Abstract:
A cooling system for a turbine engine, as well as a methodology for controlling the cooling system, is described. A valve member is disposed between a cooling fluid passage and a wheel space of the turbine engine and operates to admit cooling fluid to the wheel space for cooling thereof. The valve assembly is responsive to a condition in the wheel space and varies the flow of additional cooling fluid to the wheel space based on that condition.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to gas turbine engines, and, more particularly, to temperature management therein. 
     In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gas that flows downstream through multiple turbine stages. A turbine stage includes a stationary turbine nozzle having stator vanes that guide the combustion gas through a downstream row of turbine rotor blades extending radially outwardly from a supporting disk, which is powered by extracting energy from the hot combustion gas. 
     A first stage turbine nozzle receives hot combustion gas from the combustor, which is subsequently directed to the first stage turbine rotor blades, for extraction of energy therefrom. A second stage turbine nozzle may be disposed downstream of the first stage turbine rotor blades, and is followed in turn by a row of second stage turbine rotor blades, for extraction of additional energy from the combustion gas. Similarly, a third stage turbine nozzle may be disposed downstream of the second stage turbine rotor blades, and is followed in turn by a row of third stage turbine rotor blades. 
     As energy is extracted from the hot combustion gas, the temperature of the gas is correspondingly reduced. However, since the gas temperature is relatively high, the turbine stages are typically cooled by delivery of a coolant, such as compressed air which may be diverted from the compressor. Since the diverted cooling air is unavailable to the combustor, the overall efficiency of the engine is correspondingly reduced. It is therefore desired to improve the use of such cooling air for improving the overall efficiency of the engine. 
     The quantity of cooling air required is dependant on the temperature of the combustion gas, material selection and turbine engine design. That temperature varies from idle operation of the turbine engine to high power operation, and from low to high temperatures at the compressor inlet. For example, in a land-based gas turbine engine that powers an electrical generator, high temperature operating conditions typically occur during the hot day, peak power condition. Combustion gas temperature may therefore vary temporally over the operating or running conditions of the engine. Since combustion gas temperature directly affects the durability of the vanes and blades, the cooling air requirement for the turbine stages must be effective for withstanding high combustion gas temperature operation of the engine, although that running condition may only occur for a relatively short time during engine operation. 
     A wheel space is defined between the first stage nozzle assembly and the compressor exit diffuser. Due to its proximate location to the outlet of the combustor, the wheel space is subject to some of the higher temperatures experienced by the turbine. To maintain the wheel space within a temperature range which is suitable for the long term durability of the components in that region, cooling air is delivered to the wheel space. Under certain operating conditions, such as high ambient temperatures resulting in high temperatures at the inlet of the compressor, the volume of cooling air may be insufficient to maintain the wheel space within a desired temperature range. In such situations it is known to disassemble the turbine engine and remove plugs from the combustor inlet housing. This results in diversion of a portion of the high pressure air exiting the compressor to the wheel space through the openings formerly closed by the plugs. While the result is supplemental cooling of the wheel space region of the turbine, the modification is permanent. As such, cooling air is delivered to the wheel space when it may not be required, thereby lowering the overall performance of the turbine engine. 
     It is therefore desired to provide a gas turbine engine having improved cooling. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An exemplary embodiment of the invention is included in a cooling system for a turbine engine, as well as a methodology for controlling the cooling system thereof A valve member is disposed between a cooling fluid passage and a wheel space of the turbine engine. The valve assembly is responsive to a condition in the wheel space and varies the flow of cooling fluid to the wheel space based on that condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is an axial sectional view through a portion of a gas turbine engine in accordance with an exemplary embodiment of the invention; 
         FIG. 2  is an enlarged view of the turbine section of  FIG. 1  illustrating features of an exemplary embodiment of the invention; and 
         FIG. 3  is an enlarged view of the turbine section of  FIG. 1  illustrating features of another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrated in  FIG. 1  is a portion of a gas turbine engine  10 . The gas turbine engine  10  is axisymmetrical about a longitudinal or axial center line axis and includes, in serial flow communication, a multistage axial compressor  12 , a combustor  14 , and a multi-stage turbine  16 . During operation, air  18  is pressurized in the compressor  12  and is mixed with fuel in the combustor  14  to generate hot combustion gas  20 . The combustion gas flows downstream through the multi-stage turbine  16  which extracts energy therefrom. 
