U.S. patent application number 14/076491 was filed with the patent office on 2014-03-06 for fluid flow velocity and temperature measurement.
The applicant listed for this patent is Evangelos V. Diatzikis, Edward David Thompson, Michael Twerdochlib. Invention is credited to Evangelos V. Diatzikis, Edward David Thompson, Michael Twerdochlib.
Application Number | 20140060203 14/076491 |
Document ID | / |
Family ID | 46028163 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140060203 |
Kind Code |
A1 |
Diatzikis; Evangelos V. ; et
al. |
March 6, 2014 |
FLUID FLOW VELOCITY AND TEMPERATURE MEASUREMENT
Abstract
A method is provided for monitoring velocity of a fluid flow
through a predetermined fluid flow space. A fiber optic conductor
includes a flow measurement portion defining an elongated dimension
extending across a portion of the fluid flow space. The fluid flow
in the fluid flow space causes the measurement portion of the fiber
optic conductor to flex in a direction transverse to the elongated
dimension. Optical radiation is supplied to the fiber optic
conductor, and optical radiation is received from the fiber optic
conductor after the supplied optical radiation has passed through
the measurement portion. The received optical radiation is analyzed
to effect a determination of a flow velocity of the fluid flow.
Inventors: |
Diatzikis; Evangelos V.;
(Chuluota, FL) ; Thompson; Edward David;
(Casselberry, FL) ; Twerdochlib; Michael; (Oviedo,
FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Diatzikis; Evangelos V.
Thompson; Edward David
Twerdochlib; Michael |
Chuluota
Casselberry
Oviedo |
FL
FL
FL |
US
US
US |
|
|
Family ID: |
46028163 |
Appl. No.: |
14/076491 |
Filed: |
November 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13101350 |
May 5, 2011 |
|
|
|
14076491 |
|
|
|
|
Current U.S.
Class: |
73/861 |
Current CPC
Class: |
G01F 1/661 20130101;
G01F 1/28 20130101; G01P 5/02 20130101 |
Class at
Publication: |
73/861 |
International
Class: |
G01F 1/66 20060101
G01F001/66 |
Claims
1. A system for monitoring velocity of a fluid flow through a
predetermined fluid flow space formed by a wall defining and
extending in a fluid flow direction, the system comprising: a base
structure supported on the wall; a fiber optic conductor including
a base end supported on the base structure and an unrestrained free
end located in the fluid flow and movable relative to the base end,
the fiber optic conductor defining a flow measurement portion
including a long period grating (LPG) structure extending from the
wall across a portion of the fluid flow space and the fiber optic
conductor including an elongated dimension extending transverse to
the fluid flow direction for flexing in response to fluid flow
against the flow measurement portion; an optical radiation source
supplying optical radiation to the fiber optic conductor; a
processing unit adapted to receive and analyze optical radiation
from the fiber optic conductor after the supplied optical radiation
has passed through the measurement portion to produce a
determination of a flow velocity of the fluid flow with reference
to cladding modes formed by the LPG structure.
2. The system of claim 1, including a plurality of the fiber optic
conductors supported on the base structure and each including a LPG
structure, each of the fiber optic conductors extending outwardly
from the wall into the fluid flow space, and including a supply
fiber optic conductor extending from the optical radiation source
and a splitter providing optical radiation from the supply fiber
optic conductor to each of the fiber optic conductors.
3. The system of claim 2, wherein the plurality of fiber optic
conductors are arranged in a plurality of rows supported on the
base structure, each row including a plurality of the fiber optic
conductors.
4. The system of claim 1, wherein the fiber optic conductor
includes a reflective surface at an end distal from the base end
for reflecting optical radiation including the cladding modes
through the fiber optic conductor to the processing unit.
5. The method of claim 1, wherein a plurality of fiber optic
conductors are provided, each fiber optic conductor having a base
end supported on a base structure and a free end located in the
fluid flow, each fiber being free to bend in the fluid flow and
having an LPG structure and each LPG structure having a set of
cladding modes characteristic of the bending of a respective fiber
optic conductor.
6. The method of claim 5, wherein the received optical radiation
comprises optical radiation reflected off ends of the fiber optic
conductors distal from the base end.
