 . 
         [0016]    A bypass duct  60  circumscribes the aft fan  30  and the core engine  50  and includes a forward bypass duct  62  surrounding the aft fan  30 . The bypass duct  60  operates as a ram duct during a ramjet mode of operation of the engine  12 . A forward bypass inlet  64  is in selective flow communication with the forward fan  28 . The bypass duct  60  includes an intermediate bypass duct  66  disposed between the aft fan  30  and the core engine  50  in flow communication with the aft fan  30 . The bypass duct  60  also includes an aft bypass duct  68  surrounding the core engine  50  and in flow communication with both the forward and intermediate bypass ducts  62  and  66 . A mode selector valve  88  is disposed in the forward bypass inlet  64  and is operable in an open position which allows a first portion  89  of the inlet duct air  15  from the forward fan  28  to enter the forward bypass duct  62  and in a closed position which prevents air from the forward fan  28  from entering the forward bypass duct  62 . 
         [0017]    An augmenter  70 , which may be referred to as a ram burner because it operates also in the ramjet mode of operation of the engine  12 , is disposed in an exhaust duct  71  downstream of both the core engine  50  and the bypass duct  60  and receives bypass air  72  from the bypass duct  60  and core engine combustion discharge gases  74  from the core engine  50 . The augmenter  70  includes a plurality of fuel injectors  76  and flameholders  80  disposed downstream from the fuel injectors  76 . The augmenter  70  or ram burner is capable of powering the engine in a ramjet mode. A variable area converging-diverging exhaust nozzle  82  is disposed downstream from the augmenter  70  and in flow communication therewith. 
         [0018]    The variable cycle engine  12  is designed to operate in a non-bypass mode wherein the mode selector valve  88  is positioned in the closed position and all of the inlet duct air  15  is directed through the forward fan  28  and the aft fan  30  and then through both the intermediate bypass duct  66  and the core engine  50 . The variable cycle engine  12  is also designed to operate in a bypass mode wherein the mode selector valve  88  is positioned in the open position and the inlet duct air  15  is directed from the forward fan  28  to both the forward bypass duct  62  and the aft fan  30 , and the air from the aft fan  30  is directed to both the intermediate bypass duct  66  and the core engine  50 . The variable cycle engine  12  is also designed to operate in a ramjet mode wherein the mode selector valve  88  is positioned in the open position, the core engine  50  is idled or shut down so that little or no combustion occurs in the combustor  54  for powering the HPT  56  and the LPT  58 , and the augmenter  70  is activated as a ram burner for burning the bypass air  72  with fuel from the fuel injectors  76  in the ramjet mode of operation. 
         [0019]    The exemplary aircraft accessory system  10  illustrated in  FIG. 1  includes a direct air turbine driven constant frequency generator  90  representative of direct air turbine driven accessories. The constant frequency electrical power generator  90  is powered by an air turbine  94  having a variable geometry turbine nozzle  96  and provides constant-frequency or matched-load electrical power without the need for gearing or a frequency controller. The constant frequency electrical power generator  90  is directly connected by an air turbine shaft  92  to the air turbine  94 . In non-ramjet and ramjet engines, the elimination of the gearing or a frequency controller can result in a great savings in weight, space, and cost of the aircraft and engine. When engines operate as pure ramjets (above Mach 3.5) or in a ramjet mode, the core engine  50  is idled or shut down so that little or no combustion occurs in the combustor  54  to power the HPT  56  and the LPT  58 . In this turbofan jet operating mode, there is not a suitable means available for efficiently operating a gear driven generator. A gearbox or other type of engine main shaft mechanically driven generator for just the turbofan jet mode and a different system for the ramjet mode is unnecessarily costly. 
         [0020]    Compressor discharge pressure (CDP) air  118  bled from the compressor discharge stage bleed  114  or interstage HPC bleed air  120  bled from the interstage bleed  112  of the HPC  52  are used in the non-ramjet modes of engine operation. Bypass bleed air  124  bled from the bypass duct  60  is used during the ramjet mode of engine operation. Alternatively, instead of bypass bleed air  124  from the bypass duct  60 , ram inlet air  128  bled from the engine inlet duct  16  may use the ramjet mode of engine operation. The interstage bleed  112  includes at least one HPC bleed port  130  which is connected by an HPC bleed duct  132  to the three-way air valve  110 . The compressor discharge stage bleed  114  includes at least one CDP bleed port  138  which is connected by a CDP bleed duct  140  to the three-way air valve  110 . At least one bypass duct bleed port  134  to the bypass duct  60  is connected by a bypass bleed duct  135  to the three-way air valve  110 . Alternatively, the inlet duct  16  has at least one inlet duct bleed port  142  connected by an inlet bleed duct  144  to the three-way air valve  110 . 
