Method and apparatus for labyrinth seal packing ring

The present disclosure relates to a seal assembly for a turbomachine that includes at least one arcuate plate, a biasing member, and at least one packing ring segment. The packing ring segment includes at least one barrier that restricts circumferential flow of a fluid along the packing ring segment. In addition, the seal assembly includes a plurality of arcuate teeth disposed intermediate to the packing ring segment and the rotor. The clearances of at least two of the arcuate teeth are different from one another.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to the field of seals used in turbomachinery. More particularly, the subject matter disclosed herein relates to a progressive clearance labyrinth seal for application at the interface of a rotating component, such as a rotor in a turbine or compressor, and a stationary component, such as a casing or stator.

Labyrinth seals used in gas turbines, steam turbines, aircraft engines, compressors, and other turbomachinery systems are susceptible to leakage because a rotor clearance may be configured to be large enough to help prevent the rotor from rubbing against the seal. If the rotor does contact the seal, which is referred to as rotor-rub, the seal may be damaged creating an even larger clearance thereafter. Specifically, rotor-rub may occur in a gas turbine during a number of rotor transients that may include rotor dynamic excitation, relative thermal distortion of the rotor and stator, or shift in the center of the rotor because of development of a hydrodynamic lubricating film in the journal bearings with increasing speed. Deflection may occur when a gas turbine passes through critical speeds, such as during start-up. Distortion may be caused by thermal discrepancies between different components within the gas turbine. A large clearance between the seal and rotor is needed because a labyrinth seal may be unable to adjust its clearance during the rotor transients as it may be rigidly coupled to the stator. The clearances between rotating and stationary components of gas turbines may affect both the efficiency and performance of the turbine. In the design of gas turbines, close tolerances between components may result in greater efficiency. Similar rotor transients occur in other turbomachinery systems such as steam turbines, aircraft engines, or compressors, and the transients may often be difficult to predict.

In addition, labyrinth seals may be configured with a Variable Clearance Positive Pressure Packing (VCPPP) ring that biases the labyrinth seal away from the rotor to a large clearance by means of a spring. This helps prevent a rotor-rub during start-up rotor transients. When the differential pressure across the seal builds up beyond a certain value, the forces on the VCPPP ring cause it to close to a small rotor clearance. In the VCPPP ring design, there exists a steam-seal joint where the VCPPP ring contacts the casing or stator. The friction at this joint may introduce a hysteresis in the opening and closing of the VCPPP ring. If there are rotor transients after the VCPPP ring has closed, there will be rotor-rubs and damage to labyrinth teeth.

BRIEF DESCRIPTION OF THE INVENTION

In a first embodiment, a turbomachine includes a stationary housing and a rotor rotatable about an axis. The seal assembly for the turbomachine includes at least one arcuate plate coupled to an interior surface of the stationary housing and positioned in a radial plane. The seal assembly also includes at least one packing ring segment disposed intermediate to the rotor and the plate. The packing ring segment is positioned to move along the plate in a radial direction. The packing ring segment includes at least one barrier that restricts circumferential flow of a fluid along the packing ring segment. The seal assembly also includes a plurality of arcuate teeth disposed intermediate to the packing ring segment and the rotor. The clearances of at least two of the arcuate teeth are different from one another. In addition, the clearances of the arcuate teeth create a passive feedback in the hydrostatic forces generated by differential pressure across the seal assembly, such that as a tip clearance decreases, outward radial forces cause the packing ring segment to move away from the rotor and as the tip clearance increases, inward radial forces cause the packing ring segment to move toward the rotor. The seal assembly also includes a biasing member disposed intermediate to the arcuate plate and the packing ring segment and coupled to both.

