Patent Description:
Various hydrostatic non-contact seal assemblies are known in the art. While these seal assemblies have various benefits, there is still room in the art for improvement, in particular as regards facilitating the disconnection of components of the assembly from a static structure to enable inspection and/or repair of one or more assembly components.

<CIT> discloses a prior art assembly for a rotational equipment with an axial centerline as set forth in the preamble of claim <NUM>.

<CIT> discloses a prior art impeller for a centrifugal compressor.

<CIT> discloses a prior art friction brake lining for a disk brake and a brake caliper for such a friction brake lining.

<CIT> discloses a prior art brush seal plate.

From a first aspect of the present invention there is provided an assembly for a rotational equipment with an axial centerline as recited in claim <NUM>.

From a second aspect of the present invention there is provided a method as recited in claim <NUM>.

Features of embodiments of the present invention are set forth in the dependent claims.

<FIG> illustrate an assembly <NUM> for rotational equipment with an axial centerline <NUM>. An example of such rotational equipment is a gas turbine engine for an aircraft propulsion system, an exemplary embodiment of which is described below in further detail. However, the assembly <NUM> of the present disclosure is not limited to such an aircraft or gas turbine engine application. The assembly <NUM>, for example, may alternatively be configured with rotational equipment such as an industrial gas turbine engine, a wind turbine, a water turbine or any other apparatus in which a seal is provided between a static structure and a rotor structure.

The assembly <NUM> of <FIG> includes a static structure <NUM>, a rotor structure <NUM>, a seal support assembly <NUM> and a seal assembly <NUM>. The seal assembly <NUM> is fixedly mounted with the static structure <NUM> through the support assembly <NUM>, e.g., via radially interfering snap fits. The seal assembly <NUM> includes a primary seal device <NUM> and one or more secondary seal devices <NUM>, which seal devices <NUM> and <NUM> are configured to substantially seal an annular gap between the static structure <NUM> / a carrier structure <NUM> and the rotor structure <NUM> as described below in further detail.

The static structure <NUM> includes a static mount <NUM>. This static mount <NUM> may be a discrete, unitary annular body. Alternatively, the static mount <NUM> may be configured with another component / portion of the static structure <NUM>. The static mount <NUM> has an inner radial mount surface <NUM>. This mount surface <NUM> may be substantially cylindrical, and extends circumferentially around and faces towards the axial centerline <NUM>. The mount surface <NUM> at least partially forms a bore in the static structure <NUM>. This bore is sized to receive the seal support assembly <NUM>, at least one component (e.g., <NUM>) of which may be fixedly attached to the static mount <NUM> by, for example, a press fit connection between each component and the mount surface <NUM>. Of course, the present disclosure is not limited to such an exemplary mounting scheme between the seal support assembly <NUM> components and the static mount <NUM>.

The rotor structure <NUM> includes a seal land <NUM>. This seal land <NUM> may be a discrete, unitary annular body. Alternatively, the seal land <NUM> may be configured with another component / portion of the rotor structure <NUM>. The seal land <NUM> has an outer radial seal land surface <NUM>. This seal land surface <NUM> may be substantially cylindrical, and extends circumferentially around and faces away from the axial centerline <NUM>. The seal land surface <NUM> is disposed to face towards and is axially aligned with the mount surface <NUM>. While <FIG> illustrate the surfaces <NUM> and <NUM> with approximately equal axial lengths along the axial centerline <NUM>, the seal land surface <NUM> may alternatively be longer or shorter than the mount surface <NUM> in other embodiments.

The seal support assembly <NUM> of <FIG> includes the carrier structure <NUM>, which includes a (e.g., tubular) carrier base <NUM> and a (e.g., annular) support ring <NUM>. The carrier structure <NUM> may be configured as a monolithic carrier structure. Herein, the term "monolithic" may describe a component which is formed as a single unitary body. The carrier base <NUM>, for example, may be cast, machined, additively manufactured and/or otherwise formed integral with the support ring <NUM> as a unitary body. This monolithic carrier structure <NUM> of <FIG> has a full hoop body (see also <FIG>), which is formed without any mechanically interconnected axial and/or circumferential segments. The present disclosure, however, is not limited to the foregoing exemplary carrier structure <NUM> configuration. For example, in other embodiments, the carrier base <NUM> and the support ring <NUM> may be formed as discrete structures. In such embodiments, the support ring <NUM> may be nested radially within and mounted to the carrier base <NUM>.

