Non-axisymmetric brush seal assembly

There is disclosed a brush seal assembly including at least one annular bristle pack. The at least one annular bristle pack extends circumferentially around a central axis of the brush seal assembly. The at least one annular bristle pack has bristles extending along longitudinal axes from roots to free tips. The bristles extend toward a cylindrical plane of a the seal land. Projections of the free tips on the cylindrical plane define a bristle tip projection surface being non-axisymmetric. A method of operating a brush seal assembly is also disclosed.

TECHNICAL FIELD

The application relates generally to gas turbine engines and, more particularly, to brush seals used in such engines for sealing a gap between two parts that move relative to one another.

BACKGROUND OF THE ART

Brush seals are commonly used in gas turbine engines but are typically not intended to completely seal different engine sections from one another. Brush seals rely on the limited flow path created between bristles of bristle packs to reduce the air flow from one part of the engine to another to control the pressure drop between the parts.

Such brush seals are for example used in thrust pistons used to balance the heavy forces present in gas turbine engines. Compressed air is directed against the thrust piston to counter act the force created by the engine.

SUMMARY

In one aspect, there is provided a brush seal assembly comprising at least one annular bristle pack extending circumferentially around a central axis of the seal, the at least one annular bristle pack having bristles extending along longitudinal axes from roots to free tips, the bristles extending toward a cylindrical plane of a seal land, projections of the free tips on the cylindrical plane defining a bristle tip projection surface that is non-axisymmetric relative to the central axis.

In another aspect, there is provided a gas turbine engine comprising a casing, a seal runner for rotation about a central axis, and a brush seal assembly operatively mounted between the casing and the seal runner to be secured to one of the casing and the seal runner, the brush seal assembly including at least one bristle pack, the at least one bristle pack being annular and extending circumferentially around the central axis, the at least one bristle pack having bristles extending from roots to free tips, the free tips of the bristles facing a seal land located on the other of the casing and the seal runner, a projection of the free tips of the bristles on the seal land along a direction normal to the seal land defining a bristle tip projection surface that circumferentially extends around the axis, the bristle tip projection surface being non-axisymmetric.

In yet another aspect, there is provided a method of operating a brush seal assembly located between a stator and a rotor of a component of a gas turbine engine, comprising: separating a first zone from a second zone by a bristle pack of the brush seal assembly secured to one of the stator and the rotor, the first zone being at a higher pressure than the second zone; permitting a fluid to flow from the first zone to the second zone via a gap circumferentially extending around a central axis of the brush seal assembly and defined between tips of the bristles and a seal land of the other of the stator and the rotor; and varying at least one of a position and a width of the gap relative to the seal land along a circumference of the gap.

DETAILED DESCRIPTION

FIG. 1illustrates a gas turbine engine10of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan12through which ambient air is propelled, a compressor section14for pressurizing the air, a combustor16in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section18for extracting energy from the combustion gases. The fan12, the compressor section14and the turbine section18are in rotation about an axis11of the gas turbine engine10.

FIG. 2illustrates a cross-sectional view of a portion of the gas turbine engine10near the turbine section18. A brush seal assembly20is adapted to be operatively mounted between a stator22and a rotor24of the gas turbine engine10. The stator22may be part of or may be secured to a casing26of the gas turbine engine10and the rotor24may include a rear seal runner28secured to a shaft30of the gas turbine engine10. The rear seal runner28may also be referred to as a balance thrust piston.

The brush seal assembly20may be used to control a pressure differential or to maintain a generally constant pressure differential between a first zone32and a second zone34axially separated from the first zone32by the rear seal runner28. The pressure in the first zone32may be higher than that in the second zone34thereby creating a force on the rear seal runner28in a direction opposite to a direction of the combustion gases so that a ball bearing (not shown) may always be axially loaded. It is understood that the brush seal assembly20may be mounted between a stator or a rotor of a compressor14of the gas turbine engine10or any other component including a rotor and a stator. The brush seal assembly20may be secured to the rotor24or to the stator22. In the depicted embodiment, the brush seal assembly20is secured to the stator22corresponding herein to the engine casing26.

The brush seal assembly20may include a housing40(a.k.a., a brush seal support) and at least one bristle pack42, e.g., two in the depicted embodiment, secured to the housing40. The housing40and the at least one bristle pack42are annular and circumferentially extend around a central axis A thereof and along a full circumference thereof. As shown, the housing40of the brush seal assembly20may be secured to the engine casing26.

In the depicted embodiment, the housing40includes annular members40aaxially spaced from each other and adapted to receive the bristle packs42therebetween. The annular members40aand the bristle packs42may be made of Inconel™. Such a material may be required depending of the operating conditions to which the brush seal assembly20is submitted. In one embodiment, the rear seal runner28is downstream of the combustor16. Accordingly, it may be subjected to temperatures neighbouring 600° F. and up to 1200° F. or higher. Any other suitable material may be used provided such material can sustain the operating conditions of the gas turbine engine10.

