Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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GAS TURBINE DEVICE
CROSS REFERENCE TO THE RELATED APPLICATION
This application is based on and claims Convention priority to Japanese
patent application No. 2012-188346, filed August 29, 2012, the entire
disclosure of which
is herein incorporated by reference as a part of this application.
BACKGROUND OF THE INVENTION
(Field of the Invention)
The present invention relates to a gas turbine device for driving a power
machinery such as, for example, an electric generator by means of a gas
turbine engine.
(Description of Related Art)
The gas turbine device is generally apt to generate considerable high
frequency noises, but those high frequency noises can be effectively reduced
with, for
example, the use of a packaging utilizing an enclosure and/or the use of an
induction and
exhaust silencer. In contrast thereto, low frequency noises also generated
from the gas
turbine device are difficult to reduce. This aspect of the gas turbine device
will now be
discussed with particular reference to Figs. 5 and 6 of the accompanying
drawings.
In the gas turbine device, the flow velocity of exhaust gas discharged from
the
final stage rotor vane of the gas turbine engine is generally within a
relatively high speed
range of 300 to 400 m/sec. Therefore, in order to improve the performance, the
flow
velocity of the exhaust gas is reduced by causing the exhaust gas to flow
through a long
exhaust diffuser DF to thereby reduce the dynamic pressure of the exhaust gas
so that the
exhaust gas may regain the static pressure. The exhaust diffuser DF referred
to above
includes, as shown in Figs. 5 and 6, an inner tube 28 and an outer tube (not
shown)
disposed around the inner tube 28 so as to enclose the inner tube 28, with an
exhaust gas
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passage being defined between it and the inner tube 28 for the passage
therethrough of the
exhaust gas discharged from the turbine final stage rotor vane.
Also, the exhaust gas passage referred to above is provided with a plurality
of
exhaust struts 31 disposed circumferentially thereof for the support of the
inner tube 28
and, also, for the supply of a lubricant oil. In this respect, see the patent
document I
listed below. Each of the exhaust strut 31 is of a flattened oval-sectioned
shape and is so
disposed with its longitudinal axis oriented in an axial direction C of the
exhaust diffuser
DF so that it will not constitute a considerable flow resistance to the flow
of the exhaust
,
gas.
In the meantime, in order to increase the performance of the exhaust diffuser
DF, the standard gas turbine engine has been so designed as to achieve the
flow in the
axial direction C during the rated operation (full load operation). In other
words, during
the rated operation, as shown in Fig. 5, the vector V of the exhaust gas
absolute flow (true
flow), which is a composite of the vector V1 of the turbine rotational
direction and the
vector V2 of the relative flow velocity of the exhaust gas from the turbine
final stage rotor
vane, comes to lie in a direction substantially parallel to the axial
direction C. The
exhaust gas flow Si in this state will become that in which vortexes generated
at a
downstream side site of the direction of flow of the exhaust gas in the
exhaust struts31 has
been suppressed.
On the other hand, at the low load operation of the gas turbine engine,
particularly during the non-load operation thereof, where the power machinery
is an
electric generator and the gas turbine engine is driven at the constant
rotational speed at all
times, as shown in Fig. 6, the vector V1 of the turbine rotational direction
becomes the
same as that during the rated operation, but the vector V2 of the relative
flow of the
exhaust gas from the final stage rotor vane becomes shorter because of
reduction of the
flow velocity of the exhaust gas. For this reason, the vector V of the exhaust
gas absolute
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flow, which is the composite of the vector V1 of the turbine rotational
direction and the
vector V2 of the relative flow velocity of the exhaust gas, comes to incline
at a large angle
relative to the axial direction C and thus the exhaust gas will form a
swirling flow and then
flows within the exhaust gas passage. By the effect of the exhaust gas flow S2
which has
been so inclined, strong vortexes Vr are generated on downstream side in the
direction of
the flow of the exhaust gas in each of the exhaust struts 31.