7. The method of claim 5, including comparing cladding modes of two
or more of the fiber optic conductors to determine a direction of
fluid flow.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a Continuation Application of
U.S. patent application Ser. No. 13/101,350, filed May 5, 2011,
which application is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to measurement of
fluid flow velocity and, more particularly, to a method and system
using optical radiation to measure flow velocities.
BACKGROUND OF THE INVENTION
[0003] An electrical generator used in the field of electrical
power generation includes a stator winding having a large number of
conductor or stator bars that are pressed into slots in a base
body, in particular, a laminated stator core or a rotor body. Such
an electrical generator represents a very expensive and long-term
investment. Its failure not only endangers the power equipment
itself but may also result in very severe service reduction due to
the down time associated with repair. To avoid such a condition, a
diagnostic system may be used for early identification of defects
or deterioration in operation. The diagnostic system may further
allow a higher utilization level, making the power equipment more
financially viable.
[0004] For example, in an electrical generator, hydrogen or air may
typically be used as a cooling medium for parts of the generator
such as the stator core and the end winding region, and
additionally may be used to cool the stator coils and the rotor.
Ventilation for proper cooling of the generator components is built
into the design and generally may be essential to the continued
safe operation of the electrical generator. It has been observed
that many problems resulting in generator failure and costly power
plant outages may be traced to inadequate ventilation, i.e.,
ventilation not being provided in accordance with design
conditions. In particular, unintended flow modification of the
cooling flow may be caused by parts that come loose during
generator operation, mislocated baffles, leaking seal strips, and
dislodged and migrating insulation filler strips, which may result
in overheating of parts and insulation failure.
[0005] Existing monitoring systems include monitoring temperature
as an indication of a condition of select locations within an
electrical generator. However, such temperature monitoring may not
provide information on the cause of temperature variations, such as
causes relating to unintended flow modification of ventilation flow
through the generator.
SUMMARY OF THE INVENTION
[0006] In accordance with an aspect of the invention, a system is
provided for monitoring velocity of a fluid flow through a
predetermined fluid flow space formed by a wall defining and
extending in a fluid flow direction. The system comprises a base
structure supported on the wall and a fiber optic conductor
including a base end supported on the base structure and an
unrestrained free end located in the fluid flow and movable
relative to the base end. The fiber optic conductor defines a flow
measurement portion including a long period grating (LPG) structure
extending from the wall across a portion of the fluid flow space,
and the fiber optic conductor including an elongated dimension
extending transverse to the fluid flow direction for flexing in
response to fluid flow against the flow measurement portion. An
optical radiation source is provided supplying optical radiation to
the fiber optic conductor, and a processing unit is provided
adapted to receive and analyze optical radiation from the fiber
optic conductor after the supplied optical radiation has passed
through the measurement portion to produce a determination of a
flow velocity of the fluid flow with reference to cladding modes
formed by the LPG structure.
[0007] In accordance with additional aspects of the invention, a
plurality of the fiber optic conductors may be supported on the
base structure and each including a LPG structure, each of the
fiber optic conductors extending outwardly from the wall into the
fluid flow space, and including a supply fiber optic conductor
extending from the optical radiation source and a splitter
providing optical radiation from the supply fiber optic conductor
to each of the fiber optic conductors. The plurality of fiber optic
conductors may be arranged in a plurality of rows supported on the
base structure, each row including a plurality of the fiber optic
conductors. The fiber optic conductor may include a reflective
surface at an end distal from the base end for reflecting optical
radiation including the cladding modes through the fiber optic
conductor to the processing unit.
