U.S. patent application number 10/314212 was filed with the patent office on 2004-06-10 for gas turbine.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES LTD.. Invention is credited to Ishizaka, Kouichi, Takahashi, Ronald, Wakazono, Susumu, Yuri, Masanori.
Application Number | 20040109756 10/314212 |
Document ID | / |
Family ID | 32325886 |
Filed Date | 2004-06-10 |
United States Patent
Application |
20040109756 |
Kind Code |
A1 |
Wakazono, Susumu ; et
al. |
June 10, 2004 |
Gas turbine
Abstract
An outer shape of a section in the longitudinal direction at a
leading edge of the strut is an aerofoil whose thickness is
gradually increased along a flow direction of the combustion gas to
prevent reduction of turbine efficiency caused by a shock wave
generated at the strut of the exhaust diffuser.
Inventors: |
Wakazono, Susumu;
(Takasago-shi, JP) ; Ishizaka, Kouichi;
(Takasago-shi, JP) ; Yuri, Masanori;
(Takasago-shi, JP) ; Takahashi, Ronald; (Miami,
FL) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES
LTD.
Tokyo
JP
|
Family ID: |
32325886 |
Appl. No.: |
10/314212 |
Filed: |
December 9, 2002 |
Current U.S.
Class: |
415/142 ;
415/211.2 |
Current CPC
Class: |
F01D 25/162
20130101 |
Class at
Publication: |
415/142 ;
415/211.2 |
International
Class: |
F01D 009/02 |
Claims
What is claimed is:
1. A gas turbine comprising moving blades attached to a rotor and
an exhaust diffuser which takes up combustion gas at an exit of the
moving blades to recover pressure, wherein the exhaust diffuser
comprises a strut which supports the rotor provided in the exhaust
diffuser, wherein an outer shape of a section in the longitudinal
direction at a leading edge of the strut is an aerofoil whose
thickness is gradually increased along a flow direction of the
combustion gas.
2. A gas turbine according to claim 1, wherein an outer shape of a
section in the longitudinal direction at a trailing edge of the
strut is a semicircular shape.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a gas turbine.
[0003] 2. Description of Related Art
[0004] A gas turbine is equipped with a compressor, a combustor,
and a turbine. In the gas turbine, air is compressed in the
compressor and flows into the combustor where it is mixed with fuel
and combustion occurs. The combustion gas flows into the turbine
where energy is extracted from the gas to rotate the compressor and
to drive a generator to generate electricity. After flowing through
the turbine, the combustion gas is exhausted through an exhaust
diffuser.
[0005] FIG. 4 shows an example of a turbine equipped with an
exhaust diffuser. The turbine consists of multiple stationary
airfoils (vanes, not shown) attached to outer casing 3, and
multiple rotating airfoils 2 (blades) which are attached to rotor
shaft 1, which rotates about centerline CL. The gas flow, F, is in
the direction or left to right on FIG. 4. The turbine can consist
of multiple pairs of vanes and blades (stages) attached to rotor 1.
FIG. 4 shows the blade of the last stage of the turbine.
[0006] The exhaust diffuser, consisting of parts 5, 6, 7, and 8 is
connected coaxially to the downstream end of the turbine. The
exhaust diffuser consists of exhaust casing 6 which encases gasflow
path 5 and multiple struts 8 which support journal bearing 7 which
in turn supports rotor 1.
[0007] Each strut 8 is equipped with strut main body 8a, that
supports journal bearing 7, and strut cover 8b that covers and
protects strut main body 8a from the combustion gas F.
[0008] In the above conventional gas turbine, strong shock waves
can form at the leading edge of each strut cover 8b, resulting in
reduced turbine performance. FIG. 5 shows the conventional cross
section A-A of strut 8. The shape of strut cover 8b consists of
parallel lines in the flow direction connected by semicircles at
the leading edge LE and trailing edge TE.
