Abstract:
A gas turbine engine component has a cooling scheme that utilizes an impingement tube to cool the suction wall and the pressure wall of a mid portion of an airfoil. The impingement tube is formed to not have impingement holes on an end of the impingement tube spaced toward the trailing edge along the suction wall. Impingement holes are formed in the same portion on a side of the impingement tube facing the pressure wall. Pedestals extend from an inner face of the suction wall toward the impingement tube in this area. The use of the pedestals over this area provides greater cooling to a focused area on the suction wall of the airfoil that might otherwise receive inadequate film cooling.

Description:
[0001]     This invention was made with government support under Contract No. N-00019-02-C-3003 awarded by the United States Navy. The government therefore has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This application relates to a cooling scheme for a gas turbine engine component, such as a stationary vane, wherein an impingement tube is located within a cooling air channel, and pedestals are aligned with a portion of the tube.  
         [0003]     Gas turbine engines are provided with a number of functional sections, including a fan section, a compressor section, a combustion section, and a turbine section. Air and fuel are combusted in the combustion section. The products of the combustion move downstream, and pass over a series of turbine rotors, driving the rotors to create power.  
         [0004]     Numerous components within the gas turbine engine are subject to high levels of heat during operation. As an example, a turbine section will have a plurality of vanes over which high temperature products of combustion pass. Cooling fluid, and typically air, is passed within a body of the vanes to cool the vanes.  
         [0005]     A number of approaches have been made to cool the stationary vanes. One type of cooling is film cooling. In film cooling, air is directed from an internal cavity in the vane to an outer surface. This air creates a film passing along the outer surface, and is much cooler than the products of combustion. The film cooling thus cools an outer surface of the vane. For various reasons, the location and amount of film cooling may be limited.  
         [0006]     Other cooling schemes include the use of impingement air being directed through an impingement tube and off of an inner wall of the vane. The purpose of this impingement cooling air flow is to cool the inner wall.  
         [0007]     In one particular cooling scheme arrangement known for vanes, an impingement tube directs air through impingement holes and against inner walls of the vane at both a suction side and a pressure side. The impingement tube is positioned in a mid-location between a cavity rib and a pedestal array. Air having passed through impingement holes at both the pressure side and the suction side, then passes downstream between the impingement tube and an inner wall, and then over the trailing edge pedestal array the air exits through exit holes at the trailing edge. Further, a film cooling hole is provided on the suction side forwardly of a gage point. This position is utilized to reduce certain aerodynamic losses. The air having left this film cooling hole passes along the suction side to cool the wall. However, the cooling provided by this film cooling air degrades along a direction toward the trailing edge. Thus, and in an area roughly adjacent with an end of the impingement tube area, there is a portion of the suction wall that may not receive adequate cooling.  
         [0008]     In addition to this degradation, the impingement in this region also becomes somewhat ineffective due to “cross-flow degradation.” This is the result of the accumulation of coolant that has been injected from earlier regions. As more flow enters the cavity between the tube and the wall and heads toward the trailing edge, the impingement jets begin to become less effective.  
         [0009]     The present invention is directed to addressing this concern.  
       SUMMARY OF THE INVENTION  
       [0010]     In a disclosed embodiment of this invention, a cooling channel is formed within a gas turbine component. The gas turbine component is disclosed as a stationary vane, although other components such as turbine blades, etc., which utilize impingement tubes, can benefit from this invention. Impingement air is directed outwardly of the impingement tube against inner walls of a component body at both the suction side and the pressure side. Impingement air passes downwardly of the impingement tube, and over pedestals toward exit holes at a trailing edge of the turbine component.  
         [0011]     To improve cooling in the area mentioned above, supplemental pedestals extend from an inner wall at the suction side and toward the impingement tube. In a disclosed embodiment, there are no impingement holes formed in the impingement tube over the length of the impingement tube that has the supplemental pedestals. Impingement holes are formed in the tube at the pressure side along the same length.  
         [0012]     In addition, the geometries of the tube, the channel, and the sizing of the various holes are controlled such that the volume of air passing outwardly of the impingement holes at the suction side which reaches the trailing edge, compared to the volume of air having passed through impingement holes at the pressure side which reaches the trailing edge, is greater than 5:1. In this manner, a good deal of additional cooling is provided to the suction side, thus addressing the concern mentioned above.  
         [0013]     In other features, the supplemental pedestals increase in height in a direction from the leading edge toward the trailing edge. Further, the impingement tube is spaced from the inner wall of the suction side by a greater distance as the impingement tube extends from a leading edge end toward a trailing edge end. In this manner, more air flow is directed along the suction side and over the supplemental pedestals, providing greater cooling.  