[0008] In accordance with additional alternative aspects of the
invention, a plurality of fiber optic conductors may be provided,
each fiber optic conductor having a base end supported on a base
structure and a free end located in the fluid flow, each fiber
being free to bend in the fluid flow and having an LPG structure
and each LPG structure having a set of cladding modes
characteristic of the bending of a respective fiber optic
conductor. The method may include comparing cladding modes of two
or more of the fiber optic conductors to determine a direction of
fluid flow. The received optical radiation may comprise optical
radiation reflected off ends of the fiber optic conductors distal
from the base end.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] While the specification concludes with claims particularly
pointing out and distinctly claiming the present invention, it is
believed that the present invention will be better understood from
the following description in conjunction with the accompanying
Drawing Figures, in which like reference numerals identify like
elements, and wherein:
[0010] FIG. 1 is a cross-sectional view of an electrical generator
incorporating a monitoring structure of the present invention;
[0011] FIG. 2 is a diagrammatic cross-sectional view of a portion
of a generator blower outlet including the monitoring structure of
the present invention;
[0012] FIG. 3 is an enlarged view of a detection unit for the
monitoring structure;
[0013] FIG. 4 is an enlarged view of a section of the detection
unit of FIG. 3 including a measurement portion;
[0014] FIG. 5 is a diagrammatic view of a monitoring system
including the monitoring structure;
[0015] FIG. 6 is an alternative configuration of a detection unit
in accordance with the present invention;
[0016] FIG. 7 is a diagrammatic view of a further embodiment of a
detection unit of the present invention;
[0017] FIG. 8 is a plot illustrating cladding modes that may be
provided by the detection unit of FIG. 7;
[0018] FIG. 9 is a diagrammatic view of a monitoring system
incorporating the detection unit of FIG. 8; and
[0019] FIG. 10 is a further embodiment of a detection unit in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings that
form a part hereof, and in which is shown by way of illustration,
and not by way of limitation, specific preferred embodiments in
which the invention may be practiced. It is to be understood that
other embodiments may be utilized and that changes may be made
without departing from the spirit and scope of the present
invention.
[0021] Various locations in an electrical generator may benefit
from determining flow and temperature characteristics of cooling
fluid, e.g., hydrogen or air, passing through the interior of the
generator. For example, an outlet of a blower providing cooling
fluid to a generator may be monitored to sense flow velocities and
temperatures of the cooling fluid passing through the outlet to
determine that the flow and temperature profiles match design
profiles for this area. Specifically, in accordance with aspects of
the measurement system described herein, it may be desirable to
monitor changes in one or both of the flow velocity and temperature
over time at various locations around the blower outlet as a means
of identifying a change in the blower structure that may predict a
potentially damaging condition. Exemplary conditions that may occur
in the region of the blower outlet include loosening blower shroud
mounting hardware or damaged blower vanes provided for channeling
the cooling fluid passing into the generator. It is believed to be
desirable to detect these conditions in that if these components or
parts of these components should come loose and pass into the
generator, catastrophic mechanical and/or electrical damage to the
generator may occur. It should be understood that, while aspects of
the present monitoring system are described with particular
reference to a blower outlet duct for a generator, the system may
be implemented in other locations of the generator, as well as in
applications other than those comprising a generator.
[0022] Referring to FIG. 1, an electrical generator 10 is
illustrated including a rotor 12 and a stator 14 enclosed by a
generator frame or housing 16. The rotor 12 may typically include a
blower 18 for propelling cooling fluid, e.g., hydrogen, around the
interior of the generator 10 to promote cooling, as indicated by
the directed line segments 20 illustrating flow patterns for the
cooling fluid. The blower 18 may discharge the cooling fluid
through a generally annular outlet duct 22, defining a fluid flow
space 27 between an inner wall 24 and an outer wall 26, see FIG. 2.
In accordance with an aspect of the invention, flow from the outlet
duct 22 may be monitored to ensure that it is provided in
accordance with predetermined design requirements to provide a
desired level of cooling within the generator 10. In particular,
locations around the outlet duct 22 may be monitored to ensure that
the flow and temperature for the cooling fluid exiting the outlet
duct are at predetermined levels.
[0023] Referring to FIG. 2, a portion of the outlet duct 22 for
generator 10 is illustrated diagrammatically, including a
monitoring structure 28 in accordance with an aspect of the present
system. The monitoring structure 28 includes a plurality of
detection units 30 circumferentially spaced around the
circumference of the outlet duct 22. Each detection unit 30 is
preferably configured to provide a flow velocity and temperature
measurement for a location in the duct 22 corresponding to the
location of a respective detection unit 30.
[0024] Referring to FIGS. 3 and 4, the detection units 30 each
include a conduit structure 32 comprising a hollow member extending
in a loop to define a generally circular passage 34 for passage of
cooling fluid flow. The loop of the conduit structure 32 may be
small in relation to size of the outlet duct 22.
