Controlled flow turbine blade

Abstract

The invention is entitled "Controlled Flow Turbine Blade". The present application provides a turbine blade (300). The turbine blade includes a root portion (215) having a first curved portion (310), a tip portion (220) having a second curved portion (320), and a plurality of mean portions (225) positioned between the root portion (215) and the tip portion (220). The mean portions (225) each include a substantially prismatic shape (330).

Description

TECHNICAL FIELD

[0001] The present application and resulting patent relate generally to axial flow turbomachinery, such as steam turbines, gas turbines, and the like, and more particularly to controlled flow dynamic turbine blades used at higher aspect ratios to improve efficiency. BACKGROUND

[0002] Generally, steam turbines and the like can have a defined steam path that includes a steam inlet, turbine portions, and a steam outlet. Steam can generally flow through a plurality of turbine stages that are typically arranged in series, including first or control stage blades having a guide and a runner (or nozzle and vane), as well as subsequent guides and runners of later stages of the steam turbine. In this manner, the guides can direct steam toward the corresponding runners, thereby causing the runners to rotate and drive a load, such as an electrical generator, and the like. The steam can be contained by a circumferential shroud that surrounds the runners, which can also help direct the steam along the path. In this manner, the turbine guides, runners, and shroud can be subjected to high temperatures generated by the steam, which can result in hot spots and high thermal stresses being formed in these components. Because the efficiency of a steam turbine is partly dependent on its operating temperature, there is a continuing need for components positioned along the steam or hot gas path that can withstand increasingly higher temperatures without failing or having a reduced useful life. It is important to improve overall operational flexibility and component load performance.

[0003] Certain turbine blades can be formed with an airfoil geometry. The blades can be attached to a tip and a root, where the root is used to couple the blade to a disk or drum. Known turbine blades can have an airfoil cross-section that is straight or "prismatic" in form that extends radially between the tip and the root. The orientation of stationary and moving blades has been standardized for prismatic blade designs. Depending on the design, the geometry and size of the turbine blades can result in certain profile losses, secondary losses, leakage losses, mixing losses, and the like, which can affect the efficiency and / or performance of the steam turbine or other type of axial flow device. SUMMARY

[0004] The present application and resulting patent thus provide a turbine blade. The loss turbine blade can include a root portion having a first curved portion, a tip portion having a second curved portion, and a plurality of mean portions positioned between the root portion and the tip portion. The mean portions each include a substantially prismatic shape.

[0005] The present application and resulting patent thus provide a steam turbine blade. The steam turbine blade can include a root portion having a first curved portion, a tip portion having a second curved portion, and a plurality of mean portions positioned between the root portion and the tip portion. The mean portions can include a substantially prismatic shape and a reduced axial width as compared to the first curved portion and the second curved portion.

[0006] These and other features and improvements which characterize the present application and the resulting patent will be apparent from the following detailed description, read in conjunction with the accompanying drawings and the appended claims. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a schematic diagram of a steam turbine having a high pressure section and a mid pressure section.

[0008] Figure 2 is a schematic diagram of a portion of a steam turbine showing multiple stages having guide vanes and runner vanes.

[0009] Figure 3 is a perspective view of a pair of vanes of a conventional steam turbine. Figure 2 is a perspective view of a pair of vanes of a conventional steam turbine.

[0010] Figure 4 is a plan view of a pair of vanes of a conventional steam turbine. Figure 3

[0011] Figure 5 is a plan view of a pair of vanes of a conventional steam turbine. Figure 3

[0012] Figure 6 is a perspective view of a vane as described herein.

[0013] Figure 7 is a graph showing the variation of the ratio of throat size to pitch size (K) along a vane height of a conventional steam turbine. Figure 6

[0014] is a graph showing the variation of the ratio of throat size to pitch size (K) along a similar vane height. Figure 8 DETAILED DESCRIPTION

[0015] Referring now to the drawings, in which like reference numerals designate like elements in the several views, Figure 1 is a schematic diagram showing an example of a steam turbine 10. Generally, the steam turbine 10 can include a high pressure section 15 and a mid pressure section 20. Other pressures and other sections can also be used herein. A casing or shell 25 can be axially divided into an upper half 30 and a lower half 35. A central portion 40 of the shell 25 can include a high pressure steam inlet 45 and a mid pressure steam inlet 50. Within the shell 25, the high pressure section 15 and the mid pressure section 20 can be arranged around a rotor or disk 55. The disk 55 can be supported by a plurality of bearings 60. A steam seal unit 65 can be located inward of each of the bearings 60. An annular section divider 70 can extend radially inward from the central portion 40 toward the disk 55. The divider 70 can include a plurality of packing shells 75. Other components and other configurations can be used. ​​​