In the event that the strong vortexes so generated in the manner described
above is, after having flown towards a downstream side along with the swirling
flow of
the exhaust gas, broken down by self-excited oscillation or exfoliation
thereof, a low
to frequency noise or a low frequency vibration, which is generally referred
to as vortex
whistle, is generated. The frequency of this vortex whistle is proportional to
the flow of
the exhaust gas or the swirling velocity and does not depend on the axial
length of the
exhaust diffuser.
[Prior Art Document]
[Patent Document]
Patent Document 1: JP Laid-open Patent Publication No. 2011-
226651
SUMMARY OF THE INVENTION
Generation of the low frequency vibrations or the low frequency noises,
which is referred to as the vortex whistle, during the low load operation of
the gas turbine
engine of the type discussed above results from the reduction in number of the
exhaust
struts 31 for the purpose of reducing the exhaust pressure loss that is aimed
in recent years.
For example, while about eight to ten exhaust struts 31 has hitherto been
installed, the
recent trend is to employ four to six exhaust struts disposed equidistantly in
the
circumferential direction as shown in Figs. 4 and 5. Reducing the number of
the exhaust
struts 31 installed as discussed above may result in that the swirling flow of
the exhaust
gas moves directly through a large space between the neighboring exhaust
struts 31 to
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thereby form a stream S2 of the exhaust gas then swirling together with
intensive vortexes.
Accordingly, if a large number of the exhaust struts 31 are used as is the
case with the
conventional art, the swirling of the exhaust gas can be prevented by the
exhaust struts 31
to a certain extent, but the pressure loss of the exhaust gas will then
increase.
In view of the foregoing, the present invention has for its object to provide
a
gas turbine device in which the low frequency vibrations or the low frequency
noises
during the low load operation can be effectively suppressed with no increase
of the
pressure loss of the exhaust gas being triggered.
In order to accomplish the foregoing object, a gas turbine device according to
the present invention includes a gas turbine engine provided with an exhaust
diffuser
forming an upstream portion of an exhaust gas passage; an exhaust strut
provided in the
exhaust diffuser; and a swirling flow blocking plate disposed on a downstream
side of the
exhaust strut in the exhaust gas passage and extending in an axial direction.
Particularly when the number of the exhaust struts installed is set to be
small,
a swirling flow of the exhaust gas will be generated during a period in which
the gas
turbine engine is under the low load operation. The swirling flow of the
exhaust gas
referred to does, after having flowed towards a downstream side through a
space delimited
by the neighboring exhaust struts that are spaced a large distance from each
other, impinge
upon the swirling flow blocking plate, which extends in an axial direction on
the
downstream side of the exhaust struts, with the swirling of the exhaust gas
consequently
blocked and is then forcibly deflected so as to flow in the axial direction.
Accordingly,
since although generation of vortexes of the exhaust gas, which takes place in
a
downstream side site of the exhaust strut, cannot be suppressed, the swirling
flow of the
exhaust gas effective to flow those vortexes towards the downstream side can
be
suppressed, instability (fluctuation of vortex centers) resulting from a
swirling velocity
distribution disappears and the occurrence of self-induced oscillation and
exfoliation of the
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vortexes are suppressed, wherefore generation of the low frequency vibration
or the low
frequency noise, which is an abnormal noise generally referred to as the
vortex whistle,
can be effectively suppressed. Also, since the swirling flow blocking plate is
disposed on
a downstream side of the exhaust strut at which the flow velocity of the
exhaust gas is
lowered, and pressure loss of the exhaust gas can be further reduced from this
standpoint.
In one embodiment of the present invention, a plurality of the exhaust struts
spaced from each other in a circumferential direction may be employed, and the
swirling
flow blocking plate may be disposed at a position circumferentially
intermediate between
the neighboring exhaust struts. According to this structure, the swirling flow
of the
exhaust gas having passed through the space delimited between the neighboring
exhaust
struts can be further effectively deflected by the swirling flow blocking
plate with the swirl
thereof being consequently suppressed.