[0025] A first fiber optic conductor 36 extends within and is at
least partially enclosed in the conduit structure 32 to protect the
fiber optic conductor 36, and to position the fiber optic conductor
36 at a predetermined location within the fluid flow space 27. The
fiber optic conductor 36 defines an elongated flow measurement
portion 38 extending outside of the conduit structure 32 across a
portion of the fluid flow space 27 within the circular passage 34.
In particular, the fiber optic conductor 36 extends between a first
location defined by a first opening 40 on the conduit structure 32
and a second location defined by a second opening 42 on the conduit
structure 32. Hence, the measurement portion 38 is defined by a
portion of the fiber optic conductor 36 supported in stationary
relation to the conduit structure 32 at the first and second
openings 40, 42, and extending through a portion of the fluid flow
space 27 for contact with cooling fluid passing through the outlet
duct 22. The measurement portion 38 includes at least one velocity
fiber Bragg grating (FBG) 44, illustrated in FIG. 4 as centrally
located between the first and second openings 40, 42.
[0026] The detection unit 30 may further include a second fiber
optic conductor 46 that extends within and is substantially
enclosed in the conduit structure 32. The second fiber optic
conductor 46 may extend in side-by-side relation with the first
fiber optic conductor 36 through the conduit structure 32. The
second fiber optic conductor 46 includes at least one temperature
FBG 48 located within the conduit structure 32 at a location
generally midway between the first and second openings 40, 42.
However, it should be understood that the temperature FBG 48 may be
located at other locations along or adjacent to the loop defined by
the conduit structure 32. It should be noted that the temperature
FBGs 48 are similar in structure and operate in a similar way to
the velocity FBGs 44, in that the temperature FBGs 48 provide a
measurement of strain, as produced by a change in temperature. In
addition, the temperature FGBs 48 may be formed in the first fiber
optic conductor 36 at one or more locations within the conduit
structure 32. As is discussed below, each of the FBGs 44, 48 is
formed with a unique central Bragg wavelength, such that the
particular source or sensor producing a signal may be identified by
wavelengths at or near the unique wavelength for the sensor.
[0027] The detection unit 30 may be substantially rigidly affixed
on a base portion 50 (FIG. 3) to support the detection unit 30 in
stationary relation to an inner surface 52 of the inner wall 24,
with a plane defined by the loop of the conduit structure 32
extending perpendicular to the inner wall 24 and extending
transverse to the fluid flow direction. The base portion 50 may
comprise a small pad provided to each of the detection units 30 for
mounting the detection units 30 to the inner surface 52, such as by
an adhesive or mechanical attachment. Alternatively, the base
portion 50 may comprise a continuous base around the circumference
of the inner wall 24, and may comprise a material of sufficient
flexibility to form a flexible mat structure with the detection
units 30 attached thereto for extending around a curved surface,
such as the inner wall 24, or to extend around irregularly
contoured surfaces. The base portion 50 provides a support for the
detection units 30 that permits movement of the underlying surface
52, such as thermal expansion or contraction, without transferring
such movement to the optical fiber conduits 36, 46. The base may be
formed of any material capable of operating in the environment in
which the monitoring structure 28 is placed and capable of
isolating the detection units from movement. For example and
without limitation, the base material may comprise metal or plastic
ribbon or, in some applications, a Velco.RTM. strip.
[0028] The fiber optic conductors 36, 46 are preferably formed of
an elastically deformable material such as is typically used in FBG
sensors. In particular, the fiber optic conductors 36, 46 may
comprise a small inner glass core having an outer glass cladding
with a different index of refraction than the inner core. The Bragg
grating comprises lines of slightly different index of refraction
placed in the inner core using ultraviolet light. The fiber optic
conductors 36, 46 do not include an outer plastic jacket, such that
the diameter of the fiber is very small. In addition, although the
FBGs 44, 48 are illustrated diagrammatically herein as lines
located on the fiber optic conductors 36, 46, it may be understood
that the FBGs 44, 48 are not typically visible on the fiber optic
conductors 36, 46. The conduit structure 32 may comprise a
capillary tube structure formed of a material having greater
rigidity than the material of the fiber optic conductors 36, 46.