[0016] During operation, high pressure steam inlet 45 receives high pressure steam from a steam source. The steam can be directed through high pressure section 15 such that work is extracted from the steam by rotation of disk 55. The steam exits high pressure section 15 and can then be returned to the steam source for reheating. The reheated steam can then be redirected to the intermediate pressure section inlet 50. The steam can return to the intermediate pressure section 20 at a reduced pressure compared to the steam entering the high pressure section 15, but at a temperature approximately equal to the temperature of the steam entering the high pressure section 15.

[0017] Figure 2 A schematic view of a portion of a steam turbine 100 is shown that includes a plurality of stages 110 positioned in a steam or hot gas path 120. A first stage 130 can include a plurality of circumferentially spaced controlled flow vanes 140 and a plurality of circumferentially spaced first stage controlled flow runners 150. The first stage 130 can include a first stage shroud 160 that extends circumferentially and surrounds the first stage controlled flow runners 150. The first stage shroud 160 can include a plurality of shroud segments positioned adjacent to each other in an annular arrangement. In a similar manner, a second stage 170 can include a plurality of second stage controlled flow vanes 180, a plurality of second stage controlled flow runners 190, and a second stage shroud 200 that surrounds the second stage controlled flow runners 190. The controlled flow vanes and runners can have a reaction technology blade (RTB) design, among others. The controlled flow vanes and runners can be part of an original equipment or a retrofit. Any number of stages with corresponding vanes and runners can be included herein. Other embodiments can have different configurations.

[0018] Figure 3 A pair of blades 205, 210 are shown, such as Figure 2 The controlled flow vanes 140 are shown. The blades 205, 210 can have a known straight or prismatic orientation. In other words, the blades 205, 210 are designed such that an imaginary airfoil portion (each considered to be normal to a radial line from the rotor) can have the same shape from a blade root 215 to a blade tip 220 (and an average portion 225 therebetween), the blades 205, 210 are not twisted from the blade root 215 to the blade tip 220, and the blades 205, 210 are stacked with the leading edge 230 and the trailing edge 240 each on a straight line. Each blade 205, 210 also has a concave pressure surface 250 and a convex suction surface 260.

[0019] The following parameters related to the design of the blades 205, 210 will be described in detail herein. As Figure 5 As shown, the "blade exit angle a" of an airfoil blade is, for example, the angle of the working fluid exiting a circumferential blade row relative to the rotor circumferential, and it can be derived from the following relationship:

[0020] a = sin -1 K, where K = throat dimension (t) / pitch dimension (p).

[0021] As Figure 4 illustrated, the "throat dimension (t)" is defined, for example, as the shortest line extending from a vane blade trailing edge 240 of one vane blade perpendicular to the suction surface 260 of an adjacent vane blade in the same row. The "pitch dimension (p)" is, for example, the circumferential distance from the trailing edge 240 of one vane blade to the trailing edge 240 of an adjacent vane blade in the same row at a specified radial distance from the platform region of the vane blade.

[0022] The "set angle (β)" is, for example, the angle by which any particular vane portion at a location along the height or span of the vane is displaced from a predetermined zero reference in its own plane. For example, the reference can be taken at a radial location where the vane portion has the same "pitch angle (Ψ)" as a known prismatic vane in a known turbine utilizing such vane. The pitch angle (Ψ) is, for example, the angle between the axis A of the turbine and a tangent 290 to the trailing edge circle 270 and leading edge 280 of the vane portion (as will be discussed in more detail below), and indicates the orientation of the vane portion relative to the turbine axis A.

[0023] A "chord line" 285 is, for example, the shortest line tangent to the leading edge 230 and trailing edge 240 radii of the vane portion. A "chord length" is the distance between two lines perpendicular to and passing through the points of contact of the leading edge 230 and trailing edge 240, respectively, of the chord line. An "axial width" (W) of the vane is, for example, the axial distance between the leading edge 230 and trailing edge 240 (e.g., the distance between the leading and trailing edges as measured along the rotational axis A of the turbine). A "back surface deflection (BSD) angle" is, for example, the change in angle between the throat point and the trailing edge blend point on the suction surface of the vane. An "aspect ratio" can define the ratio of the height to the width or chord of the vane.

