REDUCED LEAKAGE AIR SEAL

Abstract

An air seal for a jet turbine engine with an upper stator, lower stator and finned turbine disk. The thermal expansion of the stators may be regulated by a control ring, which has a lower rate of thermal expansion that the stators, to prevent rubbing between the stator and fins.

Claims

1. A reduced leakage seal for a gas turbine, comprising: a control ring having a radially outward facing control surface and a radially inward facing control surface, the control ring having a thermal expansion time constant; the control ring coaxial with an axis; an outer ring having a radially inward facing outer stator; the outer ring having a radially inward contact surface cooperating with the outward radial control surface limiting the radial inward position of the outer ring with respect to the control ring; the outer ring having a second thermal expansion time constant; an inner ring having a radially outward facing inner stator, the inner ring having a radially outward contact surface cooperating with the radially inward control surface limiting the radial outward position of the inner ring with respect to the control ring; the inner ring having a third thermal expansion time constant; and, a plurality of alignment restraints, the plurality of alignment restraints restricting axial translation of the control ring, outer ring and inner ring with respect to one another; wherein the thermal expansion time constant of the control ring is greater than the second thermal expansion time constant of the outer ring.

2. The seal of claim 1, further comprising a rotating structure have an axially extending arm with a first set of outward facing knives and a second set of inward facing knives, the outward facing knives axially aligned and opposing the outer stator and the inward facing knives axially aligned and opposing the inner stator, the axially extending arm at least in part separating a first volume and a second volume.

3. The seal of claim 2, wherein the first volume contains hot combustion gases.

4. The seal of claim 2, wherein the thermal expansion time constant of the control ring is greater than or equal a thermal expansion time constant of the rotating structure.

5. The seal of claim 1, wherein the outer ring comprises a first radially extending flange, the first radially extending flange in contact with at least one of the plurality of alignment restraints.

6. The seal of claim 1, wherein the inner ring comprises a second radially extending flange, the second radially extending flange in contact with at least another of the plurality of alignment restraints.

7. The seal of claim 1, wherein each of the control ring, outer ring and inner ring are in contact with each of the others.

8. The seal of claim 1, wherein the plurality of alignment restrains are selected from the group consisting of pins, brackets and clips.

9. The seal of claim 1, further comprising a rotating structure having a plurality of axially extending arms, a first of the plurality of axially extending arms having a first set of outward facing knives and a second of the plurality of axially extending arms having a second set of inward facing knives, the outward facing knives axially aligned and opposing the outer stator and the inward facing knives axially aligned and opposing the inner stator, the axially extending arms at least in part separating a first volume and a second volume.

10. A gas turbine engine comprising: a rotor disk; a hot zone containing combustion gases; a cool zone containing cooling air, and a labyrinth seal separating the combustions gases from the cooling air in the cool zone; the labyrinth seal comprising: a control ring; a first stator; a second stator; and, a first set of knives and a second set of knives oppositely disposed from the first set, the first set cooperating with the first stator and the second set cooperating with the second stator; wherein, the control ring having a first time constant of thermal expansion; the first stator having a second time constant of thermal expansion less than the first time constant of the control ring, the second stator having a third time constant of thermal expansion less than the first time constant; and, the rotor disk having a fourth time constant of thermal expansion less than or equal to the first time constant and wherein the first set and the second set of knives extend axially from the rotor disk.

11. The engine of claim 10, wherein the control ring has an axial overlap with the first stator limiting the minimum radial position of the first stator with respect to the control ring.

12. The engine of claim 11, wherein the control ring has a second axial overlap with the second stator limiting the maximum radial position of the second stator with a respect to the control ring.

13. The engine of claim 12, wherein the axial overlap and the second axial overlap comprise a tab extending axially from the control ring.

14. A method of controlling gaps between knives and stators in a labyrinth seal for a gas turbine engine comprising: providing a labyrinth seal including a first stator, a second stator and a knife ring having a first set of knives interacting with the first stator and a second set of knives interacting with the second stator; varying the radius of a knife ring associated with the labyrinth as a function of time, temperature and rotational speed of the knife ring; varying the radius of a control ring as a function of time and temperature; limiting the radial contraction of the first stator as a function of the radius of the control ring during a first engine condition; limiting the radial expansion of the second stator as a function of the radius of the control ring during a second engine condition; wherein a first gap in the labyrinth seal is a function of the radius of the knife ring and radial expansion of the second stator during the second engine condition and a second gap of the labyrinth seal is a function of the radius of the knife ring and the radial contraction of the first stator during the first engine condition.

15. The method of claim 14, wherein the second engine condition is a transition from idle to steady state cruise.

16. The method of claim 14, wherein the first engine condition is a transition from steady state cruise to idle.

17. The method of claim 14, wherein the first engine condition and second engine condition are a transition from idle to cruise to idle.

18. The method of claim 14, wherein the step of varying the radius of the control ring comprises the step of providing the control ring with a time constant of thermal expansion greater than the time constants of thermal expansion of the first stator and second stator.