In one embodiment of the present invention, the swirling flow blocking plate
may have an axial length that is greater than an axial length of the exhaust
strut.
Specifically, the axial length of the swirling flow blocking plate may be
within the range of
2 to 4 times the axial length of the exhaust strut. According to this
structure, not only can
the pressure loss of the exhaust gas be reduced with the exhaust strut reduced
in length, but
also the swirling of the exhaust gas can be effectively suppressed in the
presence of the
long swirling flow blocking plate.
In one embodiment of the present invention, the four to six exhaust struts,
which are spaced from each other in the circumferential direction, may be
employed.
When the number of the exhaust struts is so reduced, the resistance in the
exhaust gas
passage is reduced to allow the exhaust pressure loss to be reduced.
In one embodiment of the present invention, the exhaust diffuser may include
an inner casing and an outer casing disposed coaxially with each other, and
the inner
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casing and the outer casing may be connected with each other through the
exhaust struts.
By so doing, the diffuser which is robust in structure can be obtained.
In one embodiment of the present invention, the gas turbine device of the
present invention may also include an exhaust duct fluidly connected on a
downstream
side of the exhaust diffuser and comprising inner and outer tubes which are
disposed
coaxially with each other. In this case, the swirling flow blocking plate is
fitted to the
inner tube with a gap existing between the outer tube and the swirling flow
blocking plate
at least at a cold time. According to this structural feature, since the
swirling flow
blocking plate is supported by the inner tube in the cantilevered fashion, the
thermal strain
of the swirling flow blocking plate brought about by thermal expansion of the
inner tube,
which would occur when the swirling flow blocking plate is supported with its
opposite
ends connected respectively with the inner tube and the outer tube so as to
bridge
therebetween, does not occur.
Where the swirling flow blocking plate is fixed to the inner tube, the
swirling
flow blocking plate may include a set of two plate members overlapped with
each other
and may be fixed to the inner tube with respective mounting portions at inner
diametric
ends of the plate members being curved in respective directions opposite to
each other.
According to this structure, since the swirling flow blocking plate can be
employed in the
form of thin plates that are prepared by a sheet metal processing, the
pressure loss of the
exhaust gas can be advantageously reduced as compared with the exhaust strut.
Also,
not only does the swirling flow blocking plate have a sufficient strength
despite of the fact
that it has a simplified structure in which two plate members are overlapped
with each
other, but also the undesirable increase of the weight and cost can be
suppressed. Yet, in
the event of the occurrence of the thermal strain in the swirling flow
blocking plate, the
mounting portion of the curved shape described hereinbefore undergoes a
thermal strain to
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thereby absorb the above described thermal strain, thereby suppressing the
undesirable
increase of the radial dimension of the swirling flow blocking plate.
Any combination of at least two constructions, disclosed in the appended
claims and/or the specification and/or the accompanying drawings should be
construed as
included within the scope of the present invention. In particular, any
combination of two
or more of the appended claims should be equally construed as included within
the scope
of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In any event, the present invention will become more clearly understood from
the following description of embodiments thereof, when taken in conjunction
with the
accompanying drawings. However, the embodiments and the drawings are given
only
for the purpose of illustration and explanation, and are not to be taken as
limiting the scope
of the present invention in any way whatsoever, which scope is to be
determined by the
appended claims. In the accompanying drawings, like reference numerals are
used to
denote like parts throughout the several views, and:
Fig. 1 is a schematic side view showing the entire construction of a gas
turbine device according to one embodiment of the present invention;
Fig. 2 is a longitudinal sectional view showing a gas turbine engine and an
exhaust diffuser both employed in the gas turbine device;
Fig. 3 is a rear view showing the exhaust diffuser;
Fig. 4 is a perspective view showing the flow of exhaust gas in the
embodiment;
Fig. 5 is a perspective view showing the flow of the exhaust gas during the
rated operation of the gas turbine engine; and
Fig. 6 is a perspective view showing the flow of the exhaust gas during the
low load operation of the gas turbine engine.
