Note: Descriptions are shown in the official language in which they were submitted.
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DESCRIPTION
FILM COOLING STRUCTURE
BACKGROUND OF THE INVENTION
Technical Field of the Invention
[0001]
The present invention relates to a film cooling
structure that is suitable for film cooling of the surface
of a component (turbine blade or the like) of a gas turbine
engine.
Description of the Related Art
[0002]
The efficiency of a gas turbine engine is increased
as combustion gas temperature rises. However, the
combustion gas heats a structural wall of a component (a
combustor liner, a turbine blade, a turbine shroud, or the
like), that is disposed on a flow passage for combustion
gas, to high temperature. Accordingly, in order to
efficiently cool the structural wall of such the component,
there is employed a film cooling structure. In the cooling
structure, a cooling passage is formed therein, convection
cooling is performed by making cooling air flow through the
cooling passage, and film cooling is performed by making
the cooling air be ejected from film cooling holes onto a
surface, which is exposed to high-temperature combustion
gas, in the shape of a film (for example, see the following
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Patent Documents 1 to 5).
[0003]
Figs. lA to 1C show an example of a film cooling
structure 30 of the related art. Fig. 1B is a cross-
sectional view taken along a line 1B-lB of Fig. 1A, and Fig.
lC is a cross-sectional view taken along a line 1C-1C of
Fig. 1B.
In Figs. 1B and 1C, a structural wall 31 has an
outer surface 32 that is exposed to combustion gas 1, and
an inner surface 33 that is positioned opposite to the
outer surface 32. Film cooling holes 34 are formed at the
structural wall 31 so as to be inclined with respect to the
outer surface 32 by a predetermined angle, and introduce
cooling air 5 from the inner surface 33 toward the outer
surface 32 in order to perform the film cooling of the
outer surface 32. The film cooling hole 34 includes an
introducing portion 34a that extends to a middle position
in the structural wall 31 from the inner surface 33 toward
the outer surface 32, and an enlarged portion 34b
(diffuser) of which the cross-sectional area is gradually
increased toward the outer surface 32 from an end of the
introducing portion 34a facing the outer surface 32 and
which is opened at the outer surface 32. As shown in Fig.
1B, a wall surface 35 of the enlarged portion 34b facing an
upstream side in the flow direction of the combustion gas 1
is formed in a linear shape. Further, as shown in Fig. 1C,
both wall surfaces 36 and 36 of the enlarged portion 34b in
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a direction perpendicular to the flow direction of the
combustion gas 1 are formed in a linear shape.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2006-9785
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2005-90511
[Patent Document 3]
Japanese Patent Application Laid-Open No. 2003-41902
[Patent Document 4]
Japanese Patent Application Laid-Open No. 2001-
173405
[Patent Document 5]
Japanese Patent Application Laid-Open No. 10-89005
SUMMARY OF THE INVENTION
[0005]
As for film cooling, it is preferable to spread the
cooling air 5 on the outer surface 32, which is to be
cooled, as thinly and broadly as possible, and to attach
the cooling air to the outer surface 32 as close as
possible. Accordingly, in order to spread the cooling air
5 thinly and broadly on the outer surface 32, it is
effective to increase an enlarged angle of the enlarged
portion 34b as much as possible.
However, the cross-sectional area of the hole is
linearly increased at the enlarged portion 34b of the
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above-mentioned film cooling structure 30 in the related
art. Accordingly, if an enlarged angle of the enlarged
portion 34b is excessively large, the separation of the
cooling air 5 occurs in the hole. For this reason, there
have been problems that the cooling air 5 is not
effectively diffused and it is difficult to improve average
film cooling efficiency.
[0006]
The invention has been made in consideration of the
above-mentioned problems, and an object of the invention is
to provide a film cooling structure that can increase an
enlarged angle of an enlarged portion and improve average
film cooling efficiency.
[0007]
In order to solve the above-mentioned problems, the
film cooling structure according to the invention includes
the following means.
