Seal assembly for rotary machine

A seal assembly for a rotary machine is provided. The seal assembly includes a plurality of seal segments disposed circumferentially intermediate to a stationary housing and a rotor, where each of the plurality of seal segments includes a stator interface element and a shoe plate movably supported by the stator interface element. The shoe plate includes one or more labyrinth teeth, a load-bearing surface, and one or more supply ports for facilitating supply of high pressure fluid toward the rotor. In one embodiment, the shoe plate also includes a radially extending portion that is in contact with a portion of the ring movably supported into the stator interface element. In another embodiment, each of the plurality of seal segments includes a plurality of overlapping spring-loaded leaf seal plates in contact with the stator interface element and the radially extending portion. Method of operating the seal segment is also disclosed.

BACKGROUND

The present application relates generally to a seal assembly for turbo-machinery and more particularly relates to a film riding seal assembly for facilitating sealing in the turbo-machinery.

Various types of turbo-machinery, such as, gas turbine engines, aircraft engines, and steam turbines are known and widely used for applications including power generation, propulsion, and the like. The efficiency of the turbo-machinery depends in part on clearances between the internal components of the turbo-machinery and the leakage of fluids through such clearances. For example, large clearances may be intentionally allowed at certain rotor-stator interfaces to accommodate large, thermally or mechanically-induced relative motions. Leakage of fluid through these clearances from regions of high pressure to regions of low pressure may reduce the efficiency of the turbo-machinery.

Different types of seal assemblies are used to minimize the leakage of the fluid flowing through various clearances in the turbo-machinery. The seal assemblies, however, are often subject to relatively high temperatures, thermal gradients, and thermal and mechanical expansion and contraction during various operational stages that may increase or decrease the clearance therethrough. For example, traditional labyrinth sealing assemblies are assembled to aid very tight clearance during a start-up transient phase. Use of such traditional labyrinth sealing assembly may lead to large clearances during a steady state operation, thereby leading to poor performance in the steady state operation. Moreover, such a tight sealing caused by the traditional labyrinth sealing assemblies in the start-up transient phase may also result in rubbing of the labyrinth sealing assemblies. Whereas, the labyrinth sealing assemblies arranged with large radial clearances (to avoid seals rubs) lead to increased leakage.

There is therefore a desire for improved compliant sealing assemblies for use with the turbo-machinery.

BRIEF DESCRIPTION

In accordance with an embodiment of the invention, a seal assembly for a rotary machine is provided. The seal assembly includes a plurality of seal segments disposed circumferentially intermediate to a stationary housing and a rotor, where each of the plurality of seal segments includes a stator interface element, a portion of a ring movably supported into the stator interface element, and a shoe plate movably supported by the stator interface element. The shoe plate includes one or more labyrinth teeth, a load-bearing surface radially offset from the one or more labyrinth teeth, one or more supply ports formed into the shoe plate for facilitating supply of high pressure fluid toward the rotor, and a radially extending portion that extends toward the stator interface element, where the radially extending portion is in contact with the portion of the ring.

In accordance with an embodiment of the invention, a seal assembly for a rotary machine is provided. The seal assembly includes a plurality of seal segments disposed circumferentially intermediate to a stationary housing and a rotor, where each of the plurality of seal segments includes a stator interface element and a shoe plate movably supported by the stator interface element. The shoe plate includes one or more labyrinth teeth, a load-bearing surface radially offset from the one or more labyrinth teeth, one or more supply ports formed into the shoe plate for facilitating supply of high pressure fluid toward the rotor, and a radially extending portion that extends toward the stator interface element. Each of the plurality of seal segments further includes a plurality of overlapping spring-loaded leaf seal plates in contact with the stator interface element and the radially extending portion of the shoe plate.