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DESCRIPTION OF EMBODIMENTS
Hereinafter, an embodiment of the present invention will be described in
detail with reference to the accompanying drawings. In particular as shown in
Fig. 1, a
reduction gear unit 12 having a large weight is fixedly placed on a foundation
bed 13, and
a gas turbine engine GT is supported by the reduction gear unit 12 in a
cantilevered
manner through a plurality of, for example, four in the illustrated
embodiment, stays 14.
The reduction gear unit 12 has a connecting shaft on an input side drivingly
connected
with a rotary shaft 10 of the gas turbine engine GT and also has a connecting
shaft 17 on
an output side connected with a drive shaft 18 of an electric generator 11,
which forms a
load of the gas turbine engine GT, through a coupling 19. An exhaust gas EG
discharged
substantially horizontally from the gas turbine engine GT is guided into an
exhaust
chamber 22 through an exhaust diffuser 20 and an exhaust duct 21, subsequently
deflected
in a substantially vertical direction so as to flow into a silencer 24
positioned thereabove
and then finally discharged to the outside after having been silenced by the
silencer 24.
The exhaust chamber 22 has a guide plate 23 for deflecting the exhaust gas EG
so as to
flow upwardly.
Referring now to Fig. 2, the gas turbine engine GT includes a two-staged
centrifugal compressor 1 for compressing an air A sucked thereinto through an
air inflow
port IN, a combustor 4 for combusting an air/fuel mixture formed by supplying
fuel into
the air A which has been compressed, and a turbine 7 driven by a combustion
gas G The
compressor 1 and the turbine 7 are accommodated within a housing 15, and the
combustor
4 is mounted to the housing 15 so as to protrude upwardly. A combustion gas G,
generated within a combustion chamber 5 defined in the combustor 4, is, after
having been
guided into the turbine 7 through a scroll 9, used to rotate the turbine 7 to
eventually drive
the two-staged centrifugal compressor 1, which is drivingly connected with the
turbine 7
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through the rotary shaft 10, and the electric generator 11 through the
reduction gear unit 12
best shown in Fig. 1.
The exhaust gas EG discharged from the final stage rotor vane 27 of the
turbine 7 is guided to an exhaust gas passage 30 of an annular shape defined
between an
inner casing 20a and an outer casing 20b, which form respective parts of the
exhaust
diffuser 20. The outer casing 20b is fixed to the housing 15. The inner casing
20a is
supported by the outer casing 20b through radially extending four exhaust
struts 31 that
are spaced circumferentially equidistantly, say, 90 from each other. In this
way, the inner
casing 20a of a tubular shape and the outer casing 20b of a tubular shape,
which are
disposed coaxially relative to each other, are connected together through the
exhaust struts
31 to thereby form the exhaust diffuser 20 of a robust structure.
The exhaust duct 21 is fluidly connected with a downstream end of the
exhaust diffuser 20. The exhaust duct 21 is provided with a swirling flow
blocking plate
32, which is fixed to the exhaust duct 21 by means of a fastening member 33
such as, for
example, bolts and nuts, and is so formed as to extend in a direction along
the axial
direction C to represent a rectangular thin plate. The exhaust duct 21
includes an inner
tube 21a and an outer tube 21b which cooperatively define the exhaust gas
passage 30
therebetween. Thus, the exhaust diffuser 20 forms an upstream portion of the
exhaust
gas passage 30 of an annular shape and the exhaust duct 21 forms a downstream
portion
of the exhaust gas passage 30 of the annular shape. The exhaust chamber 22 and
the
silencer 24, both best shown in Fig. 1, cooperate with each other to define a
substantially
rectangular sectioned exhaust gas passage 30A, which is in communication with
a
downstream region of the exhaust gas passage 30.
