Patent Publication Number: US-2010126960-A1

Title: Serpentine Microcircuit Vortex Turbulators for Blade Cooling

Description:
BACKGROUND 
     (1) Field of the Invention 
     The present invention relates to a cooling microcircuit for use in turbine engine components, such as turbine blades, that has a plurality of vortex generators within the legs through which a cooling fluid flows to improve cooling effectiveness. 
     (2) Prior Art 
     A typical gas turbine engine arrangement includes at plurality of high pressure turbine blades. In general, cooling flow passes through these blades by means of internal cooling channels that are turbulated with trip strips for enhancing heat transfer inside the blade. The cooling effectiveness of these blades is around 0.50 with a convective efficiency of around 0.40. It should be noted that cooling effectiveness is a dimensionless ratio of metal temperature ranging from zero to unity as the minimum and maximum values. The convective efficiency is also a dimensionless ratio and denotes the ability for heat pick-up by the coolant, with zero and unity denoting no heat pick-up and maximum heat pick-up respectively. The higher these two dimensionless parameters become, the lower the parasitic coolant flow required to cool the high-pressure blade. In other words, if the relative gas peak temperature increases from 2500 degrees Fahrenheit to 2850 degrees Fahrenheit, the blade cooling flow should not increase and if possible, even decrease for turbine efficiency improvements. That objective is extremely difficult to achieve with current cooling technology. In general, for such an increase in gas temperature, the cooling flow would have to increase more than 5% of the engine core flow. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention relates to a turbine engine component, such as a turbine blade, which has one or more vortex generators within the cooling microcircuits used to cool the component. 
     In accordance with the present invention, a cooling microcircuit for use in a turbine engine component is provided. The cooling microcircuit broadly comprises at least one leg through which a cooling fluid flows and a plurality of cast vortex generators positioned within the at least one leg. 
     Further in accordance with the present invention, there is provided a process for forming a refractory metal core for use in forming a cooling microcircuit having vortex generators. The process broadly comprises the steps of providing a refractory metal core material and forming a refractory metal core having a plurality of indentations in the form of the vortex generators. 
     Other details of the serpentine microcircuits vortex turbulators for blade cooling 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  illustrates a turbine engine component having cooling microcircuits in the pressure and suction side walls; 
         FIG. 2  is a schematic representation of a cooling microcircuit for the suction side of the turbine engine component; 
         FIG. 3  is a schematic representation of a cooling microcircuit for the pressure side of the turbine engine component; 
         FIG. 4A  illustrates a wedge shaped continuous rib type of vortex generator; 
         FIG. 4B  illustrates a series of wedge shaped broken rib vortex generators; 
         FIG. 4C  illustrates a delta-shaped backward aligned rib configuration of vortex generators; 
         FIG. 4D  illustrates a series of wedge shaped backward offset rib vortex generators; 
         FIGS. 5-7  illustrate a process for forming a refractory metal core; and 
         FIG. 8  illustrates a plurality of vortex generators in a cooling microcircuit passage. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring now to the drawings,  FIGS. 1-3  illustrate a serpentine microcircuit cooling arrangement for a turbine engine component, such as a turbine blade. Referring now to the drawings, a turbine engine component  90 , such as a high pressure turbine blade, may be cooled using the cooling design scheme shown in  FIGS. 1-3 . The cooling design scheme, as shown in  FIG. 1 , encompasses two serpentine microcircuits  100  and  102  located peripherally in the airfoil walls  104  and  106  respectively for cooling the main body  108  of the airfoil portion  110  of the turbine engine component. Separate cooling microcircuits  96  and  98  may be used to cool the leading and trailing edges  112  and  114  respectively of the airfoil main body  108 . One of the benefits of the approach of the present invention is that the coolant inside the turbine engine component may be used to feed the leading and trailing edge regions  112  and  114 . This is preferably done by isolating the microcircuits  96  and  98  from the external thermal load from either the suction side  116  or the pressure side  118  of the airfoil portion  110 . In this way, both impingement jets before the leading and trailing edges become very effective. In the leading and trailing edge cooling microcircuits  96  and  98  respectively, the coolant may be ejected out of the turbine engine component by means of film cooling. 
     Referring now to  FIG. 2 , there is shown a serpentine cooling microcircuit  102  that may be used on the suction side  118  of the turbine engine component. As can be seen from this figure, the microcircuit  102  has a fluid inlet  126  for supplying cooling fluid to a first leg  128 . The inlet  126  receives the cooling fluid from one of the feed cavities  142  in the turbine engine component. Fluid flowing through the first leg  128  travels to an intermediate leg  130  and from there to an outlet leg  132 . Fluid supplied by one of the feed cavities  142  may also be introduced into the cooling microcircuit  96  and used to cool the leading edge  112  of the airfoil portion  110 . The cooling circuit  102  may include fluid passageway  131  having fluid outlets  133 . Still further, as can be seen, the thermal load to the turbine engine component may not require film cooling from each of the legs that form the serpentine peripheral cooling microcircuit  102 . In such an event, the flow of cooling fluid may be allowed to exit from the outlet leg  132  at the tip  134  by means of film blowing from the pressure side  116  to the suction side  118  of the turbine engine component. As shown in  FIG. 2 , the outlet leg  132  may communicate with a passageway  136  in the tip  134  having fluid outlets  138 . 