         [0021]    The three-way air valve  110  provides air turbine airflow  95  to a two-way air valve  111  that provides airflow  98  through a port  97  to the variable geometry turbine nozzle  96  of the air turbine  94 . Thus, the variable geometry turbine nozzle  96  is in flow communication with the bypass duct  60 , an interstage bleed  112  of the HPC  52 , and/or compressor discharge stage bleed  114  of the engine  12 . In other words, the variable geometry turbine nozzle  96  of the air turbine  94  is in selectable direct flow communication with at least two compressed engine air sources  108 , such as a stage of the compressor, or a ram duct, such as the bypass duct  60 . The variable geometry turbine nozzle  96  is used to control flow through the air turbine  94  and, hence, air flow rate needed to satisfy turbine torque required for output power at a specific turbine speed. 
         [0022]    Under certain operating conditions, the two-way valve  111  also provides high pressure airflow  99  to one or more orifices or jets  100  in the outer casing  101  of the air turbine  94 . The orifice(s)  100  are angled such that the airflow  99  will impinge on the face of an approaching rotating blade  102  to apply a torque according to blade geometry, upstream pressure, and mass flow through the orifice(s)  100 . In this manner, the airflow  99  through the orifice(s)  100  provides a means for controlling the rotational speed of the blades  102  of the air turbine  94 . A variable valve  103  between the two-way valve  111  and the orifice(s)  100  allows the airflow  99  to pass through the orifice(s)  100  only when applying torque to the rotating blades  102  of the air turbine  94 . 
         [0023]    The air turbine  94  discharges the air turbine airflow  95  through its turbine exit  150  which is in selectable direct flow communication with at least two relatively lower pressure engine air sinks  152  such as exhaust ports  153  located for example in an aft end  154  of the bypass duct  60  and in a divergent section  156  of the exhaust nozzle  82 . A two-way air valve  160  selectively connects the turbine exit  150  of the air turbine  94  in exhaust flow communication with either the aft end  154  of the bypass duct  60  or the divergent section  156  of the exhaust nozzle  82 . This air turbine exhaust system  158  allows all of the turbine air flow  95  to be returned to the engine exhaust, thus negating the engine net thrust loss which would otherwise occur if the air were dumped overboard. 
         [0024]    As mentioned earlier, the variable valve  103  may allow the pressurized airflow  99  to pass through the orifice(s)  100  on the casing  101  of the air turbine  94  under certain operating conditions. For example, one operating condition may be an overspeed condition after loss of load or during starting of the air turbine  94 . The rotational speed of the turbine shaft  92  can be determined during operation of the air turbine  94  using means well-known in the art. Once an overspeed condition is detected, for example, the air mass flow through variable valve  103  can be controlled by a control system and strategy that detects the need to apply torque to the rotating blades  102 . Alternatively, the control strategy can operate on a choked-jet basis in the case where sufficient upstream air pressure exists. The time between the opening of the valve  103  and the applied torque to the blades  102  should be sufficiently small. Thus, the valve  103  should be placed sufficiently close to the air turbine  104 . 
         [0025]    Aeromechanical loading of the blades  102  will be affected by, among other things, the velocity of airflow  99 , the mass flow, the placement of the orifice(s)  100  with respect to spacing between blades  102 , the orientation of the blades  102 , and frequency of blade passage (solidity and speed). High frequency loading of the blades  102  may be minimized by staggering the angular position of the orifices(s) or jet nozzle(s) such that their individual torque input are out of phase. This staggering of the angular position also minimizes resonance and flutter. In addition, the blades  102  should be shaped such that the impingement of pressurized gas from the orifice(s)  100  is least axial and most tangential, thereby constraining the turning angle of the loaded stage. 
         [0026]      FIG. 3  illustrates a velocity diagram of the mass flow of the jet in the x-y plane of the blade. As shown in  FIG. 3 , the component of the jet velocity in the x-y plane of the blade is the component of the jet velocity in the −y-direction. The component of the blade velocity in the x-y plane of the blade is the component of the blade velocity in the y-direction. Thus, the component of the jet velocity in the x-y plane of the blade is in a direction opposite to the direction of rotation of the blade. 
         [0027]      FIG. 4  illustrates a velocity diagram of the mass flow of the jet in the y-z plane of the blade. The turbine shaft is shown to be along the x-axis and the blade rotates in the direction of the y-axis. As shown in  FIG. 3 , the component of the jet velocity in the y-z-plane is the component in the −y-direction and in the −z-direction. 
         [0028]    In  FIGS. 3 and 4 , it is assumed that two-thirds of the mass flow of the jet is in the x-y plane of  FIG. 3 , while one-third of the mass flow is in the y-z plane of  FIG. 4 . 
         [0029]    From the conservation of momentum: 
         [0000]    
       
