Note: Descriptions are shown in the official language in which they were submitted.
CA 02432094 2009-08-07
DOUBLE LAYER ACOUSTIC LINER AND A FLUID
PRESSURIZING DEVICE AND METHOD UTILIZING SAME
Baclkground
This invention relates to an acoustic liner of two layers and a fluid
pressurizing device
and method utilizing same.
p'luid pressurizing devices, such as centrifagat compressors, are widely used
in different
industries for a variety of applications involving the compression, or
pressurization, of a gas.
However, a typical compressor produces a relatively high noise level which is
an obvious
nuisance to the people in the vicinity of the device. This noise can also
cause vibrations and
structural failures.
For example, the dominant noise source in a centrifugal compressor is
typically generated
at the locations of the impeller exit and the diffuser inlet, due to the high
velocity of the fluid
passing through these regions. The noise level becomes higher when discharge
vanes are
installed in the diffuser to improve pressure recovery, due to the aerodynamic
interaction
between the impeller and the diffuser vanes.
Various external noise control measum such as enclosures and wrappings have
been
used to reduce the reiative high noise levels generated by compressors, and
similar devices.
These external noise reduction techniques can be relatively expensive
especially when they are
often offered as an add-on product after the device is manufactured.
Also, interaal devices, usually in the form of acoustic liners, have been
developed which
are placed in the compressors, or similar devices, for controlling noise
inside the gas flow paths. '
These liners are often based on the well-lmown Helmholtz resonator principle
according to
which the liners dissipate the acoustic energy when the sound waves oscillate
through
perforations in the liners, and reflect the acoustic energy upstream due to
the local impedance
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mismatch caused by the liner. Exainples of Helrnholtz resonators are disclosed
in U.S. patent
Nos. 4,100,993; 4,135,603; 4,150,732; 4,189,027; 4,443,751; 4,944,362; and
5,624,518.
A typical Helmholtz array acoustic liner is in the form of a three-piece
sandwich structure
consisting of honeycomb cells sandwiched between a perforated facing sheet and
a back plate.
Although these three-piece designs have been successfully applied to suppress
noise in aircraft
engines, it is questionable whether or not they would work in fluid
pressurizing devices, such as
centrifugal compressors. This is largely due to the possibility of the
perforated facing sheet of
the liner breaking off its bond with the honeycomb under extreme operating
conditions of the
compressor, such as, for example, during rapid depressurization caused by an
emergency shut
down of the compressor. In the event that the perforated facing sheet becomes
loose, it not only
makes the acoustic liners no longer functional but also causes excessive
aerodynamic losses, and
even the possibility of mechanical catastrophic failure, caused by the
potential collision between
the break-away perforated sheet metal and the spinning impeller.
Therefore what is needed is a system and method for reducing the noise in a
fluid
pressurizing device utilizing a Hemholtz array acoustic liner while
eliminating its disadvantages.
Summary
Accordingly an acoustic liner is provided, as well as a fluid processing
device and method
incorporating same, according to which the liner attenuates noise and consists
of one or more
acoustic liners each including a plurality of cells forined in a plate in a
manner to form an array
of resonators.
Brief Description of the Drawings
Fig. 1 is a cross-sectional view of a portion of a gas pressurizing device
incorporating a
pair of acoustic liners according to an embodiment of the present invention.
Fig. 2 is an enlarged cross-sectional view of one of the acoustic liners of
Fig. 1.
Fig. 3 is an enlarged elevational view of a portion of the liner of Fig. 2.
Figs. 4 and 5 are views similar to that of Fig. 1, but depicting additional
acoustic liners
disposed at other locations in the fluid pressurizing device.
Detailed Description
Fig. 1 depicts a portion of a high pressure fluid pressurizing device, such as
a centrifugal
compressor, including a casing 10 defining an impeller cavity l0a for
receiving an impeller 12
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which is mounted for rotation in the cavity. It is understood that a power-
driven shaft (not
shown) rotates the impeller 12 at a high speed, sufficient to impart a
velocity pressure to the gas
drawn into the coinpressor via the inlet.