According to the invention, a film cooling structure
includes a structural wall that has an outer surface
exposed to combustion gas and an inner surface positioned
opposite to the outer surface, and film cooling holes are
formed at the structural wall and introduce cooling air
from the inner surface toward the outer surface in order to
perform film cooling of the outer surface. The film
cooling hole includes an introducing portion that extends
to a middle position in the structural wall from the inner
surface toward the outer surface, an enlarged portion of
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which the cross-sectional area is gradually increased
toward the outer surface from an end of an outer surface
side of the introducing portion and which is opened at the
outer surface, and a partition portion that partitions the
inside of the enlarged portion into a plurality of spaces
in a width direction of the hole perpendicular to a flow
direction of the combustion gas.
[0008]
Since the film cooling hole includes the partition
portion that has been formed as described above, an
effective area expansion ratio may be reduced. Accordingly,
even though the enlarged angle of the enlarged portion in a
transverse direction is large, the separation of the
cooling air is suppressed. Therefore, since it is possible
to effectively diffuse cooling air as compared to the
related art, the enlarged angle of the enlarged portion in
the transverse direction can be made large. As a result,
it is possible to spread the cooling air thinly and broadly
on the outer surface of the structural wall, and to improve
average film cooling efficiency. Meanwhile, the definition
of the average film cooling efficiency will be described
below.
Further, since it is possible to spread the cooling
air thinly and broadly as compared to the related art, the
number of film cooling holes formed at the structural wall
may be reduced. Accordingly, the number of processes for
manufacturing the film cooling structure can be reduced.
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Furthermore, as the number of film cooling holes is reduced,
the amount of cooling air extracted from the compressor of
the gas turbine engine can be decreased. Therefore, engine
efficiency can be improved.
[0009]
In addition, in the film cooling structure, the
partition portion is formed at a middle position of the
inside of the film cooling hole in the width direction of
the hole perpendicular to the flow direction of the
combustion gas, protrudes from one of the wall surfaces
facing upstream and downstream sides in the flow direction
of the combustion gas toward the other thereof, and extends
over the entire inside of the hole from the inner surface
of the structural wall toward the outer surface.
[0010]
As described above, the partition portion does not
completely partition the film cooling hole in the
transverse direction, and extends over the entire
structural wall in a thickness direction. Therefore, it is
easy to form the film cooling hole.
[0011]
From the above description, according to the
invention, it is possible to obtain advantages of
increasing an enlarged angle of an enlarged portion and
improving average film cooling efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
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[0012]
Fig. 1A is a plan view of a film cooling structure
in the related art.
Fig. 1B is a cross-sectional view taken along a line
1B-lB of Fig. 1A.
Fig. 1C is a cross-sectional view taken along a line
1C-iC of Fig. 1B.
Fig. 2 is a perspective view of a turbine rotating
blade to which a film cooling structure according to the
invention is applied.
Fig. 3A is a plan view of a film cooling structure
according to an embodiment of the invention.
Fig. 3B is a cross-sectional view taken along a line
3B-3B of Fig. 3A.
Fig. 3C is a cross-sectional view taken along a line
3C-3C of Fig. 3B.
Fig. 4 is a perspective view showing the shape of a
film cooling hole of the film cooling structure according
to the embodiment of the invention.
Fig. 5 is a view illustrating the physical action of
a partition portion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013]
A preferred embodiment of the invention will be
described in detail below with reference to accompanying
drawings. Meanwhile, the same reference numerals are given
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to common portions in each drawing, and redundant
description thereof will be omitted.
[0014]
A film cooling structure according to the invention
is applied to a component that is disposed on a flow
passage for combustion gas in a gas turbine engine.
Examples of this component include a combustor liner, a
turbine nozzle vane, a turbine nozzle band, a turbine
rotating blade, a turbine stator blade, a turbine shroud,
and a turbine outlet liner.
[0015]
Fig. 2 is a perspective view of a turbine rotating
blade 2 to which the film cooling structure 10 according to
the invention is applied. The turbine rotating blade 2
includes a blade portion 3 that serves as a structural wall
having an outer surface 12 exposed to combustion gas 1, and
a base portion 4 that is used to mount the blade portion 3
on a rotor of an engine. A cooling circuit (not shown)
through which cooling air flows is formed in the blade
portion 3. This cooling air is extracted from a compressor
of a gas turbine engine, and flows into the cooling circuit
through a flow passage (not shown) that is formed in the
base portion 4. The cooling air, which has flown into the
cooling circuit, is ejected from a plurality of film
cooling holes 14 that is formed on an outer surface 12 of
the blade portion 3, and performs film cooling on the outer
surface 12 of the blade portion 3. The film cooling
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structure 10 according to an embodiment of the invention
will be described below.