Referring again to the carrier structure <NUM> of <FIG>, the carrier base <NUM> extends axially along the centerline <NUM> between a carrier first end <NUM> and a carrier second end <NUM>. The carrier base <NUM> extends radially between a carrier inner surface <NUM> and a carrier outer surface <NUM>, which is configured to radially engage the mount surface <NUM>.

The support ring <NUM> is located at (e.g., on, adjacent or proximate) the carrier second end <NUM>. The support ring <NUM> projects radially inward from the carrier base <NUM> and, more particularly, the inner surface <NUM> to a radial inner distal end <NUM>. The support ring <NUM> extends axially along the centerline <NUM> between a ring first side <NUM> and a ring second side <NUM>, which may be axially aligned with the carrier second end <NUM>.

Referring to <FIG> and <FIG>, the support ring <NUM> is configured with one or more ring apertures <NUM>. These ring apertures <NUM> are arranged about the centerline <NUM> in an annular array (see <FIG>). Each of these ring apertures <NUM> extends through the support ring <NUM> between the ring first side <NUM> and the ring second side <NUM>. Each of the ring apertures <NUM> may be a threaded ring aperture (e.g., a tapped bolt hole), and configured to receive a threaded shaft of a tool as described below in further detail.

The support ring <NUM> may be configured as a scalloped support ring as shown in <FIG> and <FIG>. For example, the support ring <NUM> of <FIG> and <FIG> is configured with a plurality of apertures <NUM> (e.g., scallops), which are arranged in an annular array about the centerline <NUM>. Each of these apertures <NUM> extends axially through the support ring <NUM> between the ring first side <NUM> and the ring second side <NUM>. Each of the apertures <NUM> extends, in a radial outward direction, partially into the support ring <NUM> from the radial inner distal end <NUM>.

Referring to <FIG>, the seal support assembly <NUM> also includes a secondary support structure <NUM>, the configuration of which is described below in further detail. The seal support assembly <NUM> components are configured together to position, support and/or mount the seal devices <NUM> and <NUM> of the seal assembly <NUM> with the static structure <NUM>. The carrier base <NUM> of <FIG>, for example, is configured as a carrier for the assembly components <NUM>, <NUM> and <NUM>. This enables the components <NUM>, <NUM>, <NUM> and <NUM> to be mated with the static structure <NUM> as a modular unit / cartridge. The support ring <NUM> of <FIG> is configured for axially positioning and/or supporting a second end surface <NUM> of the primary seal device <NUM> relative to the static structure <NUM>. The secondary support structure <NUM> of <FIG> is configured for positioning, supporting and/or mounting the secondary seal devices <NUM> relative to the primary seal device <NUM>. This secondary support structure <NUM> is also configured for axially positioning and/or supporting a first end surface <NUM> of the primary seal device <NUM> relative to the static structure <NUM>.

<FIG> illustrates the primary seal device <NUM> in schematic block form. This primary seal device <NUM> is configured as an annular non-contact seal device and, more particularly, a hydrostatic non-contact seal device. An example of such a hydrostatic non-contact seal device is a "HALO™" seal; however, the primary seal device <NUM> of the present disclosure is not limited to the foregoing exemplary hydrostatic non-contact seal device.

Referring to <FIG>, the primary seal device <NUM> includes a seal base <NUM>, a plurality of seal shoes <NUM> and a plurality of spring elements <NUM>. The seal base <NUM> is configured as an annular full hoop body (see <FIG>), which extends circumferentially around the axial centerline <NUM>. The seal base <NUM> is configured to circumscribe the seal shoes <NUM> as well as the spring elements <NUM>. The seal base <NUM> extends axially along the axial centerline <NUM> between and forms the second end surface <NUM> and the first end surface <NUM>. The seal base <NUM> extends radially between an inner radial base side <NUM> and an outer radial base side <NUM>, which radially engages (e.g., is press fit against) the carrier base <NUM> and, more particularly, the inner surface <NUM> (see <FIG>).

