Patent Description:
An industrial gas turbine engine typically includes a compressor section, a turbine section, and a mid-frame section disposed therebetween. The compressor section includes multiple stages of compressor rotating blades and stationary vanes and an outlet guide vane assembly aft of the last stage blade and vane. The mid-frame section typically includes a compressor exit diffusor and a combustor assembly. The compressor exit diffusor diffuses the compressed air from the compressor section into a plenum through which the compressed air flows to a combustor assembly which mixes the compressed air with fuel and ignites the mixture and transits the ignited mixture to the turbine section for mechanical power. The turbine section includes multiple stages of turbine rotating blades and stationary vanes.

Gas turbine engines are becoming larger, more efficient, and more robust. Large blades and vanes are being utilized, especially in the hot section of the engine system. In view of high pressure ratios and high engine firing temperatures implemented in modern engines, certain components, such as stationary vanes and rotating blades, require more efficient cooling to maintain an adequate component life. Cooling may be accomplished by extracting a portion of the cooler compressed air from the compressor and directing it to the turbine section, thereby bypassing combustors. However, bleeding air from the compressor may reduce gas turbine engine performance and efficiency. Cooling air may leak through gaps between components in the gas turbine engine. Thus, there is a need to provide a robust seal assembly to seal the gaps in the gas turbine engine to reduce cooling air leakage.

Such non-contact seal assemblies are known in the particular art, e.g. from <CIT>, <CIT>or <CIT>.

Briefly described, aspects of the present invention relate to a non-contact seal assembly configured to seal a gap between a stator and a rotor rotatable relative to the stator in a gas turbine engine, a method for making a non-contact seal assembly to be used for sealing a gap between a stator and a rotor rotatable relative to the stator in a gas turbine engine, and a gas turbine engine.

The invention is defined by the independent claims <NUM> and <NUM>.

Various aspects and embodiments of the application as described above and hereinafter may not only be used in the combinations explicitly described, but also in other combinations. Modifications will occur to the skilled person upon reading and understanding of the description.

Exemplary embodiments of the application are explained in further detail with respect to the accompanying drawings. In the drawings:.

A detailed description related to aspects of the present invention is described hereafter with respect to the accompanying figures.

For illustration purpose, term "axial" or "axially" refers to a direction along a longitudinal axis of a gas turbine engine, term "radial" or "radially" refers to a direction perpendicular to the longitudinal axis of the gas turbine engine, term "downstream" or "aft" refers to a direction along a flow direction, term "upstream" or "forward" refers to a direction against the flow direction.

<FIG> illustrates a schematic longitudinal section view of a portion of a gas turbine engine <NUM>. As illustrated in <FIG>, the gas turbine engine <NUM> includes a plurality of components along a longitudinal axis <NUM>. The plurality of components may include a compressor section <NUM>, a turbine section <NUM> located downstream of the compressor section <NUM> with respect to a flow direction A, and a mid-frame section <NUM> that is located there between. The gas turbine engine <NUM> also includes an outer casing <NUM> that encloses the plurality of components. A rotor <NUM> longitudinally connects the compressor section <NUM>, the mid-frame section <NUM> and the turbine section <NUM> and is circumferentially enclosed thereby. The rotor <NUM> may be partially or fully enclosed by a shaft cover <NUM>.

The compressor section <NUM> includes multiple stages of compressor rotating blades <NUM> and compressor stationary vanes <NUM>. <FIG> only shows the last stage of compressor rotating blade <NUM> and compressor stationary vane <NUM>. An outlet guide vane assembly <NUM> is arranged downstream of the last stage compressor vane <NUM>. The compressor blades <NUM> are installed into the rotor <NUM>. The compressor vanes <NUM> and the outlet guide vane assembly <NUM> are installed into a compressor vane carrier <NUM>. The compressor vane carrier <NUM> interfaces with the outer casing <NUM>. The turbine section <NUM> includes multiple stages of turbine stationary vanes <NUM> and turbine rotating blades <NUM>. <FIG> only shows the first stage of turbine stationary vane <NUM> and turbine rotating blade <NUM>. The turbine vanes <NUM> are installed into a turbine vane carrier <NUM>. The turbine vane carrier <NUM> interfaces with the outer casing <NUM>. The turbine blades <NUM> are installed into the rotor <NUM>. The mid-frame section <NUM> typically includes a combustor assembly <NUM> and a compressor exit diffuser <NUM>. The compressor exit diffuser <NUM> is located downstream of the outlet guide vane assembly <NUM>.

