Patent Publication Number: US-7581927-B2

Title: Serpentine microcircuit cooling with pressure side features

Description:
BACKGROUND 
   (1) Field of the Invention 
   The present invention relates to a turbine engine component having an airfoil portion with a serpentine cooling microcircuit embedded in the pressure side, which serpentine cooling microcircuit is provided with a way to increase coolant pressure and a way to accelerate local cooling flow and increase the ability to pick-up heat. 
   (2) Prior Art 
   The overall cooling effectiveness is a measure used to determine the cooling characteristics of a particular design. The ideal non-achievable goal is unity, which implies that the metal temperature is the same as the coolant temperature inside an airfoil. The opposite can also occur when the cooling effectiveness is zero implying that the metal temperature is the same as the gas temperature. In that case, the blade material will certainly melt and burn away. In general, existing cooling technology allows the cooling effectiveness to be between 0.5 and 0.6. More advanced technology such as supercooling should be between 0.6 and 0.7. Microcircuit cooling as the most advanced cooling technology in existence today can be made to produce cooling effectiveness higher than 0.7. 
     FIG. 1  shows a durability map of cooling effectiveness (x-axis) vs. the film effectiveness (y-axis) for different lines of convective efficiency. Placed in the map is a point  10  related to a new advanced serpentine microcircuit shown in  FIGS. 2   a - 2   c . This serpentine microcircuit includes a pressure side serpentine circuit  20  and a suction side serpentine circuit  22  embedded in the airfoil walls  24  and  26 . 
   The Table I below provides the operational parameters used to plot the design point in the durability map. 
   
     
       
         
             
           
             
               TABLE I 
             
             
                 
             
             
               Operational Parameters for 
             
             
               serpentine microcircuit 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
             
          
             
                 
               Beta 
               2.898 
             
             
                 
               Tg 
               2581 [F] 
             
             
                 
               Tc 
               1365 [F] 
             
             
                 
               Tm 
               2050 [F] 
             
             
                 
               Tm_bulk 
               1709 [F] 
             
             
                 
               Phi_loc 
               0.437 
             
             
                 
               Phi_bulk 
               0.717 
             
             
                 
               Tco 
               1640 [F] 
             
             
                 
               Tci 
               1090 [F] 
             
             
                 
               eta_c_loc 
               0.573 
             
             
                 
               eta_f 
               0.296 
             
             
                 
               Total Cooling 
               3.503% 
             
             
                 
               Flow 
               10.8 
             
             
                 
               WAE 
             
             
                 
                 
             
             
                 
               Legend for Table I 
             
             
                 
               Beta = heat load 
             
             
                 
               Phi_loc = local cooling effectiveness 
             
             
                 
               Phi_bulk = bulk cooling effectiveness 
             
             
                 
               Eta_c_loc = local cooling efficiency 
             
             
                 
               Eta_f = film effectiveness 
             
             
                 
               Tg = gas temperature 
             
             
                 
               Tc = coolant temperature 
             
             
                 
               Tm = metal temperature 
             
             
                 
               Tm_bulk = bulk metal temperature 
             
             
                 
               Tco = exit coolant temperature 
             
             
                 
               Tci = inlet coolant temperature 
             
             
                 
               WAE = compressor engine flow, pps 
             
          
         
       
     
