Patent Publication Number: US-7914257-B1

Title: Turbine rotor blade with spiral and serpentine flow cooling circuit

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to fluid reaction surfaces, and more specifically to a turbine rotor blade with a serpentine flow cooling circuit. 
     2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
     Turbine airfoils, such as rotor blades and stator vanes, pass cooling air through complex cooling circuits within the airfoil to provide cooling from the extreme heat loads on the airfoil. A gas turbine engine passes a high temperature gas flow through the turbine to produce power. The engine efficiency can be increased by increasing the temperature of the gas flow entering the turbine. Therefore, an increase in the airfoil cooling can result in an increase in engine efficiency. 
     Prior art airfoil cooling of blades makes use of a single five-pass aft flowing serpentine cooling circuit. One such prior art 5-pass serpentine flow circuit for an airfoil  10  is shown in  FIGS. 1   a  and  1   b  and includes a first up-pass channel  11  of the 5-pass serpentine flow circuit near the airfoil leading edge. A showerhead arrangement of film cooling holes  16  is included in the first up-pass channel  11  of the serpentine flow cooling channel to provide film cooling for the high heat load section of the airfoil nose. The cooling air flows into a first down-pass channel  12  downstream from and adjacent to the first up-pass channel  11 , and then into a second up-pass channel  13  and a second down-pass channel  14  before entering a trailing edge up-pass channel  15  where the cooling air is finally discharged through a row of trailing edge cooling holes  17 . The five channels  11 - 15  that form the 5-pass serpentine flow cooling circuit of  FIG. 1  each extend from the pressure side wall to the suction side wall such that each channel provides near wall cooling for both sides of the airfoil (the pressure side and the suction side). 
     In the prior art 5-pass aft flowing serpentine cooling circuit of  FIG. 1 , the internal cavities are constructed with internal ribs connecting the airfoil pressure and suction walls. In most of the cases, the internal cooling cavities are at low aspect ratio which is subject to high rotational affect on the cooling side heat transfer coefficient. In addition, the low aspect ratio cavity yields a very low internal cooling side convective area ratio to the airfoil hot gas external surface. 
     The object of the present invention is to provide for a blade with a cooling circuit that provides for a near wall spiral flow cooling arrangement which optimizes the airfoil mass average sectional metal temperature to improve airfoil creep capability for a blade cooling design. 
     Another object of the present invention is to maximize the airfoil cooling performance for a given amount of cooling air and minimize the Coriolis effects due to rotation on the airfoil internal cavities heat transfer performance. 
     BRIEF SUMMARY OF THE INVENTION 
     A turbine rotor blade having an internal cooling circuit forming a 5-pass serpentine flow circuit in which the serpentine channels also form a spiral flow circuit. The spiral serpentine flow circuit includes a first up-pass channel on the pressure side of the airfoil and a first down-pass channel adjacent to the first up-pass channel but on the suction side of the airfoil. A second up-pass channel is located adjacent to the first up-pass channel and on the pressure side of the airfoil. A second down-pass channel is located adjacent to the second up-pass channel but on the suction side of the airfoil. The last leg of the circuit is a trailing edge channel forming a third up-pass channel and includes a plurality of trailing edge cooling exit holes. The blade also includes a leading edge up-pass channel adjacent to the first up-pass channel and first down-pass channel and is connected to the first up-pass channel at the blade tip region. The leading edge up-pass channel includes a showerhead arrangement to provide film cooling for the leading edge of the blade. Each channel in the 5-pass serpentine circuit includes a plurality of pin fins extending across the channel to provide structural rigidity to the blade and to promote turbulent flow in the cooling air. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1   a  shows a prior art 5-pass serpentine flow cooling circuit. 
         FIG. 1   b  shows a diagram view of the prior art 5-pass serpentine flow circuit of  FIG. 1   a.    
         FIG. 2  shows a top view of the 5-pass serpentine flow cooling circuit of the present invention. 
         FIG. 3  shows a side view of the pressure side of the blade with the 5-pass serpentine flow circuit of the present invention. 
         FIG. 4  shows a schematic diagram of the cooling air flow for the spiral serpentine flow cooling circuit of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a turbine rotor blade with a serpentine flow cooling circuit to provide internal cooling of the airfoil. The blade  20  is shown in  FIGS. 2 and 3  with a 5-pass serpentine flow circuit. The blade  20  includes a leading edge with a leading edge cooling supply channel  31  is located in the leading edge region of the blade  20  and is connected to the cooling air supply passage in the blade root to deliver cooling air to the channel  31  and through the showerhead film cooling holes  36  arranged around the leading edge of the blade  20 . The 5-pass serpentine flow cooling circuit of the present invention includes a first pressure side up-pass channel  21  located on the pressure side of the blade. A first suction side down-pass channel  22  is located on the suction side of the blade and opposite from the first pressure side up-pass channel  21 . The two channels  21  and  22  have substantially the same chord-wise length. A second pressure side up-pass channel  23  is located on the pressure side of the blade  20 . A second suction side down-pass channel  24  is located on the suction side and opposite from the second pressure side up-pass channel  23 . The two channels  23  and  24  have substantially the same chord-wise length. A trailing edge up-pass channel  25  is located in the trailing edge region of the blade  20  and extends from the pressure side to the suction side of the blade. A plurality of cooling exit holes  27  extend along the trailing edge of the blade and connect the trailing edge channel  25  to the outside of the blade. 
