Offset blade tip chord sealing system and method for rotary machines
A rotary machine includes a rotary member disposed inside the stationary member, wherein the rotary member includes at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. A sealing system is disposed on the tip portion. The sealing system consists essentially of at least one seal strip disposed on the tip portion at an off-center position only between the downstream side wall and a central position between the upstream and downstream sidewalls.
The invention relates generally to a rotary machine and, more particularly, a sealing system for an interface between rotating and stationary components. In certain aspects, the sealing system includes a sealing system between a rotating blade and a surrounding structure of a turbine engine.
Performance and efficiency of rotary machines, e.g., turbine engines, are dependent on a clearance gap between rotating and stationary components within the turbine engine. For example, the clearance gap between the tip of rotor blades and the adjacent stationary shrouds provides a narrow flow passage between the pressure and suction sides of the rotor blade, resulting in hot gas flow leakage that can reduce the blade aerodynamic performance. As the clearance gap between the rotating and the stationary components increases, the efficiency of the turbine decreases. In addition, the hot gas flow leakage in the area of the blade tip can increase thermal loading on the rotor blade.
Several blade tip designs exist for maintaining proper pressure between the pressure side and the suction side flow surfaces of the rotor blade as well as for providing minimum clearances with the stator shroud. Existing blade tip treatments for sealing have cost implications, involving additional amounts of material to form the tip treatment for sealing. Moreover, existing blade tip designs lead to re-attachment of fluid flow at the blade tip surface causing increased tip heat load at the tip surface.
BRIEF DESCRIPTIONIn accordance with one aspect of the present invention, a rotary machine includes a rotary member disposed inside the stationary member, wherein the rotary member includes at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. A sealing system is disposed on the tip portion. The sealing system consists essentially of at least one seal strip disposed on the tip portion at an off-center position substantially between the downstream side wall and a central position between the upstream and downstream sidewalls.
In accordance with another aspect of the present invention, a turbine includes a rotor disposed inside the stationary outer casing, wherein the rotor comprises at least one rotor blade having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. At least one seal strip is disposed on the tip portion at an off-center position substantially between the downstream side wall, and a central position between the upstream and downstream side walls.
In accordance with another aspect of the present invention, a sealing system includes at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls. At least one seal strip is disposed on the tip portion at an off-center position only between the downstream side wall and a central position between the upstream and downstream side walls.
In accordance with another aspect of the present invention, a method includes rotating a rotary member having at least one airfoil disposed inside a stationary member. A flow resistance to the flow of the working fluid between a tip portion of the airfoil and the stationary member is created via at least one seal strip disposed on the tip portion at an off-center position only between a downstream side wall and a central position between an upstream side wall and the downstream side wall of the airfoil. Leakage of flow of a working fluid between the rotary member and stationary member is reduced.
DRAWINGSThese and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present invention provide a rotary machine in which an offset blade tip chord sealing system is disposed on a tip portion of at least one airfoil of a rotary member. In accordance with some embodiments of the present invention, the sealing system includes one or more seal strips (e.g., a single strip) disposed on the tip portion only at a substantially or generally off-center position between a downstream side wall and a central position between the downstream side wall and an upstream side wall of the airfoil, for example, a seal strip at or near the downstream side wall. In other words, at least a substantial portion, or most, or all of the one or more seal strips may extend along the tip portion between the central position and the downstream side wall. Thus, the sealing system may exclude seal strips disposed on the tip portion entirely or mostly between the central position and the upstream side wall, for example, a seal strip at or near the upstream side wall. The exemplary sealing system is configured to maintain minimal clearances between the rotary member and a surrounding stationary member resulting in reduced fluid leakage and increased efficiency of the rotary machine. The sealing system also facilitates usage of less exposed material on the tip portion of the airfoil to provide a tip load heat reduction since a seal strip (e.g., a single strip) is disposed on the tip portion only at an off-center position between the downstream side wall and the central position between the downstream side wall and the upstream side wall of the airfoil. Specific embodiments of the present invention are discussed below referring generally to
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The airfoil 18 extends outwardly into a working fluid flow path of the turbine assembly 10 where the working medium gases exert motive forces on a plurality of surfaces thereof. The airfoil 18 includes an upstream sidewall 22 and an opposite downstream side wall 24 (see
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In one embodiment, the entire seal strip 38 is disposed on the tip surface 34 only at a generally off-center position between the downstream side wall 24 and a central line 41 extending between the leading edge 26 and the trailing edge 28. In another embodiment, a substantial portion of the seal strip 38 is positioned between the central line 41 and the downstream side wall 24, while either ends 43,45 of the seal strip 38 extend across the central line 42 towards the upstream side wall 22.
In certain embodiments, the sealing system 32 may further include one or more additional seal strips between the central position 40 and the downstream side wall 24. The seal strip 38 enhances the flow resistance through the clearance gap 30 and thus reduces the flow of hot leakage gas for a predetermined pressure differential so as to improve the overall turbine efficiency. The width and height of the seal strip 38 may be varied for better performance, typically depending upon the size of the overall turbine assembly. Examples of configurations of the seal strip are illustrated in subsequent figures.
The offset of the seal strip 38 inward from the downstream side wall 24 creates a step 42 along the downstream side wall 24. The leakage flow is directed along the tip portion 20 from the upstream side to the downstream side of the airfoil in such a way that the fluid flows over the seal strip 38 to the recessed portion between the protruded seal strip 38 and the downstream side wall 24) that contains a separated flow region (low heat transfer region) at the downstream side. Additionally, the seal strip 38 also serves as a flow resistance element. The offset of the seal strip 38 from the downstream side wall 24 may also be varied for better performance, depending upon the size of the turbine assembly.
