Patent Publication Number: US-2018045074-A1

Title: Turbine engine ejector throat control

Description:
FIELD OF THE INVENTION 
     In gas turbine engines, a portion of the total airflow from the compressor inlet is diverted to cool various turbine components. The diverted air, however, may consume a large portion of the total airflow through the compressor. The management and control of these parasitic flows therefore can increase the overall performance of the turbine engine. 
     BACKGROUND OF THE INVENTION 
     Typically, air is extracted under pressure from the compressor for use as a cooling, sump pressurization, and load control flow for the various turbine components and thus bypasses the combustion system. Ejectors are often useful for this purpose and can extract air from two different stages of the compressor. The extraction ports, however, often provide cooling airflow at too high a pressure and/or temperature. By employing an ejector, the low pressure or temperature airflow can be mixed with the high pressure or temperature airflow to provide an airflow at an intermediate pressure and temperature substantially matching the pressure and temperature required, while simultaneously making use of the low pressure and temperature airflow that otherwise might be dissipated as wasted energy. 
     More specifically, an ejector system can provide pressurized air to a balance piston assembly within the turbine rear frame. The balance piston assembly utilizes the pressurized air to reduce an axial load on a bearing at the compressor. Thus, providing appropriate pressure to the balance piston assembly is desirable to maintain a proper load on the bearing. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, embodiments of the invention relate a gas turbine engine including a drive shaft, a compressor section mounted to the drive shaft, a turbine section mounted to the drive shaft aft of the compressor section, a bearing abutting the compressor section, and a pressure-operated balance piston abutting the turbine section and applying an axial force to the turbine section to urge the turbine section and compressor section against the bearing. The engine further includes an air pressure supply having a primary bleed air supply fluidly coupled to a first portion of the compressor having a first pressure, a second bleed air supply fluidly coupled to a second portion of the compressor having a second pressure lower than the first pressure, a mixed air supply fluidly coupled to the pressure-operated balance piston having a third pressure, and a mixing valve proportionally coupling the primary and secondary bleed air supplies to the mixed air supply in response to first, second, and third pressures to maintain a predetermined third pressure. 
     In another aspect, embodiments of the invention relate to an ejector for a gas turbine engine including a secondary conduit having an outlet and a mixing chamber upstream of the outlet and a primary conduit having a variable area throat located within the secondary conduit and upstream of the mixing chamber. 
     In yet another aspect, embodiments of the invention relate to a gas turbine engine including a compressor section and turbine section axially arranged on a common drive shaft between a bearing and a pressure balance piston applying an axial force urging the compressor section and turbine section toward the bearing. An ejector with a variable area throat fluidly couples primary and secondary bleed air sources to different pressure to a mixing chamber downstream of the throat and supplies mixed air from the primary and secondary bleed air sources to the balance piston. 
     In yet another aspect, embodiments of the invention relate to a method of providing pressurized air to a pressure balance piston of a gas turbine engine comprising sensing a first pressure at a first compressor bleed air supply, sensing a second pressure at a second compressor bleed air supply having a lesser pressure than the first pressure, sensing a third pressure at the pressure balance piston, and mixing the air from the first and second bleed air supplies in the proportion to the first, second, and third pressures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic, sectional view of a gas turbine engine. 
         FIG. 2  is a cross-sectional view of a turbine rear frame with a balance piston cavity. 
         FIG. 3  is a schematic view of the gas turbine engine of  FIG. 1  with an ejector assembly coupled to the balance piston cavity. 
         FIG. 4  is a side view of the ejector assembly of  FIG. 2 . 
         FIG. 5  is a side view of an ejector in an open position. 
         FIG. 6  is a side view of the ejector of  FIG. 5  in a closed position. 
         FIG. 7  is a rear view of the ejector of  FIG. 5  looking forward. 
         FIG. 8  is a flow chart illustrating a method of providing pressurized air to a balance piston. 
     
    
    
     DETAILED DESCRIPTION 
     The described embodiments of the present invention are directed to an ejector having a variable area throat, which may be used to provide pressurized bleed airflow to a balance piston in a gas turbine engine. For purposes of illustration, the present invention will be described with respect to the turbine for an aircraft gas turbine engine having a balance piston. It will be understood, however, that the invention is not so limited and may have general applicability within an engine, including compressors, as well as in non-aircraft applications, such as other mobile applications and non-mobile industrial, commercial, and residential applications. The invention is also not limited to just controlling the supply of air to a balance piston. 
