BACKGROUND OF THE INVENTION
Embodiments of the present invention generally relate to seals and more particularly,
to honeycomb seals for turbo machines.
A compressor is a machine which accelerates gas particles to ultimately increase the
pressure of a compressible fluid, for example, a process gas, through the use of mechanical
energy. Compressors are commonly used in the energy industry to produce, process, re-inject
and transport many different types of gases. Among the various types of compressors are the
so-called centrifugal compressors, in which a rotor mounted impeller imparts a centrifugal
acceleration to a process gas. More generally, centrifugal compressors can be said to be part of
a class of machinery known as "turbo machines" or "turbo rotating machines".
High speed rotating centrifugal compressors may be prone to rotor-dynamic
instability. The compressor seals are the major source of destabilizing forces responsible for
instability. This is particularly true in applications involving high pressure high density gas,
such as natural gas reinjection. Consequently, a seal or seals may be responsible for preventing
full speed, full load compressor operation. In more severe cases, rotor destabilizing forces
introduced to the rotating assembly by a seal or seals may cause a catastrophic failure
necessitating costly shut down and repair.
Some seals, such as honeycomb seals, are known for providing not only a relatively
low maintenance sealing solution, but also for providing a damping effect which may
counteract such destabilizing forces. Honeycomb seals are thus often implemented in
centrifugal compressor applications to enhance rotor-dynamic stability.
As shown in Figure 11, a honeycomb seal 514 may include a seal body 516 having a
plurality of honeycomb cells 518. During operation, the honeycomb cells resist the flow of
fluid through a seal gap between the seal body and the rotor to provide both a sealing function
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and a rotor stabilizing function. Unfortunately, under certain circumstances and in certain
configurations, it has been found that the honeycomb seal may actually add an undesired
negative stiffness and a destabilizing effect (cross coupled stiffness) to the rotor assembly.
One solution proposed for addressing this effect has been to add a groove, such as groove 522
in Fig. 11, to "break up" the honeycomb seal and thereby inhibit the destabilizing direct
negative stiffness effect. For a further discussion of the addition of a groove in a honeycomb
seal, see for example, Childs et aI., A Design to Increase the Static Stiffness ofHole Pattern
Stator Gas Seals, ASME Turbo Expo 2006; Power for Land, Sea and Air May 8-11, 2006,
GT2006-90778, the entirety of which is herein incorporated by reference.
It is also generally understood that fluid swirl introduced to process fluids by the
rotation of the rotor shaft may playa role in the onset of cross coupling. To inhibit swirl, it
has been proposed to add a vane or vanes to the compressor casing to direct process fluid
opposite to the direction of swirl. It has also been proposed to add another seal to the rotor
shaft to reduce swirl, see for example US Patent No. 5,540,447, issued on July 30, 1996 to
Shultz et aI., the entirety of which is herein incorporated by reference.
The addition of a vane or vanes and/or yet another extra seal to the turbo rotor shaft
results in further complexity and additional rotating mass, both of which are undesirable in the
drive to improve compressor performance. What is needed is a seal for a turbo machine
capable of providing improved sealing, improved stabilization, reduced cross coupling, and
improved turbo machine performance.
BRIEF DESCRIPTION OF THE INVENTION
According to an embodiment of the present invention, a seal for a turbo machine is
provided. The seal comprises a plurality of honeycomb cells, at least one circumferential
groove within the plurality of honeycomb cells, and at least one swirl brake within the at least
one groove.
According to another embodiment of the present invention, a turbo machine IS
provided. The turbo machine comprises a turbo machine stator, a turbo machine rotor rotatable
relative to the turbo machine stator, and a seal between the turbo machine stator and the turbo
machine rotor, wherein the seal includes a plurality of honeycomb cells, a groove within the
plurality of honeycomb cells, and at least one swirl brake within the groove.
According to another embodiment of the present invention a method for
manufacturing a seal for a turbo machine is provided. The method comprises forming a
groove in a seal body, forming a plurality of honeycomb cells in the seal body, and providing
at least one swirl brake within the groove.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the
specification, illustrate one or more embodiments and, together with the description, explain
these embodiments. In the drawings:
Figure I shows an exemplary embodiment of the present invention;
Figure 2 is a partial cross-sectional view of the exemplary embodiment shown in Fig.
I taken along the line 2-2 in Figure 1;
Figure 3 depicts a plurality of honeycomb cells;
Figure 4 is a cross-sectional view of the exemplary embodiment shown in Fig. 1
taken along the line 4-4 in Figure 2;
Figure 5 is a partial cross-sectional view of the exemplary embodiment shown in Fig.
