Patent Publication Number: US-6988367-B2

Title: Gas turbine engine cooling system and method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   Commonly assigned U.S. application Ser. No. 10/249,967 filed on May 22, 2003 discloses a rotary injector that can be used to inject fuel into a gas turbine engine. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     In the accompanying drawings: 
       FIG. 1  illustrates a cross-sectional view of gas turbine engine incorporating a system for cooling the turbine rotor and the associated blades thereof; 
       FIG. 2  illustrates a isometric view of a portion of a bladed rotor and associated fragmentary sectional views thereof; 
       FIG. 3  illustrates a diagram of the relationship between fuel pressure and radial location within the bladed rotor of the gas turbine engine illustrated in  FIG. 1 ; 
       FIG. 4  illustrates a diagram of the density and state of fuel as a function of temperature and pressure; 
       FIG. 5  illustrates a cross-sectional view of a portion of a bladed rotor and an associated thermosiphon process therein; and 
       FIG. 6  illustrates a cross-sectional view of gas turbine engine incorporating another embodiment of a system for cooling the turbine rotor and the associated blades thereof. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , in a gas turbine engine  10 , fuel  12  and air  14  are combusted in a combustion chamber  16  so as to generate relatively hot, relatively high pressure exhaust gases  18 . 1  which are directed through a turbine  20  comprising a bladed rotor  22 , e.g. a rotor  24  incorporating a plurality of blades  26  on the periphery thereof. The turbine  20  is operatively coupled to a shaft assembly  28 , e.g. with a bolt  30  through an associated flange  32 , and the shaft assembly  28  is supported from the housing  34  of the gas turbine engine  10  by one or more bearings  35  that provide for rotation of the shaft assembly  28  and turbine  20  relative thereto. The action of the exhaust gases  18 . 1  against the blades  26  rotates the turbine  20  and the shaft assembly  28 , which, for example, is operatively coupled to a compressor (not illustrated) that provides for pumping the air  14  into the combustion chamber  16 . The exhaust gases  18 . 2  discharged from the turbine  20  are at a relatively lower pressure than the exhaust gases  18 . 1  upstream thereof as a result of the work done by the exhaust gases  18 . 1  on the turbine  20 . 
   Under some conditions, for example, when operated as a turbo-jet engine to propel a high-speed aircraft at high Mach numbers, the air  14  supplied to the gas turbine engine  10  is relatively hot, which contributes to increased temperature of the exhaust gases  18 . 1 , and which is not sufficiently cool to otherwise provide for adequately cooling the turbine  20 , so that the temperature of the associated blades  26  can become excessive. Under these conditions, the fuel  12  is generally sufficiently cool to provide sufficient cooling capacity to cool the gas turbine engine  10 , and particularly, to cool the turbine  20  thereof, which might otherwise be susceptible to thermally induced failure, whereby the gas turbine engine  10  is cooled by directing fuel  12  from a source of fuel  36  through the rotor  24  and blades  26  of the turbine  20  to cool the rotor  24  and the blades  26  of the turbine  20 , and then combusting this fuel  12 —heated by the cooling process—in the combustion chamber  16 . 
   For example, fuel  12  from a source of fuel  36  comprising a fuel tank and an associated fuel pump is supplied through a first control valve  37  to an orifice  38  that is relatively fixed with respect to the housing  34  of the gas turbine engine  10 . The fuel  12  is discharged from the orifice  38  into an inlet  40  of a first rotary fluid trap  42  operatively coupled to the rotor  24  so as to rotate therewith. The outlet  44  of the first rotary fluid trap  42  is in fluid communication with a first portion  46 . 1  of a first cavity  46  that is bounded by a portion of a first side  48  of the rotor  24  and by a first bounding surface of an aft cover  50  of which the first rotary fluid trap  42  is a part. 
   The first rotary fluid trap  42  comprises a passage  52  that provides for fluid communication between the inlet  40  and the outlet  44 , wherein, in accordance with the teachings of U.S. Pat. Nos. 4,870,825 and 6,269,647, and of U.S. application Ser. No. 10/249,967, each of which is incorporated herein by reference, the passage  52  is adapted so the when the first rotary fluid trap  42  is rotated, a centrifugal acceleration at any point within the passage  52  is greater than a centrifugal acceleration at any point on either the inlet  40  or the outlet  44 . Accordingly, when the rotating passage  52  is filled with a relatively high density medium, such as liquid fuel  12 . 1 , the radial levels of the inlet  40  and outlet  44  will be equal when there is no pressure differential therebetween, and will be otherwise unequal by an amount dependent upon the magnitude of the pressure differential and the speed of rotation. For a relatively low pressure supply of liquid fuel  12 . 1  to an inlet  40  of a passage  52  feeding a relatively high pressure region at the outlet  44 , the passage  52  can prevent backflow therethrough. Accordingly, the first rotary fluid trap  42  provides for isolating the pressure in the first cavity  46 —which can be relatively high—from the pressure at the inlet  40  of the passage  52 —which is relatively lower—thereby providing for supplying fuel  12  to the inlet  40  of the first rotary fluid trap  42  across a rotary junction  54  between the rotating inlet  40  and the relatively fixed orifice  38 , whereby liquid fuel  12 . 1  sprayed from the relatively fixed orifice  38  becomes captured by an internal trough  56  associated with the inlet  40  of the first rotary fluid trap  42  as a result of centrifugal acceleration acting upon the liquid fuel  12 . 1  upon striking the internal trough  56  and rotating therewith. 