The compressor exit diffusor <NUM> typically includes an outer compressor exit diffusor <NUM> and an inner compressor exit diffusor <NUM>. The outer compressor exit diffusor <NUM> is connected to the inner compressor exit diffusor <NUM> by bolting to a strut <NUM>. The inner compressor exit diffusor <NUM> may enclose the shaft cover <NUM>. Forward side of the outer compressor exit diffusor <NUM> interfaces with the outer casing <NUM>. Forward side of the inner compressor exit diffusor <NUM> interfaces with the last stage compressor vane <NUM> and the outlet guide vane assembly <NUM>.

In operation of the gas turbine engine <NUM>, the compressor section <NUM> inducts air via an inlet duct (not shown). The air is compressed and accelerated in the compressor section <NUM> while passing through the multiple stages of compressor rotating blades <NUM> and compressor stationary vanes <NUM>, as indicated by the flow direction A. The compressed air passes through the outlet guide vane assembly <NUM> and enters the compressor exit diffuser <NUM>. The compressor exit diffuser <NUM> diffuses the compressed air to the combustor assembly <NUM>. The compressed air is mixed with fuel in the combustor assembly <NUM>. The mixture is ignited and burned in the combustor assembly <NUM> to form a combustion gas. The combustion gas enters the turbine section <NUM>, as indicated by the flow direction A. The combustion gas is expanded in the turbine section <NUM> while passing through the multiple stages of turbine stationary vanes <NUM> and turbine rotating blades <NUM> to generate mechanical power which drives the rotor <NUM>. The rotor <NUM> may be linked to an electric generator (not shown) to convert the mechanical power to electrical power. The expanded gas constitutes exhaust gas and exits the gas turbine engine <NUM>.

In operation of the gas turbine engine <NUM>, due to the high temperature of the combustion gas, cooling air is used to cool the turbine blades <NUM> and vanes <NUM> to maintain an adequate component life. Cooling air may leak at gaps or clearances between components. Cooling air leakage may negatively affect the performance and efficiency of the gas turbine engine <NUM>. The gas turbine engine <NUM> may include seals to reduce the cooling air leakage.

According to the present invention, the gas turbine engine <NUM> includes a non-contact seal assembly <NUM> to reduce the cooling air leakage at a clearance between two components of the gas turbine engine <NUM>. The two components may relatively rotate with respect to each other. As shown in the exemplary embodiment of <FIG>, the non-contact seal assembly <NUM> is arranged at a stator <NUM>, such as the stationary shaft cover <NUM> or the stationary inner compressor exit diffusor <NUM>, to reduce cooling air leakage at a gap <NUM> between the stator <NUM> and the rotating rotor <NUM>. The gap <NUM> extends in a radial direction and circumferentially around between the stator <NUM> and rotor <NUM>. It is understood that the non-contact seal <NUM> may be arranged at a rotating component, such as the rotor <NUM>. As shown in the exemplary embodiment of <FIG>, one non-contact seal assembly <NUM> is arranged at a forward side of the stationary shaft cover <NUM>. Another non-contact seal assembly <NUM> is arranged at an aft side of the stationary inner compressor exit diffusor <NUM>. It is understood that the non-contact seal assembly <NUM> may be arranged at any locations of the gas turbine engine <NUM> where cooling air leakages may occur.

<FIG> shows a schematic end view of a non-contact seal assembly <NUM> according to an embodiment. As shown in <FIG>, the non-contact seal assembly <NUM> includes a plurality of non-contact seal segments <NUM>. The non-contact seal segments <NUM> are circumferentially arranged to seal a gap <NUM> between two components in the gas turbine engine <NUM>. A small gap <NUM> may exist between adjacent non-contact seal segments <NUM>. The gap <NUM> may be used to adapt thermal expansion and/or tolerance of manufacture and assembly. As shown in the exemplary embodiment of <FIG>, the non-contact seal assembly <NUM> includes six <NUM>-degree non-contact seal segments <NUM>. It is understood that the non-contact seal assembly <NUM> may include any numbers of non-contact seal segments <NUM> to form a circular seal.