The offset of the seal strip 38 from the downstream side wall 24 also serves to reduce the tip cavity width to depth ratio, thereby providing lower cavity floor heat transfer. The seal strip 38 may also include at least one slot 44 proximate to the trailing edge 28 for exiting any tip cavity coolant flow. In other words, the seal strip 38 may include a series of sequential strips or longitudinally aligned strips, rather than a single continuous strip. Location, size, and orientation of the slot 44 may be varied depending upon the requirement. In accordance with aspects of the present invention, the seal strip 38 is located on the tip portion 20 in such a way so as to receive a cooling flow from the internal cooling passages of the airfoil 18. The seal strip 38 may be formed, for example, by integral casting with the airfoil tip portion, by electron-beam welding of flow discouragers to the airfoil tip portion, by physical vapor deposition of material to the airfoil tip portion, or by brazing, or a combination thereof. Alternately, the airfoil tip portion which has been cast to oversized dimensions, may have material removed by various methods, for example laser ablation, or the like, thereby forming the seal strip. In certain embodiments, the provision of the seal strip 38 only proximate the downstream side wall 24 of the tip portion 20 of the airfoil 18 reduces the amount of material used for tip treatment of an airfoil for sealing. Moreover, the seal strip 38 reduces the likelihood for cracking of the tip portion of the airfoil.
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The sealing system includes the seal strip disposed on the tip surface only at an off-center position between the downstream side wall and a central position between the upstream side wall and the downstream side wall. The seal strip enhances the flow resistance of leakage fluid through the clearance gap between the tip portion of the airfoil and the stationary member as represented by step 64. The offset blade tip chord sealing system disposed on the tip portion of the airfoil also reduces leakage of fluid along the tip portion from the upstream side to the downstream side of the airfoil for a predetermined pressure differential so as to improve the overall turbine efficiency as represented by step 66.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
Claims
1. A rotary machine, comprising:
- a stationary member;
- a rotary member disposed inside the stationary member, wherein the rotary member comprises at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls; and
- a sealing system disposed on the tip portion, wherein the sealing system consists essentially of:
- at least one seal strip disposed on the tip portion at an off-center position substantially between the downstream side wall and a central position between the upstream and downstream sidewalls.
2. The machine of claim 1, wherein the rotary machine comprises a turbine.
3. The machine of claim 1, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one airfoil.
4. The machine of claim 1, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one airfoil.
5. The machine of claim 1, wherein the at least one seal strip includes a first portion positioned between the downstream side wall and the central position and a second portion disposed between the upstream side wall and the central position, wherein the first portion is substantially greater than the second portion.
6. The machine of claim 1, wherein the seal strip comprises a base portion having fillets.
7. The machine of claim 1, wherein the seal strip comprises a rounded top portion.
8. A turbine, comprising:
- a stationary outer casing;
- a rotor disposed inside the stationary outer casing, wherein the rotor comprises at least one rotor blade having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls; and
- at least one seal strip disposed on the tip portion at an off-center position substantially between the downstream side wall, and a central position between the upstream and downstream side walls.
9. The turbine of claim 8, wherein a width of the at least one seal strip is in range of 0.05 to 0.125 inches.
10. The turbine of claim 8, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one rotor blade.
11. The turbine of claim 8, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one rotor blade.
12. The turbine of claim 8, wherein a height of the at least one seal strip is in the range of 0.150 to 0.250 inches.
13. The turbine of claim 12, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall equal to twice the height of the at least one seal strip.
14. The turbine of claim 8, wherein the at least one seal strip comprises a base portion having fillets.
15. The turbine of claim 8, wherein the at least one seal strip comprises a rounded top portion.
16. A sealing system, comprising:
- at least one airfoil having an upstream side wall, a downstream side wall, and a tip portion disposed between the upstream and downstream side walls; and
- at least one seal strip disposed on the tip portion at an off-center position only between the downstream side wall and a central position between the upstream and downstream side walls.
17. The sealing system of claim 16, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one airfoil.
18. The sealing system of claim 16, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one airfoil.
19. The sealing system of claim 16, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall equal to twice the height of the at least one seal strip.
20. The sealing system of claim 16, wherein the at least one seal strip comprises a base portion having fillets.
21. The sealing system of claim 16, wherein the at least one seal strip comprises a rounded top portion.
22. A method, comprising:
- rotating a rotary member having at least one airfoil disposed inside a stationary member; and
- reducing leakage of flow of a working fluid between the rotary member and stationary member, comprising:
- creating a flow resistance to the flow of the working fluid between a tip portion of the airfoil and the stationary member via at least one seal strip disposed on the tip portion at an off-center position only between a downstream side wall and a central position between an upstream side wall and the downstream side wall of the airfoil.
23. The method of claim 22, further comprising internally cooling the tip portion of the airfoil.
24. The method of 22, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a wall thickness of the at least one airfoil.
25. The method of 22, wherein the off-center position of the at least one seal strip is an offset distance from the downstream side wall at least equal to a radius of curvature of a tip edge of the at least one airfoil.
26. The method of 22, wherein the at least one seal strip comprises a base portion having fillets.
27. The method of 22, wherein the at least one seal strip comprises a rounded top portion.
Type: Application
Filed: Mar 31, 2006
Publication Date: Oct 11, 2007
Inventor: Ronald Bunker (Niskayuna, NY)
Application Number: 11/394,489
International Classification: F01D 1/00 (20060101); F01D 25/24 (20060101);