[0024] Figure 4 A radial plan view is shown of the orientation of the vanes 205, 210 relative to the turbine axis A (rotor 55) and a transverse (e.g., tangential or circumferential) plane T containing the casing 25 and normal to the turbine axis A. The vane vane portions are based on a small trailing edge circle 270 and a larger leading edge 280. The tangent 290 to these two points defines a pitch angle ψ to the direction of the turbine axis A. The larger leading edge 280 can have a continuous curvature. The axial width (W) of these known stationary vanes 205, 210 at a given radial location is the distance between the leading edge 230 and trailing edge 240 at the given radial location.

[0025] If a perpendicular line is drawn from the suction surface 260 of the vane 205 to intersect the pressure surface 250 of the adjacent vane 210, then if the shortest such line is taken, this is the throat size t, which occurs in the region of the trailing edge 240 of the vane 210. As described above and as shown in Figure 5 the ratio of the throat size (t) to the pitch size (p) of the fixed vanes is a value K, which is equal to the sine of the vane exit angle (a), as previously defined. It can be seen that this angle is approximately the vane exit angle of each vane with respect to the transverse plane T.

[0026] Figure 6 A airfoil vane 300 as described herein is shown. The airfoil vane 300 can accommodate a stage with greater height and thus greater aspect ratio. The airfoil vane 300 can have a prismatic straight trailing edge 240 extending along the height of the vane 300. Instead of the three sections described above (root 215, tip 220, and mean section 225), the vane 300 can have a root section 215, a tip section 220, and any number of mean sections 225 therebetween. In particular, the leading edge 230 can have a first curved controlled flow section 310 around the root section 215, a second curved controlled flow section 320 around the tip section 220, and any number of mean sections 225 therebetween having a straight or prismatic shape 330 for a "local mixing" region.

[0027] The term "curved" describes a surface that varies in vane exit angle (a) over a prescribed length, i.e., a "monotonically decreasing" angle. The curved controlled flow sections 310, 320 curve outward away from the mean sections 225 having a straight or prismatic shape 330, such that the mean sections 225 have a reduced axial width to improve lift, while the wider curved controlled flow sections 310, 320 provide a greater leading edge sweep angle. These sections 310, 320 can be combined with a relatively high trailing surface deflection angle along the pressure side 250, with an improved controlled flow stacking along the trailing edge 240. The controlled flow section 310 can define a first decreasing vane exit angle, the second controlled flow section 320 can define a second decreasing exit angle, and the mean sections 225 can define a substantially constant vane exit angle.

[0028] The nature of the curved controlled flow sections 310, 320 can be shown in Figure 7 and Figure 8 Figure 7 and Figure 8 ​K (the ratio of the throat dimension (t) to the pitch dimension (p)) is depicted as a function of the partial height (ht) of the vane 300. From the root portion 215 to the height hti along the first curved controlled flow portion 310, the decrease in the vane exit angle (a) increases K. From the height (hti) to the height ht2along the mean portion 225 having a straight or prismatic shape 330, K can remain substantially constant, i.e., within about ±0.1. From the height (ht2) to the end of the tip portion 220 of the second curved controlled flow portion 320, the decrease in the vane exit angle (a) causes a similar decrease in K.

[0029] Generally, for a smaller aspect ratio of about 1 to 2, the vane exit angle (a) can vary along the height of the vane 300 as shown in FIG. 3A. The vane exit angle (a) can decrease from the root portion 215 to the height hti along the first curved controlled flow portion 310. The vane exit angle (a) can remain substantially constant from the height (hti) to the height ht2along the mean portion 225 having a straight or prismatic shape 330. The vane exit angle (a) can increase from the height (ht2) to the end of the tip portion 220 of the second curved controlled flow portion 320. Figure 7 As shown in FIG. 3A, the height (hti) of the first curved portion 310 can be between about 0% and about 50% of the vane height (ht) (0 < hti < 0.5), and the height (ht2) of the second curved portion 320 can be between about 50% and 100% of the vane height (ht) (0.5 < ht2 < 1.0). As shown in FIG. 3B, for other vanes, for higher aspect ratios (i.e., aspect ratios greater than about 2), the first curved portion 310 extends from about 0% to about 15% of the vane height (0 < hti < 0.15), and the second curved portion 320 extends from about 85% to about 100% of the vane height (0.85 < ht2 < 1.0). Figure 8 As shown in FIG. 3A, the height (hti) of the first curved portion 310 can be between about 0% and about 50% of the vane height (ht) (0 < hti < 0.5), and the height (ht2) of the second curved portion 320 can be between about 50% and 100% of the vane height (ht) (0.5 < ht2 < 1.0). As shown in FIG. 3B, for other vanes, for higher aspect ratios (i.e., aspect ratios greater than about 2), the first curved portion 310 extends from about 0% to about 15% of the vane height (0 < hti < 0.15), and the second curved portion 320 extends from about 85% to about 100% of the vane height (0.85 < ht2 < 1.0).

