Abstract:
In a gas turbine engine having a rim cavity formed between a rotor disk and a stator, and a brush seal or other seal member providing an airflow seal between the stator and a side plate of the rotor disk, a thermally responsive valve device is located in the bypass passage of the stator to form a parallel air flow path with the brush seal. As the brush seal wears and the leakage airflow around the worn brush seal increases, the air flow temperature in the rim cavity would decrease. The thermally responsive valve device would detect the decreasing airflow temperature, and reduce the airflow passing through the bypass passage in order to prevent the temperature of the rim cavity from decreasing. The temperature responsive valve device makes use of a bimetallic valve member that regulates airflow based upon temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   None. 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   None. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to gas turbine engines, and more particularly to a passive cooling system for a rim or rotor cavity. 
   2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98 
   As gas turbine engine evolution reaches a mature state, factors which plays an important role in deciding which engine to choose for a particular application may ultimately come down to durability and performance in the form of specific fuel consumption (SFC) or cycle efficiency and heat rate. Engine component material selection and their material properties play a major role in performance. Engine components must be cooled to acceptable levels and there are usually many trade studies performed to optimized concepts to best maintain component temperature while using the minimum amount of cooling flow. The cooling flow is supplied by compressor extraction or bleed and while work was required to compress this air, since it is used for parasitic flow purposes, it is not passed through the turbine for work to extraction. For this reason, secondary flows are usually called chargeable flows. Most conventional turbine rotor systems encompass bladed disks as opposed to blisks which are integrally bladed disks. For these conventional disks, their maximum operating temperatures are usually well below that of flow path material such as rotating blades and stationary vanes. A secondary flow designer computes the minimum rim cavity purge flows based on a particular rim seal design and as well as flow path pressure asymmetries which are a mechanism for ingestion. It is desirable to provide the minimum flow required to resolve cavity windage rise, and prevents hot gas ingestion. For robust designs, the design point for sizing cooling systems is usually at some level of engine deterioration where components, especially seals wear and the cycle is less efficient which ultimately leads to higher turbine flow path temperatures. The secondary flow designer can predict system performance at the deteriorated condition, where the life of gas path components such as blades and vanes required replacement, or in “as shipped” configuration, when the engine is shipped out of the manufacturing facility. The ideal system would be to have constant secondary flows throughout component life cycle. 
   A Prior Art rotor or rim cavity purge arrangement is disclosed in U.S. Pat. No. 5,181,728 issued to Stec on Jan. 26, 1993 and entitled TRENCHED BRUSH SEAL (the entire disclosure of which is incorporated herein by reference) in which a rotor cavity  82  is purged with seal leakage air flow that passes through a brush seal  70  to prevent the ingress of hot gases into the cavity which otherwise would cause a detrimental increase in the temperature and consequent reduction in life of the rotor  60 . One problem with the Prior Art is that, when the brush seal wears, more seal leakage airflow passes into the cavity than when the engine was in the “as shipped” factory condition. Thus, more airflow is heated than needed, and therefore the overall engine efficiency decreases. 
   The concept for a constant flowing rim cavity encompasses the use of a brush seal, but can be used in conjunction with any seal that has considerable wear over time from its shipped state to the end of a components life. While brush seals have many advantageous applications in a gas turbine, one area of challenging application is in rotor rim cavities, especially stage  1  rim cavity since gas path conditions are most severe as well as flow path pressure asymmetry due to wakes from vane trailing edges. The excellent sealing characteristic that makes the brush seal a good candidate for many applications is the same characteristic that makes the application in rim seals a challenge. Since brush seals usually flow much less than the minimum required cavity flow to prevent hot gas ingestion and resolve cavity windage, when in the line to line or radially contacting position, a seal bypass hole can be provided to supply the additional amount of desired flow. U.S. Pat. No. 5,522,698 issued to Butler et al. on Jun. 4, 1996 entitled BRUSH SEAL SUPPORT AND VANE ASSEMBLY WINDAGE COVER (the entire disclosure of which is incorporated herein by reference) shows a bypass hole in parallel with the brush seal to provide purge airflow for the rim cavity. This flow is usually supplied with some injection angle in the direction of rotation to reduce rim cavity windage. The difficulty with this system is when the engine is shipped, the brush seal is not worn and the desired flows are mainly provided by the bypass holes. The problem becomes clear after brush seals wear. As the seals wear due to the cycling of the engine which lead to seal rubs, the brush seal flow consumption increases, but the bypass hole still exists and by the end of component life cycle, the system will flow as much or more that with a convection labyrinth seal. The economic advantage of the above mentioned system over conventional labyrinth seals is that the wear is exponential in nature where the labyrinth seal rub is instant. The area under the curve of flow versus time will translate to fuel savings over time. This savings is usually not enough to justify the cost of using the brush seal. A system that provides for constant flow would have the most economic advantage.  FIG. 1  depicts a Prior Art device in which a brush seal  34  leakage air flow is in parallel with a bypass flow thorough passages  30 . 
