Patent Description:
Hydrostatic advanced low leakage seals, or hybrid seals, exhibit less leakage compared to traditional knife edge seals while exhibiting a longer life than brush seals. Some hybrid seals may be used to seal between a stator and a rotor within a gas turbine engine. The hybrid seal is mounted to one of the stator or the rotor to maintain a desired gap dimension between the hybrid seal and the other of the stator and rotor. The hybrid seal has the ability to 'track' the relative movement between the stator and the rotor throughout the engine operating profile when a pressure is applied across the seal. The hybrid seal tracking surface is attached to a solid carrier ring via continuous thin beams.

In typical hybrid seal designs, two parallel beams support a shoe. The nature of the beams is to bend when a cantilevered load is applied. A curvature is created in the beams which in the case of a hybrid seal shoe results in tipping of the shoe, relative to a rotating sealing surface (e.g., rotor). For large radial deflection, the tipping can be equal to the desired running clearance, increasing the risk of incidental contact, and wearing of the seal teeth.

<CIT>, <CIT> and <CIT> disclose hydrostatic seals for a rotor and stator system according to the preamble of claim <NUM> of the present invention, comprising a shoe supporting two beams which are angled relative to the shoe and relative to each other, and connected to a base. The beams are separately formed before each being attached at separate locations on the shoe and the base.

Disclosed is a hydrostatic advanced low leakage seal configured to be disposed between relatively rotatable components. The seal includes a base. The seal also includes a shoe extending circumferentially. The seal further includes a radially outer beam operatively coupling the shoe to the base. The seal yet further includes a radially inner beam operatively coupling the shoe to the base, wherein one of the radially inner beam and the radially outer beam is oriented to be angled relative to the other of the radially inner and outer beam, characterized in that the radially outer beam and the radially inner beam are joined to each other by an end segment.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially inner beam is oriented substantially tangentially relative to a sealing surface of an object to be sealed by the shoe.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially outer beam angles radially inwardly in a direction from a first circumferential end of the radially outer beam to a second circumferential end of the radially outer beam, the second circumferential end of the radially outer beam being the end of the radially outer beam that is closest to a maximum radial deflection location of the seal.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially outer beam angles radially outwardly in a direction from a first circumferential end of the radially outer beam to a second circumferential end of the radially outer beam, the second circumferential end of the radially outer beam being the end of the radially outer beam that is closest to a maximum radial deflection location of the seal.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially outer beam is oriented substantially tangentially relative to a sealing surface of an object to be sealed by the shoe.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially inner beam angles radially inwardly in a direction from a first circumferential end of the radially inner beam to a second circumferential end of the radially inner beam, the second circumferential end of the radially inner beam being the end of the radially inner beam that is closest to a maximum radial deflection location of the seal.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially inner beam angles radially outwardly in a direction from a first circumferential end of the radially inner beam to a second circumferential end of the radially inner beam, the second circumferential end of the radially inner beam being the end of the radially inner beam that is closest to a maximum radial deflection location of the seal.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the angled beam is angled relative to the other beam at an angle ranging from <NUM> degrees to <NUM> degrees.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially inner beam and the radially outer beam have a common beam thickness.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that at least one of the radially inner beam and the radially outer beam has a beam length that is substantially equal to or greater than a circumferential pitch of the shoe.

Also disclosed is a seal assembly disposed in a gas turbine engine. The seal assembly includes a first component. The seal assembly also includes a second component, the first component and the second component relatively rotatable components. The seal assembly further includes a hydrostatic advanced low leakage seal disposed between the first component and the second component. The seal includes a base operatively coupled to one of the first component and the second component. The seal also includes a shoe extending circumferentially. The seal further includes a radially inner beam operatively coupling the shoe to the base, the radially inner beam oriented substantially tangentially relative to a sealing surface of one of the first component and the second component. The seal yet further includes a radially outer beam operatively coupling the shoe to the base, the radially outer beam being oriented to be relatively angled to the radially inner beam.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially outer beam is angled radially inwardly in a direction from a first circumferential end of the radially outer beam to a second circumferential end of the radially outer beam, the second circumferential end of the radially outer beam being the end of the radially outer beam that is closest to a maximum radial deflection location of the seal.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially outer beam is angled relative to the radially inner beam at an angle ranging from <NUM> degrees to <NUM> degrees.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the first component is a stator and the second component is a rotor.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the seal is operatively coupled to the stator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the seal is operatively coupled to the rotor.

