This invention was made with partial Government support under
contract number DE-FC26-05NT42643 awarded by U.S. Department of Energy. The
Government has certain rights in the invention.
BACKGROUND
The present application relates generally to seal assemblies for turbomachinery
and more particularly relates to advanced aerodynamic seal assemblies for
sealing rotorlstator gaps and the like.
Various types of turbo-machinery, such as gas turbine engines, aircraft
engines and steam turbines, are known and widely used for power generation,
propulsion, and the like. The efficiency of the turbo-machinery depends in part upon
the clearances between the internal components and the leakage of primary and
secondary fluids through these clearances. For example, large clearances may be
intentionally allowed at certain rotor-stator interfaces to accommodate large,
thermally or mechanically-induced, relative motions. Leakage of fluid through these
gaps from regions of high pressure to regions of low pressure may result in poor
efficiency for the turbo-machinery. Such leakage may impact efficiency in that the
leaked fluids fail to perform useful work.
Different types of sealing systems are used to minimize the leakage of
fluid flowing through turbo-machinery. The sealing systems, however, often are
subject to relatively high temperatures, thermal gradients, and thermal and mechanical
expansion and contraction during various operational stages that may increase or
decrease the clearance therethrough. For example, traditional labyrinth seals that are
assembled to run very tight clearance during start-up transient phase might run with
large clearances during steady state operations, thereby leading to poor performance
at steady state operation.
There is therefore a desire for improved compliant sealing assemblies
for use with turbo-machinery. Preferably such compliant sealing assemblies may
provide tighter sealing during steady state operations while avoiding rubbing, wear
caused by contact and damage during transient operations. Such sealing assemblies
should improve overall system efficiency while being inexpensive to fabricate and
providing an increased life for the associated parts.
BRIEF DESCRIPTION
In accordance with an embodiment of the invention, an aerodynamic
seal assembly for a rotary machine is provided. The assembly includes multiple
sealing device segments disposed circumferentially intermediate to a stationary
housing and a rotor. Each of the segments includes a shoe plate with a forward-shoe
section and an aft-shoe section having multiple labyrinth teeth therebetween facing
the rotor. The shoe plate is configured to allow a high pressure fluid to a front portion
of the plurality of the labyrinth teeth and a low pressure fluid behind the plurality of
the labyrinth teeth and further configured to generate an aerodynamic force between
the shoe plate and the rotor. The sealing device segment also includes multiple
bellow springs or flexures connected to the shoe plate and to a top interface element,
wherein the multiple bellow springs or flexures are configured to allow the high
pressure fluid to occupy a forward cavity and the low pressure fluid to occupy an aft
cavity. Further, the sealing device segments include a secondary seal attached to the
top interface element at one first end and positioned about the multiple bellow springs
or flexures and the shoe plate at one second end.
In accordance with an embodiment of the invention, an aerodynamic
sealing device for turbine components is provided. The sealing device includes a shoe
plate having multiple labyrinth teeth between a forward shoe plate section and an aft
shoe plate section facing a rotatable element. The shoe plate is configured to allow a
high pressure fluid to a front portion of the plurality of the labyrinth teeth and a low
pressure fluid behind the plurality of the labyrinth teeth and further configured to
generate an aerodynamic force between the shoe plate and the rotor. The sealing
device also includes multiple bellow springs or flexures connected to the shoe plate
and to a top interface element, wherein the plurality of bellow springs or flexures are
configured to allow the high pressure fluid to occupy a forward cavity and the low
pressure fluid to occupy an aft cavity. Further, the sealing device includes a
secondary seal connected to the top interface element at one first end and positioned
about the plurality of bellow springs or flexures and the shoe plate at one second end,
wherein the secondary seal disposed within the sealing device is configured to form
the forward cavity and the aft cavity towards a high pressure side and a low pressure
side of the rotary machine.