   BRIEF SUMMARY OF THE INVENTION 
   The invention provides for several ways to have a passive thermostatically controlled bypass opening such that as the brush seal wears and passes more flow, the bypass holes close down to keep the same level of flow in a deteriorated system as in factory shipped condition. 
   The first configuration is to use a spring loaded valve with or without a ratcheting device to be sized for a given thermal gradient. As the brush seals wears, leakage flow through the brush seal will increase, thereby reducing the cavity temperature. The thermostatic spring is sized to contract due to the lower temperature gradient as a result of this increased flow over time. Installing such a device would cause an oscillation in displacement as a result of its thermal cyclic environment. A ratcheting device can be provided to alleviate constant thermal cycling of the bypass mechanism as well as rotor cavity components. This concept is depicted in  FIG. 2 . 
   The second configuration employs a bimetallic strip which would be sized to have an axial displacement at some desired temperature differential from the cold side to the hot cavity side. This concept is shown in  FIG. 3 . Other shapes such as a cylindrical bimetallic valve can be used as well. As the cavity temperature drops, due to brush seal wear, the bi metallic strip would straighten to close the bypass gap. This device can be fitted with a ratcheting devise as well to avoid thermal cycling. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  shows a Prior Art gas turbine engine with a brush seal and a plurality of bypass passages to provide cooling air to the rim cavity. 
       FIG. 2  shows a cross section view of a gas turbine engine with a brush seal and a passive spring loaded valve with a ratcheting device to control bypass flow to the rim cavity. 
       FIG. 3  shows a second embodiment of the present invention in which the passive thermostatic bypass flow control device is a bimetallic member. 
       FIG. 4  shows a third embodiment of the present invention in which the passive thermostatic bypass flow control device is a spring loaded valve assembly with the air flows around the outside of the valve assembly. 
       FIG. 5  shows a fourth embodiment of the present invention in which the passive thermostatic bypass flow control device is a valve assembly with concentric cylindrical members having radial holes to pass the air flow through the valve assembly around the outside of the valve assembly. 
       FIG. 6  shows a fifth embodiment of the present invention in which the passive thermostatic bypass flow control device is a valve assembly with concentric cylindrical members having radial holes to pass the air flow through the valve assembly through the inside of the valve assembly. 
       FIG. 7  shows a sixth embodiment of the present invention in which the passive thermostatic bypass flow control device is a valve assembly with a thermally responsive valve head that moves to block the air flow through the bypass valve assembly. 
       FIG. 8  shows a seventh embodiment of the present invention in which the passive thermostatic bypass flow control device is a valve having a single piece that is threaded into the bypass hole. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A first stage turbine nozzle and blade assembly is shown in  FIG. 2 , in which a rotor disk  12  carries a plurality of blades, and a stationary nozzle  16  guides a hot gas stream onto the rotating blades  14  to drive the turbine shaft. A side plate  18  extends over the axially forward surface of the rotating rotor disk  12  assembly. A rim cavity  20  is defined by an axial separation between the stationary turbine nozzle assembly and the rotating rotor assembly  12 . The side plate  18  also includes an aperture  22  in the web of the side plate to permit cooling fluid to flow through and into a disk cavity  24  formed between the side plate  18  and the rotor disk  12 . A pre-swirler  26  delivers airflow from a compressor (not shown) and swirls the airflow before discharging the airflow into the side plate aperture  22 . The airflow then flows into the disk cavity  24  and into a passage  28  in the rotor disk  12  that leads into a plurality of passages in the blade  14  for cooling. 
