U.S. patent number 3,807,892 [Application Number 05/324,779] was granted by the patent office on 1974-04-30 for cooled guide blade for a gas turbine.
This patent grant is currently assigned to Brown-Boveri Sulzer Turbomachinery Limited. Invention is credited to Oskar Frei, Oskar Iten.
United States Patent |
3,807,892 |
Frei , et al. |
April 30, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
COOLED GUIDE BLADE FOR A GAS TURBINE
Abstract
The body of the blade is provided with a first coolant flow path
at the front of the blade and a second tortuous coolant flow path
behind the first flow path. Both flow paths terminate at the
trailing edge of the blade. The first path is subjected to a low
pressure drop and with a narrow cross-section allows the collant to
flow through at high velocity to obtain a rapid heat transfer. The
second path is also subjected to a low pressure drop, but with a
larger cross-section in the middle part of the blade body and
restrictors at the trailing edge, also allows discharge at high
velocity.
Inventors: |
Frei; Oskar (Winterthur,
CH), Iten; Oskar (Bulach, CH) |
Assignee: |
Brown-Boveri Sulzer Turbomachinery
Limited (Zurich, CH)
|
Family
ID: |
4193097 |
Appl.
No.: |
05/324,779 |
Filed: |
January 18, 1973 |
Current U.S.
Class: |
415/116; 415/178;
416/97R; 416/96R |
Current CPC
Class: |
F01D
5/187 (20130101); F01D 9/041 (20130101); F05D
2260/22141 (20130101); F05D 2260/221 (20130101) |
Current International
Class: |
F01D
5/18 (20060101); F01D 9/04 (20060101); F04d
031/00 (); F01d 005/08 (); F04d 029/58 () |
Field of
Search: |
;416/97,95,96
;415/115,116,117 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Croyle; Carlton R.
Assistant Examiner: Casaregola; Louis J.
Attorney, Agent or Firm: Kenyon & Kenyon Reilly Carr
& Chapin
Claims
What is claimed is:
1. A cooled guide blade for a gas turbine comprising
a blade body having a blade front and a trailing edge;
a first pressure chamber in said body for receiving a supply of
coolant;
means defining a first flow path in said body immediately
downstream of and parallel to said blade front, said flow path
being in communication with said pressure chamber and including at
least two parallel portions to reverse a flow of coolant
therethrough at least once;
a second pressure chamber in said body in communication with said
flow path between said parallel portions on an opposite side of
said blade body from said first pressure chamber;
a first exit in said trailing edge communicating with said flow
path for passage of a first coolant flow therethrough, said exit
extending along a part of the length of said trailing edge;
means defining a second flow path independent of said first flow
path in said body extending from said first chamber, said second
flow path having at least two parallel portions to reverse a second
flow of coolant therethrough at least once; and
a second exit at said trailing edge communicating with said second
flow path for passage of the second coolant flow therethrough.
2. A cooled guide blade as set forth in claim 1 which further
comprises an outer cover plate over said first pressure chamber and
an inner cover plate over said second pressure chamber.
3. A cooled guide blade as set forth in claim 1 wherein said second
flow path is parallel to said first flow path and wherein said
second flow path includes at least three parallel portions and a
pair of reversal portions interconnecting said parallel portions in
series to deflect the second flow of coolant through consecutive
parallel portions by 180.degree..
4. A cooled guide blade as set forth in claim 3 wherein the last of
said parallel portions of said second flow path includes means for
creating a pressure loss in the flow of coolant passing
therethrough.
5. A cooled guide blade as set forth in claim 1 wherein said means
defining said second flow path includes boundary walls and fins on
at least a portion of said walls projecting into said second flow
path.
6. A cooled guide blade as set forth in claim 1 wherein said exits
each have a constant cross-sectional exit opening and wherein said
exits are of a length relative to each other in a ratio
proportional to the amount of coolant flowing through each
exit.
7. A cooled guide blade as set forth in claim 1 wherein said body
further includes a first covering adjacent said blade front
disposed to define a portion of said first pressure chamber and a
second covering adjacent said blade front disposed to define a
portion of said second pressure chamber.
