Abstract
A method for casting a turbine blade body comprises; providing a mold defining the external geometry of the blade body; providing a core defining an internal geometry of the blade body, the core comprising a main body defining an internal chamber of the blade body and having a root end and a tip end and a plurality of pedestals defining an array of cooling channels extending from the internal chamber; casting a molten material between the mold and the core; and removing the core after the molten material has solidified, wherein the pedestals are arranged in a single row starting from the root end to a mid-portion of the main body branching into multiple and divergent rows towards the tip end of the body.
Claims
1. A method for casting a turbine blade body, the method comprising; providing a mould defining the external geometry of the blade body; providing a core defining an internal geometry of the blade body, the core comprising a main body defining an internal chamber of the blade body and having a root end and a tip end and a plurality of pedestals defining an array of cooling channels extending from the internal chamber; casting a molten material between the mould and the core; and removing the core after the molten material has solidified, wherein the pedestals are arranged in a single row starting from the root end to the main body branching into multiple rows towards the tip end of the body, the single row having a line of symmetry and all of the multiple rows branching to either side of the line of symmetry, and one or more of the pedestals has a larger cross sectional area than the remaining pedestals and a pedestal of larger cross sectional area is positioned at or near the root end of the core body.
2. A method as claimed in claim 1 wherein the number of branches is two.
3. A method as claimed in claim 2 wherein the arrangement of pedestals branches into a pair of rows arranged symmetrically about the line of symmetry.
4. A method as claimed in claim 2 wherein the arrangement of pedestals branches into a pair of rows arranged asymmetrically about the line of symmetry.
5. A method as claimed in claim 1, wherein a pedestal of larger cross sectional area is positioned at or near the tip end of the core body.
6. A method as claimed in claim 1, wherein some or all of the pedestals are grouped into numbers of pedestals with equal cross sectional areas.
7. A method as claimed in claim 1 wherein the pedestals have a cross-sectional shape selected from; circular, elliptical or race track.
8. A method as claimed in claim 1 wherein the pedestals are inclined to a surface of the main body and the resulting blade body includes channels which are inclined to surfaces of walls of the blade body.
9. A method as claimed in claim 1 wherein the single row branches at a position which is closer to the root end than to the tip end.
10. A method as claimed in claim 1 wherein the single row branches at a position in the range from 20% to 80% of the distance from the root end to the tip end.
11. A method as claimed in claim 10 wherein the single row branches at a position in the range from 30% to 70% of the distance from the root end to the tip end.
12. A method as claimed in claim 1 wherein the multiple rows diverge from the single row for at least part of the distance to the tip end.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Embodiments will now be described by way of example only, with reference to the Figures, in which:
(2) FIG. 1 is a sectional side view of a gas turbine engine;
(3) FIG. 2a shows a first array of holes known to be used in turbine blades of the prior art;
(4) FIG. 2b shows a second array of holes known to be used in turbine blades of the prior art;
(5) FIG. 2c shows a third array of holes known to be used in turbine blades of the prior art;
(6) FIG. 3a shows a radial stress field experienced by a first array of holes known to be used in turbine blades of the prior art;
(7) FIG. 3b shows a radial stress field experienced by a second array of holes known to be used in turbine blades of the prior art;
(8) FIG. 3c shows a radial stress field experienced by a third array of holes known to be used in turbine blades of the prior art;
(9) FIG. 3d shows a radial stress field experienced by a fourth array of holes known to be used in turbine blades of the prior art;
(10) FIG. 4a shows a single pedestal of a core and illustrates the bending moment experienced by the pedestal during the molten phase of casting;
(11) FIG. 4b shows a two row pedestal arrangement of a core;
(12) FIG. 5a shows a first embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(13) FIG. 5b shows the radial stress field experienced by the array of FIG. 5a;
(14) FIG. 6 shows a second embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(15) FIG. 7 shows a third embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(16) FIG. 8 shows a fourth embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(17) FIG. 9 shows a fifth embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(18) FIG. 10 shows a sixth embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(19) FIG. 11 shows a seventh embodiment of an array of holes in a turbine blade made in accordance with a method of the invention;
(20) FIG. 12 shows some example cross-sectional shapes for pedestals/holes of the present invention;
(21) FIG. 13 shows examples of how pedestals/holes of the invention may be inclined with respect to a planar surface;
(22) FIG. 14 illustrates a turbine blade body including a leading edge through which cooling channels can be provided in accordance with methods of the present invention.
DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION
(23) With reference to FIG. 1, a gas turbine engine is generally indicated at 10, having a principal and rotational axis 11. The engine 10 comprises, in axial flow series, an air intake 12, a propulsive fan 13, a high-pressure compressor 14, combustion equipment 15, a high-pressure turbine 16, a low-pressure turbine 17 and an exhaust nozzle 18. A nacelle 20 generally surrounds the engine 10 and defines the intake 12.
(24) The gas turbine engine 10 works in the conventional manner so that air entering the intake 12 is accelerated by the fan 13 to produce two air flows: a first air flow into the high-pressure compressor 14 and a second air flow which passes through a bypass duct 21 to provide propulsive thrust. The high-pressure compressor 14 compresses the air flow directed into it before delivering that air to the combustion equipment 15.
(25) In the combustion equipment 15 the air flow is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high and low-pressure turbines 16, 17 before being exhausted through the nozzle 18 to provide additional propulsive thrust. The high 16 and low 17 pressure turbines drive respectively the high pressure compressor 14 and the fan 13, each by suitable interconnecting shaft.
(26) Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. three) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan.
(27) The blades of turbines 16 and 17 are subjected to extremes of temperature by hot gases expelled from the combustion equipment 15. Relatively cool air from the compressor 14 is taken off upstream of the combustion equipment and directed to the blades for use as a cooling fluid. The blades can be provided with multiple internal channels and arrays of cooling channels in surfaces affected by the heat. The blades can be manufactured using methods in accordance with the invention.
(28) FIGS. 2a, 2b and 2c show arrays of cooling holes known to be provided in turbine blades of the prior art, for example along the leading edge of the blade. FIG. 14 illustrates a prior art blade exhibiting such an array of holes. It will be appreciated that the arrays of holes are achieved using cores having pedestals arranged in similar arrays, the blade body being cast between a mould defining its external geometry and the core. As discussed above, these arrays have been chosen to be at reduced risk of cracking due to radial stress fields to which they are subjected when the turbine blade is in use. Complex stress fields with a predominant radial component are avoided by providing the single row of holes substantially in line with the stress field and, where more than one row is present, separating the rows by sufficient distance that the stress fields experienced by each row do not interfere with each other to create a more complex stress field. FIG. 2a shows a blade surface 1 having a single row 2 of equally sized, equally spaced holes. FIG. 2b shows an array 3 of two parallel aligned rows, each row comprising equally sized, equally spaced holes. FIG. 2c shows an array 4 of two parallel aligned rows, each row comprising equally sized, equally spaced holes, but the rows are staggered.
(29) FIGS. 3a, 3b and 3c show the stress fields experienced by the arrays 2, 3 and 4 of FIGS. 2a, 2b and 2c. FIG. 3d shows a more complex stress field which results from positioning the rows of array 4 more closely together.
(30) FIG. 4a shows the bending moments (dashed line arrow) to which a single pedestal 5 of a core 6 is subjected. FIG. 4b shows a pair of pedestals 5a, 5b anchored in a core 6. It will be appreciated the two anchored pedestals 5a, 5b are far better placed to resist bending stresses caused by the bending moments than the single pedestal 5 of FIG. 4a.