     As shown in  FIG. 1 , one embodiment of a multi-stage turbine  16  may be configured in three stages having six rows of airfoils  22 ,  24 ,  26 ,  28 ,  30 ,  32  disposed axially in direct sequence with each other for channeling the hot combustion gas  20  therethrough, and extracting energy therefrom. The airfoils  22  are configured as first stage stator vanes which are circumferentially spaced apart from each other and extend radially between inner and outer bands to define nozzle assembly  38 . The nozzle assembly receives the hot combustion gas  20  from the combustor  14 . The airfoils  24  extend radially outwardly from the perimeter of a first supporting disk  40 , and are configured as first stage turbine rotor blades which receive the hot combustion gas from the nozzle assembly  38  for extracting energy to rotate the disk  40  during operation. 
     A wheel space  42  is defined between the nozzle assembly  38  and the compressor exit diffuser  44 , proximate the combustor outlet. Due to its proximate location to the outlet of the combustor  14 , the wheel space is subject to some of the highest temperatures experienced by the gas turbine engine  10 . To maintain the wheel space  42  within a temperature range which is suitable for the long term durability of the components in that region a coolant, such as compressor air  43 ,  FIG. 2 , may be supplied from compressor  12 , and is delivered to the wheel space  42  through cooling channel  46  which is defined between the compressor exit diffuser  44  and the hub  48 . 
     Under certain operating conditions, such as high ambient temperatures resulting in high temperatures at the inlet of the compressor, the compressor air  43  delivered to the wheel space  42 , through cooling channel  46 , may be insufficient to maintain the wheel space within a desired temperature range, as determined by wheel space condition sensor  47 . The condition sensor  47  may operate to directly determine the temperature in the wheel space  42 , but may also sense conditions such as component expansion resulting from temperature excursions therein. A valve assembly  50  is disposed within the compressor exit diffuser  44  and comprises a valve member  52  moveably located in passage  54  of the compressor exit diffuser wall. The valve assembly  50  has a valve actuator  56 , such as an electric motor, solenoid or other suitable device for operating the valve member  52 . The valve actuator  56  operates in conjunction with valve member  52  to vary the quantity of compressor air passing from the compressor exit diffuser  44  to cooling channel  46 , thereby varying the delivery of coolant to the wheel space  42 . The valve assembly  50  is actuated by a controller  58 , which receives an input signal from the wheel space condition sensor  47 . As the wheel space reaches a predetermined condition, such as a defined temperature, the controller  58  signals the valve actuator  56  to move valve member  52  in air passage  54 , to admit additional compressor air  43  through passage  54 . When the condition is controlled to the desired specification, the controller  58  signals the valve actuator  56  to move the valve member  52  in cooling air passage  50 , thereby reducing the flow of compressed air delivered to the wheel space  42  and increasing the overall efficiency of the turbine engine  10 . Depending on the type of valve assembly  50  which is selected, the cooling flow through passage  54  may be fixed when the valve member is opened (i.e. on/off—fully open/fully closed), or it may be variable (i.e. partially on/partially off—partially open/partially closed, or modulated). 
     Referring now to  FIG. 3 , another exemplary embodiment of the invention is shown where like numerals represent like components already described. The valve assembly  150 , in this embodiment is a standalone unit operating independently of any external influence such as controller  58  in  FIG. 2 . The valve assembly  150  may be of the bi-metal or expansion element type which has material properties which are selected to operate the valve member  152  when a predetermined limit has been reached. The expansion of element  156  will occur over a control range as the condition, such as the temperature in passage  46 , increases resulting in a variable flow which increases with increasing temperature. As the condition in cooling air passage  46  comes within an acceptable range, the expansion element  156  will retract the valve member  152  thereby reducing the flow of coolant air which is delivered to the wheel space  42 . The overall efficiency of the turbine engine  10  is thereby improved. 
     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 language of the claims.