In accordance with an embodiment of the invention, a method of
forming a gas path seal between a stationary housing of a rotary machine and a
rotatable element turning about an axis of the rotary machine is provided. The
method includes disposing multiple sealing device segments intermediate to the
stationary housing and the rotatable element. Each of the sealing device segments
comprises a shoe plate having a plurality of labyrinth teeth between a forward shoe
plate section and an aft shoe plate section configured for allowing a high pressure
fluid to a front portion of the plurality of the labyrinth teeth and a low pressure fluid
behind the plurality of the labyrinth teeth and further configured for generating an
aerodynamic force between the shoe plate and the rotor. The method also includes
attaching multiple bellow springs or flexures in each of the sealing device segments to
the shoe plate and to a top interface element, wherein the plurality of bellow springs
or flexures are configured for allowing the high pressure fluid to occupy a forward
cavity and the low pressure fluid to occupy an aft cavity. Further, the method
includes disposing a secondary seal within each of the sealing device segment to form
the forward cavity and the aft cavity, wherein the secondary seal is attached to the top
interface element at one first end and positioned about the plurality of bellow springs
or flexures and the shoe plate at one second end.
DRAWINGS
These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed description is
read with reference to the accompanying drawings in which like characters represent
like parts throughout the drawings, wherein:
FIG. 1 is a perspective view of an aerodynamic seal assembly for a
rotary machine in accordance with an embodiment of the present invention.
FIG. 2 is a perspective view of a sealing device segment in accordance
with an embodiment of the present invention.
FIG. 3 is a perspective view of a sealing device segment with flexures
in accordance with another embodiment of the present invention.
FIG. 4 is a front view of portion of an aerodynamic seal assembly in
accordance with an embodiment of the present invention.
FIG. 5 is a side view of a sealing device segment in accordance with an
embodiment of the present invention.
FIG. 6 is a bottom view of a sealing device segment in accordance with
an embodiment of the present invention.
FIG. 7 shows an aft port in a sealing device segment in accordance
with an embodiment of the present invention.
FIG. 8 shows another aft port in a sealing device segment in
accordance with an embodiment of the present invention.
FIG. 9 shows shoe-rotor curvature in an aerodynamic seal assembly in
accordance with an embodiment of the present invention.
FIG. 10 shows Rayleigh steps in a sealing device segment in
accordance with an embodiment of the present invention.
FIG. 11 is flow chart illustrating exemplary steps involved in method
of forming an aerodynamic seal between a stationary housing of a rotary machine and
a rotatable element turning about an axis of the rotary machine in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION
When introducing elements of various embodiments of the present
invention, the articles "a," "an," "the," and "said" are intended to mean that there are
one or more of the elements. The terms "comprising," "including," and "having" are
intended to be inclusive and mean that there may be additional elements other than the
listed elements. Any examples of operating parameters are not exclusive of other
parameters of the disclosed embodiments.
FIG. 1 is a perspective view of an aerodynamic seal assembly 10 for a
rotary machine in accordance with an embodiment of the present invention. The
aerodynamic seal assembly 10 is circumferentially arranged around a rotor shaft (not
shown) such that the seal assembly 10 is intermediate to a stationary housing (not
shown) and the rotor shaft. The seal assembly 10 includes multiple sealing device
segments 12 located adjacent to each other to form the seal assembly 10. Each of the
sealing device segment 12 includes a shoe plate 14 located proximate to the rotor
shaft. During operation of the rotary machine, the shoe plate 14 rides on an
aerodynamic fluid film above the rotor shaft. The seal assembly 10 also includes
multiple labyrinth teeth 16 located on the shoe plate 14 at a side facing the rotor shaft
surface. The labyrinth teeth substantially separate fluids from a high pressure region
18 from a low pressure region 20 on either sides of the aerodynamic seal assembly 10
of the rotary machine. The seal assembly 10 also includes multiple bellow springs 22
attached to the shoe plate 14 and a top interface element 24. Each of the sealing
device segments 12 are assembled relative to the rotor such that there is a clearance
gap between each shoe plate 14 and the rotor shaft. The adjacent sealing device
segments 12 also include a clearance gap between them. Each of the sealing device
segments 12 is described in details in FIG. 2.