The bristle packs42may be embedded within the housing40. As shown, each of the bristle packs42is axially bound by two annular members40a. The annular members40amay also be referred to as annular washers. The brush seal assembly20may include a stack of annular members40aand bristle packs42disposed in alternation with the annular members40a. Accordingly, more than two bristle packs42may be provided by adding more annular members40a. The members40aare thus adapted to sandwich the bristle packs42therebetween. In the illustrated embodiment, the brush seal assembly20has two bristle packs42and three annular members40adefining an annular cavity C between the two packs42. Other arrangements are considered to support the bristles in the annular configuration, such as an embedding in a single annular housing40, etc. The annular members40amight provide support to the bristle packs42against an axial force resulting from the pressure differential between zones32and34. The dimensions of the annular members40aand of the bristle packs42are function of a rotational speed of the rotor, the pressure differential between the zones32and34, a temperature in which they are operated, a size of the seal runner, etc.

In the depicted embodiment, the annular members40ainclude an aft member40a1, a middle member40a2and a fore member40a3. As shown, the aft member and the fore member40a1,40a3have a same thickness t1taken along the central axis A. The aft member40a1has a radial height R1taken along a radial direction R relative to the central axis A that may be greater than a radial height R2of the fore member40a3. The radial height R1of the aft member40a1may correspond to that of the middle member40a2. The middle member40a2has an outward portion40a2′ and an inward portion40a2″ located radially inwardly to the outward portion40a2′ relative to the central axis A. A thickness t2of the middle member40a2at the outward portion40a2′ may be greater than the thickness t1of the aft and fore members40a1,40a3. The thickness t1of the fore member40a1may correspond to that of the middle member40a2at the inward portion40a2″. A difference in the thicknesses between the outward and inward portions40a2′,40a2″ of the middle member40a2creates a spacing41such that a portion of length of the bristles42aof one of the bristle packs42is axially spaced apart from the middle member40a2. The spacing41might allow the bristles to be less constrained and to be exposed to the pressure load in order to move radially towards the rotor seal land28ato increase a sealing effect. This is referred to as the “pressure closure” of “blow down” phenomenon. The radial height R2of the fore member40a3may correspond to that of the outward portion40a2′ of the middle member40a2. In the embodiment shown, a thickness of the spacing41between the middle member inward portion40a2″ and one of the bristle packs42is constant along its circumference.

Each of the two bristle packs42includes bristles42athat extend along longitudinal axes L from roots42bto free tips42copposed to the roots42b. The longitudinal axes L may be generally parallel to the radial direction R relative to the central axis A, though with deflections from parallel being possible due to the flexible nature of the bristles42a. The roots42bare secured to the housing40whereas the free tips42care cantilevered. A sealing effect is provided at least by a cooperation of the free tips42cof the bristles42aand a seal land28alocated on the rear seal runner28. The rotor seal land28ais defined as a zone on the rotor that faces the tips42cof the bristles42aof the bristle pack42.

In the embodiment shown, the free tips42cof the bristles42aand the seal land28amay or may not be spaced from each other by a gap G. The seal land28acorresponds to a portion of the seal runner28that is aligned with the gap G. In the depicted embodiment, the seal land28aextends circumferentially around the central axis A and axially; the gap G having a height H defined along the radial direction R relative to the central axis A. It is understood that, alternatively, the seal land28amay extend radially such that the height H of the gap G is defined along the central axis A without departing from the scope of the present disclosure. Other configurations are contemplated.

Referring now toFIGS. 2-3, the bristles42aextend along their longitudinal axes L toward a plane P, a cylindrical plane in the depicted embodiment, that contains the seal land28a. A bristle tip projection surface S is defined on the cylindrical plane P and on the seal land28aby projections (e.g., imaginary) of the free tips42cof the bristles42aon the plane P. The projections of the free tips42cmay be along the longitudinal axes L or along a direction D normal to the seal land28a. The bristle tip projection surface S corresponds to a surface on the seal land28athat cooperates with the bristle free tips42cin providing at least partially the sealing effect. Stated differently, portions of the seal land28athat do not face the bristle free tips42care outside of the bristle tip projection surface S. As shown, the bristle tip projection surface S extends from a first limit S1to a second limit S2being shown in dashed lines inFIG. 3. The first and second limits S1, S2extend circumferentially around the central axis A. The gap G is contained between first limit S1and the second limit S2. In the depicted embodiment, the first limit S1is axially spaced apart from the second limit S2relative of the central axis A.

It has been observed that a flow of air F circulating via the gap G might produce flutter. The flutter is an aerodynamic phenomenon characterized by a fluid-structure interaction. More specifically, aerodynamic forces created by the flow of air F circulating via the gap G combined with the natural vibration frequency of the rear seal runner28might create self-feeding vibrations. The flutter and the associated self-feeding vibrations may be detrimental to the structural integrity of the rear seal runner28. Overtime, cracks may develop and result in the failure of the rear seal runner28.

To at least partially decrease a magnitude of the flutter, it might be advantageous to design the brush seal assembly20such that the bristle tip projection surface S defined by the bristle pack42is non-axisymmetric.