(31) FIG. 5a shows a first array of holes achievable by a method in accordance with the invention. It will be appreciated that pedestals for creating the holes would be arranged in a similar array on a core body used to cast the blade. The array has two distinct sections; the first is a single row 22 of equally sized and equally spaced holes which extend from a root end to a mid-section of a blade surface 9. In the mid-section, the array branches in a Y shaped configuration providing a pair of divergent branches 23a and 23b. The holes of branches 23a and 23b are spaced further apart than in the single row 22 and are staggered with respect to one another.
(32) The single row adjacent the root end provides maximum stress shielding for the holes in the blade surface, whilst the branched section of the array provides for improved bending stiffness of the pedestal array in the core. FIG. 5b illustrates the stress field for the array of FIG. 5a. As can be seen, there is a smooth stress field for the single row of holes 22 where the load is highest and a more complex stress field in the mid-section to tip area where the load is lower, however the benefit of a greater bending stiffness in the pedestal array of the core provides a reduced risk of core damage and consequent component rejection during the molten phase of the casting process.
(33) FIG. 6 shows a variant of the arrangement in FIG. 5a. As can be seen the single row 32 is shorter in length than in FIG. 5a and the branched section 33 diverges more gradually. The example shows an arrangement optimised further towards pedestal array bending stiffness than low stresses.
(34) FIG. 7 shows another arrangement. The array has two distinct sections; the first is a single row 42 of equally sized and equally spaced holes which extends from a root end to a mid-section of a blade surface 49. In the mid-section, the array branches in a Y shaped configuration providing a pair of divergent branches 43. The holes of branches 43 are spaced similarly to those in the single row 42 and are symmetrically aligned about a centre line passing through the single row 42. The high density of holes in the branched portion can serve to maximise cooling performance and/or improve bending stiffness in the pedestal array.
(35) FIG. 8 shows another arrangement. The arrangement is broadly similar to that of FIG. 5a but differs primarily in that in a region of the single row 52 towards the root end, the size of the holes is gradually reduced. This arrangement is beneficial in minimising stresses in the lowest holes utilising the stress shielding effect.
(36) FIG. 9 shows another arrangement. The arrangement is broadly similar to that of FIG. 5a but differs primarily in that in a region of the branched section 63 towards the tip end, the size of holes is gradually increased. This arrangement is beneficial in maximising bending stiffness of the pedestal array and strengthening the branched section of the array.
(37) FIG. 10 shows another arrangement. The arrangement is broadly similar to that of FIG. 5a but differs primarily in that “anchor” holes 73a, 73b of larger diameter than the rest are positioned one adjacent the tip end and one adjacent the root end. The “anchor” holes provide extra stiffness and strength to the extreme ends of the pedestal array to avoid ‘pedestal unzipping’.
(38) FIG. 11 shows an arrangement broadly similar to that of FIG. 10 but differs in that a first anchor hole 83a is positioned immediately adjacent the tip end and a second anchor hole 83b is positioned in a mid-section of single row 82. This arrangement is beneficial in providing stress shielding to the lowest hole whilst also providing some ‘unzipping’ protection. It provides a balance between the objectives of pedestal array bending stiffness/strength and reduced hole stress. FIG. 12 shows examples of cross sectional shapes for holes and pedestals already discussed in relation to the method of the invention. Hole selection may be based on cooling/stress/manufacturing compromises.
(39) FIG. 13 shows a wall section in a 3D perspective view illustrating a channel associated with the holes already discussed in relation to the method of the invention. It will be seen the channel 50 is inclined with respect to external surfaces of the wall. It will be appreciated that pedestals of a core used in methods of the invention can be provided at appropriate angles in order to provide such inclined channels. In the left hand image, it can be seen the channel is radially inclined. In the right hand figure, the channel is both radially and in-plane inclined.
(40) FIG. 14 shows a turbine blade 90 as known from the prior art. The blade has a leading edge surface 91 into which an array of cooling channels is provided. It will be appreciated that the array shown on surface 91 can be replaced with the arrays described in the examples of the invention discussed above in a turbine blade made according to a method of the invention.
(41) It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.