Referring to <FIG>, the seal base <NUM> is configured with one or more base apertures <NUM> and <NUM>. These base apertures <NUM> and <NUM> are arranged about the centerline <NUM> in an annular array. The base apertures include a set of one or more first base apertures <NUM> and a set of one or more second base apertures <NUM>. Referring to <FIG>, each of the base apertures <NUM>, <NUM> extends through the seal base <NUM> between the first end surface <NUM> and the second end surface <NUM>. Each of the base apertures <NUM>, <NUM> is a threaded base aperture (e.g., a tapped bolt hole), and configured to receive a threaded shaft of a tool as described below in further detail. Each of the base apertures <NUM> and <NUM> may have the same diameter, which may be the same as the diameters of the ring apertures <NUM>; however, the present disclosure is not limited to such an exemplary embodiment.

Referring now to <FIG>, <FIG>, the first base apertures <NUM> are located within the base aperture array such that each of the first base apertures <NUM> is circumferentially and radially aligned with and, thereby, coaxial with a respective one of the ring apertures <NUM>. In contrast, Referring to <FIG>, the second base apertures <NUM> are located within the base aperture array such that each of the second base apertures <NUM> is misaligned from the ring apertures <NUM>. In this manner, an end of each of the second base apertures <NUM> is closed off (e.g., covered and overlapped) by a surface <NUM> at the side <NUM> of the support ring <NUM> which axially engages (e.g., contacts) the carrier base <NUM> and its second end surface <NUM>. In the specific embodiment of <FIG>, the second base apertures <NUM> are inter-disposed with the first base apertures <NUM> such that, for example, a single one of the second base apertures <NUM> is positioned circumferentially between a respective adjacent pair of the first base apertures <NUM>. Furthermore, with the foregoing configuration, a number of the first base apertures <NUM> is equal to a number of the ring apertures <NUM>, and a total number of the first base apertures <NUM> and the second base apertures <NUM> is greater than the number of the ring apertures <NUM>.

Referring to <FIG>, <FIG> and <FIG>, the seal shoes <NUM> are configured as arcuate bodies arranged circumferentially about the axial centerline <NUM> in an annular array. This annular array of the seal shoes <NUM> extends circumferentially around the axial centerline <NUM>, thereby forming an inner bore at an inner radial side of the primary seal device <NUM>. This inner bore is sized to receive the seal land <NUM> (see <FIG>), where the rotor structure <NUM> projects axially through (or into) the inner bore formed by the seal shoes <NUM>.

Referring to <FIG> and <FIG>, each of the seal shoes <NUM> includes one or more arcuate protrusions, which collectively form one or more (e.g., a plurality of axially spaced) generally annular (e.g., circumferentially segmented) ribs <NUM> at the inner radial side of the shoes <NUM>. Distal inner radial ends of one or more of these ribs <NUM> are configured to be arranged in close proximity with (but not touch) and thereby sealingly engage the seal land surface <NUM> in a non-contact manner, where the rotor structure <NUM> project axially through (or into) the inner bore formed by the seal shoes <NUM>. The ribs <NUM> therefore are configured, generally speaking, as non-contact knife edge seal elements.

Referring to <FIG>, each of the seal shoes <NUM> extends axially along the axial centerline <NUM> between a first shoe end <NUM> and a second shoe end <NUM>. The first shoe end <NUM> may be axially offset from and project axially away from the first end surface <NUM>. The second shoe end <NUM> may be axially offset from and recessed axially from the second end surface <NUM>.

Each of the seal shoes <NUM> includes an arcuate end surface <NUM> generally at (e.g., on, adjacent or proximate) the first shoe end <NUM>. In the array (see <FIG>), these arcuate end surfaces <NUM> collectively form a generally annular (but circumferentially segmented) end surface <NUM> configured for sealingly engaging with the secondary seal devices <NUM> (see <FIG>) as described below in further detail. The seal shoes <NUM> of the present disclosure, however, are not limited to the foregoing exemplary configuration.

Referring to <FIG>, the spring elements <NUM> are arranged circumferentially about the axial centerline <NUM> in an annular array. The spring elements <NUM> are also arranged radially between the seal shoes <NUM> and the seal base <NUM>. Each of the spring elements <NUM> is configured to connect a respective one of the seal shoes <NUM> with the seal base <NUM>. The spring element <NUM> shown in <FIG>, for example, includes one or more mounts <NUM> and <NUM> (e.g., generally radial fingers / projections) and one or more springs <NUM> (e.g., cantilever-leaf springs). The first mount <NUM> is connected to a respective one of the seal shoes <NUM> at (e.g., on, adjacent or proximate) its first circumferential side, where an opposing second circumferential side of that seal shoe <NUM> is free floating. The second mount <NUM> is connected to the seal base <NUM>, and is generally circumferentially aligned with or near the second circumferential side. The springs <NUM> are radially stacked and spaced apart with one another. Each of these springs <NUM> extends laterally (e.g., tangentially or circumferentially) from the first mount <NUM> to the second mount <NUM>. These spring elements <NUM> may thereby laterally overlap a major circumferential portion (e.g., ~<NUM>-<NUM>%) of the seal shoe <NUM>. The spring elements <NUM> of the present disclosure, however, are not limited to the foregoing exemplary configuration or values.