8. A cooled guide blade as set forth in claim 7 wherein said body
and said coverings form an integral one-piece precision casting and
which further comprises a separating plate disposed in said body in
seal-tight manner between said flow paths, an outer cover plate
disposed in said body in seal-tight manner over said first chamber
and an inner cover plate disposed in said body in seal-tight manner
over said second chamber and opposite to said separating plate
relative to said second chamber.
Description
This invention relates to a cooled guide blade for a gas
turbine.
Generally, in order to achieve cooling of the gas blades, both
guide blades and rotor blades, in an operating turbine, two
contradictory conditions must be basically satisfied. First, good
cooling requires high coefficients of heat transmission which, in
turn, involve high flow velocities and relatively high pressure
losses. Second, the amount of cooling air required by each blade
should be as small as possible because the cooling air branched
off, for example, from a compressor represents a loss in a certain
sense and results in a deterioration of the efficiency of the
entire process. Moreover, in practice it frequently occurs that the
pressure gradient available between the cooling air entry into the
blade and the cooling air exit from the blade is relatively low.
Thus, the required velocities cannot be obtained or, if obtained
because a high consumption of cooling air can be tolerated, is done
only with difficulty.
In order to overcome these basic problems, it has been known to
provide constructions in which the cooling air is passed once
through the blade through a plurality of ducts radially of the
machine from the interior to the exterior. The required velocities
can be easily obtained with this system but require relatively
large quantities of air. Moreover, the cooling capacity of the air
in this system is only very incompletely utilized.
In other systems, one or more streams of cooling air are blown into
the blade, generally through the blade root. The flows have then
been branched and/or are repeatedly reversed before emerging from
the blade through air exits which may be disposed in the blade
front or tip and/or the blade root or in the trailing edge. If the
flow ducts in these constructions are relatively narrow to achieve
the necessary velocities, this will necessarily result in high
pressure losses. This applies particularly to constructions in
which the cooling air in the zone of the blade front or in the
middle of the blade is fed into the blade root and is guided to the
trailing edge after repeated reversals. In constructions in which
the cooling air streams in the blade are branched through a
perforated bulkhead, any defined distribution of branch flows can
hardly be achieved, for example, because of uneven bulkhead
perforations. Thus, in some circumstances, either specific parts
receive only insufficient cooling or unnecessarily large quantities
of cooling air are required.
Accordingly, it is an object of the invention to achieve optimum
cooling of guide blades with a relatively low consumption of
cooling air and a relatively low available pressure gradient.
It is another object of the invention to obtain high coefficients
of heat transfer and intensive cooling actions in a guide blade of
a gas turbine.
It is another object of the invention to provide a simple technique
for cooling gas turbine blades.
It is another object of the invention to provide a guide blade for
a gas turbine of relatively precise construction which can be
easily and effectively cooled.
Briefly, the invention provides a guide blade for a gas turbine
comprising a blade body having a blade front and a trailing edge
with two separate flow paths in which a coolant flow is reversed at
least once for cooling different portions of the blade. To this
end, a first means defines a first flow path in the body
immediately downstream of and parallel to the blade front. This
first flow path includes at least two parallel portions to reverse
the flow of coolant at least once and terminates in a first exit in
or near to the trailing edge of the blade. In addition, a second
means defines a second flow path in the body which includes at
least two parallel portions to reverse a second flow of coolant at
least once and also terminates in a second exit in or near to the
trailing edge of the blade. Both flow paths emanate from a common
pressure chamber in the blade body which is adapted to receive a
supply of coolant, such as air while only the first flow path
passes through a second pressure chamber on the opposite side of
the body.
The respective pressure chambers can be defined in part by blade
coverings or boundary jackets which extend outwardly from the blade
front.
By contrast to previous constructions, the direct stream flowing in
the longitudinal direction of the blade front not only cools the
blade front because of its high velocity but is also utilized to
absorb a substantial part of the heat on the trailing edge without
the pressure losses becoming excessively high. This latter effect
is due to the practically loss-free pressure chamber which is
disposed between the blade front and air exit. It is also
advantageous to proportion the blade height of the two air exits,
given an at least approximately constant exit cross-section, so
that the ratio of the relative proportions of blade height for the
two air exits vary at least approximately relative to each other as
the mount of air in the two flow paths.