4 taken along the line A-A, including a tapered swirl brake according to an embodiment of the
present invention;
Figure 6 depicts a groove, sidewalls, a plurality of honeycomb cells and a swirl brake
of an exemplary embodiment of the present invention;
Figure 7 depicts a groove, a plurality of honeycomb cells and a swirl brake of an
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exemplary embodiment of the present invention;
Figure 8 shows an exemplary embodiment including multiple grooves;
Figure 9 shows an exemplary embodiment including honeycomb cells formed by
electro-erosion machining;
Figure lOis a flowchart of a method according to an embodiment of the present
invention; and
Figure 11 depicts a honeycomb seal with a groove according to an embodiment of
the present invention.
DETAILED DESCRIPTION OF EXEMPLERY EMBODIMENTS OF THE PRESENT
INVENTION
The following description ofthe exemplary embodiments ofthe present invention refers
to the accompanying drawings. The same reference numerals in different drawings identify the
same or similar elements. The following detailed description does not limit the invention.
Instead, the scope of the invention is defmed by the appended claims. The following
embodiments are discussed, for simplicity, with regard to the terminology and structure of a turbo
machine that has a machine stator and a machine rotor. However, the embodiments to be
discussed next are not limited to these exemplary systems, but may be applied to other systems.
Reference throughout the specification to "one embodiment" or "an embodiment"
means that a particular feature, structure, or characteristic described in connection with an
embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the
appearance of the phrases "in one embodiment" or "in an embodiment" in various places
throughout the specification is not necessarily referring to the same embodiment. Further, the
particular features, structures or characteristics may be combined in any suitable manner in one or
more embodiments.
Figs. 1 to 4 show an exemplary embodiment of a honeycomb seal 14 for a turbo
machine 10 according to the present invention. Fig. 1 shows a turbo machine 10 having a
machine stator 12 and a machine rotor 22. As shown in Fig. 2, a honeycomb seal 14 between
machine stator 12 and machine rotor 22 includes a seal body 16 extending around machine
rotor 22. A gap 17 (Fig. 4) between the honeycomb cells 26 and the rotor 22 operates to
provide a leakage function as well as a damping function to the rotating assembly of the
compressor.
As further shown in Fig. 2, a groove 28 within the plurality of honeycomb cells 26
extends circumferentially around rotor axis 24. In the exemplary embodiment of Figs. 1 to 4,
groove 28 is provided with at least one swirl brake for resisting the circumferential motion of
process gas passing axially between rotor 22 and seal body 16. As shown in Figs. 2 and 4, the
at least one swirl brake is defined by a plurality of vanes 32 within groove 28. Each vane 32
extends axially between a first side wall 34 and second side wall 36 of groove 28.
As shown in Figs. 2 and 4, each vane 32 extends from groove floor 48 to groove top
56. The vanes 32 are uniformly distributed around the circumference of seal body 16 and have
a constant thickness. In alternative embodiments (not shown), vanes 32 may be distributed in a
non-uniform manner around the circumference of groove 28 and further, the thickness of each
vane may also be varied individually or across all vanes 32. For example, at least one vane 32
may exhibit a taper in the radial direction between the groove floor 48 and groove top 56.
Tapering may also be provided in the axial direction, for example, and as shown in Fig. 5, at
least one vane 32 may taper from a downstream end 23 of seal body 16 towards the upstream
• end 21 of seal body 16. Alternatively, vane 32 may taper from the upstream end 21 towards
the downstream end 23 of seal body 16.
According to the embodiment shown in Figs. 2 and 4, the groove top 56, the top
surface of each the plurality of honeycomb cells 28, and the top surface of each of the vanes
32 define a cylinder having a common axis and diameter thereby providing at least a portion
of seal body 16 with a constant through bore. However, in other embodiments (not shown) the
groove top 56, the top surface of the honeycomb cells 28 and the top surface of each of the
vanes 32 may vary. For example, the top surface of the honeycomb cells 28 may define a
cylinder having a different diameter from a cylinder defined by the top surface of the vanes
32. As further shown in Figs. 2 and 4, the depth 42 of groove 28 is greater than the height 38
of honeycomb cells 26. Also, the height 44 of each vane 32 is greater than the height 38 of the
honeycomb cells 26. One skilled in the art will appreciate that this configuration for groove
28, honeycomb cells 26 and vanes 32 is not a requirement of the present invention but merely
an exemplary embodiment.
As further shown in Figs. 2, 4, and 6, groove 28 is provided with a first side wall 34
and a second side wall 36 defining identical parallel circular paths around the seal body 16.
As shown in Fig. 6, both side wall 34 and sidewall 36 are separated from whole honeycomb
cells 58 by a margin area 59 having a constant width 60.
Alternatively, the seal body may be provided without a margin area. For example, in
the exemplary embodiment shown in Fig. 7, both side wall 134 and sidewall 136 are adjacent
partial honeycomb cells 158. As further shown in Fig. 7, vanes 132 may exhibit a constant
thickness equal to one half the width of a honeycomb cell, i.e., one half the distance between
two parallel sides ofa honeycomb cell.