For example, the conduit structure 32 is preferably a dielectric
material, such as a plastic or composite material, that is
sufficiently stiff to resist movement when subjected to forces
exerted by the cooling fluid flow. However, the conduit structure
32 may be sufficiently flexible to generally follow varying
contours of structure on which the detection units 30 are
supported. For example, the conduit structure may be formed of a
copper-nickel capillary that may be on the order of 0.10 inch in
diameter.
[0029] Each one of the first and second fiber optic conductors 36,
46 is a continuous conductor extending within a continuous conduit
structure 32 through each of the detection units 30. The first
fiber optic conductor 36 includes a plurality of velocity FBGs 44,
i.e., at least one velocity FBG 44 per detection unit 30, and each
velocity FBG 44 has a grating spacing that corresponds to a unique
central Bragg wavelength A, for reflecting light at a wavelength
that is unique to each FBG 44 in the first fiber optic conductor
36. Similarly, the second fiber optic conductor 46 includes a
plurality of temperature FBGs 48, i.e., at least one temperature
FBG 48 per detection unit 30, and each temperature FBG 48 has a
grating spacing that corresponds to a unique central Bragg
wavelength .lamda., for reflecting light at a wavelength that is
unique to each FBG 48 in the second fiber optic conductor 46.
[0030] Referring to FIG. 5, a monitoring system 54 including the
monitoring structure 28 is illustrated. The monitoring system 54
includes a fiber optic conductor structure 56 which may comprise a
continuation of the conduit structure 32 and enclosed fiber optic
conductors 36, 46 or, alternatively, may comprise a common fiber
optic conductor branching from a connector or junction 58 with the
fiber optic conductors 36, 46 for carrying the light signals from
both of the fiber optic conductors 36, 46. The monitoring system 54
may further include a source of optical radiation 60, such as a
broadband light source, coupled to the fiber optic conductor
structure 56 at a coupler 62 for providing the monitoring structure
28 with optical radiation, and which provides a predetermined range
of light wavelength (frequency) to correspond to the central Bragg
wavelength .lamda. of any FBGs 44, 48 located along the fiber optic
conductors 36, 46. Reflected light from the FBGs 44, 48 is
transmitted back through the fiber optic conductor structure 56 and
is received via the coupler 62 at an optical processor or analyzer
64. The data processed by the analyzer 64 may further be
communicated to an operator interface such as a monitor 66 and/or
to a data acquisition system 68.
[0031] In a measurement operation performed by the monitoring
system 54, a cooling fluid flow passing through the outlet duct 22
passes around the plurality of detection units 30, including flow
through the passages 34 defined within the loops of the conduit
structure 32. As the cooling fluid passes through the passages 34,
fluid flow may cause the measurement portion 38 of the first fiber
optic conductor 36 to flex in a direction that is transverse to the
elongated dimension of the measurement portion 38, i.e., generally
perpendicular or transverse to the plane of the loop of the conduit
structure 32. The flexing of the measurement portions 38 produces a
strain in the first fiber optic conductor 36 at the velocity FBGs
44 that is proportional to the velocity of the fluid flow passing
across the measurement portions 38 containing the respective
velocity FBGs 44. The flexing, and resulting strain, at the
velocity FBGs 44 causes the spacing between the gratings forming
the velocity FBGs 44 to change with a resulting change in a
wavelength of light supplied from the source of optical radiation
60 and reflected from the velocity FBGs 44 to provide a velocity
measurement for each velocity FBG 44, as may be determined by the
analyzer 64. Since the velocity FBGs 44 will always sense the air
flow in a flexed state, the reflected wavelength from each velocity
FBG 44 will be equal to or greater than the unique central Bragg
wavelength .lamda. of the respective velocity FBG 44.
[0032] In addition, the temperature at the locations of the
temperature FBGs 48 may cause the second fiber optic conductor 46
to expand and contract an amount that is proportional to the
temperature of the fluid flow. The expansion or contraction of the
second fiber optic conductor 46 causes a spacing between the
gratings forming the temperature FBGs 48 to change with a resulting
change in a wavelength of light supplied from the source of optical
radiation 60 and reflected from the temperature FBGs 48 to provide
a temperature measurement for each temperature FBG 48, as may be
determined by the analyzer 64. A variation of the reflected
wavelength for each temperature FBG 48 may be centered around the
unique central Bragg wavelength .lamda. of the respective
temperature FBG 48.
