EP2375001A2

EP2375001A2 - Rotor and assembly for reducing leakage flow

Info

Publication number: EP2375001A2
Application number: EP11161550A
Authority: EP
Inventors: Sudhakar Neeli
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2010-04-08
Filing date: 2011-04-07
Publication date: 2011-10-12
Also published as: JP2011220522A; RU2011112993A; US20110250073A1

Abstract

In a rotary machine such as a steam turbine, pressurized fluid flows through a series of stationary and rotary components. Minimizing leakage flow of the fluid enhances the operation and efficiency of the machine. At least one rotor land (240) has a groove (245) formed thereon to generate a vortex as the fluid passes over. The vortex resists the axial flow of the fluid, which reduces the leakage flow.

Description

One or more aspects of the present invention relate to rotor and assembly for reducing leakage flow, for example, in rotary machines.

BACKGROUND OF THE INVENTION

Rotary machines such as steam and gas turbines are used for power generation and mechanical drive applications. These machines generally include multiple turbine and/or compressor stages. In operation, pressurized fluid flows through a series of stationary and rotary components. Minimizing fluid leakage enhances the operation and efficiency of the rotary machine.
In a steam turbine for example, end-packing seals are used to prevent or minimize the steam leaking into the atmosphere. Leakage flows from a HP/IP (high pressure/intermediate pressure) stages are used to seal the end packing. As an example, a 1000MW machine may have a 6-flow LP stage indicating that six end packing seals are used to prevent steam leakage into the atmosphere.
A conventional end-packing seal assembly widely used in a steam turbine is illustrated in FIG. 1. The conventional end packing seal assembly 100 is of a "slant square teeth" type in which slanted teeth 120 are formed on a stator 110 and square teeth 140 are formed on a rotor 130. In FIG. 1, rotational direction of the rotor 130 is into and out of the page as shown by arrow 170, axial direction is horizontal as shown by arrow 150, and radial direction is vertical on the page as shown by arrow 160. Also, it is assumed that the fluid, e.g., steam, moves axially from right to left as shown by block arrow 180. The stator teeth 120 and the rotor teeth 140 seal against the leakage flow of steam from a relatively high pressure side (right) to a relatively low pressure side (left).
It will be appreciated that leakage flow represents energy that is not captured, i.e., it constitutes waste. If the leakage flow can be reduced, the same steam can be used to generate more output. Thus, any reduction of steam usage at the sealing end-packing will improve overall performance of the turbine.

BRIEF SUMMARY OF THE INVENTION

A non-limiting aspect of the present invention relates to a rotor of a rotary machine. The rotor comprises a plurality of rotor lands spaced apart from each other in an axial direction. At least one rotor land has a groove formed thereon, and the groove has a shape that generates a vortex as fluid flows over the rotor so as to resist axial flow of the fluid.
Another non-limiting aspect of the present invention relates to an assembly for a rotary machine. The assembly comprises a stator and a rotor. The stator includes a plurality of teeth spaced apart from each other in an axial direction, and the rotor includes a plurality of rotor lands spaced apart from each other in the axial direction. At least one rotor land has a groove formed thereon, and the groove has a shape that generates a vortex as fluid flows over the rotor so as to resist axial flow of the fluid.
The invention will now be described in greater detail in connection with the drawings identified below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a conventional end-packing seal assembly of a steam turbine;
FIG. 2 is a view of an embodiment of an assembly of a rotary machine;
FIG. 3 is a view of an example of a rotor land that is aligned with a stator tooth;
FIG. 4 is a view of an example of a rotor land that is not aligned with any stator tooth;
FIGs 5, 6, and 7 are views illustrating example groove shapes formed on rotor lands;
FIGs. 8, 9, and 10 illustrate examples of alignments of a stator tooth with a corresponding rotor land; and
FIGs. 11, 12, 13 and 14 are views of other non-limiting assembly embodiments of a rotary machine.