In accordance with an embodiment of the invention, a method for operating a seal segment of a seal assembly for a rotary machine having a stationary housing and a rotor is provided. The seal segment includes a shoe plate having a labyrinth tooth, a load-bearing surface, and a radially extending portion that extends toward the stator interface element. The method includes supplying high pressure fluid radially toward the rotor through the load-bearing surface of the shoe plate. The method further includes generating at least one of an aerostatic force or an aerodynamic force between the shoe plate and the rotor based on at least one of the supply of high pressure fluid towards the rotor, a curvature mismatch between the shoe plate and the rotor, and grooves present on the shoe plate or the rotor. The method further includes preventing leakage from a space between the shoe plate and the stator interface element due to a secondary seal that includes one of: a portion of a ring disposed in the stator interface element and in contact with the radially extending portion; or a plurality of overlapping spring-loaded leaf seal plates in contact with the stator interface element and the radially extending portion of the shoe plate.

DETAILED DESCRIPTION

The specification may be best understood with reference to the detailed figures and description set forth herein. Various embodiments are described hereinafter with reference to the figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is just for explanatory purposes as the method and the system extend beyond the described embodiments.

In the following specification and the claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise. As used herein, the term “or” is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.

As used herein, the terms “may” and “may be” indicate a possibility of an occurrence within a set of circumstances; a possession of a specified property, characteristic or function; and/or qualify another verb by expressing one or more of an ability, capability, or possibility associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a modified term is apparently appropriate, capable, or suitable for an indicated capacity, function, or usage, while taking into account that in some circumstances, the modified term may sometimes not be appropriate, capable, or suitable.

FIG. 1is a perspective view10of a seal assembly101for a rotary machine, in accordance with an embodiment of the present specification. In one embodiment, the seal assembly101may be a film riding seal assembly. The seal assembly101is shown to have an orientation in axial, radial and circumferential direction as represented by numerals102,104and106, respectively. The seal assembly101is circumferentially arranged around a rotor (not shown) that is axially located in the rotary machine such that the seal assembly101is intermediate to a stationary housing110and the rotor (not shown). The stationary housing110includes a plurality of stator interface elements such as a stator interface element112that form a radially outwards region of the seal assembly101.

The seal assembly101further includes a plurality of seal segments such as a seal segment116(seeFIG. 2for a detailed view) located adjacent to each other and disposed circumferentially intermediate to the stationary housing110and the rotor. Each of the seal segment116includes a stator interface element112and a shoe plate118located proximate to the rotor. The shoe plate118may be movably supported by a corresponding stator interface element112of the plurality of stator interface elements. During an operation of the rotary machine, the shoe plate118rides on a fluid film formed between the shoe plate118and the rotor.

The shoe plate118may include one or more labyrinth teeth such as a labyrinth tooth120at a side facing the rotor surface. In the embodiment ofFIG. 2only one labyrinth tooth120is shown, however, embodiments having more than one labyrinth teeth are also contemplated. In one embodiment, the labyrinth tooth120may be located towards forward-most region of the shoe plate118. The labyrinth tooth120is employed to substantially separate a high pressure region122from a low pressure region124on either sides of the seal assembly101of the rotary machine.

Each shoe plate118may also include one or more supply ports such as a supply port126for facilitating a flow of high pressure fluid toward a rotor of the rotary machine. AlthoughFIG. 1depicts one supply port126per each seal segment116, use of more than one supply ports is also contemplated. Furthermore, each of the shoe plate118may include a load-bearing surface128facing the rotor of the rotary machine. The load-bearing surface128may include one or more openings129. In one embodiment, each of the supply port126may discharge the high pressure fluid toward the rotor via the one or more openings129. Further details of the supply port126, the load-bearing surface128, and the openings129will be described later in the description.

Moreover, the seal assembly101may also include a secondary seal (not shown inFIG. 1) configured to reduce/stop leakage of fluid from a space between the stator interface element112and the shoe plate118. Details of the secondary seals will be described later in the description.

FIG. 2is a perspective view20of the seal segment116, in accordance with an embodiment of the present specification.FIG. 2will be explained in conjunction withFIG. 1. As previously noted, the seal segment116includes the stator interface element112, the shoe plate118movably supported by the stator interface element112, the labyrinth tooth120and the load-bearing surface128facing the rotor. The shoe plate118is configured to allow a high pressure fluid from the high pressure region122to an upstream portion132of forward-most labyrinth tooth120and a low pressure fluid from the low pressure region124to a downstream portion or cavity134of the aft-most labyrinth tooth120.