   The aft cover  50  comprises an intermediate rim  58  and an outer rim  60  that engage respective first  62 . 1  and second  62 . 2  lips formed on the first side  48  of the rotor  24 . The outer rim  60  is sealed to the second lip  62 . 2  so as to prevent leakage of fuel  12  from the joint therebetween. The intermediate rim  58  incorporates at least one passage  64  that provides for fluid communication between first  46 . 1  and second  46 . 2  portions of the first cavity  46 . The second portion  46 . 2  of the first cavity  46  is in fluid communication with a plurality of first passages  66  that extend through the rotor  24 . Referring also to  FIG. 2 , each first passage  66  has a first opening  68  on the first side  48  of the rotor  24 , and a second opening  70  on a second side  72  of the rotor  24 , the first  48  and second  72  sides being opposite to one another. 
   The first passages  66  are in fluid communication with a second portion  74 . 2  of a second cavity  74  that is bounded by a portion of the second side  72  of the rotor  24  and by a second bounding surface of a forward cover  76 , wherein the forward cover  76  comprises an intermediate rim  78  and an outer rim  80  that engage respective first  82 . 1  and second  82 . 2  lips formed on the second side  72  of the rotor  24 . The outer rim  80  is sealed to the second lip  82 . 2  so as to prevent leakage of fuel  12  from the joint therebetween. The intermediate rim  78  incorporates at least one passage  84  that provides for fluid communication between the second portion  74 . 2  of the second cavity  74  and a first portion  74 . 1  thereof. The first portion  74 . 1  of the second cavity  74  is in fluid communication with the interior  86  of a shaft  88  of the shaft assembly  28  via at least one passage  90  through the shaft  88 , and the interior  86  of the shaft  88  is in fluid communication with a first discharge orifice  92  through at least one other passage  94  through the shaft  88 . The first discharge orifice  92  is in fluid communication with the combustion chamber  16 , and thereby provides for a discharge of fuel  12  directly from the rotating shaft  88  to the combustion chamber  16 . The first discharge orifice  92  is, for example, a part of a second rotary fluid trap  96  that provides for isolating the relatively high pressure of the combustion chamber  16  from the relatively lower pressure of the interior of the shaft  88  and the first portion  74 . 1  of the second cavity  74 , whereby the principles of structure and operation of the second rotary fluid trap  96  are the same as those of the first rotary fluid trap  42  described hereinabove. 
   Referring to  FIGS. 2 and 5 , the first passages  66  and associated first  68  and second  70  openings are substantially uniform in size and shape, and uniformly distributed so as to provide a mechanically balanced rotor  24 . The axial shape  98  of the first passages  66  is adapted to at least partially conform to a profile of the associated blades  26 . For example, in the embodiment illustrated in  FIG. 2 , the first passages  66  have chevron axial shape  98 . 1  so as to at least partially conform to the camber of the blades  26 . A first set  66 . 1  of first passages  66  extend through the rotor  24  at associated circumferential locations that are substantially between the associated circumferential locations of the associated blades  26 , and a second set  66 . 2  of first passages  66  extend through the rotor  24  at associated circumferential locations that are substantially aligned with the associated circumferential locations of the associated blades  26 , whereby the first  66 . 1  and second  66 . 2  sets of first passages  66  are interleaved with respect to one another. Each of the blades  26  incorporates a plurality of second passages  100  that extend substantially radially therewithin, each of which at a first end  102  thereof intersects an associated first passage  66  of the second set  66 . 2  that is aligned therewith. For example, the second passages  100  are substantially linear along the length thereof. As illustrated in  FIG. 2 , the diameter of the second passages  100  within a particular blade  26  can be adapted in accordance with the associated blade thickness proximate thereto, so as to provide sufficient heat transfer between the outer surface  104  of the blade  26  and the surface  106  of the associated second passage  100  while providing for adequate blade strength. The distal second ends  108  of the second passages  100  are terminated in a third cavity  110  proximate to a tip  112  of the blade  26 , wherein the third cavity  110  provides for fluid communication amongst the second passages  100  within the associated blade  26 . For example, the third cavity  110  is formed by a end cap  114  that is separated from the second ends  108  of the second passages  100 , and which is secured at its periphery to the edge  116  of the blade  26 . The blades  26  are closed with respect to the combustion chamber  16  relative to the fuel  12  within the blades  26 , so that all of the fuel  12  enters the combustion chamber  12  at a location that is radially inward of the blades  26 . 