In a second embodiment, a turbomachine includes a stationary housing and a rotor rotatable about an axis. A method of manufacturing a seal assembly for the turbomachine includes forming an arcuate packing ring segment. The arcuate packing ring segment is configured to be installed intermediate to the rotor and the stationary housing. The arcuate packing ring segment includes an inner surface and an outer surface. The arcuate packing ring segment includes at least one barrier and a plurality of arcuate teeth disposed on the inner surface. In addition, the clearances of at least two of the arcuate teeth are different from one another. The method also includes coupling a biasing member to the outer surface of the packing ring segment.

In a third embodiment, a segment of a circumferentially-segmented seal assembly is configured to be disposed intermediate to a rotor and a stationary housing. The segment includes an arcuate packing ring segment configured to be disposed intermediate to the rotor and the stationary housing. The segment also includes a plurality of arcuate teeth disposed intermediate to the packing ring and the rotor. The clearances of at least two of the arcuate teeth are different from one another. The segment also includes at least one barrier disposed on the arcuate packing ring segment. The barrier is substantially perpendicular to the plurality of arcuate teeth.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a cross-sectional view of an embodiment of a turbine system10, or turbomachine, which may include a variety of components, some of which are not shown for the sake of simplicity. In the illustrated embodiment, the gas turbine system10includes a compressor section12, a combustor section14, and a turbine section16. The turbine section16includes a stationary housing18and a rotating element20, or rotor, which rotates about an axis22. Moving blades24are attached to the rotating element20and stationary blades26are attached to the stationary housing18. The moving blades24and stationary blades26are arranged alternately in the axial direction. There are several possible locations where seal assemblies with barriers according to various embodiments may be installed, such as location28between a shrouded moving blade24and stationary housing18, location30between the rotating element20and stationary blade26, or an end-packing sealing location32between rotating element20and stationary housing18.

The seal assembly described herein includes one or more barriers that restrict circumferential flow of a fluid through the seal assembly. Specifically, by restricting circumferential flow, each segment of a multi-segment seal assembly is able to adjust individually to reduce axial leakage. The seal assembly described herein may be used with any suitable rotary machine, such as, but not limited to, the turbine system10ofFIG. 1.FIG. 2is a perspective view of an embodiment of the seal assembly32.FIG. 3illustrates how transients of the rotating element20may affect typical seal assemblies.FIGS. 4-10are cross-sectional and elevational views of other embodiments of the seal assembly32.FIG. 11illustrates a process that may be used to manufacture embodiments of the seal assembly32. In the illustrated embodiments, the barriers of the seal assembly32may reduce axial leakage between the rotating element20and the stationary housing18. More specifically, in the embodiments described below, the rotating element20rotates relative to the stationary housing18.

With the preceding in mind,FIG. 2is a perspective view of an embodiment of the seal assembly32of the turbine system10ofFIG. 1. Air, fuel, steam, or other gases enters the turbine system10at an upstream side34and exits the system at a downstream side36. In the illustrated embodiment, the axial direction is indicated by axis40and the radial direction is indicated by axis42. An arcuate plate44is coupled to the arcuate surface of the stationary housing18facing the rotating element20. In certain embodiments, the plate44may be made from steel or steel alloys. Moreover, the cross-section of the plate may appear T-shaped in certain embodiments, as depicted inFIG. 2. The plate44may be rigidly attached to the housing18. In addition, the plate44may be disposed as a complete 360-degree ring, as two 180-degree arcs, or smaller arcs that together form a complete ring. Further, in certain embodiments, the plate44may consist of a plurality of plates similarly configured.