Fig. 8 shows another exemplary embodiment of seal body 316. Seal body 316
includes a first groove 328 as well as a second groove 330 which are each provided within a
plurality of honeycomb cells 326. First groove 328 and second groove 330 include a swirl
brake in the form of a plurality of vanes 332.
• As shown in Figs. 1-8, the plurality of honeycomb cells 26, the groove 28 within the
honeycomb cells 26 and the swirl brake, e.g., vanes 32, within the groove 28 may be
configured to provide a sealing function, a rotor shaft stabilizing function, and a swirl
inhibiting function in a seal for a turbo machine. Accordingly, seal 14 is capable of providing
improved sealing, improved stabilization, reduced cross coupling, and improved turbo
machine performance over conventional seals for turbo machines.
Fig. 9 shows another exemplary embodiment. Seal body 416 includes a plurality of
honeycomb cells 426 which may be formed by an electro erosion process. In such a process,
seal body 416 may be fixed at a starting position 430 where a first row of honeycomb cells is
machined into seal body 416. Seal body 416 may then be indexed to a new angular position
where another row of honeycomb cells is added. This process may be continued around the
circumference of seal body 416 until the ending position 440 is reached. Note that the buffer
area 450 may remain at the completion of the machining process. Further note that, in the
embodiment of Fig. 9, the manufacturing process is controlled so that only whole honeycomb
cells 426 are formed in seal body 416.
In an exemplary method of manufacturing a seal body 416 according to the present
invention, groove 28, as shown in Fig. 5 is machined into seal body 416. This machining
process may be performed such that a plurality of vanes 32 is formed during the machining
process. More specifically, groove 28 may be formed in sections such that the wall between
each section defmes a vane 32. After the groove 28 and vanes 32 are formed, the plurality of
honeycomb cells 26 are machined by electro erosion, as discussed above with reference to Fig.
9, such that the margin 59 is formed between the whole honeycomb cells 26 and groove 28.
Margin 59 may be configured with a width 60 equal to the width ofa margin 470 provided at a
periphery ofthe plurality of honeycomb cells 426, as shown in Fig. 9
Thus, according to an embodiment as shown in the flowchart of Fig. 10, a method
1000 of manufacturing a seal for a turbo machine can include forming 1002 a groove in a seal
body, forming 1004 a plurality of honeycomb cells in the seal body, and providing 1006 at
least one swirl brake within the groove. These steps may be performed in any desired order or
simultaneously.
The above-described embodiments are intended to be illustrative in all respects,
rather than restrictive, of the present invention. All such variations and modifications are
considered to be within the scope and spirit of the present invention as defined by the
following claims. No element, act, or instruction used in the description of the present
application should be construed as critical or essential to the invention unless explicitly
described as such. Also, as used herein, the article "a" is intended to include one or more
items.

1. A seal for a turbo machine, the seal comprising:
a plurality of honeycomb cells;
at least one circumferential groove within the plurality of honeycomb cells; and
at least one swirl brake within the at least one groove.
2. The seal of claim 1, wherein the at least one groove has a first side wall, a
second side wall, a groove floor and a groove top, and wherein the at least one swirl brake
comprises a plurality of vanes, each vane extending between the first and second side walls
and from the groove floor towards the groove top.
3. The seal of claim 2 wherein the plurality of honeycomb cells are spaced from
the at least one groove.
4. The seal of claim 2 wherein the plurality of honeycomb cells include a plurality
of partial honeycomb cells extending from the first and second side walls of the at least one
groove.
5. The seal of claim 2 wherein each vane tapers in at least one of a radial direction
and an axial direction.
6. The seal of claim 2 wherein each vane has a constant thickness.
7. The seal of claim 6 wherein a top surface of the plurality of honeycomb cells
defines a first cylinder and a top surface of each of the vanes define a second cylinder, wherein
the first cylinder and the second cylinder are coaxial and of equal diameter.
8. The seal of claim 7 wherein the at least one groove has a groove depth and the
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plurality of honeycomb cells have a cell height, and wherein the groove depth is greater than
the cell height.
9. A turbo machine comprising:
a turbo machine stator;
a turbo machine rotor rotatable relative to the turbo machine stator; and
a seal between the stator and the rotor;
wherein the seal comprises a plurality of honeycomb cells, a groove within the
plurality ofhoneycomb cells, and at least one swirl brake within the groove.
10. A method ofmanufacturing a seal for a turbo machine, the method comprising:
forming a groove in a seal body of the seal;
forming a plurality of honeycomb cells in the seal body; and
providing at least one swirl brake within the groove.