   Accordingly, the gas turbine engine  10  comprises a rotatable portion  118  that is rotatable with respect to a housing  34  of the gas turbine engine  10 , wherein the rotatable portion  118  comprises the turbine  20 /bladed rotor  22 , comprising the rotor  24  and the blades  26 ; the aft cover  50  and associated first rotary fluid trap  42 ; the forward cover  76 ; and the shaft assembly  28 /shaft  88  and associated first discharge orifice  92 /second rotary fluid trap  96 , all of which rotate in unison with a rotating frame of reference. After discharge from the relatively fixed orifice  38 , the fuel  12  is contained within the rotatable portion  118  until discharge directly into the combustion chamber  16  from the first discharge orifice  92  of the rotatable portion  118  in the rotating frame of reference Accordingly, because all of the elements of the rotatable portion  118  rotate in unison with the rotating frame of reference, these elements can be readily sealed to one another as necessary to contain the fuel  12  therein, for example, at the junctions of the outer rims  60 ,  80  of the first  50  and second  76  bounding surfaces with the second lips  62 . 2 ,  82 . 2  of the rotor  24 , which could otherwise be problematic if it were necessary to provide for sealing across a relatively moving junction of elements to be sealed to one another. 
   With the gas turbine engine  10  in operation, liquid fuel  12 . 1  provided by the source of fuel  36  and regulated by the first control valve  37  is discharged from the relatively fixed orifice  38  into the internal trough  56  of the inlet  40  of the first rotary fluid trap  42 . The discharged liquid fuel  12 . 1  is captured by the internal trough  56  as a result of the centrifugal acceleration acting upon the discharged liquid fuel  12 . 1  which commences rotation with the rotatable portion  118  upon impact with the internal trough  56  or the liquid fuel  12 . 1  contained therein. Liquid fuel  12 . 1  entering the inlet  40  of the first rotary fluid trap  42  is pumped through the associated passage  52  of the first rotary fluid trap  42  by the action of centrifugal acceleration forces acting upon the liquid fuel  12 . 1  contained within the first rotary fluid trap  42 , and this action of centrifugal acceleration forces also isolates the relatively low pressure at the inlet  40  of the first rotary fluid trap  42  from a relatively high pressure at the outlet  44  thereof. Upon exiting the outlet  44  of the first rotary fluid trap  42 , the fuel  12  is accelerated radially outwards, whereby liquid fuel  12 . 1 —which is relatively dense in comparison with associated fuel vapor—tends to follow the inside of the aft cover  50 . 
   During normal operation of the gas turbine engine  10 , the hottest portion of the turbine  20 /bladed rotor  22  are the blades  26  which are directly exposed to the relatively hot exhaust gases  18 . 1  from the combustion chamber  16 . Heat from the blades  26  is transferred to the rotor  24  and associated first  50  and second  76  bounding surfaces, which provides for heating any fuel  12  in the associated first  46  and second  74  cavities that are adjacent to the first  48  and second  72  sides of the rotor  24 . Accordingly, the temperature of the rotor  24  and adjacent aft cover  50  increases with decreasing distance from the blades  26 , so that fuel  12  within the first cavity  46  is heated as it flows radially outwards. Furthermore, referring to  FIG. 3 , the centrifugal acceleration acting upon the fuel  12  increases with increasing radial distance within the first cavity  46 , which increases the associated pressure thereof. Fuel  12  in the first  46  or second  74  cavities is rotated by viscous forces generated as a result of relative motion of the rotor  24  and aft cover  50  acting with respect to the liquid or vapors in the associated first  46  or second  74  cavities, whereas fuel  12  in the first  66  or second  100  passages is forced to rotate with the rotor  24  and blades  26 . Accordingly, as illustrated in  FIG. 3 , in the former region of viscous rotation, the fuel pressure increases at a lower rate with respect to radial distance than in the latter forced region because of slippage within the flow stream than can occur in the former region but not in the latter. Referring to  FIG. 4 , as the fuel  12  is heated in the first portion  46 . 1  of the first cavity  46 , the fuel  12  is transformed from a saturated liquid to a saturated vapor, as indicated by the locus of points labeled “A”, which is also shown in  FIG. 1 . As the fuel  12  flows from the first  46 . 1  to the second portion  46 . 1  of the first cavity  46 , the fuel  12  becomes superheated, and may exhibit a mixture of states as indicated by the points labeled “B” and “C” in  FIGS. 1 and 4 . 