     As used herein, the term “forward” or “upstream” refers to moving in a direction toward the engine inlet, or a component being relatively closer to the engine inlet as compared to another component. The term “aft” or “downstream” used in conjunction with “forward” or “upstream” refers to a direction toward the rear or outlet of the engine relative to the engine centerline. 
     Additionally, as used herein, the terms “radial” or “radially” refer to a dimension extending radially between a center longitudinal axis of the engine and an outer engine circumference. 
     All directional references (e.g., radial, axial, proximal, distal, upper, lower, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise, upstream, downstream, aft, etc.) are only used for identification purposes to aid the reader&#39;s understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and can include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to one another. The exemplary drawings are for purposes of illustration only and the dimensions, positions, order and relative sizes reflected in the drawings attached hereto can vary. 
       FIG. 1  is a schematic cross-sectional diagram of a gas turbine engine  10  for an aircraft. The engine  10  has a generally longitudinally extending axis or centerline  12  extending forward  14  to aft  16 . The engine  10  includes, in downstream serial flow relationship, a fan section  18  including a fan  20 , a compressor section  22  including a booster or low pressure (LP) compressor  24  and a high pressure (HP) compressor  26 , a combustion section  28  including a combustor  30 , a turbine section  32  including a HP turbine  34 , and a LP turbine  36 , and an exhaust section  38 . 
     The fan section  18  includes a fan casing  40  surrounding the fan  20 . The fan  20  includes a plurality of fan blades  42  disposed radially about the centerline  12 . The HP compressor  26 , the combustor  30 , and the HP turbine  34  form a core  44  of the engine  10 , which generates combustion gases. The core  44  is surrounded by core casing  46 , which can be coupled with the fan casing  40 . 
     A HP spool or HP drive shaft  48  disposed coaxially about the centerline  12  of the engine  10  drivingly connects the HP turbine  34  to the HP compressor  26 . A LP spool or LP drive shaft  50 , which is disposed coaxially about the centerline  12  of the engine  10  within the larger diameter annular HP drive shaft  48 , drivingly connects the LP turbine  36  to the LP compressor  24  and fan  20 . 
     The LP compressor  24  and the HP compressor  26  respectively include a plurality of compressor stages  52 ,  54 , in which a set of compressor blades  56 ,  58  rotate relative to a corresponding set of static compressor vanes  60 ,  62  (also called a nozzle) to compress or pressurize the stream of fluid passing through the stage. The compressor blades  56 ,  58  can rotate about a compressor rotor  51 . In a single compressor stage  52 ,  54 , multiple compressor blades  56 ,  58  can be provided in a ring and can extend radially outwardly relative to the centerline  12 , from a blade platform to a blade tip, while the corresponding static compressor vanes  60 ,  62  are positioned upstream of and adjacent to the rotating blades  56 ,  58 . It is noted that the number of blades, vanes, and compressor stages shown in  FIG. 1  were selected for illustrative purposes only, and that other numbers are possible. 
     The blades  56 ,  58  for a stage of the compressor can be mounted to a disk  51 , which is mounted to the corresponding one of the HP and LP drive shafts  48 ,  50 , with each stage having its own disk  51 ,  61 . The vanes  60 ,  62  for a stage of the compressor can be mounted to the core casing  46  in a circumferential arrangement. 
     The HP turbine  34  and the LP turbine  36  respectively include a plurality of turbine stages  64 ,  66 , in which a set of turbine blades  68 ,  70  are rotated relative to a corresponding set of static turbine vanes  72 ,  74  (also called a nozzle) to extract energy from the stream of fluid passing through the stage. In a single turbine stage  64 ,  66 , multiple turbine blades  68 ,  70  can be provided in a ring and can extend radially outwardly relative to the centerline  12 , from a blade platform to a blade tip, while the corresponding rotating blades  68 ,  70  are positioned upstream of and adjacent to the static turbine vanes  72 ,  74 . It is noted that the number of blades, vanes, and turbine stages shown in  FIG. 1  were selected for illustrative purposes only, and that other numbers are possible. 
     The blades  68 ,  70  for a stage of the turbine can be mounted to a disk  71 , which is mounted to the corresponding one of the HP and LP drive shafts  48 ,  50 , with each stage having its own disk  71 ,  73 . The vanes  72 ,  74  for a stage of the compressor can be mounted to the core casing  46  in a circumferential arrangement. 
     The portions of the engine  10  mounted to and rotating with either or both of the drive shafts  48 ,  50  are also referred to individually or collectively as a rotor  53 . The stationary portions of the engine  10  including portions mounted to the core casing  46  are also referred to individually or collectively as a stator  63 . 