An arcuate packing ring segment46is disposed intermediate to the plate44and the rotating element20. One or more arcuate packing ring segments46may together form a complete ring. In other words, the seal assembly32may be referred to as circumferentially-segmented. The surface of the packing ring segment46facing the rotating element20may be referred to as an inner surface49. Similarly, the surface of the packing ring segment46facing the stationary housing18may be referred to as an outer surface51. In certain embodiments, the arcuate packing ring segment46may be made from steel or steel alloys. Moreover, the arcuate packing ring segment46is configured to mate with the plate44, with a gap47. Biasing members48are disposed intermediate to the stationary housing18and the arcuate packing ring segment46. The biasing members48act as bearing flexures and provide a high stiffness in the axial direction40and a low stiffness in the radial direction42. The high axial stiffness restricts significant motion in the axial direction. The low radial stiffness allows the arcuate packing ring segment46to move in the radial direction. In addition, the biasing member48supports the weight of the arcuate packing ring segment46and prevents it from touching the rotating element20under no-flow conditions. In certain embodiments, the biasing member48may consist of a plurality of flexures. A first end50of each flexure may be mechanically coupled to the arcuate packing ring segment46and a second end52of each flexure may be mechanically coupled to the stationary housing18or to the plate44when it is T-shaped. In certain embodiments, examples of mechanically coupling may include bolting, welding, or other suitable techniques for mechanically affixing two structures. In other embodiments, the first end50may be an integral part of the arcuate packing ring segment46and the second end52mechanically affixed to the housing18. In yet another embodiment, the second end52may be an integral part of the stationary housing18or plate44when it is T-shaped, and the first end50mechanically affixed to the arcuate packing ring segment46. In this embodiment, each flexure is shown as a cantilever with a large width to thickness aspect ratio. Other flexure designs are possible that also achieve a high axial stiffness and low radial stiffness.

The arcuate packing ring segment46further includes a plurality of arcuate teeth54coupled to the surface of the ring facing the rotating element20. The segments of each tooth disposed on each segment of the packing ring segment46together form a complete ring around rotating element20. The spaces, or gaps, between adjacent arcuate teeth54may be referred to as pockets55. In certain embodiments, the teeth54may be made from a steel alloy. The teeth54may be arranged in one or more subsets of teeth. The clearance between the rotating element20and at least one of the teeth54is different from the clearances of the rest of the teeth54. In other words, the clearances of all of the teeth54are not identical. For example, a packing ring segment46of six teeth54may include five identical clearances and one that differs. Further examples using six teeth54include four identical clearances and two that differ, three identical clearances and three that differ, two identical clearances and four that differ, and six clearances that all differ from each other.

For example, progressive clearance labyrinth seal assemblies may include one or more arcuate teeth54with decreasing clearances going from the upstream side34to the downstream side36. Such seal assemblies may display self-correcting behavior when in operation. Specifically, when the clearances between tips of the arcuate teeth54and the rotating element20increase, hydrostatic lift-off forces decrease, thereby decreasing the clearances. When the clearances decrease, hydrostatic lift-off forces increase, thereby increasing the clearances. By maintaining the clearances, progressive clearance labyrinth seal assemblies help to reduce axial leakage and prevent turbine damage. Thus, progressive clearance labyrinth seal assemblies may use movement of arcuate packing ring segments46in a radial or circumferential direction to help maintain the desired tip clearances. Embodiments of the seal assembly32with barriers help to facilitate such movement in progressive clearance labyrinth seal assemblies and other seal assemblies that utilize packing ring movement, as described in further detail below.