       FIG. 3  shows a side view of a cross section through the blade in the pressure side section. The leading edge supply channel  31  is located on the left-most side of  FIG. 3  and includes a row of pin fins  28  that extend from the pressure side to the suction side of the blade  FIG. 2  shows one row of pin fins  28  while  FIG. 3  shows three rows that form an X pattern with trip strips connecting adjacent pin fins  28 . The number of rows of pin fins will vary and depend upon the size of the channel. The pin fins  28  provide structural rigidity to the blade and form turbulence promoters for the cooling air flow. These factors will determine how many rows of pin fins are used in the channel. The first pressure side up-pass channel  21  is shown adjacent to the leading edge supply channel  31  with three rows of pin fins  28  extending across the channel with trip strips connecting adjacent pin fins  28 . The leading edge channel  31  and the two channels  21  and  22  are connected at the blade tip by a tip discharge chamber  41 . 
     Located behind the first pressure side up-pass channel  21  is the first suction side down-pass channel  22  that is not shown in  FIG. 3 . Channel  21  is connected to channel  22  at the blade tip by a first tip turn  51  which is formed from the tip discharge chamber  41  that connects all three channels  31 ,  21 , and  22 . The first suction side down-pass channel  22  will flow downward (as shown in  FIG. 3 ) and into a first root section collector cavity  45  formed within the blade root and enclosed by a cover plate  47 . An end  42  of the first suction side down-pass channel opens into the first root section collector cavity  45  which then leads into the beginning  43  of the second pressure side up-pass channel  23  which flows upwards toward the blade tip. Behind the channel  23  in  FIG. 3  is the second suction side down-pass channel  24  with an ending  44  in a second root section collector cavity  46  that is also formed within the root section and covered by the cover plate  47 . Cooling air from the ending  44  of the second suction side down-pass channel  24  flows into the trailing edge flow channel  25  in an upward direction of  FIG. 3  toward the blade tip. The second pressure side up-pass channel  23  and the second suction side down-pass channel  24  are connected together at the blade tip region by a second tip turn  52 . The trailing edge channel  25  in connected to a plurality of cooling air exit holes  27  extending along the trailing edge from the platform to the tip of the blade  20 . 
     In operation, cooling air is fed into the 5-pass aft flowing spiral flow circuit on the leading edge cavity  31  and the first pressure side of the up-pass cooling channel  21 . the cooling air is then discharged in the first blade tip turn chamber  51  and downward through the airfoil first suction side serpentine cooling channel  22  and discharged into the first blade root section collection cavity  45 . This cooling air then flows upward from the second pressure side serpentine cooling channel  23  and across the second blade tip turn  52  and downward through the airfoil second serpentine suction side cooling channel  24  to be discharged into the second blade root section collection cavity  46 . The cooling air then flows upward from the second cooling collection cavity  46  and through the airfoil trailing edge cooling channel  25  for cooling of the trailing edge region and distributes cooling for the airfoil trailing edge discharge cooling holes  27 . Pin fins  28  extend across the channels to promote turbulent flow within the cooling air. Trip strips are used along the channel walls to also promote heat transfer from the hot wall to the cooling air. 
     The five-pass spiral serpentine flow cooling circuit of the present invention is cast into a blade by using five individual ceramic core dies that are interconnected together where adjacent channels have cooling air flowing from one channel to the other. A composite core technique is used to form the assemble core for the entire casting core. Ceramic cores for the leading edge channel  31  and first pressure side up-pass channel  21  are mated together at the blade root section and join together with the ceramic core for the first suction side down-pass channel  22  at the blade tip first tip turn region  51 . The ceramic core for the first suction side down-pass channel  22  is mated with the ceramic core for the second pressure side up-pass channel  23  at the blade attachment region. The ceramic core for the second pressure side up-pass channel is then mated with the ceramic core for the second suction side down-pass channel. The ceramic core for the second suction side down-pass channel is finally mated with the ceramic core for the airfoil trailing edge channel  25  at the blade attachment region to complete the 5-pass spiral serpentine flow circuit.  FIG. 3  shows the mate face  61  between the first suction side down-pass channel  22  and the second pressure side up-pass channel  23 , and the mater face  62  between the second suction side down-pass channel  24  and the trailing edge channel  25  with both of these mate faces being in the root or blade attachment region. The mate face  61  and  62  is the faces of the adjacent ceramic cores that will form the cooling air passage between the adjacent channels when the blade has been cast and the ceramic cores have been leached away. 
     The spiral serpentine flow cooling circuit of the present invention minimizes the airfoil “rotational effects” for the cooling channel internal heat transfer coefficient. This achieves an improved airfoil internal cooling performance for a given cooling supply pressure and flow level over the cited prior art references. Pin fins and trip strips are also incorporated in the high aspect ratio near wall cooling channels to further enhance the internal cooling performance. A lower airfoil mass average sectional metal temperature and a higher stress rupture life are achieved.