     In operation, the airflow exiting the fan section  18  is split such that a portion of the airflow is channeled into the LP compressor  24 , which then supplies pressurized ambient air  76  to the HP compressor  26 , which further pressurizes the ambient air. The pressurized air  76  from the HP compressor  26  is mixed with fuel in the combustor  30  and ignited, thereby generating combustion gases. Some work is extracted from these gases by the HP turbine  34 , which drives the HP compressor  26 . The combustion gases are discharged into the LP turbine  36 , which extracts additional work to drive the LP compressor  24 , and the exhaust gas is ultimately discharged from the engine  10  via the exhaust section  38 . The driving of the LP turbine  36  drives the LP drive shaft  50  to rotate the fan  20  and the LP compressor  24 . 
     A remaining portion of the airflow  78  bypasses the LP compressor  24  and engine core  44  and exits the engine assembly  10  through a stationary vane row, and more particularly an outlet guide vane assembly  80 , comprising a plurality of airfoil guide vanes  82 , at the fan exhaust side  84 . More specifically, a circumferential row of radially extending airfoil guide vanes  82  are utilized adjacent the fan section  18  to exert some directional control of the airflow  78 . 
     Some of the ambient air supplied by the fan  20  can bypass the engine core  44  and be used for cooling of portions, especially hot portions, of the engine  10 , and/or used to cool or power other aspects of the aircraft. In the context of a turbine engine, the hot portions of the engine are normally downstream of the combustor  30 , especially the turbine section  32 , with the HP turbine  34  being the hottest portion as it is directly downstream of the combustion section  28 . Other sources of cooling fluid can be, but is not limited to, fluid discharged from the LP compressor  24  or the HP compressor  26 . 
     The HP compressor  26  can fluidly couple to a bleed air system  86  for providing a supply of pressurized air  88  to the engine  10  aft of the compressor section  22  as well as additional portions of the engine  10 . The supply of pressurized bleed air  88  can be supplied to a turbine rear frame  90  having a plurality of circumferentially arranged struts  92 . The struts  92  can orient a flow of air moving through the engine core  44  in an axial direction. The pressurized air supply  88  passes through one or more struts  92  into a balance piston assembly  94 . The balance piston assembly  94  is coupled to a bearing  96  via the LP drive shaft  50 , being mounted radially inboard of the compressor section  22 . During engine operation, the bearing  96  is susceptible to an axially aft force. The balance piston assembly  94  provides an axially forward force through the drive shaft  50  to reduce the axial load on the bearing  96 . 
     Looking at  FIG. 2 , a close up view of the turbine rear frame  90  and the balance piston assembly  94  illustrates the supply of pressurized air  88  provided to the balance piston assembly  94 . A conduit  110  disposed within the strut  92  fluidly couples to a first inboard cavity  112 . A balance piston cavity  114  is in fluid communication with the first inboard cavity  112 . The balance piston cavity  114  fluidly couples to a forward cavity  116  and an aft cavity  118  for providing a flow of pressurized air forward and aft of the balance piston cavity  114 , respectively. A second inboard cavity  120  is disposed forward of and in fluid communication with the forward cavity  116 . 
     A seal  130  at least partially defines the balance piston cavity  114  and is coupled to the drive shaft  50 . The seal  130  can selectively feed a flow of air from the balance piston cavity  114  to the forward cavity  116  based upon the pressure of the balance piston cavity  114 . 
     In operation, the supply of pressurized air  88  is provided to the conduit  110  within the strut  92  from the bleed air system  86 . The pressurized air  88  passes from the conduit  110  into the first inboard cavity  112  where it is fed to the balance piston cavity  114 . The pressurized air  88  is used to pressurize the balance piston cavity  114 . The pressurized balance piston cavity  114  delivers an axially forward force against the seal  130 , which provides the forward force to the drive shaft  50 , being coupled to the bearing  96 . As such, the pressure within the balance piston cavity  114  is used to balance the load on the bearing  96  by providing the axially forward force to balance the axially aft force generated against the compressor section  22  during engine operation. 
     The pressurized air  88  within the balance piston cavity  114  can exhaust forward through the seal  130  to the forward cavity  116  as a forward airflow  132  or aft to the aft cavity  118  as an aft airflow  134 . The forward airflow  132  can pass through the second inboard cavity  120  and exhaust forward of the strut  92  and the aft airflow  134  can exhaust aft of the strut  92 . 