[0033] In addition to providing a temperature measurement at the
locations of the detection units 30 for monitoring the proper
operation of the cooling fluid passing through the generator 10,
the temperature FBGs 48 provide a temperature correction value for
correcting the velocity measurements of the velocity FBGs 44 with
variations in the temperature of the cooling fluid. Specifically,
the measurement portion 38 of the first fiber optic conductor 36
may expand and contract with variations in temperature, such that
the reflected wavelength from the velocity FBGs 44 may include a
temperature component associated with a temperature change as well
as a velocity component associated with flexure of the measurement
portion 38 resulting from the flow velocity. The shift in reflected
wavelength of the velocity FBGs 44 of the first fiber optic
conductor 36 that occurs with changes in temperature may be
compensated using the measured shift in wavelength at the
temperature FBG 48. That is, the change in wavelength measured by
the temperature FBG 48 may be used to subtract out the temperature
component of the change in reflected wavelength from the central
Bragg wavelength A provided by the velocity FBG 44, such that only
the velocity component of the measurement from the velocity FBG 44
remains.
[0034] In accordance with an aspect of the invention, the velocity
and temperature at the location of each detection unit 30 may be
determined. The data from the known locations for the plurality of
detection units 30 may be indicative of the condition of the
cooling system for the generator 10. A variation of either a flow
velocity from a predetermined flow velocity or a temperature from a
predetermined temperature in each of the locations of the detection
units 30 may indicate a variation in flow from design conditions,
such as may be caused by a loose or displaced component within the
generator. Hence, in addition to providing a monitoring that may
provide an indication of improper cooling provided within the
generator 10, the monitoring system 54 may provide an advance
indication of a loose or displaced component, potentially enabling
implementation of a repair or maintenance operation prior to loose
parts traveling to critical parts of the generator where they may
cause catastrophic damage.
[0035] It may be noted that a large number of the detection units
30 may be provided, including providing on the order of one-hundred
velocity FBGs 44 in the first fiber optic conductor 36, and an
equal number of temperature FBGs in the second fiber optic
conductor 46. Further, it should be understood that more than one
velocity FBG 44 and temperature FBG 48 may be provided to each of
the detection units 30.
[0036] Although the described embodiment incorporates all of the
velocity FBGs 44 into the first fiber optic conductor 36 and all of
the temperature FBGs 48 into the second fiber optic conductor 46,
it should be understood that additional fiber optic conductors may
be provided. For example, to ensure that sensing capability is
maintained in the event that a break occurs in either of the first
and second fiber optic conductors 36, 46, the velocity and
temperature FBGs 44, 48 may be formed in a plurality of respective
first and second fiber optic conductors 36, 46 that may extend from
the junction 58 (FIG. 5). Hence, light may be supplied to and
reflected from the velocity and temperature FBGs 44, 48 along a
plurality of paths to ensure continuity of the monitoring operation
in the event that one of the first and second fiber optic
conductors 36, 46 is damaged.
[0037] It should be understood that, although the present structure
is described with reference to attachment to the inner wall 24 of
the outlet duct 22, the detection units 30 described herein may be
positioned on the outer wall 26, or on any other surface within the
generator 10 where it is desired to monitor a fluid flow velocity
and a temperature. Further, the monitoring structure 28 may be
incorporated in other machines than a generator such as, for
example, within a compressor for a gas turbine engine.
[0038] Referring to FIG. 6, an alternative configuration for a
detection unit is illustrated wherein elements corresponding to the
detection unit 30 of the previous embodiment are labeled with the
same reference numeral increased by 100. The embodiment of FIG. 6
provides a detection unit 130 that may be used to map a fluid flow
across a cross-section of a flow area, such as a cross-section of a
circular duct. For example the detection unit 130 may be located in
one of the ducts 70 (FIG. 1) extending longitudinally through the
generator 10.
