The present invention relates generally to gas turbines and more particularly relates to cooling air circuits within a turbine airfoil.
Generally described, gas turbine buckets may have airfoil shaped body portions. The buckets may be connected at their inner ends to root portions and connected at their outer ends to tip portions. The buckets also may incorporate shrouds at these tip portions. Each shroud cooperates with like elements on adjacent buckets to prevent hot gas leakage past the tips. The use of the shrouds also may reduce vibrations.
The tip shrouds, however, may be subject to creep damage age due to the combination of high temperatures and centrifugally induced bending stresses. One method of cooling each bucket as a whole is to use a number of cooling holes. The cooling holes may transport cooling air through the bucket and form a thermal barrier between the bucket and the flow of hot gases.
Although cooling the buckets may reduce creep damage, the use of cooling air to cool the bucket may reduce the efficiency of the gas turbine as a whole due to the fact that this cooling air is not passing through the turbine section. The cooling air flow therefore should be at a minimum speed for the part. Likewise, the cooling holes may require optimization of the hole location, size, and style.
What is desired, therefore, is a cooling hole scheme for a turbine bucket that limits the reduction in overall system efficiency while providing adequate cooling to prevent creep. The scheme preferably also should increase part life.
The present invention thus provides an airfoil. The airfoil may include a first number of cooling holes and a second number of cooling holes positioned within the airfoil. The first number of cooling holes and the second number of cooling holes each may include a turbulated section and a non-turbulated section.
The first number of cooling holes may include five (5) cooling holes. The first number of cooling holes may include a first end and a second end such that the turbulated section extends from about thirty-five percent (35%) of the length from the first end to about seventy-five percent (75%) of the length. The turbulated section of the first number of cooling holes may include a first diameter, the non-turbulated section may include a second diameter, and the first diameter may be larger than the second diameter. The turbulated section may have a diameter of about 0.175 inches (about 4.45 millimeters) and the non-turbulated section may have a diameter of about 0.135 inches (about 3.43 millimeters). The turbulated section may include ribs therein. A number of non-turbulated sections may be used.
The second number of cooling holes may include two (2) cooling holes. The second number of cooling holes may include a first end and a second end such that the turbulated section extends from about fifty percent (50%) of the length from the first end to about seventy-five percent (75%) of the length. The turbulated section of the second number of cooling holes may include a first diameter, the non-turbulated section may include a second diameter, and the first diameter may be larger than the second diameter. The turbulated section may have a diameter of about 0.165 inches (about 4.19 millimeter) and the non-turbulated section may have a diameter of about 0.125 inches (about 3.18 millimeters). A number of non-turbulated sections may be used.
The airfoil further may include a third number of cooling holes positioned within the airfoil. The third number of cooling holes may include a non-turbulated section. The non-turbulated section may include a diameter of about 0.115 inches (about 2.92 millimeters). The first number of cooling holes, the second number of cooling holes, and the third number of cooling holes may include nine (9) cooling holes.
The airfoil further may include a tenth cooling hole positioned therein. The tenth cooling hole may include a diameter of about 0.08 inches (about 2.03 millimeters).
A further embodiment of the present invention may provide an airfoil for use with a turbine. The airfoil may include a first end, a middle portion, and a second end. The airfoil may include a number of cooling holes extending through the first end, the middle portion, and the second end. The cooling holes may be positioned in the first end according to the Cartesian coordinate values set forth in Table I and the cooling holes may be positioned in the middle portion according to the Cartesian coordinate values set forth in Table III. The cooling holes may be positioned in the second end according to the Cartesian coordinate values set forth in Table II. The airfoil may be a second stage airfoil.
These and other features of the present invention will become apparent upon review of the following detailed description when taken in conjunction with the drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
The bucket 200 may be the second bucket 80 on the second stage 40. Specifically, The General Electric Company of Schenectady, N.Y. may use this configuration for the second stage bucket of a “9FA+e” or a “7FA+e” turbine sold. The bucket 200 may be made out of a directionally solidified alloy such as DS GTD-111™ also sold by The General Electric Company.
The bucket 200 may include a blade or an airfoil portion 210. The airfoil 210 may have a profile intended to generate aerodynamic lift. The airfoil 210 may have a leading edge 220 generally oriented upstream towards the combuster 20 and a trailing edge 230 generally oriented downstream towards the exhaust section of the turbine assembly.
One end of the airfoil 210 may extend from a blade platform 240. The blade platform 240 may define the inner radius of the hot gas flow path. The blade platform 240 also may provide a barrier between the hot gas and the inboard systems. The blade platform 240 may be connected to a blade attachment portion 250. The blade attachment portion 250 may attach the bucket 200 to the turbine shaft.
The other end of the airfoil 210 may include a tip shroud 260. The tip shroud 260 may extend beyond the edges of the airfoil 210 to form a shelf 270. The tip shroud 260 also may include a sealing rail 280 extending in the direction of the airfoil 210. The shelf 270 and the sealing rail 280 may reduce the spillover of hot gases by decreasing the size of the clearance gap and interrupting the hot gas path around the end of the bucket 200.
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Cooling holes eight (8) and nine (9) 370, 380 may have a smooth area 400 throughout. These cooling holes 370, 380 may have a diameter of about 0.115 inches (about 2.92 millimeters) and may have a flow in the downstream direction. The tenth (10th) cooling hole 390 also may have a smooth area 400 throughout its length. The tenth (10th) cooling hole 390 may have a diameter of about 0.08 inches (about 2.03 millimeters) and may have a flow in the downstream direction.
The positioning of the cooling holes 290 as described above provides superior cooling based upon the number of cooling holes 290 and their respective size, shape, style, and location. The size of the cooling holes 290 may limit the amount of airflow based on the pressure difference across the bucket 200. The location of the cooling holes 290 may determine the temperature of every finite element making up the bucket 200. The style of the cooling holes 290 may reflect the way in which heat transfer occurs across the walls of each cooling hole 290. All these attributes together may create the cooling scheme provided herein.
For example, the present invention may provide a flow of about 1.11% W2 as compared to existing designs with a flow of about 1.31% W2, or an increase of about twenty percent (20%). Generally described, W2 is a measure of the mass flow rate of air traveling through the core of the turbine that enters into the compressor. Further, the bulk creep part life may be increased to about 48,000 hours. The overall unit performance may increase by about 0.3%. It should be understood that the foregoing relates only to the preferred embodiments of the present invention and that numerous changes may be made herein without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.