During operation of the primary seal device <NUM>, aerodynamic forces may develop and apply a fluid pressure to each of the seal shoes <NUM> causing the respective seal shoe <NUM> to move radially relative to the seal land surface <NUM>. The fluid velocity may increase as a gap between the seal shoe <NUM> and seal land surface <NUM> increases, thus reducing pressure in the gap and drawing the seal shoe <NUM> radially inwardly toward the seal land surface <NUM>. As the gap closes, the velocity may decrease and the pressure may increase within the gap, thus, forcing the seal shoe <NUM> radially outwardly from the seal land surface <NUM>. The respective spring element may deflect and move with the seal shoe <NUM> to create a primary seal of the gap between the seal land surface <NUM> and ribs <NUM> within predetermined design tolerances.

Under certain conditions, one or more of the seal shoes <NUM> may also move axially relative to the carrier base <NUM>. In particular, a pressure differential across the seal assembly <NUM> may cause the seal shoes <NUM> to move axially in a direction (e.g., towards left-hand-side of <FIG>) towards the support ring <NUM>. To limit this axial movement, the support ring <NUM> projects radially inwards to radially overlap the seal shoes <NUM> and is also located axially near the seal shoes <NUM>. In this manner, when one or more of the seal shoes <NUM> move axially, the shoe(s) axially engage the support ring <NUM> and prevent further axial displacement of the shoe(s). However, where the seal shoes <NUM> are in their nominal position (see <FIG>), a slight axial gap <NUM> extends between and separates the seal shoes <NUM> from the support ring <NUM>.

While the primary seal device <NUM> is operable to generally seal the annular gap between the static structure <NUM> / carrier structure <NUM> and the rotor structure <NUM> as described above, fluid (e.g., gas) may still flow axially through passages <NUM> defined by radial gaps between the components <NUM>, <NUM> and <NUM> (see <FIG>). The secondary seal devices <NUM> therefore are provided to seal off these passages <NUM> and, thereby, further and more completely seal the annular gap.

Each of the secondary seal devices <NUM> may be configured as a ring seal element such as, but not limited to, a split ring. Alternatively, one or more of the secondary seal devices <NUM> may be configured as a full hoop body ring, an annular brush seal or any other suitable ring-type seal.

The secondary seal devices <NUM> of <FIG> are arranged together in an axial stack. In this stack, each of the secondary seal devices <NUM> axially engages (e.g., contacts) another adjacent one of the secondary seal devices <NUM>. The stack of the secondary seal devices <NUM> is arranged with the secondary support structure <NUM>, which positions and mounts the secondary seal devices <NUM> with the carrier structure <NUM> axially adjacent the primary seal device <NUM>. In this arrangement, the stack of the secondary seal devices <NUM> is operable to axially engage and form a seal between the end surface <NUM> of the array of the seal shoes <NUM> and an annular surface <NUM> of the secondary support structure <NUM>. These surfaces <NUM> and <NUM> are axially aligned with one another, which enables the stack of the secondary seal devices <NUM> to slide radially against, but maintain sealingly engagement with, the end surface <NUM> as the seal shoes <NUM> move radially relative to the seal land surface <NUM> as described above.

The secondary support structure <NUM> may include a secondary seal carrier ring <NUM> and a secondary support ring <NUM> (e.g., retention ring), which are nested radially within and radially engaged with the carrier structure <NUM>. The secondary seal carrier ring <NUM> is configured with an annular full hoop body, which extends circumferentially around the axial centerline <NUM>. The secondary seal carrier ring <NUM> includes the annular surface <NUM>, and is disposed axially adjacent and engaged with the seal base <NUM>.