As illustrated inFIG. 2, the arcuate packing ring segment46also includes one or more barriers56coupled to the surface of the ring facing the rotating element20. The barriers56are configured to restrict circumferential flow of a fluid along the packing ring segment46. For example, the barriers56may restrict circumferential flow of the fluid from one side of the packing ring segment46to another, as indicated by arrow58. Further, the barriers56may restrict circumferential flow of the fluid from one packing ring segment46to another, as indicated by arrow60. Thus, the barriers56help to restrict circumferential flow of the fluid in the channels between the arcuate teeth54of the packing ring segment46. In the illustrated embodiment, the packing ring segment46includes three barriers56, with two barriers56disposed near the ends of the packing ring segment46and one barrier56disposed near the middle of the packing ring segment46, thereby dividing the packing ring segment46into two sectors. The three barriers56are configured to restrict both flow along the packing ring segment46, as indicated by arrow58, and flow from other packing ring segments46, as indicated by arrow60, as described in detail below. In other embodiments, more or fewer barriers56may be used to restrict circumferential flow along the packing ring segment46or between packing ring segments46. For example, more barriers56may be used with larger packing ring segments46or to further restrict circumferential flow along the packing ring segment46, as indicated by arrow58. In further embodiments, the barriers56may be located a distance away from the ends of the packing ring segment46, instead of being disposed at the ends of the packing ring segment46. In the illustrated embodiment, the barriers56generally lie in an axial plane defined by the axial axis40and the radial axis42to restrict circumferential flow along the packing ring segment46. In other words, the barriers56are substantially perpendicular to the arcuate teeth54. However, in other embodiments, the barriers56may be configured at an angle away from the axial axis40. In certain embodiments, the barriers56may be made from materials similar to those used for the packing ring segment46and/or arcuate teeth54. For example, the barriers56may be made from a steel alloy.

To illustrate the relationship between transients of the rotating element20and circumferential flow,FIG. 3is a cross sectional view along the axial axis40of a typical seal assembly68. The seal assembly68includes six packing ring segments70,72,74,76,78, and80disposed about the rotating element20. Each of the packing ring segments70,72,74,76,78, and80include arcuate teeth54. Thus, the seal assembly68is a progressive clearance labyrinth seal assembly, as described above. A centered position82of the rotating element20may differ from an off-set position84of the rotating element20. The difference between positions82and84may be caused by a variety of transients of the rotating element20, such as, but not limited to, vibration, run-out, and thermal distortion. Thus, when the rotating element20is at speed, some of the packing ring segments70,72,74,76,78, and80may be closer to the rotating element20than others.

For example, both packing ring segments70and76are separated from the rotating element20by a centered distance86when the rotating element20is in the centered position82. In fact, all of the packing ring segments70,72,74,76,78, and80may be separated from the rotating element20by the centered distance86when the rotating element30is in the centered position82. However, when the rotating element20is in the off-set position84, the separation between packing ring segment70and the rotating element20decreases to an off-set distance88. Correspondingly, the separation between packing ring segment76and the rotating element20increases to an off-set distance90. Thus, it would be expected that hydrostatic lift-off forces would increase for packing ring segment70, thereby increasing the clearance between packing ring segment70and the rotating element20. In addition, it would be expected that hydrostatic lift-off forces would decrease for packing ring segment76, thereby decreasing the clearance between packing ring segment76and the rotating element20. However, the pockets55between adjacent arcuate teeth54of packing ring segments70,72,74,76,78, and80of the seal assembly68communicate with one another. In other words, circumferential flow may carry fluid from one packing ring segment to another and equalize the pressures in the corresponding pockets55for the different packing ring segments. Thus, the self-correcting hydrostatic forces discussed above may be rendered ineffective. When the rotating element20is in the off-set position84, packing ring segment76may have increased axial leakage compared to packing ring segment70. However, the barriers56disposed near the ends of the packing ring segment46shown inFIG. 2restrict circumferential flow from adjacent packing ring segments46, thereby enabling each of the packing ring segments46to respond individually to the hydrostatic lift-off forces. Thus, each of the packing ring segments46of the seal assembly32is able to maintain proper clearances during transients of the rotating element20to help reduce axial leakage.