         [0014]     One main function of having the pedestals increase in height is to increase convective surface area and increase fin efficiency. This same effect could be achieved with trip strips or dimples. In fact, the term “pedestals” as utilized in this application and in the claims, extends to more than the cylindrical-shaped elements that are illustrated in the drawings of this application. The term “pedestals” would extend to any structure extending outwardly of the wall and into the flow path. The longer pedestals also serve to push the downstream end of the impingement tube toward the pressure side wall. This limits the area in which flow can enter the trailing edge via the pressure side, providing a seal between the two regions. Another function is to allow the suction side flow to diffuse into the trailing edge pedestal bank. This effect “guides” the air into the wider trailing edge cavity and increases static pressure in the transition region. This static pressure increase also helps to seal off the pressure side flow from entering the trailing edge.  
         [0015]     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1A  is a schematic view of a prior art gas turbine engine.  
         [0017]      FIG. 1B  is a cross-sectional view through a prior art stationary vane.  
         [0018]      FIG. 1C  is a view along line  1 C- 1 C from  FIG. 1B .  
         [0019]      FIG. 1D  is a schematic view showing cooling of a portion of the prior art vane.  
         [0020]      FIG. 2A  is a cross-sectional view of an inventive gas turbine vane.  
         [0021]      FIG. 2B  is a schematic view showing features of the  FIG. 2A  vane.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]      FIG. 1A  shows a gas turbine engine  10 . As known, a fan section  11  moves air and rotates about an axial center line  12 . A compressor section  13 , a combustion section  14 , and a turbine section  15  are also centered on the axial center line  12 .  FIG. 1A  is a highly schematic view, however, it does show the main components of the gas turbine engine. Further, while a particular type of gas turbine engine is illustrated in this figure, it should be understood that the present invention extends to other types of gas turbine engines.  
         [0023]     The turbine section  15  includes a rotor having turbine blades  20 , and stationary vanes  18 . As mentioned above, these turbine blades  20  and vanes  18  become quite hot as the products of combustion pass over them to create power. The present invention is directed to cooling schemes for better cooling such components.  
         [0024]     A gas turbine engine component is illustrated in  FIG. 1B , as a stationary vane. However, it should be understood that the present invention would extend to other components having impingement tube cooling, including but not limited to turbine blades.  
         [0025]     As shown, the vane  18  has an airfoil shape with a pressure side  22  and a suction side  24 . Further, the airfoil extends from a leading edge  26  toward a trailing edge  38 . An impingement tube  28  is positioned within a cooling air channel adjacent the leading edge. A second impingement tube  30  is positioned spaced toward the trailing edge from the first impingement tube  28 . Air is directed outwardly of the tubes  28  and  30 , through impingement holes  32  (on the suction side) and  34  (on the discharge side). Air having passed outwardly of these impingement tubes strikes an inner wall at both the pressure side  22  and suction side  24 . Air passes outwardly of film cooling holes  31  on the pressure side, to cool a mid-location on the pressure side.  
         [0026]     As shown in  FIG. 1B , there is a film cooling hole  231  on the suction side, and forward of an approximate location of a gage point. Film cooling air moves along the outer face of the suction side  24  and toward the trailing edge  38 .  
         [0027]     Pedestals  36  are positioned in a cooling channel that receives the impingement tube  30 . Air that has passed outwardly of the impingement holes  32  and  34 , and which has not passed outwardly of the film cooling hole  31 , passes downstream over these pedestals  36  to cool the trailing edge end of the vane  18 . Eventually, the air will pass outwardly of exit holes formed at the trailing edge  38 .  
         [0028]     As shown in  FIG. 1C , the cooling channels that receive the impingement tubes  28  and  30  extend from an end wall  21  along a length of the airfoil  20  toward a top edge  23 . Thus, as shown schematically, cooling air passes into these channels.  
         [0029]      FIG. 1D  shows a schematic view of vane  18 , to illustrate a problem area. Air having passed outwardly of the impingement holes  32  on the suction side  24  hits an inner wall  27 . Similarly, air having passed through the impingement holes  34  on the pressure side  22  hits an inner wall  29 . A plurality of areas A, B and C can be defined on the suction side  24 . In the area A, there is still a good deal of film cooling provided by the suction side film cooling hole  231  as shown in  FIG. 1B . This film cooling in combination with impingement cooling from the impingement holes  32  tends to adequately cool the suction wall in the area A.  
         [0030]     Area C is shown as provided with the pedestals  36 . As can be appreciated, the pedestals provide a good deal of cooling, and thus area C tends to be adequately cooled also. However, an intermediate area B on the suction side  24  does not always receive adequate cooling. In particular, the film cooling has somewhat degraded on the suction side prior to reaching area B. Thus, area B is provided only with the impingement cooling.  