19. The seal of claim 8, wherein the pins comprise shoulder bolts.

20. The engine of claim 13, wherein a plurality of pins maintains the control ring, first stator and second stator concentric to a center axis of the turbine engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following will be apparent from elements of the figures, which are provided for illustrative purposes.

[0009] FIG. 1 depicts a cross section of a seal while engine is in cruise according to an embodiment of the present disclosure.

[0010] FIG. 2 depicts a cross section of the seal while engine is accelerating according to an embodiment of the present disclosure.

[0011] FIG. 3 depicts a cross section of the seal while engine is decelerating according to an embodiment of the present disclosure.

[0012] FIG. 4 depicts an illustration of the gap between the upper stator and the turbine disk while engine is operating in various modes.

[0013] FIG. 5 depicts an illustration of the relative change in diameter of the upper stator, control ring and turbine disk while the engine is in various operating modes.

[0014] FIG. 6 depicts an illustration of the gap between the lower stator and the turbine disk while engine is operating in various modes.

[0015] FIG. 7 depicts an illustration of the relative change in diameter of the upper stator, control ring and turbine disk while the engine is in various operating modes.

[0016] FIG. 8 is a flow chart of the method of use for the seal.

[0017] FIG. 9 is an isometric cutout of the upper and lower stators of the seal according to embodiments of the current disclosure.

[0018] FIG. 10 is an isometric cutout of the knifes on an arm of the turbine disc according to embodiments of the current disclosure.

[0019] FIG. 11 depicts an axial view of the upper stator according to embodiments of the current disclosure.

[0020] FIG. 12 depicts an axial view of the lower stator according to embodiments of the current disclosure.

[0021] The present application discloses illustrative (i.e., example) embodiments. The claimed inventions are not limited to the illustrative embodiments. Therefore, many implementations of the claims will be different than the illustrative embodiments. Various modifications can be made to the claimed inventions without departing from the spirit and scope of the disclose. The claims are intended to cover implementations with such modifications.

DETAILED DESCRIPTION

[0022] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments in the drawings and specific language will be used to describe the same.

[0023] The present disclosure is directed to systems and methods for providing an air seal, particularly knife seals in a gas turbine engine.

[0024] FIGS. 1-3 depict an embodiment of the disclosed air seal. As shown in FIG. 1 the illustrative air seal 100 has primarily four components, and upper stator 1, a lower stator 2, a control ring 3 and knifes 10 on the protrusion (arm, or knife ring) 9 extending from the turbine disk 4. Each stator may include a separate support ring for the stator. The control ring 3 may be an annular disk that encircles the center axis of the engine and separates the upper stator 1 and the lower stator 2 from the structural support 5 situated axially upstream of a turbine disk 4. The upper stator 1, lower stator 2, and control ring 3 may be held concentric to the turbine shaft by locating pins 6 distributed at a set radius around the center axis of the engine. The upper stator 1 may be an L-shaped annular disk, extending radially and axially. The radially extending portion may be situated between the control ring 3 and the lower stator 2. The lower stator 2 may also be L-shaped extending radially and axially with the radial portion between the upper stator 1 and the heads of the locator pins 6. The locator pins 6 may be fixed in place with shoulder bolts 7. A portion of the control ring 3 radially separates and may be in physical communication with both the upper stator 1, through an outward radial control surface 11, and lower stator 2, through an inward radial control surface 12. The upper stator 1, lower stator 2 and control ring 3 each have a large bore hole 8 through which the locator pin is placed. This hole is sized to provide a clearance that allows for thermal expansion and contraction during engine operation. The axially extending portions of the upper stator 1 and lower stator 2 are separated radially producing an annular gap between the stators. The turbine disk 4 has a circular protrusion 9 which extends into the annular gap between the upper and lower stators. This protrusion has a plurality of fins 10 distributed axially on both the inner and outer side of the protrusion 9. These fins combined with the upper and lower stators produce a series of knife seals which create a torturous flow path that air cannot pass. During steady-state operations, i.e. the airplane is cruising or the engine is idling, clearances between the stators and the fins are kept very small. This changes when the airplane is either accelerating or decelerating.

[0025] As shown in FIG. 2, when the airplane accelerates the increase in heat transfer leads to the stators and disk 4 expanding quickly. The control ring 3 being thicker or of a different material, expands at a rate slower than the stators. This difference produces a gap between the upper stator 1 and the control ring 3. Due to the portion of the control ring 3 in contact with the lower stator 2, the expansion rate of the lower stator 2 is arrested. This increases the space between the lower stator 2 and the fins 10 of the turbine disk 4, ensuring that no rubbing occurs and that neither the lower stator 2 or the fins 10 are damaged. The upper stator 1 continues to expand at a rate quick enough to maintain the small clearance between the upper stator 1 and the fins 10, preventing rubbing and ensuring the illustrated seal 100 continues to function. As the expansion of the control ring 3 completes the expansion of the lower stator 2 restores the small clearance between the lower stator 2 and the fins 10.

