Abstract:
A clearance control apparatus for controlling the clearance between a rotary assembly ( 17 ) and a casing ( 24 ) surrounding the rotary assembly ( 17 ) is disclosed. The clearance control apparatus comprises a temperature measuring device ( 34 ) to measure the temperature of a radially outer portion of the rotary assembly and a cooling arrangement ( 28 ) to cool the casing ( 24 ). A control system ( 36 ) is associated with the temperature measuring device ( 34 ) and the cooling arrangement ( 28 ) to control the extent of cooling of the casing ( 24 ). The extent of cooling is dependent upon the temperature of the aforesaid portion.

Description:
This application claims priority to British Patent App&#39;n Ser. No. 0609312.4, field 11 May 2006. 
     FIELD OF THE INVENTION 
     This invention relates to clearance control apparatus for controlling the clearance between rotary assemblies and the casing surrounding the rotary assemblies. More particularly, but not exclusively the invention relates to clearance control apparatus for controlling the clearance between the blade tips for turbine and the turbine casing. 
     BACKGROUND OF THE INVENTION 
     Gas turbine efficiency is affected by the clearance between the tip of a turbine blade and the turbine casing. Clearance needs to be minimised for maximum turbine efficiency. 
     Turbine design calculations take into account all the related thermal expansions. The clearance is consequently set to avoid causing the tips of the blades to rub against the casing during certain manoeuvres. The design considerations ensure that the clearance is optimum at, for example, steady state operation. However, there is no control of the clearance during none steady state performance. 
     SUMMARY OF THE INVENTION 
     According to one aspect of this invention, there is provided a clearance control apparatus for controlling the clearance between a rotary assembly and a casing surrounding the rotary assembly, said apparatus comprising a temperature measuring device to measure the temperature of a portion of the rotary assembly, a cooling arrangement to cool the casing, and a control system associated with the temperature measuring device and the cooling arrangement to control the extent of cooling of the casing, said extent of cooling being dependent upon the temperature of the aforesaid portion. 
     Preferably, said portion of the rotary assembly is an outer portion. 
     Thus, in the preferred embodiment, the cooling arrangement controls the extent of thermal expansion of the casing and thereby maintains a desired clearance between the casing and the rotary assembly. 
     The preferred embodiment of the clearance control apparatus is suitable for use with a rotary assembly having a rotary support member and a radially outer portion comprising a plurality of circumferentially mounted, radially outwardly extending blades, for example a turbine. 
     The preferred embodiment of the clearance control apparatus advantageously controls the clearance between the tips of the blades and the casing, which surrounds the blades. 
     The cooling arrangement may comprise a supply of a cooling medium, whereby the cooling medium is supplied to the casing to cool it. Preferably, the cooling arrangement includes a flow regulator, which advantageously regulates the supply of the cooling medium to the casing. The cooling arrangement may comprise a conduit arrangement to carry the cooling medium. Preferably the cooling medium is air. The flow regulator is conveniently mounted in the conduit arrangement to regulate the flow of the cooling medium therethrough. 
     The temperature measuring device may comprise a pyrometer. 
     The control system is preferably an electronic control system. The temperature measuring device may be arranged to provide a temperature signal to the control system, said temperature signal relating to the temperature of said outer portion of the rotary assembly. Preferably, the control system is configured to transmit a flow regulation signal to the flow regulator to regulate the flow of the cooling medium through the flow regulator. The flow regulator may comprise a valve and the control means may transmit the flow regulation signal to open or close the valve by a desired extent, to increase or reduce the flow of said fluid therethrough. 
     Preferably, the control system is programmed to calculate the extent of expansion of the radially outer portion of the rotary assembly, based on the temperature of radially outer portion. 
     Desirably, the control system is programmed to calculate the supply condition of the cooling medium. For example, the control system may calculate the supply condition of the cooling medium in terms of the temperature and pressure as a function of engine condition. 
     Preferably, the rotary assembly comprises a rotary member upon which the radially outer portion is provided. The rotary member may be a disc upon which the blades are mounted. 
     Desirably, the control system can calculate the diameter of the rotary member, said calculation being based upon engine performance parameters. The engine performance parameters may be provided for reasons not connected with the present invention, such as for engine control. 
     Preferably the control system can calculate the diameter of the casing based on the condition of the engine and the extent of cooling by the cooling medium. 