Further disclosed is a gas turbine engine including a compressor section, a combustor section, a turbine section, and a seal assembly disposed in a gas turbine engine, the seal assembly comprising relatively rotatable components and a hydrostatic advanced low leakage seal disposed between the relatively rotatable components. The seal includes a base. The seal also includes a shoe extending circumferentially. The seal further includes a radially outer beam operatively coupling the shoe to the base. The seal yet further includes a radially inner beam operatively coupling the shoe to the base, wherein one of the radially inner beam and the radially outer beam is oriented to be angled relative to the other of the radially inner and outer beam.

In addition to one or more of the features described above, or as an alternative, further embodiments may include that the radially inner beam is oriented substantially tangentially relative to a sealing surface of a component to be sealed by the seal, the radially outer beam being oriented to be relatively angled to the radially inner beam.

In one disclosed embodiment, the engine <NUM> bypass ratio is greater than about ten (<NUM>:<NUM>), the fan diameter is significantly larger than that of the low pressure compressor <NUM>, and the low pressure turbine <NUM> has a pressure ratio that is greater than about five (<NUM>:<NUM>). The geared architecture <NUM> may be an epicycle gear train, such as a planetary gear system or other gear system, with a gear reduction ratio of greater than about <NUM>:<NUM>. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present disclosure is applicable to other gas turbine engines including direct drive turbofans.

The fan section <NUM> of the engine <NUM> is designed for a particular flight condition--typically cruise at about <NUM> Mach (<NUM>/s) and about <NUM>,<NUM> feet (<NUM>,<NUM> meters). The flight condition of <NUM> Mach (<NUM>/s) and <NUM>,<NUM> feet (<NUM>,<NUM> meters), with the engine at its best fuel consumption--also known as "bucket cruise Thrust Specific Fuel Consumption ('TSFC')"--is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point.

<FIG> schematically illustrates a hydrostatic advanced low leakage seal, or hybrid seal, indicated generally at <NUM>. Although the hybrid seal <NUM> is mounted on a stator in some embodiments, it will be appreciated that the hybrid seal <NUM> could alternatively be mounted to a rotor. The hybrid seal <NUM> is intended to create a seal of the circumferential gap between two relatively rotating components, such as a fixed stator and a rotating rotor. The hybrid seal <NUM> includes a base portion <NUM> and at least one, but often a plurality of circumferentially spaced shoes <NUM> which are located in a non-contact position along the exterior surface of the rotor. Each shoe <NUM> is formed with a sealing surface <NUM>. For purposes of the present disclosure, the term "axial" or "axially spaced" refers to a direction along the longitudinal axis of the stator and rotor, whereas "radial" refers to a direction perpendicular to the longitudinal axis.

Under some operating conditions, it is desirable to limit the extent of radial movement of the shoes <NUM> with respect to the rotor to maintain tolerances, such as the spacing between the shoes <NUM> and the facing surface of the rotor. The hybrid seal <NUM> includes at least one circumferentially spaced spring element <NUM>. Each spring element <NUM> is formed with a radially inner beam and a radially outer beam.

Particularly when the hybrid seal <NUM> is used in applications such as gas turbine engines, aerodynamic forces are developed which apply a fluid pressure to the shoe <NUM>, which is counter balanced with the spring <NUM>, causing it to move radially with respect to the rotor. The initial assembly point has a defined radial gap between the shoe <NUM> and the rotating surface, with no forces acting upon the shoe <NUM>. In operation, the hybrid seal <NUM> is used to restrict flow between a high pressure region and a lower pressure region. The pressure drop across the shoe <NUM> creates a radial force on the shoe which is counter balanced by the spring <NUM>. In operation, when the gap between the shoe <NUM> and rotor increases, the pressure drop across the axial length of the seal shoe decreases. The reduction in pressure across the shoe <NUM> reduces the radial force acting on the shoe <NUM> such that the force balance between the pressure force and the spring <NUM> force causes the shoe <NUM> to be pushed radially inwardly toward the rotor, thus decreasing the gap. Conversely, in operation, when the gap closes below a desired level, the pressure drop across the shoe <NUM> increases, causing an increase in radial pressure force, which overcomes the spring force, thus forcing the shoe <NUM> radially outwardly from the rotor. The spring elements <NUM> deflect and move with the shoe <NUM> to create a primary seal of the circumferential gap between the rotor and stator within predetermined design tolerances.

Energy from adjacent mechanical or aerodynamic excitation sources (e.g. rotor imbalance, flow through the seal, other sections of the engine, etc.) may be transmitted to the seal <NUM>, potentially creating a vibratory response in the seal <NUM>. Such vibratory responses create vibratory stress leading to possible reduced life of the seal <NUM>, and can be large enough to cause unintended deflections of the shoes <NUM>. The vibratory response of the shoes <NUM> at their natural frequencies, while interacting with mechanical excitation or aerodynamic flow through the system, can reinforce each other causing unwanted vibration levels and possible deflection of the shoes <NUM> as the vibration is transmitted to all of the shoes <NUM>. Because the resonant frequency response is a function of the square root of the ratio of spring element <NUM> stiffness to the mass, design considerations include increasing the first order natural frequency by reducing the mass of the shoes <NUM> and/or increasing the stiffness of the beams <NUM>.