The impeller 12 includes a plurality of impeller blades 12a arranged axi-
symmetrically
around the latter shaft for discharging the gas into a diffuser passage, or
channe114 formed in the
casing 10 radially outwardly from the chamber 10a and the impeller 12. The
channel 14 receives
the high pressure fluid from the iinpeller 12 before it is passed to a volute,
or collector,16. The
diffuser channel 14 f-unctions to convert the velocity pressure of the gas
into static pressure which
is coupled to a discharge volute, or collector 16 also formed in the casing
and connected with the
channel. Although not shown in Fig. 1, it is understood that the discharge
volute 16 couples the
compressed gas to an outlet of the compressor.
Due to centrifugal action of the impeller blades 12a, gas can be compressed to
a relatively
high pressure. The compressor is also provided with conventional labyrinth
seals, thrust
bearings, tilt pad bearings and other apparatus conventional to such
compressors. Since this
structure is conventional, it will not be shown or described in any further
detail.
A mounting bracket 20 is secured to an inner wall of the casing 10 defining
the diffuser channel
14 and includes a base 22 disposed adjacent the outer end portion of the
impeller and a plate 24
extending from the base and along the latter wall of the casing.
Two one-piece, unitary, annular acoustic liners 28 and 30 are mounted in a
groove in the
plate 24 of the bracket 20 in a abutting relationship and each is annular in
shape and extends
around the impeller 12 for 360 degrees. The upper section of the liner 28 is
shown in detail in
Figs. 2 and 3, and is formed of an annular, relatively thick, unitary shell,
or plate 32 preferably
made of steel. The plate 32 is attached to the bracket plate 24 in any
conventional manner, such
as by a plurality of bolts, or the like.
A series of relatively large cells, or openings, 34 are formed through one
surface of the
plate 32 and extend through a majority of the thickness of the plate but not
through its entire
thiclcness. A series of relatively small cells 36 extend from the bottom of
each ce1134 to the
opposite surface of the plate 32. Each ce1134 is shown having a disc-like
cross section and each
ce1136 is in the form of a bore for the purpose of example, it being
understood that the shapes of
the cells 34 and 36 can vary within the scope of the invention.
According to one embodiment of the present invention, each ce1134 is formed by
drilling
a relative large-diameter counterbore through one surface of the plate 32,
which counterbore
extends through a majority of the thickness of the plate but not though the
complete thickness of
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the plate. Each ce1136 is formed by drilling a bore, or passage, through the
opposite surface of
the plate 32 to the bottom of a corresponding cell 34 and thus connects the
ce1134 to the diffuser
channel 14.
As shown in Fig. 3, the cells 34 are formed in a plurality of annular
extending rows along
the entire annular area of the plate 32, with the cells 34 of a particular row
being staggered, or
offset, from the cells of its adjacent row(s). A plurality of cells 36 are
associated with each cell
34 and the cells 36 can be randomly disposed relative to their corresponding
cell 34, or,
alternately, can be formed in any pattern of uniform distribution.
With reference to Fig. 1, the liner 30 is similar to the liner 28 and, as
such, is formed of
an amzular, relatively thick, unitary shell, or plate 42 (Fig. 1), preferably
made of steel, and is
attached to the liner 28 in any conventional manner such as by a plurality of
bolts, or the like. A
series of relatively large cells, or openings, 44 are formed througli one
surface of the plate 42 and
a series of relatively small cells 46 extend from the bottom of each cel134 to
the opposite surface
of the plate 32. Since the cells 44 and 46 are similar to the cells 34 and 36,
respectively, they
will not be described in further detail. Although not shown in the drawings,
it is understood that
the liners 30 and 28 can be of different thiclrness.
The liners 28 and 30 are mounted in the bracket plate 24 witll the surface of
the liner 28
through which the cells 34 extend abutting the surface of the liner 30 through
which the cells 46
extend. Also, the cells 34 of the liner 28 are in alignment with the cells 44
of the liner 30. The
open ends of the cells 44 of the liner 30 are capped by the underlying wall of
the plate 24 of the
22 0 bracket 20, and the open ends of the cells 34 of the liner 28 are capped
by the corresponding
surface of the liner 30. The cells 34 of the liner 28 and the cells 44 of the
liner 30 are connected
by the cells 46 of the liner 30, due to their alignment.
Due to the firm contact between the liners 28 and 30, and between the liner 30
and the
corresponding wall of the plate 24 of the bracket 20, and due to the cells 36
and 46 connecting
7-5 the cells 34 and 44 to the diffuser channel 14, the cells worlc
collectively as an array of acoustic
resonators in series. As such, the liners 28 and 30 attenuate the sound waves
generated in the
casing 10 by the fast-rotation of the impeller 12, and by its associated
components, and eliminate,
or at least minimize, the possibility that the noise will by-pass the liners
and pass through a
different path.