By completely separating the two flow paths, a defined distribution
of the cooling air flow rate over the two part flows is obtainable.
This dispenses with the need to make unnecessarily large quantities
of cooling air available to compensate for a fluctuating
distribution over both flows. In constructional terms, defined
distribution over the part flows may be achieved in known manner by
the use of suitable restrictors in the air exits. Such restrictors
may be varied to a certain extent and may be individually adjusted
on the basis of tests in order to vary the distribution over a
small range and, for example, to compensate for manufacturing
inaccuracies.
The second flow path may be advantageously constructed to extend
parallel to the first flow path with at least two reversals through
180.degree. and to be practically free of pressure losses as far as
the second reversal. The portions of the body which define this
second flow path may also be provided with boundary walls on which
fins are provided at least over a portion of the walls to project
into the flow path. The purpose of this is to increase the cooled
surface in the low-pressure loss zone of low flow velocity and thus
to improve cooling thereat.
It is generally known that because of their higher mechanical
strength, more particularly of the higher high-temperature
strength, their materials and simpler method of production, or in
the absence of the need for finish-machining, cast blades are
preferred over forged and welded blades. The novel blade is
therefore advantageously constructed so that the blade together
with the blade coverings or boundary jackets of the pressure
chambers is a precision casting. This casting can then be provided
with a separating plate, as an insert, which is mounted in the
casting in gas-tight manner, for example by welding, to separate
the two flow paths from each other as well as with two cover plates
which enclose the pressure chambers against the ambient zone.
If a plurality of individual blades are combined in known manner
into a blade segment, the construction enables the entire blade
segments, that is the blades of the segment and the jacket
boundaries of the common external and internal pressure chambers to
be integrally cast while a separate separating plate is provided
for each blade and cover plates are provided which are common to
the entire segment.
These and other objects and advantages of the invention will become
more apparent from the following detailed description and appended
claims taken in conjunction with the accompanying drawings in
which:
FIG. 1 illustrates a longitudinal sectional view taken along line
I--I of FIG. 2 of a guide blade according to the invention;
FIG. 2 illustrates a sectional view taken on line II--II of FIG. 1;
and
FIGS. 3 and 4 each illustrates in the same manner as in FIG. 2 a
detail of the trailing edge of a blade according to FIG. 1 but of
different construction.
Referring to FIG. 1, the guide blade to which hot gases flow from
the left (arrow A) as viewed, through a flow duct 2 from one or
more combustion chambers (not shown) is retained in a guide blade
support 3 within a gas turbine (not shown). The hot gas duct 2 is
defined in the upstream direction by different parts of a hot gas
casing 4 in which flow paths 5, 6 are provided for cooling the
blade from the outside. These flow paths are adapted to conduct a
coolant such as cooling air from an air receiver (not shown) which
surrounds the guide blade support 3 along the inner and outer
boundaries of the duct 2. The cooling air flow paths 5, 6 also cool
the parts 4a of the hot gas casing 4 of high-temperature resistant
materials and separate these parts 4a from another part 4b of the
casing 4 which is not directly subjected to the hot gases or from
the guide blade support 3. Both of these latter parts 4b, 3 are
constructed of ferritic material having a lower high-temperature
strength. Downstream of the illustrated guide blade, the guide
blade support 3 is also protected against hot gases by a filler
ring segment 9 which is also constructed of high-temperature
resistant material. The cooling air for the blade first passes from
the air receiver (not shown) through an aperture 10 in the blade
support 3 into an intermediate chamber 11. The air then flows
through an aperture 12 into a pressure chamber 13 which is disposed
in an outer blade covering or boundary jacket 14.