   The stationary nozzle assembly  13  includes a bypass passage  130  and a brush seal assembly  34  as in the prior art. But, the present invention includes a passively controlled thermally responsive valve in the bypass passage  132  to regulate airflow into the rim cavity  20 . The stationary nozzle assembly  13  includes a chamber box assembly  136  that contains a bypass valve head  138 , a valve stem  140 , and a biasing spring  142 . A ratcheting device includes a plurality of ratcheting teeth  144  that engage with ratcheting fingers  146  that extend from an inner surface of the chamber box  136 . An airflow opening  148  is located on the upstream end of the chamber box  136  to allow for airflow from the pre-swirler  26  to enter the chamber box  136 . The brush seal assembly  34  includes a brush seal that extends from the stationery nozzle assembly and forms a seal with the rotating surface  50  of the side plate  18 . Air from the compressor flows through the pre-swirler  26  and into the opening  148  in the chamber box  136 , and then into the rim cavity  20  to purge the rim cavity  20  and prevent an inflow of hot gas from the gas stream and to resolve undue heating in the rim cavity  20 . Some of the airflow from the pre-swirler  26  also flows past the brush seal  34  as leakage and into the rim cavity  20  to also aid in purging the rim cavity  20 . 
   The valve assembly within the camber box  136  is made of a material such that the airflow temperature in the rim cavity  20  will cause the bypass valve head  138  to move toward a closed position. The bypass valve head  138  is exposed to the airflow temperature in the rim cavity  20 . As the airflow temperature in the rim cavity  20  drops (due to wear of the brush seal resulting in a higher leakage flow into the rim cavity  20 ) the bypass valve head  138  temperature will approach the temperature of the airflow in the box rim cavity  20 . The valve stem  140  and spring  142  will also be cooled by heat transfer to the bypass valve head  138 , resulting in the metal spring assembly to contract and close the bypass valve passage  132 . As the brush seal  34  wears, more airflow leaks past the brush seal  34  and into the rim cavity  20 . More cooling airflow into the rim cavity  20  results in the temperature of the airflow in the rim cavity  20  to drop. This drop in temperature is used as an indication of wear from the brush seal  34 . As the airflow temperature in the rim cavity decreases, the valve assembly passively detects this and acts to close the valve head  138  to reduce the airflow through the bypass passage  32 . As the airflow through the bypass passage  32  is reduced, the airflow temperature in the rim cavity  20  will increase to the normal operating design temperature, even with increased airflow leakage through the brush seal  34  due to wear. 
   One of the features of the present invention is a ratcheting device to limit the oscillation of the bypass valve head  138  as a result of a thermally cyclic environment. The ratcheting device includes a plurality of ratcheting teeth  144  extending from the valve stem  140  that engage ratcheting fingers  146 . The teeth  146  and fingers  146  are oversized in the figure to show the concept only. As the rim cavity temperature decreases due to wear of the brush seal  134 , the bypass valve head  138  will move toward the closed position, and the fingers  146  will engage the teeth to prevent the valve head  138  from returning to the original position. The number and size of the ratcheting teeth will be such that the valve head  138  will provide enough bypass air flow into the rim cavity  20  when the brush seal has zero wear (and, therefore minimum leakage) to purge the rim cavity in the most opened position to the most closed position in which the bypass airflow is minimum and the leakage airflow past the brush seal  34  is the maximum due to the most wear (before needing to be replaced). 
   The bypass valve assembly can be made from any material that will produce the results required to close the valve when the airflow temperature in the rim cavity  20  drops due to the wear of the brush seal  34 . 
   A second embodiment of the present invention is shown in  FIG. 3 . The passive thermostatic bypass flow control device in the  FIG. 3  embodiment is a bimetallic member  266  made of an inside metallic sheet  262  bonded to an outside metallic sheet  264  in which one of the two sheets has a different thermal expansion coefficient than the other in order to cause the bimetallic member  266  to block the airflow in the bypass passage  30  against an air flow restriction forming member  260 . The bimetallic member  266  and flow restriction forming member  260  are formed within the bypass passage  30  of the stator  13 . The brush seal  34  extends from the bottom of the stator  13  as in the prior art device. The size of the bypass passage  30  and bimetallic flow restricting assembly ( 266  and  260 ) are shown much larger than normal for illustration purposes. The outside metal sheet  264  is located near the exit of the bypass passage  30  so that the sheet is exposed to the airflow in the rim cavity. The material properties of the two metallic sheets are such that, with a temperature decrease of the airflow in the rim cavity due to brush seal  34  wear, the bimetallic member  266  will bend such that the tip approaches the upper ledge of the air flow passage forming member  260  and reduce the air flow through the bypass passage  30  and into the rim cavity  20 . 