         [0031]     In some applications, this has proven to be inadequate cooling.  
         [0032]     In addition to this degradation, the impingement in this region also becomes somewhat ineffective due to “cross-flow degradation.” This is the result of the accumulation of coolant that has been injected from earlier regions. As more flow enters the cavity between the tube and the wall and heads toward the trailing edge, the impingement jets begin to become less effective.  
         [0033]     In this prior art example, the volume flow of air from the suction side impingement holes  32  which reaches the exit holes at the trailing edge  38  compared to the volume of air having left the impingement holes  34  on the pressure side  22  which reaches the exit holes at the trailing edge  32 , is roughly on the order of 2:1. As can also be appreciated, the impingement tube  30  is roughly centered within the channel. Of course, the shape of vane  18  in  FIG. 1D  is not true to the part (the shape of  FIG. 1B  is accurate).  FIG. 1D  is a simplified view to illustrate the flow of cooling air.  
         [0034]     An inventive gas turbine vane  50  is illustrated in  FIG. 2A . The tube  130  has impingement holes  132  and  134 . The vane  50  has film cooling holes  131  and  231 , pedestals  36 , and leading and trailing edges  26  and  38 , respectively, as in the prior art. However, adjacent to the trailing edge end of the tube  130 , there are improvements over the prior art. In particular, pedestals  160  extend from an inner wall  162  on the suction side  24  toward a suction side wall  164  of the tube  130 . A wall  166  of the tube  130  facing an inner side of the pressure wall  167  has impingement holes  134  spaced along its entire length. In contrast, the outer wall  164  stops having impingement holes  132  at a location before pedestals  160 . While only a few impingement holes are illustrated in the figures of both  FIGS. 1B, 1D ,  2 A and  2 B, it should be understood that a good deal of additional holes may be included. Fewer holes are illustrated for the purposes of simplicity of illustration.  
         [0035]      FIG. 2B  is a highly schematic view, similar to  FIG. 1D , and is utilized to illustrate the basic cooling air flow in the inventive turbine component. As can be best seen in  FIG. 2B , the pedestals  160  increase in height, since the outer wall  164  is spaced by a greater distance from the inner wall  162  at an end adjacent the trailing edge, than it is spaced in a direction toward the leading edge. This increase in distance ensures the pedestals  160  will be providing increased cross-sectional cooling area for cooling the suction wall in the area mentioned above as being challenging.  
         [0036]     One main function of having the pedestals increase in height is to increase convective surface area and increase fin efficiency. This same effect could be achieved with trip strips or dimples. In fact, the term “pedestals” as utilized in this application and in the claims, extends to more than the cylindrical-shaped elements that are illustrated in the drawings of this application. The term “pedestals” would extend to any structure extending outwardly of the wall and into the flow path. The longer pedestals also serve to push the downstream end of the impingement tube toward the pressure side wall. This limits the area in which flow can enter the trailing edge via the pressure side, providing a seal between the two regions. Another function is to allow the suction side flow to diffuse into the trailing edge pedestal bank. This effect “guides” the air into the wider trailing edge cavity and increases static pressure in the transition region. This static pressure increase also helps to seal off the pressure side flow from entering the trailing edge.  
         [0037]     Further, the size of the holes  134  and  131  are designed such that the bulk of the air exiting the holes  134  passes through the film cooling holes  131 . The air passing through the impingement holes  132  and against the inner wall  162  passes over the pedestals  160 , the pedestals  36 , and out of the holes at the trailing edge  38 . In one disclosed embodiment, the ratio of the volume of air reaching the trailing edge  38  from the suction side impingement holes  132  compared to the pressure side holes  134  is on the order of 10:1.  
         [0038]     While the flow ratio in the disclosed embodiment is 10:1, a main focus of this invention is to increase the flow ratio compared to the prior art, which was on the order of 2:1. Thus, flow ratios of 5:1 and greater would come within the scope of this invention. Again, a worker of ordinary skill in the art would recognize how to size the various holes, etc. to achieve this flow ratio.  
         [0039]     The increased suction side flow creates a static back pressure limiting the flow from the pressure side. Thus, by sizing the various openings and dimensions to increase the flow from the suction side relative to the pressure side, the invention self-regulates the flow from the pressure side by providing sealing from this back pressure to limit the flow from the pressure side. On the other hand, mechanical seals can also be utilized to further limit the pressure side flow, if desired.  
         [0040]     While the invention has been disclosed for use in a vane, other appropriate gas turbine engine components having impingement tube cooling may benefit from this invention. As an example, turbine blades could benefit from this invention. While the invention has application to a wide variety of airfoils in gas turbine engine components, in one disclosed embodiment the invention is utilized as a first stage gas turbine engine vane.  
         [0041]     Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.