As shown, the blade body has a blade front 8 facing the duct 2 and
a trailing edge 19 disposed downstream of the blade front 8. In
addition, two flow paths are defined by various means within the
blade body. These flow paths serve to pass cooling air through the
blade and extend from the pressure chamber 13. The first flow path
leads into a second pressure chamber 16 through a relatively narrow
duct 15 disposed immediately downstream of the blade front 8. The
second pressure chamber 16 is shown disposed in an inner blade
covering or boundary jacket 17. Air which passes through the first
path leaves the pressure chamber 16, through which the air flows
practically without pressure loss, and passes through an air exit
18 which extends over part of the blade height in the zone of the
trailing edge 19. This air exit 18 may be disposed in the trailing
edge itself as shown in FIG. 2 or may be disposed on the suction
side (FIG. 3) or on the delivery side (FIG. 4) of the blade.
The second flow path extends parallel to the first flow path and
includes a relatively wide duct 20 in the blade body which is
connected via a reversal chamber 21 in which the flow passes
through a first reversal of 180.degree. to a duct 22 which is also
relatively wide and is disposed in the middle part of the blade.
The duct 22 communicates via a reversal chamber 23, of optimum
construction for the flow because of the pressure loss, in which
the flow passes through a further reversal of 180.degree. to an air
exit 24 which is also disposed in the zone of the trailing edge 19.
This exit 24 is separated by a bulkhead 26 from the air exit 18 for
the first flow path and fills the height of the blade 1 which is
not covered by the exit 18. The air exit 24 may, of course, also be
disposed in the trailing edge 19 itself or on the suction side or
on the delivery side of the blade. In addition, the duct 22 is
provided with fins 25 over the height of the opposed boundary walls
to increase the heat dissipating surfaces.
The relatively low available pressure gradient between the pressure
chamber 13 and the first duct 2 in the zone of the trailing edge 19
of the blade in the first flow path allows a relatively high
velocity to be obtained in the arrow duct 15. This, therefore,
allows a large coefficient of heat transfer and intensive cooling
of the blade front 8 to be achieved. In a practical embodiment,
approximately half the pressure gradient is utilized in this way.
After flowing through the pressure chamber 16 practically without
loss, the remaining positive pressure relative to the duct 2
results in high velocities in the air exit 18 and therefore in good
cooling of part of the blade height in the zone of the trailing
edge 19.
In the second flow path, the air enters the reversal chamber 23
with relatively low velocities and practically without pressure
losses, that is, with the exception of the two reversals through
180.degree.. The entire available pressure gradient is thus
utilized to achieve the most uniform possible discharge at high
velocities and corresponding good cooling of the trailing edge 19
over the remaining blade height in the zone of the air exit 24.
The flow resistances, which may be altered to a certain extent by
modification of the fins 30 which act as restrictors and guide
surfaces in the air exits 18 and 24, may be experimentally matched
to each other in both flow paths so that the available amount of
cooling air is distributed over both paths in a ratio which is at
least approximately constant. This ratio will then also define the
relative height of the bulkhead 26 by means of which the entire
blade height is subdivided over the two air exits 18 and 24
approximately in the ratio of the part quantities, if the exit
cross-section is approximately constant over the entire height.
By contrast to known constructions, subdivision of the amount of
cooling air in an at least approximately constant ratio ensures
reliable cooling of all blade parts in all cases with the lowest
consumption of cooling air. Subdivision over two flow paths and
loss-free flow over certain sections on these two paths provides
high velocities in the other parts of the flow path even if the
available pressure gradients are low. Accordingly, high
coefficients of heat transfer and intensive cooling actions are
obtained in these ranges. In terms of manufacture, the blade
together with the coverings 14 and 17 can be made as a precision
casting of a high-temperature resistant cast alloy. After
completion of the casting, a separating plate 27 is welded therein
sealtight manner to separate the reversing chamber 21 from the
delivery chamber 16. Cover plates 28 and 29 which are also
subsequently welded in position in seal-tight manner are provided
to separate the delivery chambers 13, 16 from the ambient zone.
Where the guide blades are constructed as blade segments in a guide
blade ring with the blade segments comprising a plurality of
blades, such can also be produced as a casting by the precision
casting method. In this case, the separating plates 27 are then
co-ordinated to the individual blades but the cover plates 28 and
29 are common to the entire segment.
* * * * *