Increasing the stiffness of the beams <NUM> can only be considered if the available pressure drop is still sufficient to deflect the shoe <NUM> relative to the rotor. In practice, the beams have a very low spring rate to maintain the force balance with the pressure drop across the shoe <NUM>, and create the desired, small, controlled gap. The hybrid seal <NUM> operation requires low stiffness beams, making it difficult to achieve large increases in the resonant frequency through stiffness. For this reason it is preferable to decrease shoe mass.

Decreasing the mass of the shoes <NUM>, by increasing the number of shoes <NUM> in the assembled hybrid seal <NUM> is beneficial. With conventional hybrid seal designs, the length of the spring <NUM> would also decrease. However, the radial deflection limiters would impose a fixed circumferential geometric constraint, due to manufacturing and structural requirements and therefore the radial deflection limiters would become a proportionally larger percentage of the circumferential space available for the spring <NUM> and the deflection limiters. Thus it can be shown, increasing the shoe quantity to reduce the shoe <NUM> mass, would reduce the circumferential arc length available for shoe <NUM> and spring <NUM>, and the deflection limiters would impose a proportionally greater reduction in the spring <NUM> length, which results in a stiffer spring <NUM>. However, the pressure balance force is proportional to the arc length, and would require a reduction in spring stiffness to maintain the ability to control the gap. For a given length of spring <NUM>, the practical means to reduce the stiffness is to reduce the thickness of the beams <NUM>. In practice, the ability to design thin beams is not only limited by manufacturing techniques, but can result in beams which might be easily damaged during manufacture, assembly and use. Therefore, it is desired to decouple the arc length of the shoe <NUM> from the length of the spring <NUM>.

Referring now to <FIG>, rather than relying on end stops and radial deflection limit features that extend completely, or nearly completely, between the shoe <NUM> and the base portion <NUM> of the seal <NUM> - as with prior hybrid seals - the embodiments disclosed herein include tab and slot features on adjacent shoes <NUM> that provide deflection shared end stops. As shown in <FIG>, a tab <NUM> extending from a first shoe 108a is in engagement with a slot feature <NUM> extending from a second shoe 108b that is adjacent shoe 108a to limit radial deflection of the seal. The radial deflection is limited by deflection limiting posts <NUM> extending axially from a rear support <NUM> of the structure to which the seal <NUM> is mounted to, such as a stator. Each post <NUM> is disposed within a respective aperture <NUM> that is defined by a structure extending radially from the shoe <NUM>.

Each of the above-described deflection limiting features have a small radial height impact, which allows for a reduction in mass of the shoes <NUM> and providing an increased design space within the seal <NUM>. For example, the location of the beams <NUM> becomes independent of the shoe <NUM> since the beams <NUM> no longer must have a length that is less than the arc length of each shoe <NUM>, as shown well in <FIG>, without having to increase the radial design space that would be required if the angle of the beams were required to be changed.

<FIG> illustrates a comparison of four embodiments of the seal <NUM>, with each having a different number of shoes <NUM> and therefore shoe arc lengths. Each illustrated seal <NUM> includes beams <NUM> with a common beam length. As shown, the arc length of each shoe <NUM> in each illustrated seal design does not impact or impair the ability to maintain a beam that is substantially equal to or longer than the arc length of the shoes.

Referring again to <FIG>, the term "beam length" used herein is defined by length L. The beam length L includes end segments <NUM>, which join the beams <NUM>. The end segments <NUM> are part of the beams <NUM>, either in an integrally formed manner or via a joining process, and it is the overall length of the beams <NUM> and the end segments <NUM> that constitute the beam length. It is this beam length that is substantially equal to or longer than the arc length, or circumferential pitch, of the shoes <NUM>. "Substantially equal" to the arc length of the shoe <NUM> refers to <NUM>% or more of the shoe length.

The above-described embodiments illustrated in <FIG> include beams <NUM> that may not be oriented tangentially to the rotor due to the extended beam length. In such embodiments, as well as any other embodiment of a hybrid seal, reducing tipping of the shoe <NUM> is advantageous, as such tipping may result in contact between an end of the shoe <NUM> and the rotating sealing surface. "Tipping", as used herein, refers to relative rotation of ends of the shoe <NUM> in a longitudinal (i.e., circumferential) direction of the shoe which occurs when one end of the shoe is radially deflected to a greater extent than the other end of the shoe. As shown in <FIG>, the average running clearance <NUM> must increase if the magnitude of the tipping is such that possible shoe contact can occur at the ends of the shoe <NUM>. The average clearance may be one value, but the local clearance may be too small and cause local contact with the rotor <NUM>, which is undesirable for long term durability.