The non-contact seal segment <NUM> of the non-contact seal assembly <NUM> includes a plurality of components. <FIG> shows a schematic perspective exploded view of a non-contact seal segment <NUM> of the non-contact seal assembly <NUM> according to an embodiment. As shown in <FIG>, the non-contact seal segment <NUM> includes a seal carrier <NUM>. The seal carrier <NUM> includes an outer ring <NUM>, a front plate <NUM> and a back plate <NUM>. The front plate <NUM> and the back plate <NUM> extend circumferentially along the outer ring <NUM> and radially from two axial ends of the outer ring <NUM> forming a U-shaped seal ring carrier <NUM> (better shown in <FIG>). The front plate <NUM> may have a wave shape to allow for the passage of air. The front plate <NUM>, the back plate <NUM> and the outer ring <NUM> may be integrally formed as a single piece. The front plate <NUM> and the back plate <NUM> include a plurality of circumferentially spaced pin holes <NUM> for receiving a plurality of pins <NUM>.

The non-contact seal segment <NUM> includes a primary seal <NUM>. The primary seal <NUM> includes a seal base <NUM> and a seal shoe <NUM> arranged at an inner radial side. The seal shoe <NUM> includes a plurality of circumferentially spaced seal shoe segments <NUM>. A small gap <NUM> may exist between adjacent seal shoe segments <NUM>. The gap <NUM> may be used to adapt thermal expansion and/or tolerance of manufacture and assembly. As shown in the exemplary embodiment of <FIG>, the non-contact seal segment <NUM> includes four <NUM>-degree seal shoe segments <NUM>. It is understood that the non-contact seal segment <NUM> includes any numbers of seal shoe segments <NUM>. The non-contact seal segment <NUM> includes a plurality of circumferentially spaced seal springs <NUM>. Each seal spring <NUM> is connected to each seal shoe segment <NUM>. Each seal spring <NUM> includes at least two seal beams <NUM> radially spaced apart from each other (shown in <FIG>). Slot <NUM> exist between the seal beams <NUM>. Slots <NUM> exist between the seal beams <NUM> and the seal base <NUM> and the seal shoe <NUM>.

In operation of the gas turbine engine <NUM>, aerodynamic loads are developed which apply a fluid pressure to the seal shoe <NUM> causing the seal shoe <NUM> to move radially inwardly and outwardly with respect to the rotor <NUM>. Each seal shoe segment <NUM> moves independently to adjacent seal shoe segments <NUM>. Each seal spring <NUM> deflects and moves radially inwardly and outwardly with each seal shoe segment <NUM>. The radial movement of the seal shoe <NUM> with respect to the rotor <NUM> creates a primary seal reducing cooling air flow through the gap <NUM> between the rotor <NUM> and the stator <NUM> within a predetermined design clearance. The predetermined design clearance between the rotor <NUM> and the stator <NUM> may be less than <NUM> due to a pressure gradient between the forward side pressure zone and the aft side pressure zone of primary seal <NUM>. The non-contact seal assembly <NUM> thus provides sufficient sealing between the rotor <NUM> and the stator <NUM>. The seal base <NUM> includes a plurality of circumferentially spaced pin holes <NUM> for receiving the plurality of pins <NUM>.

Referring to <FIG>, the non-contact seal segment <NUM> includes a mid-plate <NUM> disposed forward to the primary seal <NUM>. The non-contact seal segment <NUM> includes an aft secondary seal <NUM> disposed forward to the mid-plate <NUM> and a forward secondary seal <NUM> disposed forward to the aft secondary seal <NUM>. The mid-plate <NUM> and the forward secondary seal <NUM> include a plurality of circumferentially spaced pin holes <NUM> for receiving the plurality of pins <NUM>. For illustration purpose, only one forward secondary seal <NUM> is illustrated in <FIG>. It is understood that the non-contact seal segment <NUM> may include more than one forward secondary seals <NUM> placed side by side in the axial direction.

The aft secondary seal <NUM> includes a plurality of circumferentially spaced aft secondary seal segments <NUM>. The number of aft secondary seal segments <NUM> may correspond to the number of seal shoe segments <NUM>. A small gap <NUM> exists between adjacent aft secondary seal segments <NUM>. The gap <NUM> may be used to adapt thermal expansion and/or tolerance of manufacture and assembly. The gap <NUM> between adjacent aft secondary seal segments <NUM> may align with the gap <NUM> between adjacent seal shoe segments <NUM>. Each aft secondary seal segment <NUM> aligns with and is attached to each seal shoe segment <NUM>. As shown in the exemplary embodiment of <FIG>, the aft secondary seal <NUM> includes four <NUM>-degree aft secondary seal segments <NUM>. Each aft secondary seal segment <NUM> includes at least a notch <NUM> at outer radial side. Circumferential locations of the notches <NUM> correspond to circumferential locations of the pin holes <NUM>.