   A third embodiment of the present invention is shown in  FIG. 4 . The passive thermostatic bypass flow control device in the  FIG. 4  embodiment is a valve assembly  430  that is inserted into a hole of the stator assembly  13  extending from the vane. The valve assembly  430  includes a valve head  432 , a valve stem  434  extending from the valve head  432 , and a valve stem tip  436  extending from the valve stem  434  at an opposite end from the valve head  432 . The valve head and stem is supported for axial movement within a valve outer cylinder member  446 . An angled surface  450  is formed on the valve outer cylinder member  446  and forms a flow restriction with the valve head  432 . A valve inner cylinder member  442  is secured to an open end of the valve cylinder member  446  to close that end. A thermally responsive biasing spring member  440  is positioned within a spring chamber  444  of the valve outer cylinder  446  between the valve stem tip  436  and the surface of the valve inner cylinder member  442 . Radial holes  452  are formed around the valve outer cylinder member  446 , and the valve assembly  430  fits within a stepped hole formed in the stator assembly  13  such that an outer axial passages  448  is formed around the outer surface of the valve outer cylinder member  446 . The brush seal assembly  34  extends from the stator assembly  13  as in the previous embodiments. A ratcheting member is secured between a flat surface of the valve stem  434  and a tip nut  438  threaded to the valve stem tip member  436 . The ratcheting member extends radially outward from the valve stem  434  to engage a plurality of latching teeth that extend radially inward from the valve cylinder closure member  442 . The ratcheting device functions to limit the oscillation of the bypass valve head  432  as a result of a thermally cyclic environment as in the  FIG. 2  embodiment. 
   The operation of the  FIG. 4  embodiment is now described. The open bypass passage holes  30  that already appear in the stator  13  of the prior art have the valve assembly  430  of the  FIG. 4  present invention inserted therein, one valve assembly  430  per bypass passage hole  30  in the stator  13 . The valve head  432  is in the most open position when the brush seal  34  is new (or, without wear), the valve head  432  being positioned to allow for the proper amount of air to flow through the valve assembly  430  and into the rim cavity  20  in order to purge the rim cavity  20  when the brush seal  34  allows for the minimum leakage flow. Bypass air flows between the valve head  432  and an angled surface  450  on the end of the valve outer cylinder member  446 , through the radial holes  452 , into the outer axial passage  448 , and out of the valve assembly  430  and into the rim cavity  20 . As the brush seal  34  wears, the leakage air flow increases into the rim cavity  20 , decreasing the temperature of the air in the rim cavity. As the air temperature in the rim cavity  20  decreases, the heat transfer through the valve cylinder closure member  442  passes into the spring chamber  444  and the spring  440 . As the spring  440  cools—due to the decrease air flow temperature in the rim cavity  20 —the spring contracts to gradually move the valve head toward a closed position. The air flow through the valve restriction (formed between head  432  and surface  450 ) decreases as the spring  440  contracts to reduce the air flow through the valve assembly. Thus, as the leakage flow around the brush seal  34  increases, the valve head  432  closes to decrease the bypass flow through the valve assembly  430  in order to maintain a constant air temperature in the rim cavity  20 . 
   A fourth embodiment of the present invention is shown in  FIG. 5 , which is a valve assembly  530  that is intended to be inserted into the unobstructed passage  30  of the prior art  FIG. 1  assembly. With the  FIG. 5  embodiment, the airflow through the passage  30  can be regulated as the brush seal  34  wears and the bypass flow increases at the brush seal. The valve assembly  530  includes a main stem member  502  with a central axial passage  503  open on the upstream side and a plurality of radial holes  504  and  506  located in series along the central axial passage  503 . A valve sleeve member  510  also includes as plurality of radial holes  512  and  514  located in series. Booth the main stem member  502  and the valve sleeve member  510  include annular projections that abut stepped portions that are formed in the passage  30  of the stator  13  in order to secure the valve assembly  530  in the passage  30 . An outer axial passage  548  is formed between the inner surface of the passage  30  and the outer surface of the valve member  530 . Axial holes  516  in the annular projection of the valve sleeve member  510  provide a fluid communication between the outer axial passage  548  and the rim cavity  20 . The main operation of the valve member  530  is provided by forming the main stem member  502  and the valve sleeve  510  from materials having different thermal expansion coefficients such that the radial holes are displaced. When the brush seal  34  is new (no wear such that leakage is minimum), the radial holes  506  and  514  are in alignment and radial holes  504  and  512  are in alignment such that the maximum airflow occurs through the valve assembly  530 . As the brush seal  34  wears, and the leakage airflow past the seal  34  increases, the rim cavity  20  temperature decreases, the valve assembly  530  senses this decrease in temperature and the radial holes move out of alignment such that airflow through the valve assembly  530  decreases. 