     Referring now to  FIG. 3 , there is shown the serpentine cooling microcircuit  100  for the pressure side  116  of the airfoil portion  110 . As can be seen from this figure, the microcircuit  100  has an inlet  141  which communicates with one of the feed cavities  142  and a first leg  144  which receives cooling fluid from the inlet  141 . The cooling fluid in the first leg  144  flows through the intermediate leg  146  and through the outlet leg  148 . As can be seen, from this figure, fluid from the feed cavity  142  may also be supplied to the trailing edge cooling microcircuit  98 . The cooling microcircuit  98  may have a plurality of fluid passageways  150  which have outlets  152  for distributing cooling fluid over the trailing edge  114  of the airfoil portion  110 . The outlet leg  148  may have one or more fluid outlets  153  for supplying a film of cooling fluid over the pressure side  116  of the airfoil portion  110  in the region of the trailing edge  114 . 
     It is desirable to increase the convective efficiency of the cooling microcircuits  100  and  102  within the turbine engine component  90  so as to increase the corresponding overall blade effectiveness. To accomplish this increase in convective efficiency, internal features  180  may be placed inside the cooling passages. The existence of the features  180  enable the air inside the cooling microcircuits  100  and  102  to pick-up more heat from the walls of the turbine engine component  90  by increasing the turbulence inside the passages of the cooling microcircuits  100  and  102 . 
       FIGS. 4A-4D  illustrate a series of vortex generator features  180  which could be placed in the legs  128 ,  130 ,  132 ,  144 ,  146 , and  148  of the cooling microcircuits  100  and  102  within the turbine engine component  90 .  FIG. 4A  illustrates a wedge shaped continuous rib type of vortex generator.  FIG. 4B  illustrates a series of wedge shaped broken rib vortex generators.  FIG. 4C  illustrates a delta-shaped backward aligned rib configuration of vortex generators.  FIG. 4D  illustrates a series of wedge shaped backward offset rib vortex generators. As the cooling flow F flowing in the respective legs  128 ,  130 ,  132 ,  144 ,  146 , and/or  148  passes over these features, a series of vortices are generated. 
     If the legs  128 ,  130 ,  132 ,  144 ,  146 , and  148  of the serpentine cooling microcircuits  100  and  102  are formed using refractory metal cores, a machining operation can be done to place these vortex generators in the core.  FIGS. 5-7  illustrate a photo-lithography method of forming these features onto a refractory metal core material  200 . The machining process may be done through a chemical etching process. Sufficient material may be taken out of the refractory metal core  200  to form the desired vortex generators/turbulators  180 . During an investment casting process, these machined indentations are filled with superalloy material to form the vortex generators  180  within the legs of the cooling microcircuits. The overall process is referred to as a photo-etch process prior to investment casting. The process consists of using the refractory metal core as the core material in an investment casting technique to form the cooling passages with vortex generators in the blade cooling passage. The photo-etch process consists of two sub-processes: (1) the preparation of mask material through the process of photo-lithography; and (2) a subsequent process of chemically attacking the refractory metal core material by etching away as small surface indentions. 
     As shown in  FIG. 5 , a layer of polymer film mask material  202  is placed over the refractory metal core  200  and is subjected to UV light  204 . The ultraviolet light  204  is programmed to impinge onto the polymer film mask material  202  for curing purposes. As certain designated parts of the polymer film mask material  202  are cured by light, the other surface areas of the polymer film mask material  202  are not affected by the light. 
     Referring now to  FIG. 6 , non-cured polymer film material is chemically removed from the area  210 , while the cured polymer film material  202  is maintained so as to form a mask. 
     Referring now to  FIG. 7 , areas of the refractory metal core material  200  not protected by the mask are attacked by an etching chemical solution through acid dip or spray. The etching process leaves an indentation  212  in the refractory metal core  200  to form a turbulator, such as a trip strip or a vortex generator. 
     Alternatively, a laser beam can be used to outline the vortex generators in the refractory metal core material  200  with beams that penetrate the refractory metal core substrate  200  to form the desired features shown in  FIGS. 4A-4D . 
       FIG. 8  illustrates how the photo-etch process leads to the legs  128 ,  130 ,  132 ,  144 ,  146 , and  148  in the turbine engine component  90  after the casting process. In general, in an investment casting process, a wax pattern leads to the solidification of the superalloy, and the refractory metal core  200 , as the core material, leads to the open spaces for the legs of the cooling microcircuits. The refractory metal core  200  is eventually removed through a leaching process. When alloy solidification takes place, the series of vortex generators  180  are placed on the walls of the legs  128 ,  130 ,  132 ,  144 ,  146 , and/or  148  as shown in  FIG. 8 . 
     Extending the principle of creating turbulence, several vortex configurations can be designed to create areas of high heat transfer enhancements everywhere in a cooling passage. In terms of the design shown in  FIGS. 1-3 , both the pressure side and the suction side peripheral serpentine cooling microcircuits may not include film cooling with the exception of the last leg/passage of the serpentine arrangement for the pressure side circuit and for the tip of the suction side serpentine arrangement. Therefore, film cooling may not protect upstream sections of the serpentine cooling design. This is particularly important from a performance standpoint which allows for no mixing of the coolant from film with external hot gases. Since the cooling circuits  100  and  102  are embedded in the walls, their cross sectional area is small and internal features, such as the vortex generators  180  shown in  FIGS. 4A-4D , are needed to increase the convective efficiency of the circuits  100  and  102 , leading to an overall cooling effectiveness for the turbine engine component  90 . Naturally, the cooling flow may be reduced from typical values of 5% core engine flow to about 3.5%. 
     It is apparent that there has been provided in accordance with the present invention serpentine microcircuits vortex turbulators for blade cooling 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 unforeseeable 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.