In operation of the gas turbine engine <NUM>, each aft secondary seal segment <NUM> moves radially inwardly and outwardly with each seal shoe segment <NUM> independently to adjacent aft secondary seal segments <NUM> in response to the application of fluid pressure as noted above. The aft secondary seal <NUM> thus creates a secondary seal reducing cooling air flow through slots <NUM> between the seal beams <NUM> and between the seal beams <NUM> and the seal base <NUM> and the seal shoe <NUM> of the primary seal <NUM>. The aft secondary seal <NUM> seals the slots <NUM> in the primary seal <NUM> and separates the forward side high pressure zone from the aft side low pressure zone of the primary seal <NUM> while undergoing constant motion along with the seal shoe <NUM>. The pressure gradient between the forward side pressure zone and the aft side pressure zone of the primary seal <NUM> is thus maintained which allows the primary seal <NUM> self-adjusting its positioning and creating the primary seal in the gap <NUM> between the rotor <NUM> and the stator <NUM> within the predetermined design clearance during operation of the gas turbine engine <NUM>.

<FIG> shows a schematic assembled end view of the non-contact seal segment <NUM> of the non-contact seal assembly <NUM>. As illustrated in the exemplary embodiment of <FIG>, components of the non-contact seal assembly <NUM> including the forward secondary seal <NUM>, the aft secondary seal <NUM>, the mid-plate <NUM>, and the primary seal <NUM> are assembled to the seal carrier <NUM> into the U-shape between the front plate <NUM> and the back plate <NUM>. The plurality of pins <NUM> extend axially passing through the pin holes <NUM> to hold the components together to the seal carrier <NUM> between the front plate <NUM> and the back plate <NUM>.

<FIG> shows a schematic cross section view of the non-contact seal assembly <NUM> looking along <NUM>-<NUM> of the non-contact seal segment <NUM> in <FIG>. As shown in <FIG>, the non-contact seal assembly <NUM> is mounted on a stator <NUM> of the gas turbine engine <NUM>. The stator <NUM> may be the shaft cover <NUM> or the inner compressor exit diffusor <NUM>. The non-contact seal assembly <NUM> is used to reduce cooling air leakage at a gap <NUM> between the stator <NUM> and the rotating rotor <NUM>. As shown in <FIG>, the primary seal <NUM>, the mid-plate <NUM>, the aft secondary seal <NUM>, and the forward secondary seal <NUM> are assembled into the U-shaped seal carrier <NUM> between the front plate <NUM> and the back plate <NUM>. The seal shoe <NUM> of the primary seal <NUM> is located at a non-contact location along the exterior surface of the rotor <NUM>. The forward secondary seal <NUM>, the mid-plate <NUM> and the primary seal <NUM> are held together to the seal carrier <NUM> between the front plate <NUM> and the back plate <NUM> by the pin <NUM>. The aft secondary seal <NUM> is attached to the seal shoe <NUM> of the primary seal <NUM>. The aft secondary seal <NUM> may be attached to the seal shoe <NUM> by welding, such as laser welding. The aft secondary seal <NUM> may be attached to the seal shoe <NUM> by any other techniques known in the industries, such as caulking, brazing, etc..

As shown in the exemplary embodiment of <FIG>, the forward secondary seal <NUM> is positioned more radially outwardly by the pin <NUM> than the aft secondary seal <NUM> attached to the seal shoe <NUM>. The forward secondary seal <NUM> at least partially overlap the aft secondary seal <NUM> in the radial direction to partially cover the gaps <NUM> between the aft secondary seal segments <NUM>. The aft secondary seal <NUM> may thus provide sufficient sealing and separation of the forward side high pressure zone from the aft side low pressure zone of the primary seal <NUM> when the aft secondary seal <NUM> moves radially inwardly and outwardly along with the seal shoe <NUM>. Such arrangement may thus eliminate using spring members for pre-loading the secondary seals <NUM> and <NUM> to the primary seal <NUM>. Spring members, such as whiskers, for pre-loading the secondary seals <NUM> and <NUM> to the primary seal <NUM> tend to crack under constant high cycle fatigue loading. By attaching the aft secondary seal <NUM> to the seal shoe <NUM>, the aft secondary seal <NUM> does not require spring element for initial pre-loading and reduces risk of high cycle fatigue failures.