An upstream region 21ba of the outer tube 21b, as shown in Fig. 2, which
confronts the swirling flow blocking plate 32, is configured to move relative
to a
downstream region 21bb thereof in the axial direction C by means of a thermal
expansion
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absorbing mechanism 34. The thermal expansion absorbing mechanism 34 includes
a
bellows-shaped expandable tubular body 37 which is expandable in a direction
parallel to
the axial direction, and an adjustment bolt 38 for limiting the stroke of
expansion of the
upstream region 2 lba. With the use of the thermal expansion absorbing
mechanism 34,
the thermal expansion of the outer tube 21b by the effect of the exhaust gas
EG can be
absorbed.
Fig. 3 is a rear view of the exhaust diffuser 20 as viewed from the right side
of
Fig. 2 that corresponds to the rear of the diffuser 20. The swirling flow
blocking plate 32
is disposed at a position circumferentially intermediate between the
neighboring two struts
of the four exhaust struts 31, which are spaced 900 from each other in the
circumferential
direction, so as to extend radially, and is fixed to the inner tube 2Ia by
means of the
fastening member 33. Each swirling preventive plate 32 includes a set of two
plate
members 39 and 40 overlapped with each other to represent a symmetrical shape
with
respect to a mid center plane passing through the longitudinal axis of the
exhaust gas
passage 30. In other words, the swirling flow blocking plate 32 is so
structured that
respective blocking plate portions 30a and 40a of the plate members 39 and 40
are
overlapped in tightly contact with each other while respective mounting
portions 39b and
40b of respective inner diametric ends of the plate members 39 and 40 are so
curved as to
extend in respective directions opposite to each other, in which the mounting
portions 39b
and 40b are in turn fixed to the inner tube 21a by means of the fastening
member 33.
The fastening member 33 is disposed at two locations on the swirling flow
blocking plate 32 that are spaced from each other in the axial direction C. A
small gap is
defined between a radially outer end of the swirling flow blocking plate 32
and an inner
surface of the outer tube 21b at least under a cold state, which occurs during
the stop of the
engine. Accordingly, the swirling flow blocking plate 32 is supported in a
cantilevered
fashion by the inner tube 21a.
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Since in the gas turbine device of the structure hereinbefore described the
number of the exhaust struts 31 installed is set to four, which is a small
number, the
exhaust gas pressure loss brought about by a passage resistance can be
suppressed, but on
the other hand, as shown in and described with particular reference to Fig. 4,
the swirling
flow TS of the exhaust gas EG occurs during the low load operation of the gas
turbine
engine GT. The swirling flow TS impinges upon the swirling flow blocking plate
32 at
the downstream side of the exhaust strut 31 with the swirling blocked
consequently, and is
therefore forcibly deflected to form a flow S directed along the axial
direction C.
Accordingly, since although generation of vortexes of the exhaust gas GT at
the
downstream side of the exhaust strut 31 cannot be suppressed completely, the
swirling
flow TS of the exhaust gas EG which tends to cause the vortexes to flow
towards the
downstream side can be suppressed. As a result thereof, instability
(fluctuation of vortex
centers) resulting from a swirling velocity distribution disappears and the
occurrence of
self-induced oscillation of the vortexes is suppressed, whereby generation of
the low
frequency vibration or the low frequency noise, which is an abnormal noise
generally
referred to as the vortex whistle, can be suppressed effectively.
While the vortex whistle referred to previously may often records the peak
value at a few tens Hz, the result of actual measurement has affirmed that the
use of the
swirling flow blocking plate 32 reduces the peak value by a value higher than
10 dB.
Accordingly, it has been found that the mere use of the swirling flow blocking
plate 32 is
effective to prevent the generation of the low frequency vibration or the low
frequency
noise with a simplified construction.