         
           
             
               
                 
                   
                     F 
                     blade 
                   
                   = 
                   
                     
                       
                         W 
                         jet 
                       
                       3 
                     
                      
                     
                       
                         ( 
                         
                           
                             V 
                             jet 
                           
                           + 
                           
                             V 
                             blade 
                           
                         
                         ) 
                       
                        
                       
                         [ 
                         
                           1 
                           + 
                           
                             cos 
                              
                             
                                 
                             
                              
                             
                               β 
                               2 
                             
                           
                           + 
                           
                             cos 
                              
                             
                                 
                             
                              
                             
                               β 
                               3 
                             
                           
                         
                         ] 
                       
                     
                      
                     
                       cos 
                       2 
                     
                      
                     θ 
                   
                 
               
               
                 
                   ( 
                   
                     Eq 
                     . 
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
         [0030]    where, 
         [0031]    F blade =the force exerted by the pressurized gas on the blade, 
         [0032]    W jet =the mass flow of the jet of pressurized gas, 
         [0033]    V jet =the velocity of the jet of pressurized gas, 
         [0034]    V blade =the velocity of the blade, 
         [0035]    β 2 =the angle of one side of the blade with respect to the x-axis, and 
         [0036]    β 3 =the angle of the other side of the blade with respect to the x-axis. 
         [0037]    The applied torque on the blade by the pressurized gas can be obtained by multiplying the force exerted by the pressurized gas on the blade by the radius of the blade. 
         [0038]    Tests were conducted to determine the effectiveness of the applied torque on various configurations. Specifically, a total of fifteen tests were conducted at five different rotational speeds (4 k, 6 k, 8 k, 10 k and 12 k rpm) of the blades  102  and three different number of orifices or jets  100  (4, 6 and 8 jets) arranged with the largest possible spacing. 
         [0039]    The results of the tests suggest that the best use of air (most torque per mass flow) occurs when the orifice(s) or jet(s)  100  are spaced widely apart. In particular, the best use of air occurs when the orifice or jet  100  is isolated from another orifice or jet. Tests also indicated that noise may be a concern and proper acoustic isolation may be required. 
         [0040]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.