[0016]
Figs. 3A to 3C show the film cooling structure 10
according to the invention. Fig. 3A is a plan view of the
film cooling structure 10. Fig. 3B is a cross-sectional
view taken along a line 3B-3B of Fig. 3A. Fig. 3C is a
cross-sectional view taken along a line 3C-3C of Fig. 3B.
Further, Fig. 4 is a perspective view showing the shape of
the film cooling hole 14 of the film cooling structure 10
according to the embodiment of the invention.
[0017]
As described above, the film cooling structure 10 is
applied to a component such as a turbine rotating blade
that is disposed on a flow passage for combustion gas 1 in
a gas turbine engine. As shown in Figs. 3B and 3C, the
film cooling structure 10 includes a structural wall 11
that has the outer surface 12 exposed to the combustion gas
1 and an inner surface 13 positioned opposite to the outer
surface 12. If the component of the gas turbine is, for
example, a turbine rotating blade, a wall forming the blade
portion of the turbine rotating blade is the structural
wall 11. Cooling air 5 flows into the inner surface 13 of
the structural wall 11.
[0018]
The film cooling hole 14, which introduces the
cooling air 5 from the inner surface 13 to the outer
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surface 12 in order to perform the film cooling of the
outer surface 12, is formed in the structural wall 11. As
shown in Fig. 3B, an axis of the film cooling hole 14 is
inclined with respect to the outer surface 12 of the
structural wall 11 by a predetermined angle so that the
cooling air 5 is blown from the film cooling hole 14 in a
direction corresponding to the flow of the combustion gas 1.
[0019]
The film cooling hole 14 includes an introducing
portion 14a that extends to a middle position in the
structural wall 11 from the inner surface 13 toward the
outer surface 12, and an enlarged portion 14b of which the
cross-sectional area is gradually increased toward the
outer surface 12 from an end of an outer surface side of
the introducing portion 14a and which is opened at the
outer surface 12.
[0020]
The film cooling hole 14 further includes a
partition portion 16 that partitions the inside of the
enlarged portion 14b into a plurality of spaces in a width
direction of the hole perpendicular to the flow direction
of the combustion gas 1. In this case, the "width
direction of the hole perpendicular to the flow direction
of the combustion gas 1" is a direction perpendicular to
the plane of in Fig. 3B, and is a horizontal direction in
Fig. 3C.
In the embodiment shown in Figs. 3A to 3C and 4, the
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partition portion 16 is formed at a middle position of the
inside of the film cooling hole 14 in the width direction
of the hole perpendicular to the flow direction of the
combustion gas 1, protrudes from the wall surface facing an
upstream side in the flow direction of the combustion gas 1
toward the upstream side in the flow direction of the
combustion gas 1, and extends over the entire inside of the
hole from the inner surface 13 of the structural wall 11
toward the outer surface 12. A gap is formed between the
partition portion 16 and a wall surface facing a downstream
side in the flow direction of the combustion gas 1.
[0021]
One partition portion 16 has been formed in the
embodiment shown in Figs. 3A to 3C and 4, but a plurality
of partition portions may be formed at intervals in the
width direction of the hole.
Further, in the embodiment shown in Figs. 3A to 3C
and 4, the partition portion 16 has protruded from the wall
surface facing the upstream side in the flow direction of
the combustion gas 1 toward the upstream side in the flow
direction of the combustion gas 1. However, in contrast to
this, the partition portion may protrude from the wall
surface facing a downstream side in the flow direction of
the combustion gas 1 toward the downstream side in the flow
direction of the combustion gas 1. In this case, a gap is
formed between the partition portion 16 and a wall surface
facing the upstream side in the flow direction of the
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combustion gas 1.
[0022]
According to this embodiment, it is possible to
obtain the following effects.