[0039] The detection unit 130 may include a conduit structure 132
extending around an inner circumference of the duct 70. A first
fiber optic conductor 136 and a second fiber optic conductor 146
extend within the conduit structure 132 for obtaining velocity and
temperature measurements, respectively. In the present embodiment,
the first fiber optic conductor 136 may comprise a plurality of
optical fibers 136a-e. The first fiber optic conductor 136 defines
a plurality of elongated flow measurement portions 138,
individually identified as 138a-e, extending outside of the conduit
structure 132. Each measurement portion 138a-e may be formed by a
portion of a respective optical fiber 136a-e forming the first
fiber optic conductor 136. In particular, the individual optical
fibers 136a-e may extend between respective pairs of a plurality of
first locations 140a-e and second locations 142a-e defined by
openings in the conduit structure 132 for passage of the optical
fibers 136a-e between the interior of the conduit structure 132 and
a fluid flow passage 134. The locations 140a-e and 142a-e define
locations supporting generally stationary ends of the respective
measurement portions 138a-e.
[0040] Each measurement portion 138a-e may be provided with a FBG
144, which may be located generally centrally of each of the
measurement portions 138a-e. Each velocity FBG 144 has a grating
spacing that corresponds to a unique central Bragg wavelength A,
for reflecting light at a wavelength that is unique to each FBG 144
in the first fiber optic conductor 136. Flow of cooling fluid
through the flow passage 134 causes the measurement portions 138a-e
to flex and create a strain in the fiber optic conductor 136 an
amount that is proportional to the flow velocity, and which may be
detected at the various locations of the velocity FBGs 144.
Variations in flow velocity across the cross-section of the flow
space 134 may cause a varying flexing and strain in the velocity
FBGs 144 located in the measurement portions 138a-e to provide
velocity measurements corresponding to the different locations of
the velocity FBGs 144. Hence, a velocity profile for the fluid flow
through the flow space 134 may be mapped to provide data to
evaluate fluid flow in structures such as the duct 70.
[0041] The second fiber optic conductor 146 may be provided with a
plurality of temperature FBGs 148 to provide temperature
measurements that may be used to correct the velocity measurement
for temperature variations in a manner similar to that described
for the temperature FBGs 48 of the previous embodiment. It should
be understood that the present embodiment may include any number of
measurement portions 138, and any number of velocity FBGs 144 and
temperature FBGs 148 may be provided. In addition, the temperature
FBGs 148 may be formed in one or more of the velocity FBGs 144,
such that the separate, second fiber optic conductor 146 may not be
required for obtaining temperature measurements.
[0042] Referring to FIG. 7, a further embodiment of the invention
is illustrated including a detection unit 210 that may be mounted
in a generator blower outlet duct or in other locations, as
described for the previous embodiments. The detection unit 210
comprises a base portion 212 supporting a plurality of optical
fibers 214 extending generally perpendicular to the base portion
212 and parallel to each other into or across a fluid flow space.
The optical fibers 214 may be arranged in at least one row
extending perpendicular to a direction of flow 215 of a cooling
fluid flow past the detection unit 210 within the fluid flow space.
As is illustrated diagrammatically in one of the optical fibers
214, a long period grating (LPG) 216 may be provided in the core
218 along an elongated or lengthwise extending portion of each of
the optical fibers 214.
[0043] The LPGs 216 provided to the optical fibers 214 are similar
to the FBGs of the previous embodiments in that both have periodic
structures in the core of the optical fiber. However, unlike the
FBG, the LPG structure is usually 5 to 10 times longer and the
grating pitch is longer, giving the LPG a characteristic function
of coupling the propagation modes to the cladding modes. Thus, in
transmission, the optical signal, after passing the LPG structure,
has a series of wavelength "notches". These notches are wavelength
bands, in the interrogation signal, that have been removed, i.e.,
converted to cladding modes. The cladding modes are highly
dependent on the bending of the optical fiber 214 with a resulting
change in spacing of the gratings forming the LPG 216. Hence, a
force that causes the optical fiber to bend will in turn manifest
itself in a perturbation of the cladding modes. FIG. 8 illustrates
a typical transmission spectrum that may be provided by the
cladding modes 220 of the LPG 216. Any bending of the optical
fibers 214, and corresponding change of the spacing between the
gratings of the LPGs 216, will result in a greater loss of the
light passing though the LPGs 216 to the cladding modes. Each of
the optical fibers 214 may be provided with an LPG structure 216
having a unique set of cladding modes 220, such that a unique set
of cladding mode wavelengths correspond to each location of an
optical fiber 214.