     The apparatus may include a position sensor which may be provided on the flow regulator to provide a flow regulation feedback signal to the control system, said flow regulation feedback signal relating to the condition of the flow regulator, and the extent of supply of the cooling medium, thereby enabling the control system, in the preferred embodiment, to determine more accurately the rate of flow of the cooling medium, and to adjust the flow regulator as appropriate. 
     The apparatus may include a flow sensor, which may be provided upstream or downstream of the flow regulator. The flow sensor may provide a flow rate feedback signal to the control system, whereby the control system can control the flow regulator to adjust the rate of flow of fluid therethrough, as appropriate. In the preferred embodiment, this feature provides the advantage of being able to control more accurately the rate of flow of the cooling medium. 
     The apparatus may include a temperature sensor on the casing to provide a casing temperature feedback signal to the control system to enable the control system to determine the extent of expansion of the casing, and thereby allow the control means control the flow regulator to regulate the rate of flow of the cooling medium to adjust the extent of expansion of the casing. 
     The apparatus may include a rotary member temperature sensor means to sense the temperature of the rotary member to measure the temperature of cooling air supplied to the rotary assembly. The apparatus may include a first rotary member temperature sensor upstream of the rotary assembly and second rotary member temperature sensor downstream of the rotary assembly. The, or each, rotary member temperature sensor may provide a respective feedback signal relating to the temperature of the support member, in the preferred embodiment, this feature has the advantage of allowing accurate measurement of the extent of expansion of the rotary support member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       At least one embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which; 
         FIG. 1  is a sectional side view of the upper half of a gas turbine engine; and 
         FIG. 2  is a diagrammatic sectional side view of the upper half of a turbine; and 
         FIGS. 3 to 7  are diagrammatic sectional side views of the respective different embodiments of a turbine incorporating a clearance control arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a gas turbine engine is generally indicated at  10  and comprises, in axial flow series, an air intake  11 , a propulsive fan  12 , an intermediate pressure compressor  13 , a high pressure compressor  14 , a combustor  15 , a turbine arrangement comprising a high pressure turbine  16 , an intermediate pressure turbine  17  and a low pressure turbine  18 , and an exhaust nozzle  19 . 
     The gas turbine engine  10  operates in a conventional manner so that air entering the intake  11  is accelerated by the fan  12  which produce two air flows: a first air flow into the intermediate pressure compressor  13  and a second air flow which provides propulsive thrust. The intermediate pressure compressor compresses the air flow directed into it before delivering that air to the high pressure compressor  14  where further compression takes place. 
     The compressed air exhausted from the high pressure compressor  14  is directed into the combustor  15  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low pressure turbines  16 ,  17  and  18  before being exhausted through the nozzle  19  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  16 ,  17  and  18  respectively drive the high and intermediate pressure compressors  14  and  13  and the fan  12  by suitable interconnecting shafts. 
     Referring to  FIG. 2 , there is a sectional side view of the upper half of a turbine, for example the high pressure turbine  16 . The turbine  16  comprises a rotary support disc  20  upon which is mounted a plurality of radially outwardly extending blades  22 , circumferentially around the disc  20  in  FIG. 2 . Only one of the blades  22  is shown for clarity. The turbine blades are surrounded by an annular casing  24 . A plurality of nozzle guide vanes  25  (only one of which is shown for clarity) are circumferentially arranged upstream of the turbine blades  22  to direct air from the combustor  15  onto the turbine blades  22  as shown by the arrow  27 . The casing  24  has mounted thereon an annular plenum chamber  26  extending therearound which is supplied with cooling air via a conduit arrangement  28 . The conduit arrangement  28  extends to a source of cooling air as represented by the arrow  30 , via a flow regulator  32 , which is shown in  FIG. 3 . The plenum chamber  26  and the conduit arrangement  28  form part of a clearance control arrangement, as explained below, to control the clearance between the radially outer tips of the blades  22  and the radially inner wall of the casing  24 . 
     Referring to  FIG. 3 , there is shown schematically, the high pressure turbine  16 , in which a flow regulator  32  is provided in the conduit arrangement  28  to regulate the flow of air passing therethrough. 
     Temperature measuring means in the form of a pyrometer  34  is provided upstream of the turbine  17 , and is mounted radially outwardly therefrom. The pyrometer  34  is directed towards the turbine blades  22 . 