     It should be appreciated that pressure provided to the balance piston assembly  94  and the pressure within the balance piston cavity  114  can be variable. In order to properly balance the bearing  96 , it is desirable to maintain a predetermined pressure within the balance piston cavity  94  by providing a consistent air pressure to the balance piston cavity  94  in order to maintain a proper load on the bearing  96 . 
     Looking at  FIG. 3 , a schematic view illustrates the bleed air system  86  for providing a supply of pressurized air  88  to the balance piston assembly  94 . A primary bleed air supply  140  and a secondary bleed air supply  142  can feed the pressurized air  88  to a mixing valve  144  from a first and second portion  146 ,  148  of the compressor  22 , respectively. The primary bleed air supply  140  is fed from the first portion  146  disposed aft or downstream of the second portion  148 . As such, the primary bleed air supply  140  feeds the mixing valve  144  with the supply of pressurized air  88  at a first air pressure being a higher air pressure relative to the second air pressure fed from the secondary bleed air supply  142 . The mixing valve  144  feeds a mixed air supply  150  to the balance piston assembly  94  at third pressure. The third pressure can be maintained at a predetermined pressure that can be based upon feedback from the balance piston assembly  94 . As such, the mixing valve  144  can proportionally couple the primary and secondary bleed air supplies  140 ,  142  to maintain the predetermined third pressure. Optionally, an orifice plate  152  can be included within the mixed air supply  150  to meter the flow from the mixing valve  144  to the balance piston assembly  94 . The orifice plate  152  can be beneficial for balancing the air pressures between operational and ambient conditions. 
     Looking at  FIG. 4 , a schematic view of an ejector  160  can be disposed within the mixing valve  144 . The ejector  160  can include a primary conduit  162  and a secondary conduit  164 . The primary conduit  162  can feed the primary bleed air supply  140  to the ejector  160  and the secondary conduit  164  can feed the secondary bleed air supply  142  to the ejector  160 . The ejector  160  can further include a converging section  166 , a mixing section  168 , and a diverging section  170 . The primary and secondary bleed air supplies  140 ,  142  can be mixed within the converging section  166 , accelerating the airflow into a mixing section  168  where the bleed air supplies  140 ,  142  mix. The mixed air supply  150  flows into the diverging section  170  where the mixed air supply  150  can be decelerated as pressurized air supplied to the balance piston assembly  94 . 
       FIG. 5  illustrates the ejector  160  having the secondary conduit  164  further including a conduit chamber  180  between the primary conduit  162  and the secondary conduit  164 . The primary conduit  162  includes an outlet  182  located within the conduit chamber  180  fluidly coupling the primary bleed air supply  140  to the conduit chamber  180 . The primary bleed air supply  140  fed from the primary conduit  162  can mix with the secondary bleed air supply  142  downstream of the outlet  182 . 
     A variable ejector throat  184  can further define outlet  182 . The variable ejector throat  184  can include a fixed portion  186  and a movable portion  188 . The movable portion  188  can move relative to the fixed portion  186  to partially open or close the variable ejector throat  184 . The movable portion  188  can have a first surface  190  exposed to the primary bleed air supply  140  and a second surface  192  exposed to the secondary bleed air supply  142 . 
     The ejector  160  can further include a housing  200  mounted to the fixed portion  186  and disposed adjacent to the movable portion  188 . The housing  200  can house a biasing element  202 , which can be a spring or similar in non-limiting examples. The biasing element  202  can be sandwiched between the housing  200  and a biasing surface  204 . The biasing surface  204  contacts the movable portion  188  such that the biasing element  202  can bias the movable portion  188  via the biasing surface  204  relative to the housing  200  and the fixed portion  186 . The housing  200  can have an aperture  206  fluidly coupling the interior of the housing  200  to the conduit chamber  180 . 
     The variable ejector throat  184 , as shown in  FIG. 4 , is in an open position defining an open distance  210  for the outlet  182 . In the open position, the biasing surface  204  is spaced from the bottom of the fixed portion  186 , having the biasing element  202  at least partially compressed. During operation, the balance piston assembly  94  can provide feedback to the ejector  160  through the pressure of the mixed air supply  150 . The pressure of the mixed air supply  150  will increase or decrease the pressure within the housing  200  through the aperture  206 . The increase or decrease of pressure within the housing  200  will cause the biasing element  202  to actuate the biasing surface  204  which moves the movable portion  188  relative to the fixed portion  186  to open and close the variable ejector throat  184 . 