DETAILED DESCRIPTION OF THE INVENTION

For ease of distinction between the teeth of the stator and the rotor, the rotor teeth will be referred to as rotor "lands" from this point on. Thus, unless specifically noted, "tooth" or "teeth" will generally refer to the stator and "land" or "lands" will generally refer to the rotor.
Leakage flow has two main drivers - effective clearance and axial velocity. Effective clearance may be associated with resistance to fluid flow in general - lower the clearance, higher the resistance to fluid flow. Axial velocity is related to how fast the steam flows axially from the high pressure side on the right and exits to the low pressure side on the left - faster the axial velocity component, more leakage flow occurs. Thus, reduction(s) in one or both of these drivers will reduce the leakage flow and enhance efficiency.
One way to reduce the leakage flow is to reduce the clearance between the stator and the rotor. In an assembly for a rotary machine, the best sealing position is when a stator tooth sits on a rotor land, i.e., the tooth and the corresponding land are aligned vertically, i.e., aligned in the radial direction. This is where physical minimum clearance (or simply "minimum clearance") occurs. The worst position is when the land is in between two teeth. Leakage flow can be reduced by reducing the minimum clearance so that less steam flows through. This requires very tight tolerances in forming the stators and rotors, and great strides have been made in this area.
Another way to the leakage flow is to dynamically oppose the flow of the fluid during operation of the turbine. As noted above, of one primary concern is the leakage flow in the axial direction. Any resistance to this axial flow also reduces the effective clearance. However, in the conventional end-packing seal assembly 100 of FIG. 1, once the fluid passes through the minimum clearance, rotor land 140 does not oppose the axial flow. Indeed, the fluid is guided to flow in the undesirable axial direction.
FIG. 2 illustrates a non-limiting embodiment of an assembly, e.g., for a rotary machine, that addresses one or more shortcomings of the conventional end-packing seal assembly. The assembly 200 could be an end packing seal assembly for a steam turbine or can be an assembly for many types of rotary machines. As shown, the assembly 200 includes a stator 210 with a plurality of slanted teeth 220 each with tips 225 and spaced apart from each other in the axial direction. The pitch of the stator teeth is denoted "Ps". The assembly 200 includes a rotor 230 with plurality of lands 240 also spaced apart in the axial direction, the pitch of the rotor lands 240 is denoted "Pr". The axial, radial and rotational directions are represented as 250, 260 and 270, respectively. Unless otherwise specifically stated or shown, it can be assumed that the directions for the remaining figures are the same as FIG. 2. In this particular embodiment, the stator teeth 220 outnumber the rotor lands 240. But this is not a requirement.
Unlike the conventional seal assembly 100 of FIG. 1, the assembly 200 includes at least one rotor land 240 that has a groove 245 formed thereon. The groove 245 has a depth "d" and the rotor land 240 has a height of "h" as illustrated in FIG. 3. Both the depth and the height of the groove 245 and land 240 are not particularly limited. As non-limiting examples, the depth d may range between 20 and 40 mils and the height h may be 125 mils. At all clearances, the groove 245 (also referred to as "slots") acts as a vortex generator generating a vortex that oppose the axial flow of the fluid.
FIG. 3 also shows that the clearance "c" between the tooth 220 and the land 240 is at the minimum when the tooth 220 is aligned with the land 240. Minimum clearance may be defined as a difference in the radial height of the tip 225 of the stator tooth 220 and the radial height of the rotor land 240. At the minimum clearance, the vortex generated by the groove 245 aerodynamically resists the flow of the fluid. The effect of the groove 245, at least in part, is that the fluid flow encounters increased losses in pressure ratios across the rotor lands 240 due to the vortex generated by the grooves 245. The losses in the pressure ratios reduce the flow's velocity.
In addition to reducing the flow's velocity, simulations reveal that at the minimum clearance, the vortex also changes the fluid's axial velocity component. In other words, the axial component of the fluid flow is changed to flow tangentially to the rotational direction and/or to flow in the radial direction.
Even when there is no alignment between the rotor land 240 and the stator teeth 220, i.e., when the land 240 is in between two teeth 220 (see FIG. 4), the groove 245 still generates a vortex that reduces the leakage flow by opposing the fluid flow and changing the axial velocity component of the fluid flow. However, the axial velocity component change is a greater contributor towards reducing the leakage flow when there is no alignment.
Regardless of how the rotor lands 240 are positioned relative to the stator teeth 220, each groove 245 generates a vortex that make the fluid's flow path more torturous reducing the effective clearance and changing the axial velocity component of the fluid flow. In short, each groove generates a vortex that resists the axial flow of the fluid when the fluid passes over the rotor.