[0026] As shown in FIG. 3, during cooling the process is reversed. The stators and the turbine disk 4 contract at a higher rate the control ring 3. The difference in contraction rates produces a small gap between the control ring 3 and the lower stator 2. The control ring 3 arrests the contraction rate of the upper stator 1, increasing the distance between the upper stator 1 and the fins 10, thereby preventing rubbing between the upper stator 1 and the fins 10. The lower stator 2 contracts at a rate quick enough compared to the turbine disk 4 to maintain the small clearance between the lower stator 2 and the fins 10, ensuring the illustrated seal 100 continues to function. As the contraction of the control ring 3 completes the contraction of the upper stator 1 restores the small clearance between the upper stator 1 and the fins.

[0027] FIG. 4 qualitatively shows the seal clearances between the upper stator 1 and the turbine disk 4 during engine operation. FIG. 5 qualitatively shows the diameters of the upper stator 1, control ring 3 and turbine disk 4. The clearance is initially static while the engine is idling. When the engine powers up to cruise the upper stator 1 quickly expands to it maximum diameter, increasing the seal clearance. As the disk heats the it begins to expand reducing the size of the clearance reducing the clearance to a minimum as the expansion rate matches the rate of the structural support 5. When the engine is idled the turbine disk 4 contracts quickly as it cools. The contraction rate of the upper stator 1 is slowed by the control ring 3. This causes the clearance to temporarily increase again. The clearance decreases as the control ring 3 settles.

[0028] FIG. 6 qualitatively shows the seal clearances between the lower stator 2 and the turbine disk 4 during engine operation. FIG. 7 qualitatively shows the diameters of the lower stator 2, control ring 3 and turbine disk 4. The clearance is initially static while the engine is idling. When the engine powers up to cruise the lower stator 2 begins to expand its diameter but its expansion is impeded by the control ring 3. The turbine disk 4 is free to expand and initially expands at a rate much greater than the control ring 3, increasing the seal clearance. As the disk temperature nears operating temperature its expansion rate slows enabling the control ring 3 to expand at a higher rate than the disk. This reduces the size of the clearance to a minimum. As the control ring 3 reaches temperature its expansion is then halted, stopping the expansion of the lower stator 2 as well. The clearance begins to increase as the turbine continues expanding, and continues until the expansion rate of the structural support 5 and turbine disk 4 match or the turbine disk 4 reaches its final size. When the engine is idled the lower stator 2 contracts quickly as it cools to a minimum size, at a rate greater than the turbine disk 4, increasing the clearance between the two. The contraction rate of the upper stator 1 is slowed by the control ring 3. This causes the clearance to temporarily increase again. The clearance decreases as the turbine continues to contract.

[0029] FIG. 9 shows an isometric view of a cutout of the illustrated seal. Although depicted as thin and L-shaped the upper stator 1 and lower stator 2 thickness may be chosen for proper thermal expansion rates.

[0030] FIG. 10 shows an isometric view of a cutout of the turbine disk 4. Although depicted as having four fins, two on either side of the circular protrusion it can have any number chosen for ideal functioning of the knife seal.

[0031] FIGS. 11 and 12 depict axial views of the upper stator 1 and lower stator 2 respectively. As can be seen the stators are annular, with a plurality of bore holes. Any number of bore holes can be used, and would be based on the required number of locator pins 6 needed to ensure the stators and control ring 3 remain concentric. Although the bore holes are depicted as circular they can be radially extending slots.

[0032] FIG. 8 is a block diagram of a method for use of the illustrated seal. Block 801 illustrates varying the radius of a knife ring associated with the labyrinth as a function of time, temperature and rotational speed of the knife ring. This may include increasing or decreasing engine power.

[0033] Block 802 illustrates varying the radius of a control ring as a function of time and temperature. This may involve ensuring a proper coefficient of thermal expansion for the control ring.

[0034] Block 803 illustrates limiting the radial contraction of the upper stator as a function of the radius of the control ring during idling or cool down of the engine. This may be done by ensuring the control ring contracts at a slower rate than the upper stator.

[0035] Block 804 illustrates limiting the radial expansion of the second stator as a function of the radius of the control ring during acceleration or heat up of the engine. This may be done by ensuring the control ring expands at a slower rate than the lower stator.

[0036] Block 805 illustrates maintaining a gap in the labyrinth seal between the knife ring and the second stator by controlling the expansion of the second stator during engine acceleration or heat up.

[0037] Block 806 illustrates maintaining a gap in the labyrinth seal between the knife ring and the upper stator by controlling the radial contraction of the first stator engine idling or cool down.

[0038] Although examples are illustrated and described herein, embodiments are nevertheless not limited to the details shown, since various modifications and structural changes may be made therein by those of ordinary skill within the scope and range of equivalents of the claims.