<FIG> shows a schematic perspective view of a portion of the primary seal <NUM> of the non-contact seal assembly <NUM>. As shown in <FIG>, the primary seal <NUM> includes a seal base <NUM>, a seal shoe segment <NUM> and a seal spring <NUM>. The seal spring <NUM> includes at least one seal beam <NUM>. In the exemplary embodiment shown in <FIG>, the seal spring <NUM> includes two seal beams <NUM> radially spaced apart from each other. The seal beams <NUM> are formed by cutting out a plurality of slots <NUM> from the seal base <NUM>, for example, slots <NUM> between the seal beams <NUM> and between the seal beams <NUM> and the seal base <NUM> and the seal shoe segment <NUM>. One end of the seal beams <NUM> is mounted to or integrally formed with the seal base <NUM>. The other end of the seal beams <NUM> is mounted to or integrally formed with a seal strip <NUM>. The seal strip <NUM> extends radially downwardly and is mounted or integrally formed with the seal shoe segment <NUM>. The seal shoe segment <NUM> includes two seal stops <NUM> located at two circumferential ends. Each seal stop <NUM> includes a stop leg <NUM> and a stop arm <NUM>. The seal base <NUM> has a recess <NUM> to receive the stop arm <NUM>. The recess <NUM> includes an inner shoulder <NUM> and an outer shoulder <NUM>. Gap <NUM> exists between the stop arm <NUM> and the inner shoulder <NUM>. Gap <NUM> exists between the stop arm <NUM> and the outer shoulder <NUM>.

Referring to <FIG> and <FIG>, in operation of the gas turbine engine <NUM>, aerodynamic loads are developed which apply a fluid pressure to each seal shoe segment <NUM> of the seal shoe <NUM> causing the seal shoe segment <NUM> to move radially inwardly and outwardly with respect to the rotor <NUM>, as indicated by the dual arrows. The seal beams <NUM> of the seal spring <NUM> deflect and move with the seal shoe <NUM> to create a primary seal of the gap <NUM> between the rotor <NUM> and the stator <NUM> within a predetermined design tolerance.

The seal stops <NUM> define the maximum extent of the radially inward and outward movement of the seal shoe segment <NUM> with respect to the rotor <NUM> for safety and operational consideration. The radial inward movement of the seal shoe segment <NUM> is limited by engagement of the stop arm <NUM> with the inner shoulder <NUM> thus closing the gap <NUM> between the stop arm <NUM> and the inner shoulder <NUM>, as illustrated in <FIG>. The radial inward movement limitation of the seal shoe <NUM> reduces the likelihood of contact between the seal shoe <NUM> and the rotor <NUM> or exceeding the predetermined design tolerance for the gap <NUM> between the rotor <NUM> and the stator <NUM>. The radial outward movement of the seal shoe segment <NUM> is limited by engagement of the stop arm <NUM> with the outer shoulder <NUM> thus closing the gap <NUM> between the stop arm <NUM> and the outer shoulder <NUM>, as illustrated in <FIG>.

Each aft secondary seal segment <NUM> of the aft secondary seal <NUM> includes at least a notch <NUM> at the outer radial side to accommodate the radial movement of each seal shoe segment <NUM>. As shown in the exemplary embodiments of <FIG>, the notch <NUM> of the aft secondary seal segment <NUM> is cut downwardly from the outer radial side of the aft secondary seal segment <NUM>. A circumneutral location of the notch <NUM> may correspond to a circumferential location of the pin <NUM> after assembled into the pin hole <NUM>. As shown in <FIG>, the notch <NUM> receives the pin <NUM> when the seal shoe segment <NUM> moves to the maximum radially outward location to accommodate the radial movement of the seal shoe segment <NUM>. The notch <NUM> may thus reduce the risk of failure of the aft secondary seal <NUM> due to the radial movement of the seal shoe segment <NUM> in operation of the gas turbine engine <NUM>.