At low physical clearances, the quantity of fluid leakage will generally be low. However, the leakage increases rapidly with increase in the clearance. Experiments indicate that compared to seal assemblies without grooves on lands (e.g., FIG. 1), seal assemblies with grooves on lands (e.g., FIG. 2) can achieve reduction in the leakage flow. Simulations reveal that at various clearances, leakage flow reduction can be above 8%, which can represent significant savings. Simulations also reveal that shapes of grooves affect the amount of reduction.
FIG. 2 illustrates an embodiment in which the grooves 245 are formed on every land 240. While this is preferable, it is not strictly necessary. Having a groove formed on at least one rotor land will contribute to reducing the leakage flow.
Also, FIGs. 2, 3 and 4 illustrate the groove 245 as having a wide "U" shape, but the groove shape is not so limited, and shapes such as a rectangle, square, curve, semi-circle, trapezoid, triangle and so on are also contemplated. An example of a rectangular shaped groove is illustrated in FIG. 5. It is also not strictly necessary that the groove shape be symmetrical about a center of the land as illustrated in FIG. 6. In this figure, a centerline 610 is drawn which represents a center of an axial width 620 of the rotor land. As seen, the groove (trapezoidal shape in this example) is not a mirror image about centerline 610. Further, the bottom of the groove need not be strictly horizontal. As seen in FIG. 7, the groove's bottom may be slanted. While not illustrated, the groove can also have an irregular shape.
All these examples are provided to indicate that any shape that promotes vortex generation is contemplated. It is recognized that for machining purposes, some shapes may be preferred over others. Yet further, all grooves need not be shaped the same. Some grooves may be rectangular, some may be U shaped, others may be semi-circular and so on so as to generate a mixture of vortices. Indeed, some rotor lands may not have grooves at all. Again for ease of machining the grooves, minimizing the number of shapes may be preferred.
Referring back to FIG. 2, note that some lands 240 are vertically (i.e., in a radial direction) aligned with at least one stator tooth 220 so as to have the minimum clearance, while other lands 240 are in between two of the teeth 220. Here, alignment simply indicates that the tip 225 of the stator tooth 220 vertically overlaps with some part of the axial width 620 of the rotor land 240 as illustrated in FIGs. 8, 9 and 10. In FIG. 8, the tip 225 is substantially aligned with the centerline 610 of the axial width 620 of the rotor land 240. In FIG. 9, the stator tooth tip 225 overlaps the rotor land 240 on the downstream side of the centerline 610, and in FIG. 10, the tooth tip 225 overlaps the land 240 on the upstream side.
Also as illustrated in FIG. 2, it is seen that the pitch Pr of the rotor land is not the same as the pitch Ps of the stator. Experiments indicate that the rotor pitch Pr has different degrees of effectiveness for a given clearance "c" between the stator teeth and the rotor lands. Thus, in a non-limiting embodiment, the rotor pitch Pr can be optimized for a particular minimum clearance design.
In the embodiment illustrated in FIG. 2, the radial height of the rotor lands are all substantially equal. But in many steam turbines, the radial height of the turbine can vary along on at least a portion of its axial length. FIG. 11 illustrates a non-limiting variation of a assembly illustrating a "stepped" seal. In this instance, the radial height of at least one rotor land 240 is different from other rotor lands 240. While not illustrated, it should be noted that the radial heights of the lands 240 need not be monotonicallv increasing or decreasine.
In the above disclosed figures, stators with slanted teeth are illustrated. But this is not a strict requirement. Stators that have substantially no slant in their teeth are also contemplated as illustrated in FIG. 12. In another non-limiting variation, the rotor pitch Pr can vary. In FIG. 2, it is assumed that the rotor pitch Pr is assumed to be regular. But this is not strictly necessary. In FIG. 13, two different rotor pitches Pr1 and Pr2 are illustrated. Of course, more than two are contemplated. These non-limiting embodiments demonstrate that the rotor lands can be created in regular and/or irregular intervals.
FIG. 14 illustrates yet another non-limiting embodiment of the assembly. In this embodiment, the axial width 620 of the rotor lands 240 is greater than the stator pitch Ps. When each rotor land 240 is wider than the stator pitch, all rotor lands 240 will be aligned with at least one stator tooth 220. But in FIG. 14, it is seen that there is at least one stator 220 that is not aligned with any land 240.
While not illustrated, just as the groove shapes can vary, the axial widths of the rotor lands can vary as well. It also bears repeating that while an assembly of a steam turbine has been described, one or more aspects are applicable to many types of rotary machines.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
For completeness, various aspects of the invention are now set out in the following numbered clauses:

1. A rotor for a rotary machine, comprising:
- a plurality of rotor lands spaced apart from each other in an axial direction,
wherein at least one rotor land has a groove formed thereon, and
wherein the groove has a shape that generates a vortex as fluid flows over the rotor so as to resist an axial flow of the fluid.
2. The rotor of clause 1, wherein the shape of the groove formed on at least one rotor land is different from the shape of the groove formed on at least one other rotor land.
3. The rotor of clause 1, wherein a shape of the groove is one of rectangle, square, curve, semi-circle, trapezoid, and triangle.
4. The rotor of clause 1, wherein a bottom of the groove is slanted.
5. The rotor of clause 1, wherein the rotor lands are created in regular intervals.
6. The rotor of clause 1, wherein the rotor lands are created in irregular intervals.
7. The rotor of clause 1, wherein a radial height one rotor land is different from a radial height of at least one other rotor land.
8. An assembly for a rotary machine, comprising:
- a stator with a plurality of teeth spaced apart from each other in an axial direction; and
- a rotor with a plurality of rotor lands spaced apart from each other in the axial direction,
wherein at least one rotor land has a groove formed thereon, and
wherein the groove has a shape that generates a vortex as fluid flows over the rotor so as to resist an axial flow of the fluid.
9. The assembly of clause 8, wherein the shape of the groove formed on one rotor land is different from the shape of the groove formed on at least one other rotor land.
10. The assembly of clause 8, wherein a shape of the groove is one of rectangle, square, curve, semi-circle, trapezoid, and triangle.
11. The assembly of clause 8, wherein a bottom of the groove is slanted.
12. The assembly of clause 8, wherein the rotor lands are created in regular intervals.
13. The assembly of clause 8, wherein the rotor lands are created in irregular intervals.
14. The assembly of clause 8, wherein a pitch of the rotor lands is adjusted based on a minimum clearance between the rotor lands and the stator teeth.
15. The assembly of clause 8, wherein a radial height one rotor land is different from a radial height of at least one other rotor land.
16. The assembly of clause 8, wherein at least one stator tooth is slanted.
17. The assembly of clause 8, wherein at least one rotor land is aligned with a corresponding stator tooth such that a tip of the corresponding stator tooth vertically overlaps an axial width of the rotor land.
18. The assembly of clause 17, wherein at least rotor land is not aligned with any stator tooth.
19. The assembly of clause 18, wherein at least one stator tooth is not aligned with any rotor land.
20. The assembly of clause 8, wherein the rotary machine is a steam turbine and the assembly is an end-packing seal assembly of the steam turbine.

Claims

A rotor (230) for a rotary machine, comprising:
a plurality of rotor lands (240) spaced apart from each other in an axial direction,
wherein at least one rotor land (240) has a groove (245) formed thereon, and
wherein the groove (245) has a shape that generates a vortex as fluid flows over the rotor (230) so as to resist an axial flow of the fluid.
The rotor (230) of claim 1, wherein the shape of the groove (245) formed on at least one rotor land (240) is different from the shape of the groove (245) formed on at least one other rotor land (240).
The rotor of claim 1, wherein a shape of the groove is one of rectangle, square, curve, semi-circle, trapezoid, and triangle.
The rotor of claim 1, wherein a bottom of the groove is slanted.
The rotor of claim 1, wherein the rotor lands are created in regular intervals.
The rotor of claim 1, wherein the rotor lands are created in irregular intervals.
The rotor (230) of claim 1, wherein a radial height of one rotor land (240) is different from a radial height of at least one other rotor land (240).