FIG. 2 is a perspective view of the sealing device segment 12 in
accordance with an embodiment of the present invention. As shown, the sealing
device segment 12 includes the shoe plate 14 with a forward shoe section 26 and an
aft-shoe section 28 having the multiple labyrinth teeth 16 therebetween facing the
rotor shaft (not shown). The sealing device segment 12 includes one or more bellow
springs that comprises of a forward bellow spring 30 and an aft bellow spring 32. The
sealing device segment 12 further includes a secondary seal 34 attached to the top
interface element 24 via a cantilever beam section 36 at one first end and positioned
about the plurality of bellow springs 30, 32 and the shoe plate 14 at one second end,
wherein each of the secondary seal 34 forms a line contact with the shoe plate 14 at
the one second end. In one embodiment, the secondary seal 34 may be directly
attached to the top interface element 24. As shown in this embodiment, the bellow
springs 30, 32 and the secondary seal 34 are straight in the circumferential direction.
The straight bellows springs 30, 32 and the straight secondary seal 34 allow the
mechanical stresses to remain low. In another embodiment, the bellow springs 30, 32
and the secondary seal 34 may be curved in the circumferential direction.
In the seal assembly 10 (as shown in FIG. I), the secondary seals 12
fiom neighboring sealing device segments 12 form a resistance path for a flow of
fluid between the top interface element 24 and the shoe plate 14. In one embodiment,
the forward bellow spring 30 and the aft bellow spring 32 are located symmetrically
on either side of the line of contact between the secondary seal 34 and the shoe plate
14. This symmetric arrangement allows the shoe plate 14 to translate radially with
minimum tilt (edge of the forward shoe section 26 closer to the rotor than the edge of
the aft shoe section 28 or vice versa). The reduced tilt caused by the symmetric
design also ensures that the shoe plate 14 can travel large displacements both radially
inwards and radially outwards (during rotor growth events) in a robust manner.
There exists a small leakage past the line of contact between the
secondary seal 34 and the shoe plate 14. The secondary seal 34 is configured to
partition the sealing device segment 12 into a forward cavity 38 towards the high
pressure side 18 and an aft cavity 40 towards the low pressure side 20 of the rotary
machine.
In one embodiment as shown in FIG. 3 a sealing device segment 13
includes multiple flexures 31, 33 connected to the shoe plate 14 and the top interface
element 24. Each of the multiple flexures 3 1, 33 of FIG. 3 or the bellow springs 30,
32 of FIG. 2 comprise of a circumferential width less than each of the circumferential
widths of the top interface element 24 and the shoe plate 14. This ensures that upon
pressurization of the rotary machine, the fluid flows around the forward bellow spring
30 or the flexure 31 and pressurizes the forward cavity 38. Similarly, at the low
pressure side 20 of the rotary machine, the low pressure fluid flows around the aft
bellow spring 32 or the flexure 33 to create a low pressure behind the secondary seal
34 within the aft cavity 40.
Further, in one embodiment of FIG. 2, the sealing device segment 12
includes forward shoe feeding grooves 42 and aft shoe feeding grooves 44 at sides of
the shoe plate 14 towards a high pressure side 18 and a low pressure side 20 of the
rotary machine respectively. A top portion 46 of the shoe plate 14 includes a
circumferential width that is wider than a bottom portion 48 forming the feeding
grooves 42,44. Between adjacent sealing device segments 12 in the seal assembly 10
(as shown in FIG. I), there exists a clearance gap between the adjacent secondary
seals 36. In addition to the clearance gap, there are radial gaps as discussed in FIG. 4.
FIG. 4 is a portion of the seal assembly 10 (as shown in FIG. 1) that
shows radial gaps between adjacent sealing device segments 12 (as shown in FIG. 1).
As shown, the top interface elements 24 for a part of the stator housing and has a
stator-stator radial gap between adjacent sealing device segments 12. The adjacent
secondary seals 34 also reveal a radial gap. Moreover, in the forward shoe section 26
(as shown in FIG. 2), the top portion 46 and the bottom portion 48 of the shoe plate 14
form the forward shoe feeding groove 42. The multiple labyrinth teeth of neighboring
shoes form the segment gap between neighboring shoes. In seal assembly 10, the
segment radial gaps between neighboring shoe plates 14 and neighboring secondary
seals 34 are designed so that the radial motion of the sealing device segments 12
towards the rotor and any circumferential thermal expansion of the segments 12 does
not cause segment binding.