Fig. 5 is a graph where a length ratio is
represented on a horizontal axis in logarithmic scale, a
value obtained by subtracting 1 from an inlet-outlet area
ratio is represented on a vertical axis in logarithmic
scale, and a pressure recovery rate (reduction rate) Cp is
used as a parameter, as for a diffuser. In this case, if
inlet-outlet area ratios are equal to each other, an
enlarged angle is smaller when a length ratio is larger.
Further, when a pressure recovery rate is high, separation
hardly does occur. A straight line, which is represented
by a pressure recovery rate Cp** of the drawing, is
obtained by connecting points where the maximum pressure
recovery rate is obtained when an inlet-outlet area ratio
of a diffuser is constant. Meanwhile, a straight line of
Cp* is a line where the maximum pressure recovery rate is
obtained when a length ratio is constant. Accordingly, it
is found out that if an inlet-outlet area ratio is constant,
when an enlarged angle is small, a pressure recovery rate
is high and separation hardly does occur. If a passage of
the diffuser is divided into two or three equal parts, an
enlarged angle of each of the small passages becomes a half
or a third and becomes smaller than an enlarged angle
determined by Cp*. For this reason, a high pressure
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recovery rate is obtained over the entire passage.
[0023]
Accordingly, according to this embodiment, if the
film cooling hole 14 includes the partition portion 16
formed as described above, an effective area expansion
ratio is suppressed. Therefore, even though an enlarged
angle of the enlarged portion 14b is increased in a
transverse direction, the separation of the cooling air 5
is suppressed. For this reason, since it is possible to
effectively diffuse the cooling air 5 as compared to the
related art, the enlarged angle of the enlarged portion 14b
in the transverse direction can be increased. Accordingly,
it is possible to spread the cooling air 5 thinly and
broadly on the outer surface 12 of the structural wall 11,
and to improve average film cooling efficiency. In this
case, the average film cooling efficiency is given by (fuel
gas temperature-surface temperature of structural
wall)/(combustion gas temperature-cooling air temperature).
[0024]
Further, since it is possible to spread the cooling
air 5 thinly and broadly on the outer surface 12 of the
structural wall 11 as compared to the related art, the
number of film cooling holes 14 formed at the structural
wall 11 can be reduced. For this reason, the number of
processes for manufacturing the film cooling structure 10
can be reduced. Further, as the number of film cooling
holes 14 is reduced, the amount of cooling air extracted
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from the compressor of the gas turbine engine can be
decreased. Therefore, engine efficiency can be improved.
[0025]
When the film cooling holes 14 are formed using a
method such as electric discharge machining, an electric
discharge machining electrode needs to be inserted into
each of the divided holes in order to form holes if the
partition portion 16 completely partitions the film cooling
hole 14 in a transverse direction. Further, if the
partition portion 16 is formed in a shape that is broken at
a position in a thickness direction of the structural wall
11, a plurality of processes is required to form one film
cooling hole 14 (for example, electric discharge machining
electrodes need to be inserted from the outer surface 12
and the inner surface 13 in order to form the hole.)
Furthermore, even though other machining means is used,
forming processes are complicated likewise.
In contrast, in this embodiment, the partition
portion 16 does not completely partition the film cooling
hole 14 in the transverse direction, and extends over the
entire structural wall 11 in the thickness direction.
Accordingly, if an electric discharge machining electrode,
which is formed to form the film cooling hole 14 shown in
Figs. 3A to 3C and 4, is inserted from the outer surface 12,
it is possible to form the film cooling hole 14 by a single
process. Therefore, it is easy to form the film cooling
hole 14.
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[0026]
Meanwhile, the embodiment of the invention has been
described above. However, the above-mentioned embodiment
of the invention is only illustrative, and the scope of the
invention is not limited to the embodiment of the invention.
For example, the invention has been applied to the turbine
rotating blade 2 in the above-mentioned embodiment, but may
be applied to other components, such as a combustor liner,
a turbine nozzle vane, a turbine nozzle band, a stationary
turbine blade, a turbine shroud, and a turbine outlet liner,
which are disposed on a flow passage for combustion gas in
a gas turbine engine.
The scope of the invention is defined by the
description of claims, and includes all modifications that
are in a meaning and a scope equivalent to the description
of claims.