The embodiments described herein provide beam geometry that offsets the tendency for the shoe <NUM> to tip. As shown in <FIG>, two different beam configurations are illustrated. In particular, each illustrated embodiment includes a pair of beams, referred to as a first beam 116a and second beam 116b. Each beam 116a, 116b extends from a first end <NUM> to a second end <NUM>. These ends do not include the end segments <NUM> that join the beams. The beams 116a, 116b extend substantially circumferentially about the engine central longitudinal axis A, with one of the ends being a leading end and the other end being a trailing end during operation of the gas turbine engine. The first beam 116a is a radially outer beam and the second beam 116b is a radially inner beam. In the embodiment of <FIG>, the radially outer beam 116a is angled relative to the radially inner beam 116b, such that the beams are not parallel. In such an embodiment, the radially outer beam 116a tapers radially inwardly in the direction of the beam 116a extending from the first end <NUM> to the second end <NUM>. In other embodiments, the radially inner beam 116b is angled relative to the radially outer beam 116a, such that the beams are not parallel. In such an embodiment, the radially inner beam 116b tapers radially inwardly or outwardly in the direction of the beam 116b extending from the first end <NUM> to the second end <NUM>. The illustrated embodiments are merely examples and it is to be appreciated that it is contemplated that either beam may be the angled beam, with such angled beam being angled radially inwardly or outwardly - in a direction from first end <NUM> to second end <NUM>.

In some embodiments, the beams 116a, 116b have a common thickness, although it is contemplated that different thicknesses may be combined with the non-parallel orientation described herein. Beam thickness refers to a dimension of the beams that measures a dimension generally normal to the beam length, while width refers to the axial dimension of the beams. The beam length is defined above.

The extent of the angle of the outer beam 116a or the inner beam 116b may vary depending upon the particular application of use. In some embodiments, the angle of the angled beam 116a or 116b ranges from about <NUM> degrees to about <NUM> degrees relative to the other beam. For example, the angled beam may be angled at <NUM> degrees, <NUM> degrees or <NUM> degrees to the other beam. Although the disclosed range of angles is not drastic, adding the small amount of taper angle between the beams 116a, 116b reduces or eliminates the tendency of the shoe <NUM> to tip. For example, in an embodiment with the outer beam 116a being the angled beam, the inner beam 116b remains substantially tangent to the rotor <NUM>, since this controls the relative radial position and ability to move the beams 116a, 116b as close to the rotating seal lands as possible. The outer beam 116a angles inwardly, as described above, starting from the mount end <NUM> of the beam and ending up closer to the inner beam.

<FIG> shows an embodiment of the angled beam orientation (i.e., non-parallel orientation) captured during a common computer simulation that quantifies tipping due to relative radial deflection of ends of the shoe <NUM>. As shown, minimum radial deflection of the overall seal assembly occurs at location <NUM>, while maximum radial deflection occurs proximate a first end <NUM> of the shoe <NUM>. Comparing the maximum radial deflection to radial deflection at a second end <NUM> of the shoe <NUM> provides a difference that quantifies the amount of tipping of the shoe.

It has been demonstrated that an angled beam that forms a trapezoidal geometry (rather than a parallelogram) reduces tipping of the shoe <NUM>. A taper angle ranging from between about <NUM> degrees to about <NUM> degrees has been shown to virtually eliminate the shoe tipping. However, the entire above-described range of about <NUM> degrees to about <NUM> degrees would be beneficial. By reducing tipping of the shoe <NUM>, the risk of contact with the sealing surface is advantageously reduced, and a consistently tight running clearance will be possible without excessive instances of incidental contact between the shoe and the rotating sealing surface.

Claim 1:
A hydrostatic advanced low leakage seal (<NUM>) configured to be disposed between relatively rotatable components, the seal comprising:
a base (<NUM>);
a shoe (<NUM>) extending circumferentially;
a radially outer beam (116a) operatively coupling the shoe (<NUM>) to the base (<NUM>); and
a radially inner beam (116b) operatively coupling the shoe (<NUM>) to the base (<NUM>), wherein one of the radially inner beam (116b) and the radially outer beam (116a) is oriented to be angled relative to the other of the radially inner and outer beam,
characterized in that
the radially outer beam (116a) and the radially inner beam (116b) are joined to each other by an end segment (<NUM>).