In jet turbine engines an air seal is used to separate hot post combustion gasses which drive the turbine from colder cooling air which prevents over heating of the engine components. One type of such seal is the knife seal. Knife or labyrinth seals are generally made up of a stator or ring, and a series of knives, fins or baffles normal to the stator with a very small clearance between them. This produces a torturous flow path for the air, preventing leakage.
Knife seals may be mounted horizontally within a turbine engine allowing for the stators to be mounted to support structures and the baffles mounted to the turbine disks. Two concentric stators may be mounted with an inner and outer stator with the turbine disk having a set of baffles for each. The stator portions of the seal are often extensions of the structural support.
To function well, knife seals require the very small clearance between the stator and baffle or fin to be maintained. Dissimilar thermal expansion of the stator/stator support and the turbine disk can be detrimental to the function of the seal, as this can lead to rubbing between the stator and the fins/baffles. The rubbing can result in damage of the stator and/or fins and reduce the efficiency of the seal. The difference of expansion between the stator and the fins is often accounted for by increasing the distance between the inner and outer stator allowing the disk to expand and contract while preventing rubbing. This extra clearance, although small, itself can reduce the efficiency of the seal. Thus it is advantageous for an air seal to expand and contract with the disk while preventing rubbing and maintaining the small clearance between both stators and their respective sets of baffles during the majority of engine operations.
According to some aspects of the present disclosure, a reduced leakage seal for a gas turbine may have a control ring with a radially outward facing control surface and a radially inward facing control surface. The control ring may be coaxial with an axis and have a thermal expansion time constant. The seal may also have an outer ring with a radially inward facing outer stator and 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 may have a second thermal expansion time constant. The seal may also include an inner ring with a radially outward facing inner stator and 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 may have a third thermal expansion time constant. The seal may include a plurality of alignment restraints which restrict axial translation of the control ring, outer ring and inner ring with respect to one another. The thermal expansion time constant of the control ring is greater than the second thermal expansion time constant of the outer ring.
According to another aspect the seal may further include a rotating structure with 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, with the axially extending arm at least in part separating a first volume and a second volume. The first volume contains hot combustion gases. In addition, the thermal expansion time constant of the control ring may be greater than or equal a thermal expansion time constant of the rotating structure. The outer ring may also have a first radially extending flange in contact with at least one of the plurality of alignment restraints. The inner ring also may have a second radially extending flange in contact with at least another of the plurality of alignment restraints. The control ring, outer ring and inner ring may each be in contact with each of the others. The plurality of alignment restrains may be pins, brackets or clips. The seal may further have a rotating structure with a plurality of axially extending arms, a first of the plurality of axially extending arms may have a first set of outward facing knives, a second of the plurality of axially extending arms may have a second set of inward facing knives. The outward facing knives may be axially aligned oppose the outer stator while the inward facing knives may be axially aligned and oppose the inner stator; the axially extending arms at least in part separates a first volume and a second volume.
A gas turbine engine in accordance with the present disclosure may include, a rotor disk, a hot zone containing combustion gases, a cool zone containing cooling air (typically less than 900K), and a labyrinth seal separating the combustions gases from the cooling air in the cool zone. The labyrinth seal may include a control ring, a first stator, a second stator, first and second sets of knives oppositely disposed from each other. The first set may cooperate with the first stator and the second set may cooperate with the second stator. The control ring may have a first time constant of thermal expansion, while the first stator may have a second time constant of thermal expansion, which is less than the first time constant of the control ring. The second stator may have a third time constant of thermal expansion that may be also less than the first time constant. The rotor disk may have a fourth time constant of thermal expansion that is less than or equal to the first time constant. The first set and the second set of knives may extend axially from the rotor disk. According to another aspect, 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. In addition to this aspect 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; the axial overlap and the second axial overlap may have a tab extending axially from the control ring.
A method of controlling gaps between knives and stators in a labyrinth seal for a gas turbine engine in accordance with the present disclosure may include 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, also varying the radius of a control ring as a function of time and temperature, as well as limiting the radial contraction of the first stator as a function of the radius of the control ring during a first engine condition, and limiting the radial expansion of the second stator as a function of the radius of the control ring during a second engine condition. A first gap in the labyrinth seal may be a function of the radius of the knife ring and radial expansion of the second stator during the first engine condition and a second gap of the labyrinth seal may be a function of the radius of the knife ring and the radial contraction of the second stator during the second engine condition. The method may include the second engine condition may be a transition from idle to steady state cruise. The method may also include the first engine condition may be a transition from steady state cruise to idle. The method may include as well, the first engine condition and second engine condition may be a transition from idle to cruise to idle. In accordance with another aspect of the method, the step of varying the radius of the control ring may involve 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.
The following will be apparent from elements of the figures, which are provided for illustrative purposes.
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.
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.
The present disclosure is directed to systems and methods for providing an air seal, particularly knife seals in a gas turbine engine.
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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.
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.
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.
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.
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.
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.