It is, however, to be noted that in order to secure the effect of generation
suppression of such low frequency noise or low frequency vibration, both
discussed above,
the length L2 of the swirling flow blocking plate 32 in the axial direction C
may be greater
than the length Li of the exhaust strut 31 in the axial direction. In
particular, the length
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L2 of the swirling flow blocking plate 32 in the axial direction C may be more
preferably
set to a value within the range of two to four times the length Li of the
exhaust strut 31 in
the axial direction C. If it is smaller than the two times, the deflecting
effect achieved by
the swirling flow blocking plate 32 will be insufficient, and if it exceeds
the four times, the
frictional loss of the exhaust gas EG brought about by the swirling flow
blocking plate 32
will become excessive. The exhaust strut 31 is a reinforcing member for
connecting the
inner casing 20a and the outer casing 20b together and its radial length
(height) H1 is
within the range of about 1.0 to 2.0 times the axial length Li.
Also, while the exhaust strut 31 is generally made of casting, the swirling
flow blocking plate 32 is formed by means of a sheet metal processing and,
therefore, not
only can the pressure loss of the exhaust gas EG, when the thickness thereof
is reduced, be
markedly reduced as compared with the exhaust strut 31, but the undesirable
increase of
the weight and cost can also be suppressed. Also, since the swirling flow
blocking plate
32 is disposed on the downstream side of the exhaust strut 32 at which the
flow velocity of
the exhaust gas EG is lowered, the pressure loss of the exhaust gas EG can
further be
reduced from this standpoint.
In addition, since the swirling flow blocking plate 32 is of the structure in
which the set of the two plate members 39 and 40 best shown in Fig. 3 are
overlapped
with each other and are then fixed, not only does the swirling flow blocking
plate 32 have
a sufficient strength despite of the fact that they are prepared from thin
plates, but in the
event of the occurrence of thermal strain in the swirling flow blocking plate
32 under the
influence of the high temperature of the exhaust gas EG, the curved mounting
portions 39b
and 40b of the plate members 39 and 40 are thermally deformed to absorb the
previously
described thermal strain and, therefore, the radial dimension of the swirling
flow blocking
plate 32 can be maintained substantially constant. Yet, since the swirling
flow blocking
plate 32 is supported by the inner tube 21a in the cantilevered fashion, the
thermal strain
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brought about by thermal expansion of each of the inner tube 21a and the outer
tube 21b,
which would occur when the swirling flow blocking plate is supported with its
opposite
ends connected respectively with the inner tube 21a and the outer tube 21b so
as to bridge
therebetween, does not occur.
In describing the foregoing embodiment, the swirling flow blocking plate 32
has been shown and described as supported by the inner tube 21a in the
cantilevered
fashion, but the present invention is not necessarily limited thereto and
effects similar to
those afforded by the previously described embodiment can be appreciated even
when the
swirling flow blocking plate 32 is supported by the outer tube 21b in the
cantilevered
fashion.
The present invention may be implemented based on the aforementioned
embodiments with various addition, modification and/or omission made thereupon
as long
as they are encompassed within the concept of the present invention.
Although the present invention has been fully described in connection with
the embodiments thereof with reference to the accompanying drawings which are
used
only for the purpose of illustration, those skilled in the art will readily
conceive numerous
changes and modifications within the framework of obviousness upon the reading
of the
specification herein presented of the present invention. Accordingly, such
changes and
modifications are, unless they depart from the scope of the present invention
as delivered
from the claims annexed hereto, to be construed as included therein.
[Reference Numerals]
20 = = = = Exhaust diffuser
20a = = = Inner casing
20b = = = = Outer casing
30 = = = = Exhaust gas passage
31 = = = = Exhaust strut
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32 = = = = Swirling flow blocking plate
GT = = = = Gas turbine engine
C = = = = Axial direction
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