The load-bearing surface128may be located radially offset from the labyrinth tooth120. The load-bearing surface128is configured to generate radial aerostatic-aerodynamic force between the shoe plate118and the rotor. In one embodiment, the load-bearing surface128may be coated with lubricating coatings to minimize unintentional rubs between the shoe plate118and the rotor. Examples of the lubricating coatings may include, but are not limited to PS304 or PS400 (developed by NASA). In some embodiments, lubricants used in the lubricating coatings may be embedded in hard materials to balance the lubrication, wear and thermal growth properties of the coating. Such, hard materials may include, but are not limited to graphite or diamond-like carbon, hexagonal boron nitride, chromium molybdenum nitride, chrome titanium aluminum nitride or combinations thereof. Moreover, in certain embodiments, surface of the rotor interfacing with the load-bearing surface128may be coated with materials, including but not limited to, chromium carbide, titanium aluminum nitride, hexagonal boron nitride, and the like to improve hardness, corrosion resistance, and an ability to maintain a good surface finish of the surface of the rotor.

The seal segment116may also include one or more flexible elements such as the flexible element136disposed between the shoe plate118and the stator interface element112to aid in the radial movement of the shoe plate118relative to the stator interface element112. In one embodiment, two (seeFIG. 4) such flexible elements may be disposed between the shoe plate118and the stator interface element112of which only one is visible in the perspective view ofFIG. 2. It is to be noted that the present specification is not limited with respect the specific number of flexible elements.

The flexible element136may provide radial compliance and/or rotational rigidity about the circumferential and axial directions106,102. The purpose of the flexible element136is to support the shoe plate118with radial, tangential and axial stiffness properties and guide the motion of the shoe plate118relative to the stator interface element112. Non-limiting examples of the flexible elements may include bellow springs, flexures, or other spring-like elements including flexible beams, leaf springs or coil springs.

In the embodiment ofFIG. 2, the flexible element136includes a bellow. The radial stiffness of the bellow may be controlled by changing one or more of an axial width, a tangential width, a thickness of the bellow, and spacing between the bellow turns and the material for the bellow springs. In one embodiment, the bellows are formed from Inconel X750 or Rene41 or similar high temperature alloys or in the case of low temperature applications will be made from an appropriate metal or composite material. The bellow may be formed from sheet metal and brazed to the stator interface element112and the shoe plate118or could be fabricated by a machining process like wire EDM.

As shown inFIG. 2, the shoe plate118may further include one or more crossover holes such as a crossover hole138. The crossover hole138may be located axially downstream of the aft-most labyrinth tooth120. The crossover hole138aids in allowing a flow of a low pressure fluid from the downstream portion134of the aft-most labyrinth tooth120to a rear cavity140. The rear cavity140may be defined by the space between the stator interface element112and the shoe plate118. In one embodiment, the crossover hole138may be angled for allowing the flow of the low pressure fluid in a radial direction from behind the labyrinth tooth120into the rear cavity140. In another embodiment, the crossover hole138is angled for allowing the flow of the low pressure fluid in a circumferential direction causing the low pressure fluid to swirl as the low pressure fluid transfers from behind the labyrinth tooth120to radially above the shoe plate118. Such swirl in the low pressure fluid may cause the low pressure fluid to gain tangential velocity in a direction of rotation of the rotor or opposite to the direction of rotation of the rotor.

Moreover, as previously noted, the shoe plate118also includes one or more supply ports (only one supply port126is shown inFIG. 2). The supply port126may be formed axially in the shoe plate118for facilitating supply of the high pressure fluid toward the rotor. In one embodiment, the supply port126discharges the high pressure fluid toward the rotor via the openings129(shown inFIG. 1andFIG. 3) formed in the load-bearing surface128.FIG. 3is a cross-sectional view30of the seal segment116ofFIG. 2, in accordance with an embodiment of the present specification. In one embodiment, as shown inFIG. 3, each supply port such as the supply port126discharges the high pressure fluid toward the rotor via three openings129. Each of the openings129includes a feed port130and a counter bore131formed in the shoe plate118as depicted in an enlarged view127. In some embodiments, as depicted in the enlarged view127, the diameter or width of the counter bore131may be greater than the diameter or width of the feed port130. Although the embodiment ofFIG. 3depicts three feed ports130and three counter bores131, embodiments having lesser or greater number of feed ports and counter bores have also been contemplated. It is to be noted that embodiments of the present specification are not limited to the specific positioning of the feed ports130and counter bores131, as depicted inFIG. 3. Also, embodiments with one or more feedports130but no counter bores have also been contemplated.