As shown in FIG. 2, the shoe plate 14 also includes multiple forward
ports 50 located before the line contact at the high pressure side 18 of the rotary
machine for allowing an axial flow of a fluid to a front portion of the multiple
labyrinth teeth 16. Further, the shoe plate 14 includes one or more aft ports 52 located
after the line contact at a low pressure side 20 of the rotary machine. In one
embodiment, the one or more aft ports 52 are angled in a circumferential direction to
impart a tangential flow to a fluid flowing from behind the multiple labyrinth teeth 16
into the aft cavity 40. In another embodiment, the one or more aft ports 52 are
straight ports or circumferential angled ports for allowing the flow of fluid from
behind the labyrinth teeth 16 to the aft cavity 40 of the sealing device segment 12.
FIG. 5 is a side view of the sealing device segment 12 in accordance
with an embodiment of the present invention. As shown in one embodiment, the
forward bellow spring 30 and aft bellow spring 32 are connected to the top interface
element 24 and the shoe plate 14 by braze joints. FIG. 5 also shows various pressure
forces acting on the shoe plate 14 and the secondary seal 34. In the forward cavity 38
and the aft cavity 40, the pressurization of the sealing device segment 12 causes the
shoe plate 14 to move towards the rotor during start-up operation of the rotary
machine. In a non-limiting example, the shoe plate 14 may ride on a fluid film in an
aerostatic mode of operation, which fluid film thickness may range from about 311 000
inches to 511000 inches depending on an initial seal assembly clearance with the rotor.
In the aerostatic operation mode, the pressurization causes the
secondary seal 34 to deflect radially inwards pushing the shoe plate 14 towards the
rotor. While the secondary seal 34 pushes the shoe plate 14 towards the rotor, the
bellows springs 30, 32 support and guide the motion of the shoe plate 14. Apart from
secondary seal contact force and bellow spring forces, the shoe plate 14 is also
subjected to aerostatic pressure loads. These aerostatic pressure loads are caused by
the presence of fluid around the shoe plate 14. As shown in the radially outer face of
FIG. 5, the shoe plate 14 is subjected to high pressure and low pressure fluid on either
side of the secondary seal line contact between the secondary seal 34 and the shoe
plate 14.
In one embodiment, the forward ports 50 and the two forward shoe
feeding grooves 42 (as shown in FIG. 2, FIG. 3) bring the high pressure fluid from the
forward cavity 38 to a front side of the multiple labyrinth teeth 16. Similarly, the one
or more aft ports 52 and the aft shoe feeding grooves 44 (as show in FIG. 2, FIG. 3)
bring a low pressure fluid from the aft cavity 40 to a back side of the multiple
labyrinth teeth 16. Thus the multiple labyrinth teeth 16 are subjected to the pressure
drop across the sealing device segment 12 and perform the function of providing the
flow restriction for leakage along the rotor-shoe plate gap. Due to the presence of the
forward ports 50, all faces of the shoe plate 14 upstream of the secondary seal 34 are
subjected to a high pressure fluid. Similarly, the one or more aft ports 52 ensure that
all faces of the shoe plate 14 downstream of the secondary seal 34 are subjected to
low pressure fluid. When the fluid film thickness is 311000 to 511000 inches or larger
between the shoe plate 14 and the rotor surface, the rotation of the rotor does not
cause the fluid film pressure beneath the shoe plate 14 to be significantly different
from the high and low pressures caused by the forward ports 50 and the aft ports 52.
As a consequence, the net fluid load on the shoe plate 14 is approximately zero. The
shoe plate 14 moves radially inwards under the influence of an almost zero net fluid
load, a secondary seal contact force pushing the shoe plate 14 inwards, and the bellow
springs supporting it against this radially inwards motion.
