Patent Publication Number: US-7713026-B1

Title: Turbine bladed with tip cooling

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to fluid reaction surfaces, and more specifically to turbine blade with a cooling circuit in the blade tip. 
   2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98 
   In the prior art, blade tip cooling is accomplished by drilling holes into the upper extremes of the serpentine flow coolant passages from both the pressure and suction side surfaces near the blade tip edge and the top surface of the squealer cavity. The cooling flow distribution and pressure ratio across these film cooling holes for the airfoil pressure and suction sides as well as the tip region is subject to severe secondary flow field, which translates into a large quantity of film cooling holes and cooling flow that is required for cooling the blade tip peripheral.  FIG. 1  shows a prior art turbine blade tip cooling hole arrangement on the pressure side and  FIG. 2  shows the same prior art turbine blade tip cooling hole arrangement for the suction side of the blade tip. 
   It is an object of the present invention to provide for a blade tip cooling circuit that will provide adequate blade tip cooling with less cooling air flow. 
   It is another object of the present invention to provide for a turbine blade with a blade tip cooling circuit that provides both impingement cooling and vortex flow cooling for the blade tip circuit. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is a turbine blade with a blade tip cooling circuit formed between a tip ceiling and tip floor and the pressure side and suction side walls of the blade that forms a blade tip passage extending from the leading edge to the trailing edge of the tip. A cooling air supply hole is located in the tip floor to supply cooling air to the passage. A plurality of fins extend across from pressure side to suction side in the passage and have an opening in the corners that alternate from the pressure side to the suction side and allow the passage of the cooling air. The openings in the fins also alternate from the tip floor to the tip ceiling for the passage of the cooling air. Film cooling holes on the blade pressure side wall between each of the fins discharge cooling air from the blade tip passage to the airfoil surface. This alternating arrangement of fins provides for an impingement plus vortex cooling flow in the blade tip. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  shows a prior art turbine blade with film cooling holes on the pressure side tip region of the blade. 
       FIG. 2  shows a prior art turbine blade with film cooling holes on the suction side tip region of the blade. 
       FIG. 3  shows a front cross section view of the turbine blade cooling circuit of the present invention. 
       FIG. 4  shows a top cross section view of the blade tip cooling circuit of the present invention. 
       FIG. 5  shows a schematic view of a section of the blade tip cooling passage with the alternating fins of the present invention. 
       FIG. 6  shows another schematic view of a section of the blade tip cooling passage with the alternating fins of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The turbine blade with the blade tip cooling circuit of the present invention is shown in  FIGS. 3 through 6 . in  FIG. 3 , the main internal blade cooling circuit is shown and includes a leading edge single pass cooling channel  11 , a middle three pass serpentine flow circuit  12  with a cover plate enclosing the cavity formed in the blade root at the turn of the second and third legs of this three pass circuit, and a trailing edge single pass cooling channel  14  extending along the trailing edge portion of the blade. Each of these channels includes trip strips to promote turbulence within the cooling air flow through the passage or channel. 
   The main feature of the present invention is the cooling circuit located within the tip cap of the blade and shown best in  FIGS. 4 through 6 . In  FIG. 4 , a top view of the tip cap cooling circuit is shown. The tip cap includes a tip cap floor  21  that forms the top surface for the blade internal cooling channels or passages shown in  FIG. 3 . A cooling air supply hole  22  is located in the tip cap floor at the position shown in  FIG. 4  that connects to the leading edge cooling supply channel  11  in the leading edge portion of the blade. The cooling air supply hole  22  also acts as a metering and impingement hole to meter the cooling air flow and to provide impingement cooling to the blade tip ceiling immediately above the supply hole  22 . Extending along the tip cap passage as seen in  FIG. 4  is a plurality of fins  23  and  24  that extend from the pressure side wall to the suction side wall of the tip cap passage. The fins  23  and  24  also extend from the tip cap floor  21  to the tip cap ceiling which forms the top of the overall blade. If a squealer cavity is formed on the tip of the blade, the tip cap ceiling would form the bottom of the squealer cavity. Each of the fins includes an opening  25  in one of the four corners of the fin to allow for the passage of cooling air through the tip cap channel. As seen in  FIG. 4 , the fins  23  have the opening  25  on the pressure side of the blade while the fins  24  have the opening on the suction side of the blade. The fins alternate within the tip cap channel such that the openings also alternate and produce a sinusoidal flow path through the tip cap channel. 