The support ring <NUM> is configured with an annular full hoop body, which extends circumferentially around the axial centerline <NUM>. The support ring <NUM> is disposed axially adjacent and engaged with the secondary seal carrier ring <NUM>, thereby capturing the stack of the secondary seal devices <NUM> within an annular channel formed between the rings <NUM> and <NUM>. The stack of the secondary seal devices <NUM>, of course, may also or alternatively be attached to one of the rings <NUM> and <NUM> by, for example, a press fit connection and/or otherwise.

<FIG> is a flow diagram of an exemplary method <NUM> involving a rotational equipment assembly such as the assembly <NUM> described above. During this method, the support assembly <NUM> and the seal assembly <NUM> are removed from the piece of rotational equipment. One or more components <NUM>, <NUM>, <NUM> and <NUM> of the assemblies are also disassembled, which may enable inspection and/or repair of one or more assembly components <NUM>, <NUM>, <NUM> and <NUM>. The various parts may be held together by radially interfering snap fits, which must be overcome during the disassembly process.

In step <NUM>, one or more tools <NUM> are provided. Referring to <FIG>, each of these tools <NUM> includes a threaded shaft <NUM>, which may be completely threaded or partially threaded with an unthreaded shank for example. Each of the tools <NUM> may also include a tool base <NUM>, where the threaded shaft <NUM> projects out from the tool base <NUM>. In the specific embodiment of <FIG>, each tool is configured as a threaded bolt, where the tool base <NUM> is a head of the bolt. However, the present disclosure is not limited to such a tool configuration. For example, in other embodiments, the tool base <NUM> may be configured as a handle or otherwise with threads that engage tapped hole <NUM> and/or <NUM>.

In step <NUM>, the one or more tools <NUM> are mated with the carrier base <NUM> and the support ring <NUM>. For example, as shown in <FIG>, the threaded shaft <NUM> of each tool may be threaded into a respective one of the ring apertures <NUM> and a respective one of the first base apertures <NUM>.

In step <NUM>, the support assembly <NUM> and the seal assembly <NUM> are removed from the piece of rotational equipment as a single unit; e.g., a cartridge. For example, as shown in <FIG>, the tools <NUM> and, more particularly, the tool bases <NUM> are pulled axially (e.g., towards the right-hand-side of <FIG>). In general, an equal axial pulling force should be applied to each of the tools <NUM> in order to prevent skewing of the assemblies during the removal process. In this manner, the support assembly <NUM> and the seal assembly <NUM> are disconnected from the static structure <NUM> and unmated from the rotor structure <NUM>.

In step <NUM>, the secondary support structure <NUM> and the secondary seal devices <NUM> are removed from the assemblies. For example, as shown in <FIG>, the tools <NUM> are rotated such that each tool <NUM> and its threaded shaft <NUM> applies a generally equal axial force against the surface <NUM> of the secondary support structure <NUM>. The application of these axial forces cause the secondary support structure <NUM> and the secondary seal devices <NUM> to be pushed out of and thereby decoupled from the carrier base <NUM>.

In step <NUM>, the tools <NUM> are decoupled from the apertures <NUM> and <NUM>. Then, in step <NUM>, the tools <NUM> are reoriented and mated with the seal base <NUM>. For example, as shown in <FIG>, the threaded shaft <NUM> of each tool may be threaded into a respective one of the second base apertures <NUM>.

In step <NUM>, the primary seal device <NUM> is removed from the carrier structure <NUM>. For example, as shown in <FIG>, the tools <NUM> are rotated such that each tool <NUM> and its threaded shaft <NUM> applies a generally equal axial force against the surface <NUM> of the support ring <NUM>. The application of these axial forces cause the seal base <NUM> to be pulled out of and thereby decoupled from the carrier structure <NUM>.

The present disclosure is not limited to the exemplary primary seal device <NUM> type or configuration described above. Various other non-contact seals are known in the art and may be reconfigured in light of the disclosure above to be included with the assembly <NUM> of the present disclosure. Other examples of non-contact seals are disclosed in <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>.

As described above, the assembly <NUM> of the present disclosure may be configured with various different types and configurations of rotational equipment. <FIG> illustrates one such type and configuration of the rotational equipment - a geared turbofan gas turbine engine <NUM>. Such a turbine engine includes various static structures (e.g., bearing supports, hubs, cases, etc.) as well as various rotor structures (e.g., rotor disks, shafts, etc.) as described below, where the static structure <NUM> and the rotor structure <NUM> can respectively be configured as anyone of the foregoing structures in the turbine engine <NUM> of <FIG>, or other structures not mentioned herein.