   As the fuel  12  flows through the first opening  68  into the first passage  66 , it becomes further heated and pressurized. Fuel  12  in the first set  66 . 1  of first passages  66  flows therethrough, out of the second openings  70  thereof, and then into the second portion  74 . 2  of the second cavity  74 , and in the process, provides for cooling the rim  120  of the rotor  24  in the regions between the blades  26 . Referring to  FIG. 5 , the centrifugal acceleration field causes relatively dense fuel  12  in the second set  66 . 2  of first passages  66  to flow into the second passages  100  intersecting therewith, which displaces fuel  12  therein that has become relatively more heated and less dense, responsive to a thermosiphon process that is driven by the centrifugal acceleration field and by the decrease in density as fuel  12  becomes heated as a result of heat transfer from the blades  26  which cools the blades  26 . The thermosiphon flow  122  within the second passages  100  and between the first  66  and second  100  passages causes a continuous exchange of relatively cooler fuel  12 . 2  for relatively hotter fuel  12 . 3 , which is also illustrated by the points “D”, “E” and “F” in  FIGS. 4 and 5 . The relatively hotter fuel  12 . 3  ultimately flows through the second opening  70  of the second set  66 . 2  of first passages  66  and into the second portion  74 . 2  of the second cavity. The second set  66 . 2  of first passages  66  provides for the flow of fuel  12  either directly therethrough from the first opening  68  to the second opening  70  along a first flow path  124 , which provides for cooling the rotor  24  at the base of the associated blade  26 ; or indirectly after first flowing along a second flow path  126  which includes one or more second passages  100  responsive to a thermosiphon process, which provides for cooling the associated blade  26  of the turbine  20 . 
   The relatively less dense heated fuel  12 . 3  in the second portion  74 . 1  of the second cavity  74  flows through the passage  84  into the first portion  74 . 1  of the second cavity  74  after being displaced by relatively more dense less heated fuel  12  from the first passages  66 . As the fuel flows radially inwards in the second cavity  74 , the pressure thereof is reduced, and the fuel  12  is cooled by exchange of heat with the relatively cooler surroundings, transforming from a superheated vapor to a saturated vapor then a saturated liquid, as indicated by the locus of points labeled “G” on  FIG. 4  corresponding to the location similarly labeled in  FIG. 1 . The fuel  12  then flows through the passage  90  through the shaft  88 , through the interior  86  of the shaft  88 , out of a second passage through the shaft  88  and into the combustion chamber  16  through the first discharge orifice  92  which is part of a second rotary fluid trap  96 . 
   The above-described system and method of cooling the turbine  20 —wherein fuel  12  is delivered by a first fuel distribution circuit  128  from the source of fuel  36  through the first control valve  37  to the rotor  24  and blades  26 —is beneficially used when the turbine  20  is at a temperature that is sufficient to vaporize the fuel  12  so as to mitigate against interfering with the mechanical balance of the turbine  20 . In accordance with another aspect, it is beneficial to utilize a second fuel distribution circuit  130  that provides for injecting fuel directly into the combustion chamber  16  without involving flow through the rotor  24  and blades  26 . Referring to  FIG. 1 , liquid fuel  12 . 1  supplied from the source of fuel  36  is regulated by a second control valve  132  and delivered to a second discharge orifice  134 , for example, a part of a third rotary fluid trap  136 , for example, operatively coupled to the shaft  88 , wherein fuel  12  is supplied from the second control valve  132  through a separate passage  138  in the interior of the shaft  88 . For example, the first  37  and second  130  control valves would be controlled so that all of the fuel  12  to the gas turbine engine  10  is delivered by the second fuel distribution circuit  130  during startup and warm-up conditions. After the gas turbine engine  10  has warmed up, in one embodiment, the second fuel distribution circuit  130  provides for a sufficient amount of fuel  12  to maintain an idle operating condition, and the remaining fuel  12  is provided by the first control valve  38  via the first fuel distribution circuit  128  responsive to operationally dependent demand. In another embodiment, all of the fuel  12  might be delivered by the first fuel distribution circuit  128  after the gas turbine engine  10  has warmed up. In yet another embodiment, some other relative distribution of fuel  12  between the first  128  and second  130  fuel distribution circuits is used. 
   Referring to  FIG. 6 , in accordance with another embodiment, the first discharge orifice  92  and associated second rotary fluid trap  96  are incorporated in the forward cover  76 , so as to provide for injection of fuel  12  directly into the combustion chamber  16  therefrom, without involving the shaft  88  as an associated flow path. 
   In addition to providing for cooling the blades  26  and rotor  24  of the turbine  20 , the first fuel distribution circuit  128  also provides for a regenerative recovery of heat from the exhaust  18 . 1  so as to provide for improved operating efficiency, particularly for stationary applications. 
   While specific embodiments have been described in detail in the foregoing detailed description and illustrated in the accompanying drawings, those with ordinary skill in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.