The feed ports130and counter bores131may be arranged such that the aerostatic-aerodynamic pressure distribution may cause a uniform lift of the shoe plate118without any front-aft tilting. For example, the three feed ports130and counter bores131disposed at forward, center, and aft locations in the load-bearing surface128, as depicted, may facilitate uniform lift of the shoe plate118without any front-aft tilting of the shoe plate118.

In one embodiment, the seal assembly101and hence the seal segment116may be configured in a line-on-line configuration with the rotor (i.e., without a gap between the shoe plate118and the rotor). During the initial start-up phase, the flow of the high pressure fluid through the feed ports130and counter bores131toward the rotor may cause an opening force that moves the shoe plate118radially outwards by a predefined distance, such as about 0.0005 inch to about 0.002 inch. This initial lift of the shoe plate118may be important for the seal segments to avoid damaging the shoe plate118due to contact by the rotor at low speeds when the fluid film does not possess sufficient aerodynamic strength to lift the shoe plate118. Following such initial lift-off, the shoe plate118may find an equilibrium position away from the rotor. The equilibrium force balance for this embodiment where the shoe plate118starts with a zero gap between the shoe plate118and the rotor is described later.

In yet another embodiment, the seal assembly101and hence the seal segment116may be arranged to have a non-zero gap between the shoe plate118and the rotor at start. In this case, during the start-up phase, the shoe plate118moves radially inwards towards the rotor under the influence of a closing force. Moreover, after this radially inwards motion, the shoe plate118may find an equilibrium riding clearance away from the rotor. The equilibrium force balance for this embodiment where the shoe plate118starts with a non-zero gap between the shoe plate118and the rotor is described later.

Certain physical characteristics such as a curvature (seeFIG. 4) of the shoe plate118, grooves (not shown), Rayleigh steps (seeFIG. 5), pockets (not shown) formed in the load-bearing surface128, and/or pockets/grooves formed on the rotor may aid in creating aerodynamic force between the shoe plate118and the rotor. Additionally, the flow of high pressure fluid through feed ports130and counter bores131may also create an aerostatic force between the shoe plate118and the rotor. Consequently, the shoe plate118maintains an equilibrium clearance away from the rotor in the non-contact or the film-riding mode due to a combination of the aerodynamic and the aerostatic forces.

FIG. 4is a perspective view40depicting a shoe-rotor curvature for the seal segment116, in accordance with an embodiment of the present specification. The shoe-rotor curvature as depicted inFIG. 4may aid in creation of an aerodynamic force. In particular, in the presence of rotational speed and when the gap between a rotor141and the shoe plate118is small (typically 0.0003 inch to 0.002 inch), a thin fluid film142builds an additional pressure. In this embodiment, the radius of curvature of the shoe plate118may be intentionally machined to be larger than the radius of the rotor141to achieve a required curvature mismatch. Consequently, the fluid film142having either monotonically converging or converging-diverging in the direction of rotation may be formed. This fluid film142in a form of fluid wedge may cause an additional pressure to build-up due to a negative gradient in the thickness of the fluid film142in the direction of rotation. The additional pressure caused by the thin fluid film142keeps the shoe plate118from contacting the rotor141.

FIG. 5is a perspective view50depicting Rayleigh steps144in the load-bearing surface128of the seal segment116, in accordance with an embodiment of the present specification. In the presence of rotational speed, the thin fluid film142may generate additional aerodynamic force due to the presence of the Rayleigh steps144. Although, the Rayleigh steps144have been shown in the embodiment ofFIG. 5, other features such as grooves and/or pockets (not shown) may also be formed in the load-bearing surface128. Additionally, features like grooves and/or pockets may also be present on the rotor (not shown inFIG. 5).