FIG. 6 is a bottom view of a sealing device segment 12 in accordance
with an embodiment of the present invention. In this embodiment, the sealing device
segments 12 show the forward ports 50 that includes four ports. In other
embodiments, the forward ports 50 may be fewer ports or more than four ports. In the
current embodiment, the forward ports 50 are configured to allow the fluid to flow
from the forward ports 50 to the front of the multiple labyrinth teeth 16 in an axial
direction. In another embodiment, the forward ports 50 are angled in a
circumferential direction to impart the fluid to swirl (gain tangential velocity) as the
fluid flows from a forward cavity 38 to a front portion of the multiple labyrinth teeth
16. In this embodiment, one first end of the aft port 52 is shown from a bottom view
of the sealing device segment 12. The aft port 52 connects the backside of the
labyrinth teeth 16 to the aft cavity 40. As shown, one first end opening of the aft port
52 is located at a first edge of the aft shoe section 28 facing the backside of the
labyrinth teeth 16. One second end opening of the aft port 52 in the aft cavity 40 is
shown in FIG. 7. In one embodiment, the aft port 52 may be split into more ports. In
a hrther embodiment, the one or more aft ports 52 are angled in a circumferential
direction to impart a tangential flow to a fluid flowing from behind the multiple
labyrinth teeth 16 into the aft cavity 40.
FIG. 8 shows another aft port 52 in a sealing device segment 12 in
accordance with an embodiment of the present invention. In this embodiment, the
one or more aft ports 52 are straight ports or circumferential angled ports for allowing
a flow of fluid from behind the multiple labyrinth teeth 16 directly to a downstream
cavity of the sealing device segment 12. The first end opening of the one or more aft
ports 52 may be located at the first edge of the aft shoe section 28 facing the backside
of the labyrinth teeth 16. As shown in this embodiment, the second end opening of
the one or more aft ports 52 may be located at a second edge of the aft shoe section of
the shoe plate 14 directing the flow of fluid from behind the multiple labyrinth teeth
16 directly to a downstream cavity of the sealing device segment 12.
FIG. 9 shows shoe-rotor curvature in the aerodynamic seal assembly
10 in accordance with. an embodiment of the present invention. The seal assembly 10
also operates in an aerodynamic mode of operation. When the rotor-shoe plate gap
starts reducing (e.g. during a thermal or mechanical transient event causing clearance
change), the thin fluid film starts building additional pressure. In this embodiment,
the radius of curvature of the shoe plate 14 is intentionally larger than the rotor radius.
As a consequence, when the rotor-shoe plate gap becomes small (less than 1/1000
inch), the fluid film is either monotonically converging or converging-diverging in the
direction of rotation. This fluid film in a form of fluid wedge causes additional
pressure to build-up. The physics of thin film is well understood from hydrodynamic
journal bearings or foil bearings, and can be modeled using appropriate fluid flow
models. The basic principle is that any negative gradient in the fluid film thickness in
the direction of rotation will increase the pressure in the fluid film above its boundary
pressure. The additional pressure caused by the thin fluid film squeezes the bellow
springs 30, 32, thereby, moving the shoe plate 14 radially outwards and keeping the
rotor from contacting the shoe plate 14. In this sense, any outward excursion of the
rotor is tracked by the shoe plate 14 on every sealing device segment 12.
In another embodiment as shown in FIG. 10, the thin fluid film
generates additional force due to the presence of one or more Rayleigh steps 60, 62 on
the shoe plate 14 in the direction of rotation. As shown, the forward shoe section 26
includes a first Rayleigh step 60 and the aft shoe section 28 includes a second
Rayleigh step 62. It should be noted that the multiple forward ports 50 and one or
more aft ports 52 also serve the purpose as cooling ports for carrying away the
additional heat that might be generated in the thin film aerodynamic mode of seal
operation. The presence of two shoes sections, i.e. forward shoe section 26 and the
aft shoe section 28 allows the generation of aerodynamic moments (about the
circumferential axis) in both directions. For example, if the shoe plate 14 is tilted
such that an aft edge of the aft shoe section 28 is closer to the rotor than the forward
edge of the forward shoe section 26, then the aft shoe section 28 will generate more
aerodynamic force than the forward shoe section 26 and the resulting aerodynamic
moment will correct the tilt of the shoe. Similarly, the forward shoe section 26 allows
for aerodynamic tilt correction in the event that the forward shoe section 26 is closer
to the rotor. Overall, a two shoe plate section arrangement with curvature mismatch
with the rotor or one or more Rayleigh steps 60, 62 allows for self-correcting seal
behavior that can correct not only radial clearance changes but also forward-aft tilts in
the seal.