[0044] Referring to FIG. 9, a monitoring system 222 incorporating
the detection unit 210 is illustrated. The monitoring system 222
includes a source of optical radiation 224, such as a broadband
light source for supplying light to the optical fibers 214 via a
coupler 226, and a supply fiber optic conduit structure 228
extending from the coupler 226 to a splitter 230. The splitter 226
may be provided to the base portion 212 of the detection unit 210
to distribute light conveyed from the optical radiation source 224
to each of the optical fibers 214.
[0045] As discussed above, the light passing through the LPGs 216
will exhibit a loss of light in particular wavelength bands to the
cladding modes 220. A free end 232 of each of the optical fibers
214 is provided with a reflective surface 234 (FIG. 7) that will
reflect the light propagated through the LPG 216 back through the
optical fiber 214 to the optical fiber conductor structure 228 via
the splitter 230. The reflected light from the optical fibers 214
is then received via the coupler 226 at an optical processor or
analyzer 236 where a determination of the cladding mode losses may
be performed to determine an amount of bending of each of the
optical fibers 214, corresponding or proportional to a velocity of
the cooling fluid flow past each optical fiber 214 in the detection
unit 210.
[0046] The sensitivity or responsiveness of the detection unit 210
may be altered or adjusted by changing physical characteristic of
the optical fibers 214, such as by changing the diameter and/or
length of the optical fibers 214. That is, by providing a thinner
or longer optical fiber 214, the resistance of the optical fibers
214 to bending may be decreased, such as may be desirable in an
application having a lower velocity flow.
[0047] In addition, a fiber optic conductor having temperature FBGs
(not shown) may be provided associated with the optical fibers 214,
such as in the base portion 212 of the detection unit 210, to
provide a temperature measurement and/or to provide a temperature
correction for the velocity measurement obtained from the optical
fibers 214, as described for the embodiment of FIGS. 2-4.
[0048] Referring to FIG. 10, an alternative embodiment of the
embodiment of FIG. 7 is illustrated, in which elements of the
embodiment of FIG. 10 corresponding to the embodiment of FIG. 7 are
labeled with the same reference numeral increased by 100. FIG. 10
illustrates a detection unit 310 including a plurality of optical
fibers 314 arranged in an array 317 on a base portion 312 and
comprising multiple rows of the optical fibers 314, illustrated
herein as rows 317a, 317b, 317c extending transverse to a direction
of fluid flow 315, and including free ends 332 that are generally
freely movable in the fluid flow. The optical fibers 314 each
include LPGs and a reflective end surface 334, and operate in the
same manner as described for the optical fibers 214 of the
embodiment of FIG. 7. Further, the optical signals from the
multiple rows of optical fibers 314 may be processed to determine a
direction of fluid flow. For example, a direction transverse to a
direction parallel to a predetermined fluid flow path through a
duct, or a curvature to the fluid flow may be detected by comparing
or mapping the differential bending of adjacent and/or successive
optical fibers 314 to determine the relative strength of current
flow across portions of the detection unit 310, which current flow
may extend at angles relative to a direction perpendicular to the
extent of the rows of the array 317, as is depicted by the angled
flow line 315.
[0049] From the above description of the invention, it should be
apparent that embodiments of the invention provide a method and
system capable of obtaining multiple and simultaneous velocity and
temperature measurements that may be distributed through a fluid
flow space. Further, the configuration of the measurement system
provides a degree of flexibility that permits it to be located
within and along complex structures to provide fluid flow and
temperature measurements at locations that may not be accessible by
conventional sensing devices.
[0050] It may also be noted that the use of fiber optic conductors
as the sensing elements of the system described herein provides a
sensor that may have a higher level of acceptance in monitoring
electrical generating equipment. The relatively small and light
weight optical fibers generally present a reduced risk of causing
damage within the electrical generating equipment if the optical
fibers should become damaged and/or enter the cooling fluid flow
for the equipment.
[0051] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
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