Returning toFIG. 3, transients of the rotating element20and circumferential flow may also affect packing ring segments72,74,78, and80. Specifically, using packing ring segment72as an example, the clearance between the packing ring segment72and the rotating element20is the centered distance86when the rotating element20is in the centered position82. However, when the rotating element20is in the off-set position84, the clearance between the packing ring segment72and the rotating element20decreases at one end to an off-set distance94. The separation between the other end of the packing ring segment72and the rotating element20remains at approximately the centered distance86. Thus, where the separation has decreased to the off-set distance94, hydrostatic lift-off forces would be expected to increase, thereby increasing the clearance between that end of the packing ring segment72and the rotating element20. However, the pockets55between adjacent teeth54at one end of the packing ring segment72of the seal assembly68are in communication with the pockets55at the other end of the packing ring segment72. In other words, fluid may flow circumferentially from one end to the packing ring segment72to the other end and equalize the pressures circumferentially along the pockets55. Accordingly, the pressure along the packing ring segment72is approximately uniform. Thus, when the rotating element20is in the off-set position84, one end of the packing ring segment72has a greater clearance than the other end, which may cause increased axial leakage. However, the barrier56disposed near the middle of the packing ring segment46shown inFIG. 2restricts circumferential flow along the packing ring segment46, thereby enabling each end of the packing ring segment46to respond relatively independently to the hydrostatic lift-off forces. Thus, the barriers56of the seal assembly32enable passive feedback and hydrostatic forces to maintain equilibrium clearances between the arcuate teeth54and the rotating element20, such that the arcuate teeth54are prevented from contacting the rotating element20during transients of the rotating element20, which also helps to reduce axial leakage.

Returning to the barrier56of the seal assembly32in more detail,FIG. 4is a cross sectional view of an embodiment of the barrier56along the line labeled4-4inFIG. 2. As shown inFIG. 4, the lengths of the arcuate teeth54increase progressively moving from the upstream side34to the downstream side36. An upstream side110of the barrier56generally follows the contour of the arcuate tooth54located at the upstream side34. Similarly, a downstream side112of the barrier56generally follows the contour of the arcuate tooth54located at the downstream side36. In other words, the upstream and downstream sides110and112are generally not parallel with the radial axis42. A bottom side114connects the upstream and downstream sides110and112of the barrier56. As shown inFIG. 4, the bottom side114generally follows the contour of the tips116of the arcuate teeth54. Thus, the bottom side114slopes, such that an upstream height118of the barrier56is less than a downstream height120. In other words, the barrier56has a generally trapezoidal shape. The configuration of the barrier56restricts circumferential flow of the fluid passing between the arcuate teeth54of the seal assembly32. In other embodiments, the shape of the barrier56may be different from that shown inFIG. 4, as described in detail below.

To illustrate the structure of the barriers56from another view,FIG. 5is an elevational view of the upstream side34of the seal assembly32along the line labeled5-5inFIG. 2. As shown inFIG. 5, the barriers56help to restrict circumferential flow of the fluid, as indicated by arrows58and60. A thickness126of each of the barriers56may be configured to provide sufficient strength for the barriers56to restrict circumferential flow. In addition, the barriers56may be separated by a distance128. In the illustrated embodiment, the seal assembly32includes three barriers56separated by approximately equal distances128. In other embodiments, the seal assembly32may include additional barriers56, which are also separated by approximately equal distances128. In further embodiments, the separation distances128between the barriers56may be irregular or unequal.

The barriers56of the seal assembly32need not follow the contour of the tips116of the arcuate teeth54. As illustrated inFIG. 6, the barrier56may have a generally rectangular shape. Specifically, the upstream side110may be generally parallel to the radial axis42and longer than the arcuate tooth54located at the upstream side34. The downstream side112may also be parallel to the radial axis42and approximately the same length as the arcuate tooth54located at the downstream side36. In other words, the upstream and downstream heights118and120of the barrier56may be approximately the same. Thus, the bottom side114may be generally parallel to the axial axis40. In addition, the bottom side114of the barrier56may be generally straight. Such a configuration of the barrier56may further restrict circumferential flow compared to the barrier56shown inFIG. 4. That is, the barrier56shown inFIG. 6not only restricts circumferential flow of the fluid between the arcuate teeth, but also substantially all the circumferential flow along the packing ring segment46.