The notch <NUM> may have any types of shape. As shown in <FIG>, the notch <NUM> has an arc shape. As shown in an exemplary embodiment of <FIG>, the aft secondary seal segment <NUM> has a U-shaped notch <NUM>. Dimension of the notch <NUM> is larger than dimension of the pin <NUM> to allow relative movement between the notch <NUM> and the pin <NUM> and manufacture and assembly tolerance.

<FIG> illustrates a schematic perspective view of a non-contact seal segment <NUM> of a non-contact seal assembly <NUM>. As illustrated in the exemplary embodiment of <FIG>, the non-contact seal segment <NUM> includes a primary seal <NUM> and a mid-plate <NUM> attached to the primary seal <NUM>. The primary seal <NUM> includes a seal shoe <NUM> including four seal shoe segments <NUM>. The non-contact seal segment <NUM> includes an aft secondary seal <NUM> attached to the seal shoe <NUM>. The aft secondary seal <NUM> includes four aft secondary seal segments <NUM>. Each aft secondary seal segment <NUM> aligns with each seal shoe segment <NUM> and is attached to each seal shoe segment <NUM>. Circumferential dimension of each aft secondary seal segment <NUM> corresponds to circumferential dimension of each seal shoe segment <NUM>. Gaps <NUM> between adjacent seal shoe segments <NUM> aligns with gaps <NUM> between adjacent aft secondary seal segments <NUM>. Each aft secondary seal segment <NUM> includes at least a notch <NUM> at the outer radial side. As show in <FIG>, each seal shoe segment <NUM> moves radially independently to adjacent seal shoe segments <NUM> in response to an aerodynamic load. Each aft secondary seal segment <NUM> moves radially independently to adjacent aft secondary seal segments <NUM> along with the seal shoe segment <NUM>. The notch <NUM> receives the pin <NUM> when the seal shoe segment <NUM> moves to the maximum radially outward position to accommodate the radial outward movement of the seal shoe segment <NUM>.

The non-contact seal segment <NUM> may be a <NUM>-degree segment. The primary seal <NUM> of each non-contact seal segment <NUM> may include four <NUM>-degree seal shoe segments <NUM>. The aft secondary seal <NUM> of each non-contact seal segment <NUM> may include four <NUM>-degree aft secondary seal segments <NUM>. The non-contact seal assembly <NUM> may include six <NUM>-degree non-contact seal segments <NUM>.

According to an embodiment, material may be applied to regions of the non-contact seal assembly <NUM> that are prone to fatigue failure to improve mechanical properties of the non-contact seal assembly <NUM> against fatigue failure in operation of the gas turbine engine <NUM>. Such regions include sliding surfaces of components that move relatively to each other in operation of the gas turbine engine <NUM>. Material may be applied as bulk material to at least one of the relatively moving components in a desired concentration during manufacturing process. Alternatively, material may be applied as a coating layer to at least one adjacent sliding surface of the relatively moving components. The material may include carbon structures (for example, carbon nanotubes, graphene, fullerene, etc.), ceramic, or any types of high strength materials known in the industrial. The material may be applied to the components or the adjacent sliding surface by additive manufacturing, laser injection, or any types of techniques known in the industrial.

Referring to <FIG>, the aft secondary seal <NUM> moves radially relative to the mid-plate <NUM> and the forward secondary seal <NUM>. The material may be applied as bulk material to the aft secondary seal <NUM>, and/or to the mid-plate <NUM>, and/or to the forward secondary seal <NUM>. The material may be applied as a coating layer <NUM> to at least one adjacent surface between the aft secondary seal <NUM> and the mid-plate <NUM>. The material may also be applied as a coating layer <NUM> to at least one adjacent surface between the aft secondary seal <NUM> and the forward secondary seal <NUM>. As illustrated in the exemplary embodiment of <FIG>, the coating layer <NUM> is applied to a surface of the aft secondary seal <NUM> facing to the mid-plate <NUM> and a surface of the mid-plate <NUM> facing to the aft secondary seal <NUM>. The coating layer <NUM> is applied to a surface of the aft secondary seal <NUM> facing to the forward secondary seal <NUM> and a surface of the forward secondary seal <NUM> facing to the aft secondary seal <NUM>. It is understood that the coating layer <NUM> may be applied to one adjacent surface between the aft secondary seal <NUM> and the mid-plate <NUM> and/or one adjacent surface between the aft secondary seal <NUM> and the forward secondary seal <NUM>. The coating layer <NUM> may be applied to the adjacent surface to a radial extent that covers the maximum radial movement in operation of the gas turbine engine <NUM>. The coating layer <NUM> may also be applied to the entire radial length of the adjacent surface. As shown in <FIG>, the coating layer <NUM> is applied to the entire radial length of the surface of the aft secondary seal <NUM>. The coating layers <NUM> are applied to the surfaces of the mid-plate <NUM> and the forward secondary seal <NUM> up to radial position of the pin <NUM>.