     An electronic controller  36  is connected to the pyrometer  34  and to the flow regulator  32 , as represented by the arrows  38 ,  40  respectively. 
     In use, the rotation of a turbine  17  is effected by the combustion gases from the combustor  15 . The combustion gases are at exceedingly high temperatures which causes expansion of the turbine blades  22  and of the casing  24 . In order to ensure that a desired clearance is maintained between the tips of the turbine blades  22  and the casing  24 , the pyrometer  34  measures the temperature of the turbine blades  22 . A signal relating to the temperature of the blades  22  is passed to the controller  36  which is programmed to calculate from the temperature signal the likely extent of expansion of the turbine blades  22 . The controller then activates the flow regulator  32  so that a flow of air passes to the plenum chamber  26  to provide appropriate cooling to the casing  24  to mitigate the expansion and maintain a desired clearance  41  between the tip of the turbine blades  22  and the casing  27 . 
     In general, the measurement of the temperature of the turbine blades is carried out at various stages in the flight cycle, particularly during cruise. The pyrometer  34  provides an indication of the temperature of the turbine blades  22  as a function of the emitted infra red radiation from the turbine blades  22 . 
     The controller  36  is programmed to calculate the height of the blades  22  as a function of the relayed temperature measured by the pyrometer  34  and the turbine blade material properties. The controller  36  then calculates the supply condition for the cooling air in terms of the temperature and pressure of the air as a function of engine condition. The controller  36  also calculates the diameter of the turbine support disc as a function of the engine condition, and calculates the diameter of the casing  24 , as a function of the engine condition and the temperature and pressure of the cooling air. Thus, in effect, the controller  36  controls a supply of cooling air to the casing  24  to limit the expansion of the casing  24  and maintain a desired clearance between the tips of the turbine blades  22  and the casing  24 . 
       FIG. 4  shows a further embodiment, which comprises many of the same features as shown in  FIG. 3  and these have been designated with the same reference numerals. In  FIG. 4  a position sensor  42  is provided on the flow regulator  32  to provide a position feedback signal to the controller  36  relating to the setting of the flow regulator  32 . The connection of the position sensor  42  to the controller  36  is represented by the arrow  44 . This signal enables the controller  36  to control more accurately the setting of the flow regulator  32  and thereby the extent of supply of cooling air to the annular plenum chamber  26 . 
       FIG. 5  shows a further embodiment which also comprises many of the same features as shown in  FIG. 3 , and these have again been designated with the same reference numerals, in which a flow sensor  46  is provided downstream of the flow regulator  32  to sense the level of cooling air supplied to a plenum chamber  26 . The connection of the flow sensor  46  to the controller  36  is represented. A flow sensor feedback signal is provided to the controller  36  from the position sensor  44  to enable the controllers to regulate the level of cooling air supplied to the plenum chamber  26 . 
     In a further embodiment shown in  FIG. 6 , which also comprises many of the same features as shown in  FIG. 3 , and these have again been designated with the same reference numerals, a temperature sensing device  50  is provided in the casing  24  to sense the temperature of the casing. The connection of the temperature sensing device  50  to the controller  36  is represented by the arrow  52 . A temperature casing feedback signal is provided to the controller  36  which enables it to calculate the extent of expansion of the casing  24  based on the temperature of the casing  24  and thereby enables it to adjust the flow regulator  32  to provide a supply of cooling air accordingly. 
     In the embodiment shown in  FIG. 7 , which also comprises many of the same features as shown in  FIG. 3 , and these have again been designated the same reference numerals, the first and second temperature sensors  54 ,  56  are provided to sense the temperature of cooling air upstream and downstream respectively of the turbine rotary disc support  20  and thereby provide respective first and second disc temperature feedback signals to the controller. The connection of the first and second temperature sensors  54 ,  56  to the controller  36  is represented respectively by the arrows  58 ,  60 . This allows the controller to determine accurately the level of expansion of the turbine disc and thereby obtain a more accurate indication of the clearance between the turbine blade tip and the casing. 
     Although as shown in  FIG. 7  the first or upstream temperature sensor  54  appears to be directly in line with the pyrometer  34 , it will be appreciated that, the upstream temperature sensor  54  is, in fact, circumferentially offset from the pyrometer  34 . 
     It will be appreciated that an embodiment of the clearance control arrangements may comprise any or all of the features described with reference to  FIGS. 2 to 7 . 
     Various modifications can be made without departing from the scope of the invention.