Barriers56may also be used in conjunction with seal assemblies32that include raised lands130on the rotating element20, as illustrated inFIG. 7. Such “hi-lo” features may be useful in creating a more tortuous path for the leakage flow. In other words, clearances132between the arcuate teeth54and the raised lands130may progressively decrease moving from the upstream side34to the downstream side36. In the illustrated embodiment, the upstream and downstream sides110and112of the barrier56generally follow the contours of the arcuate teeth54at the upstream and downstream sides34and36. The bottom side114may be generally straight and spaced away from the raised lands130to help prevent the barrier56from running into the raised lands130during transients of the rotating element20. In other embodiments, the bottom side114may have a generally sawtooth shape that follows the contour of the tips116of the arcuate teeth54. In further embodiments, the bottom side114may have a generally square sawtooth shape that follows the contour of the raised lands130. Thus, in certain embodiments, the bottom side114is not straight. Such configurations of the barrier56help to both restrict circumferential flow and accommodate the particular configurations of the seal assembly32.

In certain embodiment, the arcuate teeth54of the seal assembly32may be arranged in sets of repeating or non-repeating patterns, as illustrated inFIG. 8. Accordingly, the bottom side114of the barrier56may be configured to follow the contour of the tips116of the arcuate teeth54. As shown inFIG. 8, a first portion150of the bottom side114may generally slope toward the rotating element20to follow the contour of the tips116of the first set of arcuate teeth54. A second portion152of the bottom side114may follow the contour of the tips116of the second set of arcuate teeth54. Thus, the bottom side114has a generally sawtooth shape and is not straight. In various embodiments, the barrier56may be configured with a variety of shapes to be generally compatible with different configurations of progressive clearance labyrinth seal assemblies32.

In addition to the embodiments of the seal assemblies32discussed above, in certain embodiments, the sides of the packing ring segments46may be inclined at an angle170from the radial axis42, as illustrated in the elevational view ofFIG. 9. Such embodiments of the seal assembly32may enable the packing ring segments46to move both in radial and circumferential directions. In such embodiments, the barriers56may also be inclined at the angle170from the radial axis42. Alternatively, the barriers56may be generally parallel to the radial axis42. In the illustrated embodiment, the seal assembly32includes three barriers56. The outer two barriers56are separated by approximately equal distances172from the edges of the seal assembly32. In other embodiments, the two outer barriers56may be offset from the edges of the seal assembly32by unequal distances172. In such embodiments, the separation distances128between the outer two barriers56and the inner barrier56may also be different.

In further embodiments, the edges of the seal assembly32may be arcuate, as illustrated in the elevational view ofFIG. 10. Such embodiments of the seal assembly32may enable the packing ring segments46to move radially and circumferentially in a curved direction. In addition, the arcuate edges of the packing ring segment46may be inclined at the angle170from the radial axis42. In such embodiments, the barriers56may also be arcuate. In the illustrated embodiment, the seal assembly32includes two barriers56separated from one another by the distance128and from the edges of the seal assembly by the distance172. Both barriers56may help to restrict circumferential flow along the packing ring segment46and from other packing ring segments46. In other respects, the seal assembly32shown inFIG. 10is similar to other embodiments discussed in detail above.

The various embodiments of the seal assembly32discussed in detail above may be manufactured using a process190, as illustrated in the flow chart ofFIG. 11. In a step192, the arcuate packing ring segment46of the seal assembly32is formed. The packing ring segment46is configured to be installed between the rotating element20and the stationary housing18of the turbine system10. The packing ring segment46includes inner and outer surfaces49and51. At least one barrier56and one or more arcuate teeth54are disposed on the inner surface49of the packing ring segment46. The barrier56helps to restrict circumferential flow along the inner surface49of the packing ring segment46. In addition, the clearance of at least one of the arcuate teeth54is different from the clearances of the rest of the arcuate teeth54. In a step194, a biasing member48is coupled to the outer surface51of the packing ring segment46. The biasing members are configured to act as bearings and allow the packing ring segment46to move in a radial direction but restrict movement in an axial direction.