The features of the curvature mismatch (FIG. 4), the Rayleigh steps on the load-bearing surface (FIG. 5), the pockets and/or grooves on the load-bearing surface, and/or the pockets and/or grooves on the rotor give rise to aerodynamic forces that are active in the presence of a combination of non-zero rotational speed and small fluid film gaps (typically 0.0003 inch to 0.002 inch).

Referring again toFIG. 2andFIG. 3, andFIG. 6, the thin fluid film142may also generate an additional aerostatic force due to the presence of the feed ports130and counter bores131.FIG. 6depicts cross-sectional views (60and61) of the seal segment116and a rotor such as a stepped rotor158, in accordance with embodiments of the present specification. More particularly, the presence of the feed ports130or the presence of feed ports130and counter bores131leads to gap-dependent feedback characteristics as described herein with the aid ofFIG. 6. It is to be noted that the description provided in the context ofFIG. 6is for an embodiment when both the feed port130and counter bore131are present, however, the same description may also be applicable for an embodiment when only the feed ports130are present and counter bores131are not present. Each of the feed ports130may be sized in diameter and radial height such that when the fluid film142between the shoe plate118and the rotor158is large (typically larger than 0.005 inch as exaggeratedly shown in the cross-sectional view60), the radially outer end of the feed port130has high pressure fluid and the radially inner end of the feed port130and counter bore131has low pressure fluid. The pressure drops from about Phighto about Plowacross the feed port130leading to a pressure distribution dominated by low pressure on the load-bearing surface128.

However, when the gap between the shoe plate118and the rotor158is small (typically smaller than 0.003 inch as exaggeratedly shown in the cross-sectional view61), the fluid film142may become a choke point (i.e. the point across which the pressure drop occurs). Consequently, high pressure is developed on the radially inner end of the feed port130and the counter bore131. This high pressure fluid at the radially inner end of the feed port130and counter bore131modifies the pressure distribution on the load-bearing surface128to generate additional aerostatic force. This aerostatic force increases in magnitude as the fluid film142becomes thinner and leads to gap-dependent feedback characteristics for a radially outward force on the load-bearing surface128. The absence of counter bores131may create qualitatively similar force-gap characteristics but slightly lower in magnitude compared to the case where counter bores131are present.

The additional pressure created on the load-bearing surface128due to the presence of feed ports130and counter bores131depends on the presence of pressurized fluid, the dimensions of the feed ports130, the dimensions of counter bores131and the gap between the shoe plate118and the rotor158. This additional pressure may be present even in the absence of rotational speed.

Overall, the presence of the feed ports130and counter bores131, the curvature mismatch between the rotor and shoe plate118(as depicted inFIG. 4), the Rayleigh steps144(as depicted inFIG. 5), the grooves, and/or pockets allow the fluid film142between the spinning rotor and the load-bearing surface128to generate a combination of aerostatic and aerodynamic force. The combined aerostatic force and the aerodynamic force may have feedback characteristics such that a smaller running clearance generates a larger force. Such feedback characteristics allow the shoe plate118to find an equilibrium running clearance such that the force and moments generated by the fluid film142can support the net closing force & net moment load on the shoe plate118. Thus, the shoe plate118rides on the fluid film142(non-contact operation) such that the radially inwards aerostatic closing force, the radially outwards aerostatic-aerodynamic film force, the spring and/or friction resistances are in equilibrium. A detailed force balance is described later.

The shoe plate118further includes a radially extending portion148that extends toward the stator interface element112. Moreover, a slot150may be formed in the stator interface element112to accommodate a radial movement of the radially extending portion148relative to the stator interface element112. In one embodiment, the radially extending portion148may be configured to remain in contact with a portion of a ring152that may be disposed in a slot156in the stator interface element112. Such a contact between the radially extending portion148and the portion of the ring152may act as a secondary seal154for stopping or reducing leakage of fluid through an interface between the shoe plate118and the stator interface element112. During an operation of the seal assembly101, upon pressurization, a differential pressure urges the portion of the ring152axially towards the radially extending portion148and radially outwards into the slot156of the stator interface112.