30 Moreover, the dominant noise component commonly occurring at the blade
passing
frequency, or other high frequency can be effectively lowered by tuning the
liners 28 and 30 so
that the maximum sound attenuation occurs around the latter frequency. This
can be achieved by
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varying the volume of the cells 34 and 44, and/or the cross-section area, the
number, and/or the
length of the cells 36 and 46. The provision of the two liners 28 and 30
enables them to attenuate
noise in a much wider frequency range than if a single liner were used, thus
enabling a maximum
amount of attenuation of the acoustic energy generated by the rotating
impeller 12 and its
associated components to be achieved.
According to the embodiment of Fig. 4, two one-piece, unitary, annular liners
48 and 50
are secured in a groove formed in the internal wall of the casing 10 opposite
to the liners 28 and
30. The liner 48 extends in the bottom of the groove and is connected to the
structure forming
the groove in any conventional manner, such as by a plurality of bolts, or the
like; and the liner
50 extends in the groove in an abutting relationship to the liner 48 and is
connected to the liner
48 in any conventional manner, such as by a plurality of bolts, or the like.
The liner 50 partially
defines, with the liner 30, the diffuser channel 14. Since the liners 48 and
50 are similar to, and
functions the same as, the liners 28 and 30, they will not be described in any
further detail.
Due to the firm contact between the liners 48 and 50, and between the liner 48
and the
corresponding wall of the casing 10, and due to the arrangement of the
respective cells of the
liners, the cells work collectively as arrays of acoustic resonators in
series. As such, the liners 48
and 50 attenuate the sound waves generated in the casing 10 by the fast-
rotation of the impeller
12, and by its associated components, and eliminate, or at least minimize, the
possibility that the
noise will by-pass the liners and pass through a different path.
Moreover, the dominant noise component commonly occurring at the blade passing
frequency, or other high frequency can be effectively lowered by tuning the
liners 48 and 50 so
that the maximum sound attenuation occurs around the latter frequency. This
ca.n be achieved by
varying the volume and/or the cross-section area, the number, and/or the
length of their
respective cells. The provision of the two liners 48 and 50 enables them to
attentuate noise in a
much wider frequency range than if a single liner were used, thus enabling a
maximum amount
of attenuation of the acoustic energy generated by the rotating impeller 12
and its associated
components to be achieved.
Also, two one-piece, unitary, annular liners 54 and 56 are mounted in a groove
formed in
the casing 10 to the rear of the impeller 12. The liner 54 extends in the
bottom of the groove and
is connected to the structure forming the groove in any conventional manner,
such as by a
plurality of bolts, or the like; and the liner 56 extends in the groove in an
abutting relationship to
the liner 54 and is connected to the liner 54 in any conventional manner, such
as by a plurality of
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bolts, or the like. The liner 56 partially defines, with the liner 52, the
chamber in which the
impeller 12 rotates.
The liners 54 and 56 have a smaller outer diameter than the liners 28, 30, 48
and 50, but
otherwise are similar to, and are mounted in the same manner as, the latter
liners.
Due to the firm contact between the liners 54 and 56, and between the liner 54
and the
corresponding wall of the casing 10, and due to the arrangement of the
respective cells of the
liners, the cells work collectively as arrays of acoustic resonators in
series. As such, the liners 54
and 56 attenuate the sound waves generated in the casing 10 by the fast-
rotation of the impeller
12, and by its associated components, and eliminate, or at least minimize, the
possibility that the
noise will by-pass the liners and pass through a different path.
Moreover, the dominant noise component commonly occurring at the blade passing
frequency, or other high frequency can be effectively lowered by tuning the
liners 54 and 56 so
that the maximum sound attenuation occurs around the latter frequency. This
can be achieved by
varying the volume and/or the cross-section area, the number, and/or the
length of their
respective cells. The provision of the two liners 54 and 56 enables them to
attenuate noise in a
broader frequency range than if a single liner were used, thus enabling a
maximum amount of
attenuation of the acoustic energy generated by the rotating impeller 12 and
its associated
components to be achieved.
Still another preferred location for liners is shown in Fig. 5 which depicts
an inlet
conduit 60 that introduces gas to the inlet of the iinpeller 12. The upper
portion of the conduit 60
is shown extending above the centerline C/L of the conduit and the casing 10,
as viewed in Fig.