   
   It should be noted that the overall cooling effectiveness from the table is 0.717 for a film effectiveness of 0.296 and a convective efficiency (or ability to pick-up heat) of 0.573. Also note that the corresponding cooling flow for a turbine blade having this cooling microcircuit is 3.5% engine flow.  FIG. 3  illustrates the cooling flow distribution for a turbine blade with the serpentine microcircuits of  FIGS. 2   a - 2   c  embedded in the airfoils walls. 
   It should be noted from  FIG. 3  that the flow passing through the pressure side serpentine microcircuit  20  is 1.165% WAE (compressor engine flow) in comparison with 0.428 WAE for the suction side serpentine microcircuit  22 . This represents a 2.7 fold increase in cooling flow relative to the suction side microcircuit. The reason for this increase stems from the fact that the thermal load to the part is considerably higher for the airfoil pressure side. As a result, the height of the microcircuit channel should be 1.8 fold increase over that of the suction side. That is 0.022 inches vs. 0.012 inches. Besides the increased flow requirement, the driving potential in terms of source to sink pressures for the pressure side circuit  20  is not as high as that for the suction side circuit  22 . In considering the coolant pressure on the pressure side circuit  20 , at the end of the third or outlet leg, the back flow margin, as a measure of internal to external pressure, is low. As a consequence of this back flow issue, the metal temperature increases beyond the required metal temperature close to the third leg of the pressure side circuit  20 . It is desirable to eliminate this problem. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, there is provided two solutions. The first is to include communication holes between the internal cavity and the microcircuit third leg so as to have an increased source of local pressure. It should be noted that the flow inside the inner cavity is high compared to that on the microcircuit legs with many loss mechanisms. The second is to include a set of features which are used to locally accelerate the flow and increase the ability for heat pick-up in the third leg of the pressure side circuit. 
   In accordance with the present invention, there is provided a turbine engine component having an airfoil portion with a pressure side and a suction side, a first microcircuit embedded in a wall forming the pressure side, an internal cavity containing a supply of cooling fluid, the first microcircuit having an inlet leg, an intermediate leg, and an outlet leg, and means for locally increasing pressure within the outlet leg. The means for locally increasing pressure within the outlet leg preferably comprises a plurality of communication holes between the internal cavity and the outlet leg. 
   Further, in accordance with the present invention, there is provided a turbine engine component having an airfoil portion with a pressure side and a suction side, a first microcircuit embedded in a wall forming the pressure side, said first microcircuit having an inlet leg, an intermediate leg, and an outlet leg, and means in the outlet leg for locally accelerating cooling flow in the outlet leg and for increasing heat pick-up ability. 
   Other details of the serpentine microcircuit cooling with pressure side features of the present invention, as well as other objects and advantages attendant thereto are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a graph showing cooling effectiveness versus film effectiveness for a turbine engine component; 
       FIG. 2A  shows an airfoil portion of a turbine engine component having a pressure side cooling microcircuit embedded in the pressure side wall and a suction side cooling microcircuit embedded in the suction side wall; 
       FIG. 2B  is a schematic representation of a pressure side cooling microcircuit used in the airfoil portion of  FIG. 2A ; 
       FIG. 2C  is a schematic representation of a suction side cooling microcircuit used in the airfoil portion of  FIG. 2A ; 
       FIG. 3  illustrates the cooling flow distribution for a turbine engine component with serpentine microcircuits embedded in the airfoil walls; 
       FIG. 4A  is a schematic representation of a suction side circuit used in a turbine engine component in accordance with the present invention; 
       FIG. 4B  is a schematic representation of a pressure side circuit used in a turbine engine component in accordance with the present invention. 
       FIG. 5  illustrates a turbine engine component having embedded pressure side and suction side cooling microcircuits; and 
       FIG. 6  illustrates a trip strip arrangement which can be used in a pressure side circuit; 
       FIG. 7  illustrates a side view of the trip strip arrangement of  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
   Referring now to  FIG. 5 , there is shown an airfoil portion  30  of a turbine engine component. The turbine engine component may comprise a turbine blade or any other component having an airfoil portion. 
   The airfoil portion  30  has a pressure side  32  formed by a pressure side wall  34  and a suction side  36  formed by a suction side wall  38 . The airfoil portion  30  further has a plurality of internal cavities  40  through which a cooling fluid flows. Embedded in the pressure side wall  34  is a serpentine cooling microcircuit  42 . Embedded in the suction side wall  38  is a serpentine cooling microcircuit  44 . 
   Referring now to  FIG. 4A , there is shown a schematic representation of the serpentine cooling microcircuit  44 . The serpentine cooling microcircuit  44  includes an inlet  46  which communicates with one of the internal cavities  40 . The microcircuit  44  further includes an inlet leg  48 , an intermediate leg  50 , and outlet leg  52 . The outlet leg  52  has a first portion  54  with a plurality of film cooling holes  56  for allowing cooling fluid to flow over a tip portion  57  of the airfoil portion  30 . The outlet leg also has a second portion  58  with at least one film cooling hole  60  for allowing cooling fluid to flow over the tip portion  57 . A U-shaped portion  62  is provided as part of the cooling microcircuit  44 . Within the space defined by the U-shaped portion  62 , there is located an outlet nozzle of the pressure side cooling microcircuit  42 . 
   Referring now to  FIG. 4B , there is shown a pressure side cooling microcircuit  42 . The pressure side cooling microcircuit  42  also has an inlet  70  which communicates with one of the internal cavities. The inlet  70  supplies cooling fluid to the inlet leg  72 . Cooling fluid flows through the inlet leg  72  to the intermediate leg  74  and eventually to the outlet leg  76 . The outlet leg  76  has at least one outlet cooling hole  77 . 
   In accordance with a preferred embodiment of the present invention, a plurality of communication holes  78  are provided in the outlet leg  76 . The communication holes  78  are spaced apart in a direction of flow of the cooling fluid within the outlet leg  76 . The communication holes  78  allow cooling fluid to flow from one of the internal cavities  40  into the outlet leg  76 . The communication holes  78  provide an increased source of pressure locally. 
   Further in accordance with a preferred embodiment of the present invention, the outlet leg  76  is also provided with a plurality of features  80  which are used to locally accelerate the cooling fluid flow and increase the ability for heat-pick up in the outlet leg  76 . Referring now to  FIGS. 6 and 7 , each of the features  80  preferably comprises a series of round trip strips  82  placed on top of each other. Each of the trip strips  82  are preferably connected to a hot wall  84  of the pressure side. The trip strips  82  may be cast trip strips. Alternatively, the trip strips  82  may be trip strips which are bonded to the wall  84  using any suitable bonding technique known in the art. 
   The trip strips  82  provide a number of advantages. First the approach flow  90  of cooling fluid is split into two major branches. The first branch is a top flow  92  and the second branch is the bottom flow  94 . As the flow is split, the top flow branch  92  picks up heat by transport over the series of features through turbulation and through the thermal conduction efficiency of the pin fins  96  protruding in the main flow field. As the flow is split, the bottom flow branch  94  enters the mini-crevices  98  underneath the trip strips  82 , thus accelerating the flow locally and transporting heat into the main stream. In this way, the re-supply or communication holes  78  provide a way to increase the coolant pressure and the sets of features  80  provide ways to accelerate the flow locally and increase the ability to pick-up heat, thus increasing the internal convective efficiency. The combined effect substantially eliminates the low back flow margin and overtemperature problems in the aft pressure side portion of the airfoil portion  30 . 
   As can be seen from the foregoing description, there has been provided in accordance with the present invention a serpentine microcircuit cooling with pressure side features which fully satisfies the objects, means, and advantages set forth hereinbefore. While the present invention has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.