In one embodiment, the ring152may be a continuous ring. For example, the ring152may be a 360 degree circular ring or a continuous multi-sided polygon with number of sides equal to the number of seal segments. In another embodiment, the ring152may be a segmented ring formed by multiple portions equal to the number of seal segments, where each portion of the ring152is disposed in corresponding stator interface element112.

FIG. 7is a side view70of the seal segment116illustrating various forces acting on the shoe plate118, in accordance with an embodiment of the present specification. The crossover hole138allows introduction of low pressure air into the cavity140and cavity134downstream of the aft-most labyrinth tooth120.

The presence of the crossover hole138allows the load-bearing surface128(non-rotor-facing side) to experience a low pressure (denoted by Plowt). The load-bearing surface128(rotor-facing side) experiences Pload-bearing. A combination of low-pressure in cavity134and large thickness of fluid film142(larger than about 0.005 inch) causes Pload-bearingto be almost equal to Plow1. Thus, at large thickness of the fluid film142(larger than about 0.005 inch), the rotor-facing side and the non-rotor facing side of the shoe plate118experience Plow1, thereby resulting in an almost zero net force on the shoe plate118for axial locations downstream of the radially extending wall148. The portion of the shoe plate118axially upstream of the radially extending wall148, experiences a high pressure (denoted by Phigh1) on the non-rotor facing side whereas a low pressure (denoted by Plow2) on the rotor facing side, thereby resulting in a radially inward closing force upon pressurization. Apart from this net closing force, the shoe plate118experiences an axial load (denoted by Phigh2and Plow3) due to pressure differential, a contact force at the contact of the portion of the ring152and the radially extending portion148, and a radial spring force (denoted by Fspring) & springs moments (denoted by Mspring) about different axes. The contact force between the portion of the ring152and the radially extending portion148is a combination of an axial force N and a radial friction resistance force IN. The axial force N may be adjusted using various friction coatings at the interface of the portion of the ring152and the slot156. Moreover, the axial force N may also be adjusted by modifying a pressure-loaded area of the ring152(i.e. by changing a chamfer dimension of the ring152).

Under the influence of the closing force (caused by the difference in Phigh1and Plow2), the spring resistance (Fspringand Mspring), and the friction force (N), the shoe plate118moves radially inwards towards the rotor. The radially inwards motion continues until the fluid film142between the shoe plate118and the rotor becomes thin enough to generate a combined aerostatic-aerodynamic force acting in the radially outwards direction. As described earlier, the aerostatic-aerodynamic force (i.e., Pload-bearinglarger than Plow1) is caused at small gaps (e.g., when the fluid film142smaller than about 0.003 inch) due to the presence of some combination of feed ports130, counter bores131, curvature mismatch, Rayleigh steps, and/or grooves on the rotor or the shoe plate118.

For instances where the seal starts with an initial contact with the rotor (i.e., in case of line-on-line arrangement when the thickness of fluid film142is zero), the force balance described above is valid except the starting value of Pload-bearingmay not be equal to Plow1. Unlike the embodiment described above, upon pressurization, Pload-bearingis larger than Plow1because of the zero fluid film thickness142. This leads to a radially outwards opening force, which after overcoming the closing force (present on the front portion of the shoe due to the difference Phigh1and Plow2), the friction force (μN), the spring force (Fspring) may cause the shoe plate118to move radially outwards till an equilibrium gap is attained. At equilibrium, the balance of forces is identical to the one described earlier.

FIG. 8is a perspective view80of the seal segment116riding over the stepped rotor158, in accordance with an embodiment of the present specification. The rotor158includes a stepped section160towards a high pressure side122of the rotary machine. The stepped section160includes a portion of the rotor158with locally decreased radius for a predefined length. The stepped section160may aid in reducing an axial momentum of a flow of fluid across the labyrinth tooth120of the shoe plate118from the high pressure side122to the low pressure side124. This reduction in the axial momentum allows for reliable operation of the seal assembly101.