5.
A one-piece, unitary, liner 64 is flush-mounted on the inner wall of the
conduit 60 with
the radial outer portion being shown. The liner 64 is in the form of a curved
shell, preferably
cylindrical or conical in shape, is disposed in an annular groove formed in
the inner surface of
the conduit 60, and is secured in the groove in any known manner. Since the
liner 64 is
otherwise similar to the liners 28, 30, 48, 50, 52, 54, and 56, it will not be
described in further
detail.
A one-piece, unitary, liner 66 is also disposed in the latter annular groove
and extends
around the liner 64 with its inner surface abutting the outer surface of the
liner 64. The liner 66
is in the form of a curved shell, preferably cylindrical or conical in shape
having a diameter
larger than the diameter of the liner 64 and is secured to the liner 64 in any
conventional manner,
such as by a plurality of bolts, or the like. Since the liners 64 and 66 are
otherwise similar to the
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liners 28, 30, 48, 50, 52, 54, and 56, and function in the same manner to
significantly reduce the
noise in the casing 10, they will not be described in further detail.
Due to the firm contact between the liners 64 and 66, and between the liner 66
and the
corresponding wall of the casing 10 defining the latter groove, and due to the
arrangement of the
respective cells of the liners, and their location relative the inlet conduit
60, the cells work
collectively as arrays of acoustic resonators in series. As such, the liners
64 and 66 attenuate the
sound waves generated in the casing 10 by the fast-rotation of the impeller
12, and by its
associated components, and eliminate, or at least minimize, the possibility
that the noise will by-
pass the liners and pass through a different path.
Moreover, the dominant noise conlponent commonly occurring at the blade
passing
frequency, or other high frequency can be effectively lowered by tuning the
liners 64 and 66 so
that the maximum sound attenuation occurs around the latter frequency. This
can be achieved by
varying the volume and/or the cross-section area, the number, and/or the
length of their
respective cells. The provision of the two liners 64 and 66 enables thein to
attenuate noise in a
broader frequency range than if a single liner were used, thus enabling a
maximum amount of
attenuation of the acoustic energy generated by the rotating impeller 12 and
its associated
components to be achieved.
Also, given the fact that the frequency of the dominant noise component in a
fluid
pressurizing device of the above type varies with the compressor speed, the
number of the
smaller cells per each larger cell of each liner can be varied spatially
across the liners so that the
entire liner is effective to attenuate noise in a broader frequency band.
Consequently, the liners
28, 30, 48, 50, 52, 54, 56, 64, and 66 can efficiently and effectively
attenuate noise, not just in
constant speed machines, but also in variable speed compressors, or otller
fluid pressurizing
devices.
In addition to the attenuation of the acoustic energy and the elimination of
by-passing of
the latter energy, as discussed above, the one-piece unitary construction of
the liners in the above
embodiments renders the liners mechanically stronger when compared to the
composite designs
discussed above. Thus, the liners provide a very rigid inner wall to the
internal flow in the fluid
pressurizing device, and have less or no deformation when subject to
mechanical and thermal
loading, and thus have no adverse effect on the aerodynamic performance of a
fluid pressurizing
device, such as a centrifugal compressor, even when they are installed in the
narrow passages
such as the diffusor channels, or the like.
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Variations
The specific arrangement and nuinber of liners in accordance with the above
embodiments are not limited to the number shown. Thus, the liners to either
side of the diffuser
channel and/or the impeller and/or the inlet conduit.
The specific technique of forming the cells in the liners can vary from that
discussed
above. For example, a one-piece liner can be formed in which the cells are
molded in their
respective plates.
The relative dimensions, shapes, numbers and the pattern of the cells of each
liner can
vary.
The liners are not limited to use with a centrifugal compressor, but are
equally applicable
to other fluid pressurizing devices in which aerodynamic effects are achieved
with movable
blades.
Each liner can extend for degrees around the axis of the impeller and the
inlet conduit as
disclosed above; or each liner can be formed into segments which extend an
angular distance less
than 360 degrees.
The spatial references used above, such as "bottom", "inner", "outer", "side"
etc, are for
the purpose of illustration only and do not limit the specific orientation or
location of the
structure.
Since other modifications, changes, and substitutions are intended in the
foregoing
disclosure, it is appropriate that the appended claims be construed broadly
and in a maimer
consistent with the scope of the invention.
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