     Looking now at  FIG. 6 , an increased pressure of the mixed air supply  150  from feedback from the balance piston assembly  94  can increase the pressure within the housing  200  providing a closing force to the movable portion  188 . The biasing element  202  pushes the biasing surface  204  to move the movable portion  188  toward a closed condition having a closed distance  212 . It should be appreciated that in a closed condition, the outlet  182  is not fully closed, permitting at least a portion of the primary bleed air supply  140  to pass through the outlet  182 . In the closed condition, a gap  214  is created between the housing  200  and the bottom of the movable portion  188 . 
     Thus as pressure increases at the balance piston assembly  94 , the pressure feedback is passed through the mixed air supply  150  to the housing  200 . As pressure within the housing  200  increases, the outlet  182  closes and as pressure within the housing  200  decreases, the outlet  182  opens. As the outlet  182  opens and closes, the amount of the primary bleed air supply  140  provided through the primary conduit  162  increases and decreases, respectively, metering the airflow provided from the primary conduit  162 . Thus, by metering the airflow provided from the primary conduit  162 , the pressure supplied to the balance piston assembly  94  can be metered. It should be appreciated, then, that the balance piston assembly  94  provides air pressure feedback via the mixed air supply  150  to determine the air pressure being supplied from the primary bleed air supply  140 . This way the balance piston assembly  94  can automatically define and maintain predetermined air pressure being supplied thereto. 
     Turning now to  FIG. 7 , the biasing element  202  can be a spring  220  to actuate the movable portion  188  relative to the fixed portion  186 . The fixed portion  186  can include two cavities  222 . The cavities  222  are shaped to receive two upper ends  224  of the movable portion  188  during actuation of the spring  220 . The cavities  222  permit the actuation of the movable portion  188  and provide a terminal surface  226  to define a minimum value for the closed distance  212 . Thus, the size and dimension of the housing  200  and the size of the cavity  222  can determine maximum and minimum positions for the movable portion  188  to define a maximum and minimum flow rate or air pressure that can be fed from the primary conduit  162 . These maximum and minimums can be determined respective of the desired predetermined air pressure to be supplied to the balance piston assembly  94 . 
     Looking at  FIG. 8 , a method  230  can utilize the engine  10  having the ejector  160  to provide pressurized air to the balance piston assembly  94 . The method  230  can include, at  232 , sensing a first pressure at a first compressor bleed air supply. The first pressure can be the primary bleed air supply  140  fed through the primary conduit  162 . At  234 , the method  230  further includes sensing a second pressure at a second compressor bleed air supply having a pressure that is less than the first pressure. The second pressure can be the secondary bleed air supply  142  fed from the secondary conduit  164  at a pressure lesser than the primary bleed air supply  140 . At  236 , the method  230  further includes sensing a third pressure at the balance piston assembly  94 . The mixed air supply  150  provided to the balance piston assembly  94  can be used to determine the third pressure as fed to the balance piston assembly  94 . At  238 , the air can be mixed from the first and second bleed air supplies in proportion to the first, second, and third pressures. The ejector  160  having the movable portion  188  can receive feedback from the third pressure at the balance piston assembly  94  to actuate the biasing element  202  in the housing  200  based upon that feedback. The biasing element  202  proportionately controls the primary bleed air supply  140  fed from the primary conduit  162  to mix the first and second bleed air supplies in proportion to the first, second, and third pressures. The ejector  160  can automatically control the ratio of the first and second bleed air supplies fed from the primary and secondary conduits  162 ,  164  via the biasing element  202 . Controlling the ratio of the first and second bleed air supplies can achieve a predetermined third pressure fed to the balance piston assembly  94  and can be based upon the first and second pressures from the primary and secondary bleed air supplies  140 ,  142  to set the predetermined third pressure. 
     It should be appreciated that the variable ejector throat  184  provides for automatic throat control utilizing the movable portion  188  coupled to the biasing element  202 . The automatic throat control is based upon feedback air pressure from the balance piston assembly  94  to open or close the outlet  182  relative to the feedback to increase or decrease the air pressure fed from the primary conduit  162 . The outlet  182  automatically opens or closes based upon the feedback to maintain a predetermined air pressure fed to the balance piston assembly  94 . It should be further appreciated that the apparatus and method described herein utilizes a minimal amount of parts and required reduced manual intervention such as repair and servicing. Furthermore, the apparatus and method provides optimal air pressure to the balance piston assembly  94  to improve engine efficiency and overall engine performance, while reducing the risk of engine shutdown due to an unbalanced load. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. 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.