Additionally, the radially extending portion148may also include one or more slots such as a slot162on at least one side for allowing disposal of at least one spline seal shim for reducing leakage between neighboring seal segments.

FIG. 9is a perspective cross-section view90of the seal segment116having a plenum164with openings, in accordance with an embodiment of the present specification. In one embodiment, the plenum164may be formed as an integral part of the shoe plate118. In another embodiment, the plenum164may be formed in a separate component166that is attachable to the shoe plate118. For example, the component166may be slidable into slots formed in the shoe plate118. The side of the plenum that faces the rotor forms the load-bearing surface128.

The plenum164is configured to receive the flow of the high pressure fluid from one or more supply ports such as the supply port126. Moreover, in one embodiment, as depicted inFIG. 9, the plenum164may have at least one opening165in the load-bearing surface128of the shoe plate118for directing a flow of the high pressure fluid toward the rotor. It is also contemplated that the at least one opening165may have a counter bore (not shown inFIG. 9, but similar to the combination of the feed port130and counter bore131as depicted inFIG. 3).

In yet another embodiment, as depicted inFIG. 10, the plenum164may have a porous media on the side facing the rotor.FIG. 10is a perspective cross-section view100of seal segment having the plenum164with a porous media168, in accordance with an embodiment of the present specification. The supply port126discharges the high pressure fluid toward the rotor via the porous media168of the plenum164.

FIG. 11is a perspective view1100of the seal segment116having a leaf seal arrangement as a secondary seal170, in accordance with an embodiment of the present specification. The purpose of the secondary seal170is to reduce the leakage of flow through the radial space between the shoe plate118and the stator interface112.

The secondary seal170includes arrangement of an outer leaf seal plate172and an inner leaf seal plate174in a slot171formed in the stator interface element112. More particularly, the outer leaf seal plate172and the inner leaf seal plate174may not be fixed to the stator interface112. The outer and inner leaf seal plates172,174are loaded axially against two noses—a radially outer nose176of the stator interface element112and radially inner nose178of the radially extending portion148. The inner leaf seal plate174of a given seal segment is in contact with the radially outer nose176and inner nose178. The outer leaf seal plate172may be disposed circumferentially offset from the inner leaf seal plate174such that the outer leaf seal plate172covers the radial segment gaps between adjacent inner leaf seal plates.

Moreover, one or more flexible elements such as a spring180depicted inFIG. 11are used to load the outer and inner leaf seal plates172and174toward the noses176and178. On one embodiment, the spring180may be arranged to apply a spring force at a pre-defined position on the outer leaf seal plate172between the radially outer nose176and inner nose178. For example, the pre-defined position on the outer leaf seal plate172may be in middle of the radially outer nose176and inner nose178. As depicted inFIG. 11, the spring180may be a u-shape spring. Other types of springs may also be used in place of the u-shape spring without limiting the scope of the present specification. One or more blocking elements such as a pin182may be used for supporting the outer and inner leaf seal plates172,174, and the spring180. It is to be noted that in addition to the force applied by the spring180, the outer leaf172also experiences the high pressure122that urges the two layers of leaf seals172and174axially towards the noses176and178.

Contact force between the noses176,178and the outer and inner leaf seal plates172,174includes a normal reaction (due to a force caused by the spring180and pressure load) as well as a friction force (due to the radial movement of the radially extending portion148). Desired values of the normal force are attained by adjusting the stiffness of the spring180and the pressure load on one or more of the outer and inner leaf seal plate172,174.

Additionally, the stator interface element112may be designed to have a protrusion184. The protrusion184reduces the turbulent or dynamic effects of high pressure fluid and improves reliability of the flexible element or spring180and the outer leaf172.