In a non-limiting example, both the bellows springs 30, 32 and the
secondary seal 34 (as shown in FIG. 2) are formed from high temperature metal alloy
shims like Inconel X750 or Rene41. Both ends of the bellow springs 30, 32 are
brazed to the top interface element 24 and the shoe plate 14. The secondary seal 34 is
cantilevered (brazed) to the stator or top interface element 24 and free to slide axially
on the shoe plate surface. In the present embodiment, the free end of the secondary
seal 34 touches the shoe plate 14 (as shown) and remains in contact with the shoe
plate 14 at all times. In one embodiment, there may be a gap (no-contact) between the
secondary seal 34 and the shoe plate 14 before pressurization, and this gap will close
upon pressurization to establish a contact between the secondary seal 34 and the shoe
plate 14. In one embodiment, the shoe plate 14 and the stator interface piece or the
top interface element 24 are machined or cast. In one embodiment, the radially
innermost surface of the shoe plate may be coated with lubricating coatings like
NASA PS304 or NASA PS400 or a similar solid-lubricant coating that can handle
unintentional rubs between the shoe plate 14 and the rotor at the seal operating
environment conditions. In another embodiment, the rotor surface interfacing with
the shoe plate 14 may be coated with Chromium carbide or Titanium aluminum
Nitride or similar coatings to improve the rotor's hardness, corrosion resistance and
ability to maintain good surface finish.
FIG. 11 is flow chart 100 illustrating steps involved in method of
forming an aerodynamic seal between a stationary housing of a rotary machine and a
rotatable element turning about an axis of the rotary machine in accordance with an
embodiment of the present invention. At step 102, the method includes disposing
multiple sealing device segments intermediate to the stationary housing and the
rotatable element, wherein each of the sealing device segments include a shoe plate
having multiple labyrinth teeth between a forward shoe plate section and an aft shoe
plate section. The shoe plate further includes a forward shoe feeding groove and an
aft shoe feeding groove at sides of the shoe plate towards a high pressure side and a
low pressure side respectively. At step 104, the method includes attaching a plurality
of bellow springs in each of the sealing device segments to the shoe plate and to a top
interface element. Finally, at step 106, the method includes disposing a secondary
seal within each of the sealing device segment to form a forward cavity and an aft
cavity, wherein the secondary seal is attached to the top interface element via a
cantilever beam section at one first end and positioned about the plurality of bellow
springs and the shoe plate at one second end.
Advantageously, the present aerodynamic seal assemblies are reliable,
robust seal for several locations in rotating machinery with high pressure drops and
large transients. The seal assemblies are also economical to fabricate. The noncontact
operation of the seals makes them especially attractive for the large rotor
transient locations. Furthermore, the present invention allows independent controlling
of the spring stiffness and the pressure resisting capability (because the springs are not
pressure-loaded), thereby allowing the design of compliant seals that still withstands
high pressure drops. Furthermore, the present invention allows for a shoe plate to
remain parallel to the rotor in aerostatic operation and translate parallel to the rotor
during the aerodynamic mode. The present invention also includes improved
predictability for the radial motion (increased predictability for leakage performance
and robustness).
Furthermore, the skilled artisan will recognize the interchangeability of
various features from different embodiments. Similarly, the various method steps and
features described, as well as other known equivalents for each such methods and
feature, can be mixed and matched by one of ordinary skill in this art to construct
additional systems and techniques in accordance with principles of this disclosure. Of
course, it is to be understood that not necessarily all such objects or advantages
described above may be achieved in accordance with any particular embodiment.