   A fifth embodiment of the present invention is shown in  FIG. 6 , and is similar to the fourth embodiment of  FIG. 5 . The valve assembly  630  includes a main stem member  602  with axial holes  604  spaced around the axis of the main stem member  602 , the main stem member  602  forming an central axial passage  603 , a valve sleeve member  610 , and radial holes  604  and  606  in the main stem member  602  and radial holes  612  and  614  in the valve sleeve member  610 . An outer axial passage  648  is formed between the inner wall of the passage  30  in the stator  13  and the outer surface of the valve assembly  630 . A plug member  620  with a central axial hole  622  closes the opening of the central axial passage  603  in the main stem member  602 . Airflow passes through the axial holes  604  and into the outer axial passage  648 , through the radial holes into the central axial passage  603 , and through the central axial hole  622  of the plug member  620  and out into the rim cavity  20 . As in the fourth embodiment of  FIG. 5 , the valve assembly is formed of two materials having different coefficients of thermal expansion so that the airflow through the valve assembly can be regulated by displacing the alignment of the radial holes as the temperature in the rim cavity  20  changes due to wear of the brush seal  34 . When the brush seal  34  is new, the radial holes are in alignment for maximum airflow, and move out of alignment to progressively block the airflow as the holes move out of alignment. 
   A sixth embodiment of the present invention is shown in  FIG. 7 , and is similar to the third embodiment of  FIG. 4 . The valve assembly  730  is inserted into the passage  30  of the stator  13  in which an annular outer axial passage  748  is formed. The valve assembly  730  includes an inner valve stem member  736  with a valve head  732  and valve stem  734 , and an outer sleeve member  746  having radial holes  752  spaced around the sleeve and an angled surface that forms a restricted passageway  750  with the valve head  732 . The inner valve stem member  736  and the outer sleeve member  746  are made of materials having different thermal expansion coefficients in order to produce relative movement and close reduce the restricted passageway  750 . The restricted passageway  750  is at the maximum opened position when the brush seal is new, where the restricted passageway  750  progressively closes as the brush seal  34  wears. The temperature in the rim cavity  20  is exposed to the surface of the valve stem member  736 . As the rim cavity  20  temperature drops, the valve stem  734  temperature also drops and shortens in length, resulting in the restricted passageway  750  to become more restricted. 
   A seventh embodiment of the present invention is shown in  FIG. 8 . This is the simplest embodiment of the present invention in that the thermally responsive valve  830  formed from a single piece and is threaded into the hole by screw threads  860  formed on the valve and the inner surface of the hole. The valve  830  includes a ring member with a plurality of holes  855  therein to allow passage of the cooling air, a stem portion  834  that forms a cooling air passage  848  in the bypass passage, and a valve head  832  that forms a flow restriction  850  between the head  832  and a beveled portion  851  formed on the exit end of the bypass passage in the stator. To insert the valve  830  of the  FIG. 8  embodiment, threads  860  must be formed in the bypass passage and a beveled portion  851  formed on the exit end of the bypass passage. The beveled portion  851  is optional, but is desired in order to form a good flow restriction surface. As the temperature in the rim cavity  20  increases, the heat will transfer to the head  832  of the valve  830  and into the stem  834  and cause the valve to grow in length, resulting in the flow restriction  850  to increase to allow more cooling air flow through the valve  830 . As the brush seal  34  wears and the cooling air flows through the brush seal and into the rim cavity  20 , the temperature drops and the valve  830  will shrink in length, decreasing the flow restriction and lowering the cooling air flow through the valve  830  and into the rim cavity  20 . 
   The present invention improves the overall efficiency of the gas turbine engine by preventing excess bypass flow from entering the rim cavity by using a passive controlled bypass valve that is responsive to thermal temperature of the airflow in the rim cavity. The bypass valve is also positioned by a ratcheting device to limit oscillation of the valve head.