FIG. 12is flow chart1200illustrating an example method of operating a seal segment such as the seal segment116, in accordance with an embodiment of the present specification. As noted previously, one or more seal segments such as the seal segment116may be employed in a rotary machine having the stationary housing110and a rotor. Moreover, the seal segment116may include the stator interface element112, the shoe plate118having the labyrinth tooth120, the load-bearing surface128, and the radially extending portion148. The method may include following steps:

At step1202, a high pressure fluid is supplied radially toward the rotor through the load-bearing surface128of the shoe plate118. In one embodiment, supplying the high pressure fluid includes flowing the high pressure fluid through one or more supply ports such as the supply port126formed in the shoe plate118. More particularly, in one embodiment, the high pressure fluid from the supply port126is directed toward the rotor via the feed ports130and counter bores131formed in the load bearing surface128. In another embodiment, supplying the high pressure fluid includes flowing the high pressure fluid from the supply port126via the plenum164toward the rotor. More particularly, in one embodiment, the high pressure fluid from the plenum164is directed toward the rotor via the at least one opening165formed in the load bearing surface128. In another embodiment, the high pressure fluid from the plenum164is directed toward the rotor via the porous media168disposed on a side of the plenum facing the rotor. Moreover, as previously noted the plenum164may be integral to the shoe plate118or formed in the separate component166attachable to the shoe plate118.

If the starting gap between the shoe plate118and the rotor is large, for example, more than about 0.005 inches, the forces on the seal segment116are such that the seal moves inwards towards the rotor. As the gap between the shoe plate118and the rotor becomes small (smaller than about 0.003 inch), the flow of the high pressure fluid from the supply port126toward the rotor may lead to generation of an aerostatic force between the shoe plate118and the rotor, as indicated by step1204. If however, the starting gap between the shoe plate118and the rotor is zero, then flow of the high pressure fluid from supply port126toward the rotor may lead to generation of an aerostatic force causes the shoe to move away from the rotor. As previously noted, application of such aerostatic force avoids any start-up rubs between the shoe plate118and the rotor.

In addition to the aerostatic force indicated in step1204, in the presence of rotational speed and for small gaps, for example, smaller than about 0.002 inches (and as small as about 0.0003 inches), an aerodynamic force is generated between the shoe plate118and the rotor, as indicated by step1206. As previously noted, the fluid film142may be monotonically converging or converging-diverging in the direction of rotation (FIG. 4). Presence of such thin fluid film142aids in generating the aerodynamic force that moves the shoe plate118radially outwards and keeps the rotor from contacting the shoe plate118. Moreover, some additional aerodynamic force may also be caused due to the presence of various features such as the Rayleigh steps144(seeFIG. 5), grooves, pockets formed on the load-bearing surface128of the shoe plate118, and/or or grooves, and/or pockets on the rotor. Consequently, during an operation of the rotary machine, the presence of the aerostatic and aerodynamic forces aid in ensuring a compliant primary sealing where the shoe plates of each seal segment rides on the thin fluid film142.

Additionally, at step1208, a leakage from a space between the shoe plate118and the stator interface element112may also be prevented or reduced due to the presence of a secondary seal. In one embodiment, the contact between radially extending portion148and the portion of the ring152may lead the secondary seal such as the secondary seal154. In another embodiment, of the contact between the radially inner nose178formed on the radially extending portion148, radially outer nose176of the stator interface element112, and the inner leaf seal plate174may form the secondary seal such as the secondary seal170.

Any of the foregoing steps and/or system elements may be suitably replaced, reordered, or removed, and additional steps and/or system elements may be inserted, depending on the needs of a particular application, and that the systems of the foregoing embodiments may be implemented using a wide variety of suitable processes and system elements.

In accordance with some embodiments of the invention, the described seal assembly may be operated with both aerostatic and aerodynamic modes of operation, which increases load-bearing capacity of the seal assembly. Moreover, the use of the supply ports may also aid in cooling of the shoe plate. Any leakage between neighboring seal segments may also be reduced by the use of the splines seals. Furthermore, suitable arrangement of the feed ports and counter bores leads to either a uniform lift of the shoe plate (where the shoe plate118is parallel to the rotor) or allow for the correction of tilt of the shoe plate118(where, for example, the forward edge of the shoe plate118is closer to the rotor than the aft edge of the shoe plate118). Additionally, various types of secondary seal arrangements as described herein may reduce or prevent the leakage of fluid from a space between the stator interface element and the shoe plate.

Furthermore, those skilled in the art will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.