Thus, for example, those skilled in the art will recognize that the systems and
techniques described herein may be embodied or carried out in a manner that achieves
or optimizes one advantage or group of advantages as taught herein without
necessarily achieving other objects or advantages as may be taught or suggested
herein.
While only certain features of the invention have been illustrated and
described herein, many modifications and changes will occur to those skilled in the
art. It is, therefore, to be understood that the appended claims are intended to cover
all such modifications and changes as fall within the true spirit of the invention.

We Claim:
1. An aerodynamic seal assembly for a rotary machine, the seal assembly
comprising:
a plurality of sealing device segments disposed circumferentially intermediate
to a stationary housing and a rotor, wherein each of the segments comprises:
a shoe plate with a forward-shoe section and an aft-shoe section having
a plurality of labyrinth teeth therebetween facing the rotor, wherein the shoe
plate is configured to allow a high pressure fluid to a front portion of the
plurality of the labyrinth teeth and a low pressure fluid behind the plurality of
^ the labyrinth teeth and further configured to generate an aerodynamic force
between the shoe plate and the rotor,
a plurality of bellow springs or flexures connected to the shoe plate and
to a top interface element, wherein the plurality of bellow springs or flexures
are configured to allow the high pressure fluid to occupy a forward cavity and
the low pressure fluid to occupy an aft cavity; and
a secondary seal attached to the top interface element at one first end
and positioned about the plurality of bellow springs or flexures and the shoe
plate at one second end.
•
2. The aerodynamic seal assembly of claim 1, wherein the shoe plate
comprises a forward shoe feeding groove formed due to different circumferential
width of a top portion of the shoe plate and the forward shoe plate section towards a
high pressure side of the rotary machine.
3. The aerodynamic seal assembly of claim 2, wherein the shoe plate
comprises an aft shoe feeding groove formed due to different circumferential width of
15
the top portion of the shoe plate and the aft shoe plate section towards a low pressure
side of the rotary machine.
4. The aerodynamic seal assembly of claim 1, wherein each of the
plurality of bellow springs comprises a circumferential width less than each of
circumferential widths of the top interface element and the shoe plate.
5. The aerodynamic seal assembly of claim 1, wherein the plurality of
bellow springs comprises a forward bellow spring and an aft bellow spring.
•
6. The aerodynamic seal assembly of claim 5, wherein each of the sealing
device segments comprises a line contact between the secondary seal and the shoe
plate separating the the forward bellow spring and the aft bellow spring symmetrically
or almost symmetrically on either side of the line contact between the secondary seal
and the shoe plate.
7. The aerodynamic seal assembly of claim 6, wherein the shoe plate
comprises of a plurality of forward ports located before the line contact at a high
pressure side of the rotary machine for allowing an axial flow of a fluid to a front
w portion of the plurality of the labrinth teeth.
8. The aerodynamic seal assembly of claim 7, wherein the plurality of the
forward ports are angled in a circumferential direction to impart the fluid to swirl as
the fluid flows from the forward cavity to a front portion of the pluraUty of labyrinth
teeth.
16
9. The aerodynamic seal assembly of claim 8, wherein the forward cavity
is formed by the top interface element, the secondary seal, the forward bellow spring
and the shoe plate at a high pressure side of the rotary machine.
10. The aerodynamic seal assembly of claim 6, wherein the shoe plate
comprises one or more aft ports located after the line contact at a low pressure side of
the rotatary machine and configured to connect a backside of the plurality of labyrinth
teeth to the aft cavity.
11. The aerodynamic seal assembly of claim 10, wherein the aft cavity is
w formed by the top interface element, the secondary seal, the aft bellow spring and the
shoe plate at a low pressure side of the rotary machine.
12. The aerodynamic seal assembly of claim 10, wherein the one or more
aft ports are angled in a circumferential direction to impart a tangengial flow to a fluid
flowing fi-om behind the plurality of the labyrinth teeth into the aft cavity.
13. The aerodynamic seal assembly of claim 10, wherein the one or more
aft ports are straight ports or circumferential angled ports for allowing a flow of fluid
from behind the plurality of the labyrinth teeth to a downstream cavity of the sealing
device segment.
