ROTOR AND ASSEMBLY FOR REDUCING LEAKAGE FLOW
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 has a groove 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.
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 INVENTIONRotary 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 1000 MW 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
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 INVENTIONA 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.
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
Unlike the conventional seal assembly 100 of
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
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.,
Also,
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
Also as illustrated in
In the embodiment illustrated in
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
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.
Claims
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 claim 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 claim 1, wherein a shape of the groove is one of rectangle, square, curve, semi-circle, trapezoid, and triangle.
4. The rotor of claim 1, wherein a bottom of the groove is slanted.
5. The rotor of claim 1, wherein the rotor lands are created in regular intervals.
6. The rotor of claim 1, wherein the rotor lands are created in irregular intervals.
7. The rotor of claim 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 claim 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 claim 8, wherein a shape of the groove is one of rectangle, square, curve, semi-circle, trapezoid, and triangle.
11. The assembly of claim 8, wherein a bottom of the groove is slanted.
12. The assembly of claim 8, wherein the rotor lands are created in regular intervals.
13. The assembly of claim 8, wherein the rotor lands are created in irregular intervals.
14. The assembly of claim 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 claim 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 claim 8, wherein at least one stator tooth is slanted.
17. The assembly of claim 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 claim 17, wherein at least rotor land is not aligned with any stator tooth.
19. The assembly of claim 18, wherein at least one stator tooth is not aligned with any rotor land.
20. The assembly of claim 8, wherein the rotary machine is a steam turbine and the assembly is an end-packing seal assembly of the steam turbine.
Type: Application
Filed: Apr 8, 2010
Publication Date: Oct 13, 2011
Inventor: Sudhakar NEELI (Bangalore)
Application Number: 12/756,443
International Classification: F04D 29/38 (20060101);