According to an aspect, the proposed non-contact seal assembly <NUM> provides a robust non-contact seal assembly <NUM> in a gas turbine engine <NUM>. The proposed non-contact seal assembly <NUM> segments the seal shoe <NUM> and the aft secondary seal <NUM>. Each aft secondary seal segment <NUM> is attached to each seal shoe segment <NUM>. The proposed non-contact seal assembly <NUM> thus eliminates spring elements for pre-loading the secondary seals <NUM>. The proposed non-contact seal assembly <NUM> may withstand infinite high cycle fatigue loading.

According to an aspect, the proposed non-contact seal assembly <NUM> allows each aft secondary seal segments <NUM> moves radially independently along with each seal shoe segments <NUM> in response to the aerodynamic loads. Each aft secondary seal segment <NUM> provides an independent secondary sealing and separates the forward high pressure zone from the aft low pressure zone of the primary seal <NUM> while undergoing constant radial movements along with the seal shoe segments <NUM>.

According to an aspect, each aft secondary seal segment <NUM> includes at least one notch <NUM> at the outer radial side. The notch <NUM> may receive the pin <NUM> when the seal shoe segment <NUM> moves to the maximum radially outward position to accommodate the large radial movement of the seal shoe segment <NUM> in operation of the large gas turbine engine <NUM>.

Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The invention is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings, but is exclusively defined by the appended claims.

Claim 1:
A non-contact seal assembly (<NUM>) for a gas turbine engine (<NUM>), the non-contact seal assembly (<NUM>) being configured to seal a gap (<NUM>) between a stator (<NUM>) and a rotor (<NUM>) rotatable relative to the stator (<NUM>) of the gas turbine engine (<NUM>) comprising:
a primary seal (<NUM>) comprising a seal shoe (<NUM>), wherein the seal shoe (<NUM>) comprises a plurality of seal shoe segments (<NUM>) circumferentially spaced apart from each other, and wherein each seal shoe segment (<NUM>) is configured to be movable in a radial direction;
a mid-plate (<NUM>) disposed forward to the primary seal (<NUM>);
an aft secondary seal (<NUM>) disposed forward to the mid-plate (<NUM>), wherein the aft secondary seal (<NUM>) comprises a plurality of aft secondary seal segments (<NUM>) circumferentially spaced apart from each other, and wherein each aft secondary seal segment (<NUM>) is attached to each seal shoe segment (<NUM>) and is configured to be movable in the radial direction along with each seal shoe segment (<NUM>), wherein in operation each aft secondary seal segment (<NUM>) moves radially inwardly and outwardly with each seal show segment (<NUM>) independently to adjacent aft secondary seal segments (<NUM>);
a forward secondary seal (<NUM>) disposed forward to the aft secondary seal (<NUM>);
a seal carrier (<NUM>) comprising an outer ring (<NUM>) and a front plate (<NUM>) and a back plate (<NUM>), wherein the front plate (<NUM>) and the back plate (<NUM>) extend circumferentially along the outer ring (<NUM>) and radially from two axial sides of the outer ring (<NUM>) forming a U-shape, and wherein the primary seal (<NUM>), the mid-plate (<NUM>), the aft secondary seal (<NUM>) and the forward secondary seal (<NUM>) are assembled in the U-shape; and
a pin (<NUM>) to hold the primary seal (<NUM>), the mid-plate (<NUM>), and the forward secondary seal (<NUM>) to the seal carrier (<NUM>) between the front plate (<NUM>) and the back plate (<NUM>)., wherein each aft secondary seal segment (<NUM>) comprises at least a notch (<NUM>) at an outer radial side, and wherein the notch (<NUM>) is configured to receive the pin (<NUM>) for accommodating a radial movement of each seal shoe segment (<NUM>).