14. The aerodynamic seal assembly of claim 1, wherein each of the
forward-shoe section and the aft-shoe section comprises a Rayleigh step for
generating a thin film for an additional upward thrust on the sealing device segment.
15. The aerodynamic seal assembly of claim 1, wherein a side of the shoe
plate facing the rotor comprises a radius of curvature different from radius of
curvature of the rotor.
17
16. The aerodynamic seal assembly of claim 15, wherein the radius of
curvature of the side of the shoe plate facing the rotor is more than the radius of
curvature of the rotor.
17. An aerodynamic sealing device for turbine components, comprising:
a shoe plate having a plurality of labyrinth teeth between a forward shoe plate
section and an aft shoe plate section facing a rotatable element, wherein the shoe plate
is configured to allow a high pressure fluid to a front portion of the plurality of the
^ labyrinth teeth and a low pressure fluid behind the plurality of the labyrinth teeth and
^ P fiirther configured to generate an aerodynamic force between the shoe plate and the
rotor;
a plurality of bellow springs or flexures coimected to the shoe plate and to a
top interface element, wherein the plurality of bellow springs or flexures are
configured to allow the high pressure fluid to occupy a forward cavity and the low
pressure fluid to occupy an aft cavity; and
a secondary seal connected to the top interface element at one first end and
positioned about the plurality of bellow springs or flexures and the shoe plate at one
second end, wherein the secondary seal is disposed within the sealing device to form
the forward cavity and the aft cavity towards a high pressure side and a low pressure
^ side of the rotary machine.
18. The aerodynamic sealing device of claim 17, fiirther comprising a
forward shoe feeding groove and an aft shoe feeding groove at sides of the shoe plate
towards a high pressure side and a low pressure side of the rotary machine
respectively.
19. The aerodynamic sealing device of claim 17; wherein each of the
plurality of bellow springs comprises a circumferential width less than each of
circumferential widths of the top interface element and the shoe plate.
18
20. The aerodynamic sealing device of claim 17; further comprising a
plurality of forwards ports located in the forward cavity and one or more aft ports
located in the aft cavity.
21. A method of forming an aerodynamic seal between a stationary
housing of a rotary machine and a rotatable element turning about an axis of the
rotary machine, the method comprising:
disposing a plurality of sealing device segments intermediate to the stationary
housing and the rotatable element, wherein each of the sealing device segments
comprise a shoe plate having a plurality of labyrinth teeth between a forward shoe
1 ^ plate section and an aft shoe plate section configured for allowing a high pressure
fluid to a front portion of the plurality of the labyrinth teeth and a low pressure fluid
behind the plurality of the labyrinth teeth and fiirther configured for generating an
aerodynamic force between the shoe plate and the rotor;
attaching a plurality of bellow springs or flexures in each of the sealing device
segments to the shoe plate and to a top interface element, wherein the plurality of
bellow springs or flexures are configured for allowing the high pressure fluid to
occupy a forward cavity and the low pressure fluid to occupy an aft cavity; and
disposing a secondary seal within each of the sealing device segment to form
the forward cavity and the aft cavity, wherein the secondary seal is attached to the top
^ interface element at one first end and positioned about the plurality of bellow springs
or flexures and the shoe plate at one second end.
22. The method of claim 21, wherein the shoe plate comprises a forward
shoe feeding groove and an aft shoe feeding groove at sides of the shoe plate towards
a high pressure side and a low pressure side respectively.
23. The method of claim 21, wherein each of the plurality of bellow
springs comprises a circumferential width less than each of circumferential widths of
the top interface element and the shoe plate.
19
24. The method of claim 21, wherein the shoe plate comprises a plurlaity
of forwards ports located in the forward cavity and one or more aft ports located in the
aft cavity.
25. The method of claim 21, wherein the shoe plate comprises a solid
lubricating coating coating chosen from a group of NASA PS304, NASA PS400,
graphite, diamond-like carbon, hexagonal boron nitride or similar other solid lubricant
coatings.