[0030] Similarly, the vane exit angle (a) can vary by about 2 < Da1 < 8°, and 2 < Da2 < 8°. Interestingly, the closure at the end wall can be greater than the range of K ± 0.1 along the straight or prismatic shape 330 of the mean portion 225, i.e., both the variation in K along the first curved controlled flow portion 310 and the variation in K along the second curved controlled flow portion 320 are greater than the range of K ± 0.1 along the number of mean portions 225.

[0031] Accordingly, the airfoil blade 300 can accommodate aspect ratios of about 1 to about 6 or so for stages with greater height, and can result in reduced profile and secondary losses. In particular, use of the average portion 225 having a straight or prismatic shape 330 provides increased lift with lower profile losses due to higher open / pitch with high aft surface deflection and curved controlled flow portions 310, 320 with forward leading edge sweep angle that reduces total secondary flow losses. In view of this, the blade 300 has a more constant K distribution over most of the total height (about 15% to about 85%) with only local controlled flow closure losses toward the endwall. All portions have high aft loading to reduce further profile losses and secondary losses.

[0032] Accordingly, the airfoil blade 300 can improve overall efficiency while reducing possible component damage and / or failure. In particular, the improved airfoil blade 300 improves overall efficiency through ease of retrofitting capabilities.

[0033] It should be apparent from the foregoing that the foregoing relates only to certain embodiments of the present application and the resulting patent. Numerous changes and modifications can be made herein by those of ordinary skill in the art without departing from the general spirit and scope of the application as defined by the following claims and the specification.

Claims

1. A turbine blade (300) comprising: a leading edge (230); a root portion (215) comprising a first curved portion (310); a tip portion (220) comprising a second curved portion (320); and a plurality of mean portions (225) positioned between the root portion (215) and the tip portion (220), wherein each of the plurality of mean portions (225) comprises a prismatic shape (330); wherein the first curved portion (310), the second curved portion (320), and the plurality of mean portions (225) are distributed along the leading edge (230); wherein the first curved portion (310) comprises a first decreasing blade exit angle (a) that decreases away from the plurality of mean portions, the second curved portion (320) comprises a second decreasing blade exit angle (a) that decreases away from the plurality of mean portions, and the plurality of mean portions (225) comprises a constant blade exit angle (a) that is greater than the first decreasing blade exit angle (a) and the second decreasing blade exit angle (a); wherein the prismatic shape comprises a ratio of a throat dimension (t) to a pitch dimension (p) that is K ± 0.1, the first curved portion (310) comprises a first ratio of a throat dimension (t) to a pitch dimension (p), the second curved portion (320) comprises a second ratio of a throat dimension (t) to a pitch dimension (p), and the plurality of mean portions (225) comprises a constant K that is greater than each of the first ratio and the second ratio; wherein the plurality of mean portions (225) comprises a decreasing axial width (W) compared to the first curved portion (310) and the second curved portion (320); and wherein the first curved portion (310) and the second curved portion (320) comprise an inward bend away from the plurality of mean portions (225), wherein blade exit angle refers to an angle of a working fluid exiting a circumferential blade row relative to a rotor circumference, wherein axial width refers to a distance between a leading edge and a trailing edge measured along a rotational axis of a turbomachine.

2. The turbine blade (300) of claim 1, wherein a change in the first decreasing blade exit angle (a) and a change in the second decreasing blade exit angle (a) are each between two and eight degrees.

3. The turbine blade (300) of claim 1, wherein a first change in the first ratio along the first curved portion (310) and a second change in the second ratio along the second curved portion (320) are greater than an average change in the ratio along the plurality of mean portions (225). ​ 4. The turbine blade (300) of claim 1, wherein for an aspect ratio higher than two, the first curved portion (310) extends from zero to fifteen percent of a total height (ht) of the blade (300) along a first height (hti) of the blade (300), and the second curved portion (320) extends from eighty-five to one hundred percent of the total height (ht) of the blade (300) along a second height (ht2) of the blade (300), wherein the aspect ratio refers to a ratio of a height to a width of an airfoil blade.

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