   The openings in the fins also alternate from the tip floor to the tip ceiling as seen in  FIGS. 5 and 6  in which the pressure side wall and the suction side wall are shown, and the fins  23  and  24  extend from the walls with the openings  25  alternating from the tip cap floor (back of  FIG. 5 ) to the front or tip cap ceiling (front of  FIG. 5 ). The film cooling holes  31  are shown in  FIG. 5  in the pressure side wall with one hole positioned between each fin  23  or  24 . the film cooling holes  31  are also shown in  FIGS. 3 and 4  where in  FIG. 4  all of the spaces between adjacent fins  23  and  24  have a film cooling hole except for the space with the cooling air supply hole  22  and the space adjacent to and downstream from the front space. However, these two spaces could also have a film cooling hole to discharge cooling air from the space onto the pressure side wall of the airfoil.  FIG. 6  shows another schematic view of the fins and the openings positioned within the tip cap channel that forms the spiral shaped cooling air flow pattern also shown in  FIG. 5 . 
   In  FIGS. 4 through 6 , the fins have cooling air openings  25  on the pressure or the suction side walls of the fins that extend all the way to the respective wall. in other embodiments of the present invention, the openings could extend close to the wall without the opening touching the wall. Each opening in the alternating series forming the cooling air passage must be offset form the adjacent openings in order to force the cooling air to flow in this pattern. Having fins without alternating openings would not provide as much of a serpentine flow as would the alternating fins and the heat transfer coefficient would decrease. 
   Operation of the cooling flow circuit of the present invention is now described. Pressurized cooling air enters the blade root in each of the three cavities located in the blade root as seen in  FIG. 3  and flows up and into the blade through the leading edge channel  11 , the middle three-pass serpentine flow channel  12 , and the trailing edge channel  14 . The cooling air flowing through the middle three-pass serpentine flow circuit will eventually flow out from the blade through film cooling holes arranged along the pressure or suction side walls of the airfoil. The cooling air flow through the trailing edge channel  14  will flow through a row of exit cooling holes arranged along the trailing edge of the blade. The cooling air flow through the leading edge channel  11  will flow through leading edge film cooling holes in the blade (not shown in the figure) with the remainder flowing through the cooling air supply hole  22  in the tip cap floor and into the tip cap cooling passage. 
   The cooling air that passes through the supply hole  22  will then flow through the opening  25  in the first fin  23 , and then spiral around the tip cap passage through the alternating arrangement of openings in a spiral-like flow. In each of the spaces between adjacent fins, if a film cooling hole  31  is present some of the cooling air flow will pass through the film cooling hole  31  to provide film cooling for the pressure side tip edge of the blade. As the spirally cooling air flows through the tip cap passage, film cooling air is diverted out from the blade until the cooling air enters the last space in the tip cap passage and exits the blade through the last film cooling hole  31 . 
   In the present invention, the blade tip could include a squealer tip formed above the tip cap cooling circuit with the alternating fins  23  and  24  and openings  25 . The tip cap cooling flow circuit can also be compartmentalized for tailoring the gas side pressure distribution. The convective cooling air is then channeled from the blade mid-chord serpentine flow circuit  12  or the trailing edge flow circuit  14  and into the blade tip section through an additional cooling air supply hole to form impingement plus serpentine channels to form the spiral shaped cooling air flow through the circuits. 
   The advantages of the blade tip cooling circuit of the present invention are as follows. Reparability of the blade tip treatment—any blade tip treatment layer can be stripped and re-applied without the possibility of hole plugging or the difficulty of re-opening tip cooling holes. Elimination of blade tip drilling holes—since the entire cooling scheme can be cast into the airfoil, drilling cooling holes on top of the blade squealer floor can be eliminated, which will reduce the blade manufacturing cost and improve the blade life cycle cost. Elimination of blade core print out hole—the horizontal cooling channel and the metering hole can be used as the blade core print out hole. Elimination of the welding of the core print out holes is this accomplished. Also, this integral blade tip cooling scheme will prevent core shift by inter-connecting the horizontal channels. Enhancing coolant flow—compartment of the horizontal cooling channel can also be incorporated into the current cooling concept which allows each individual cooling channel to be tailored for tip cooling flow to the various supply and discharge pressures around the airfoil tip. Higher overall blade tip cooling effectiveness—since coolant air is used first to cool the blade top surface by means of impingement plus vortex channel convection cooling and then discharges into the airfoil surface as film cooling. A higher heat transfer coefficient is generated by the vortex flow mechanism in the horizontal flow channel, yielding a cooler blade tip. This double usage of cooling air improves the overall cooling efficiency.