A plurality of designs of the bristle packs42that would generate a bristle tip projection surface S being non-axisymmetric are possible. A few possible embodiments are described herein below with reference toFIGS. 4-5. The scope of the present disclosure should not be limited thereby.

Referring now toFIG. 4, as shown, the brush seal assembly120includes two bristle packs142a,142bthat are described below. The bristle tip projection surfaces S created by both of the two bristle packs142a,142bhave a width W that is constant along their circumference. Herein, the width W is defined as a distance between the first and second limits S1, S2. In the embodiment shown, the width W is taken along the axial direction. An aft one of the two bristle packs, referred to below as the aft bristle pack142a, and a fore one of the two bristle packs, or fore bristle pack142b, are described below. The bristle tip projection surfaces S created by the aft and fore bristle packs142a,142bare non-axisymmetric. In the depicted embodiment, a distance D1between the two bristle tip projection surfaces S of the fore and aft bristle packs142a,142bvaries along the circumference. In a particular embodiment, a distance between the bristle tip projection surfaces of the fore and aft bristle packs may be constant along a circumference of the brush seal assembly120.

In the depicted embodiment, a position of the bristle tip projection surface S of the aft bristle pack142avaries monotonically between a first position P1and a second position P2along one of two equal halves142a′ of the aft bristle pack142a. In the depicted embodiment, the first and second positions P1, P2are axially spaced apart from each other relative to the central axis A. In the embodiment shown, the bristle tip projection surface S reaches the first position P1at a first circumferential position and reaches the second position P2at a second circumferential position being diametrically opposed to the first circumferential position. For a first one of two equal halves142a′ of the aft bristle pack142a, the position of the bristle tip projection surface moves monotonically from the first position P1at the first circumferential position to the second position P2at the second circumferential position. And, for a second one of the two equal halves142a′ of the aft bristle pack142a, the position of the bristle tip projection surface S moves monotonically from the second position P2at the second circumferential position to the first position P1at the first circumferential position.

A position of the bristle tip projection surface S of the fore bristle pack142bmoves along its circumference in an alternating manner. Stated otherwise, the position of the bristle tip projection surface S moves in alternation in opposed directions along both of two equal halves142b′ of the fore bristle pack142b.

Referring now toFIG. 5, as shown, the brush seal assembly220includes two bristle packs242a,242bthat are described below. The bristle tip projection surfaces S created by both of the two bristle packs242a,242bhave a width W that varies along their circumference. An aft one of the two bristle packs, referred to below as the aft bristle pack242a, and a rear one of the two bristle packs, or rear bristle pack242b, are described below. The bristle tip projection surfaces S created by the aft and fore bristle packs242a,242bare non-axisymmetric. In the depicted embodiment, the bristle tip projection surfaces S created by the fore and aft bristle packs242a,242bare each symmetric about center lines L′ located between the first and second limits S1, S2.

In the depicted embodiment, the width W of the bristle tip projection surface of the aft bristle pack242avaries monotonically between a maximal value and a minimal value along half of the circumference of the aft bristle pack242a. In the embodiment shown, the width W of the bristle tip projection surface S reaches the maximum value at a first circumferential position and reaches the minimal value at a second circumferential position being diametrically opposed to the first circumferential position. For a first one of two equal halves242a′ of the aft bristle pack242a, the width W of the bristle tip projection surface S increases monotonically from the minimal value at the first circumferential position to the maximal value at the second circumferential position. And, for a second one of the two equal halves242a′ of the aft bristle pack242a, the width W of the bristle tip S surface decreases monotonically from the maximum value at the second circumferential position to the minimal value at the first circumferential position.

A width W of the bristle tip projection surface of the fore bristle pack242bvaries along its circumference in an alternating manner. Stated otherwise, the width W of the bristle tip projection surface S alternately increases and decreases along both of two equal halves242b′ of the fore bristle pack242.

In a particular embodiment, having a brush seal assembly with two different bristle packs may prevent an aero-structural coupling. From an acoustic point of view, having two different bristle packs may cause a volume of the annular cavity C between the two bristle packs to be non-uniform (i.e., non-axisymmetric) through its circumference so that the annular cavity C might act as an acoustic wave disrupter.

It is understood that a brush seal assembly may include only one, two, or more than two of the disclosed bristle packs. A brush seal assembly may include any combinations of the disclosed bristle packs without departing from the scope of the present disclosure. The bristle packs of a brush seal assembly may be identical to each other or different from one another.

In the embodiment shown, a total thickness of the brush seal assembly is constant along its circumference; thicknesses of annular members140a,240avarying along their circumference to accommodate fluctuations in the position and/or the width W of the bristle packs142a,142b,242a,242b.

For operating the brush seal assembly20, the first zone32is separated from the second zone34by the bristle pack42of the brush seal assembly20. A fluid is permitted to flow from the first zone32to the second zone34via the gap G circumferentially extending around the central axis A and defined between the free tips42cof the bristles42aand the seal land28a. At least one of a position and a width W of the gap G relative to the seal land28ais varied along a circumference of the gap G.