Referring still to <FIG>, the turbine engine <NUM> extends along an axial centerline <NUM> (e.g., the centerline <NUM>) between an upstream airflow inlet <NUM> and a downstream airflow exhaust <NUM>. The turbine engine <NUM> includes a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. The compressor section <NUM> includes a low pressure compressor (LPC) section 135A and a high pressure compressor (HPC) section 135B. The turbine section <NUM> includes a high pressure turbine (HPT) section 137A and a low pressure turbine (LPT) section 137B.

The engine sections <NUM>-<NUM> are arranged sequentially along the centerline <NUM> within an engine housing <NUM>, a portion or component of which may include or be connected to the static structure <NUM>. This housing <NUM> includes an inner case <NUM> (e.g., a core case) and an outer case <NUM> (e.g., a fan case). The inner case <NUM> may house one or more of the engine sections <NUM>-<NUM>; e.g., an engine core. The outer case <NUM> may house at least the fan section <NUM>.

Each of the engine sections <NUM>, 135A, 135B, 137A and 137B includes a respective rotor <NUM>-<NUM>. Each of these rotors <NUM>-<NUM> includes a plurality of rotor blades arranged circumferentially around and connected to one or more respective rotor disks. The rotor blades, for example, may be formed integral with or mechanically fastened, welded, brazed, adhered and/or otherwise attached to the respective rotor disk(s).

The fan rotor <NUM> is connected to a gear train <NUM>, for example, through a fan shaft <NUM>. The gear train <NUM> and the LPC rotor <NUM> are connected to and driven by the LPT rotor <NUM> through a low speed shaft <NUM>. The HPC rotor <NUM> is connected to and driven by the HPT rotor <NUM> through a high speed shaft <NUM>. The shafts <NUM>-<NUM> are rotatably supported by a plurality of bearings <NUM>; e.g., rolling element and/or thrust bearings. Each of these bearings <NUM> is connected to the engine housing <NUM> by at least one stationary structure such as, for example, an annular support strut.

During operation, air enters the turbine engine <NUM> through the airflow inlet <NUM>. This air is directed through the fan section <NUM> and into a core gas path <NUM> and a bypass gas path <NUM>. The core gas path <NUM> flows sequentially through the engine sections 135A, 135B, <NUM>, 137A and 137B. The bypass gas path <NUM> flows away from the fan section <NUM> through a bypass duct, which circumscribes and bypasses the engine core. The air within the core gas path <NUM> may be referred to as "core air". The air within the bypass gas path <NUM> may be referred to as "bypass air".

The assembly <NUM> may be included in various aircraft and industrial turbine engines other than the one described above as well as in other types of rotational equipment; e.g., wind turbines, water turbines, rotary engines, etc. The assembly <NUM>, for example, may be included in a geared turbine engine where a gear train connects one or more shafts to one or more rotors in a fan section, a compressor section and/or any other engine section. Alternatively, the assembly <NUM> may be included in a turbine engine configured without a gear train. The assembly <NUM> may be included in a geared or non-geared turbine engine configured with a single spool, with two spools (e.g., see <FIG>), or with more than two spools. The turbine engine may be configured as a turbofan engine, a turbojet engine, a prop fan engine, a pusher fan engine or any other type of turbine engine. The present invention therefore is not limited to any particular types or configurations of turbine engines or rotational equipment.

Claim 1:
An assembly (<NUM>) for rotational equipment with an axial centerline (<NUM>), comprising:
a static structure (<NUM>);
a rotor structure (<NUM>);
a carrier structure (<NUM>) extending axially along and circumferentially around the centerline (<NUM>), the carrier structure (<NUM>) nested radially within and radially engaging the static structure (<NUM>); and
a seal assembly (<NUM>) configured to seal an annular gap between the static structure (<NUM>) and the rotor structure (<NUM>), the seal assembly (<NUM>) comprising a hydrostatic non-contact seal device (<NUM>) nested radially within the carrier structure (<NUM>),
the hydrostatic non-contact seal device (<NUM>) comprising a seal base (<NUM>),
characterised in that:
a plurality of threaded base apertures (<NUM>, <NUM>) are arranged about the centerline (<NUM>) in an annular array, and each of the threaded base apertures (<NUM>, <NUM>) extends axially through the seal base (<NUM>), wherein each of the threaded base apertures (<NUM>, <NUM>) is configured to mate a threaded shaft (<NUM>) of a tool (<NUM>).