[0009] As the combustion gas F, having high Mach number (for
example, M=0.65), flows over the strut leading edge, the flow speed
rapidly increases to achieve supersonic speed. A shock is generated
in the regions indicated by "a" of FIG. 5. The presence of the
shock has the effect of reducing turbine efficiency.
[0010] This effect on turbine efficiency is increased when the
ambient temperature (temperature at the compressor inlet) is low.
The amount of air flowing into the gas turbine at low ambient
temperature is larger than that at normal ambient temperature, and
as a result, the Mach number of the combustion gas flowing into the
exhaust diffuser is increased. Accordingly, the shock wave
generated at the leading edge LE becomes stronger, resulting in
further reductions in turbine efficiency.
BRIEF SUMMARY OF THE INVENTION
[0011] In view of the above problems, an object of the present
invention is the provision of a gas turbine which can prevent
reduction of turbine efficiency caused by the shock wave generated
at struts of the exhaust diffuser.
[0012] In order to solve the above problems, the following means is
adopted in the present invention.
[0013] The shape of the strut cover, 8b of FIG. 5, is modified to
prevent or minimize the generation a shock at the leading edge. As
a result, reduction of turbine efficiency due to the shock is
reduced or prevented.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0014] FIG. 1 is a view explaining a schematic structure of an
embodiment of a gas turbine according to the present invention.
[0015] FIG. 2 is a sectional view showing the outer shape of a
strut of an exhaust diffuser.
[0016] FIG. 3 is a graph showing Mach number distribution along the
strut of the gas turbine, in which x-axis indicates distance from a
leading edge in the direction of gas flow, and y-axis indicates
Mach number.
[0017] FIG. 4 is a sectional view along the rotational shaft line
of the rotor, showing a structure of the turbine and exhaust
diffuser.
[0018] FIG. 5 is a sectional view showing the outer shape of a
conventional strut equipped in the exhaust diffuser along line A-A
shown in FIG. 4.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention and its use in the gas turbine are
explained below with reference to the figures. However, as a matter
of course, the present invention is not limited to the present
embodiment.
[0020] FIG. 1 shows a schematic structure of the gas turbine of the
present embodiment. FIG. 1 shows compressor 10, combustor 20, and
turbine 30. Compressor 10 takes up and compresses a large amount of
air therein. Combustor 20 carries out combustion after mixing air
compressed in compressor 10 and fuel. The combustion gas generated
in combustor 20 is introduced into turbine 30 where it is expanded,
and is run through moving blades 34 attached to rotor 32 to convert
heat energy of the combustion gas into mechanical rotation energy,
and as a result, power is generated. In the gas turbine, generally,
a part of the power obtained in turbine 30 is used as power for
compressor 10.
[0021] Multiple moving blades 34 attached to rotor 32 and also
multiple stationary vanes 33 attached to casing 31 (stationary
member side) are equipped in turbine 30. Moving blades 34 and
stationary vanes 33 are alternately placed along the rotational
shaft line of rotor 32. When rotor 32 is connected with a generator
(not shown), power generation can be carried out.
[0022] Casing 31 forms combustion gas flow path 35 therein by
covering the periphery of moving blades 33 and rotor 32. Casing 31
corresponds to a combination of turbine casing 3 and exhaust casing
6 of FIG. 4.
[0023] The details of the shape of strut 8 is described as
follows:
[0024] FIG. 2 corresponds to a cross-section along line A-A shown
in FIG. 4. As shown in FIG. 2, a strut (given reference number 100
to discriminate from conventional strut 8) of the present
embodiment comprises strut main body 101 which supports rotor 1
with journal bearing 7, and strut cover 102 which covers and
protects strut main body 101 from the combustion gas F.
[0025] The outer shape of the cross-section of strut cover 102 is a
wing shape in which the thickness of leading edge LE1 is gradually
increased along the flow direction of the combustion gas F. The
strut leading edge of the present invention is elliptical in shape,
compared to semi-circular for the conventional strut.
[0026] Using the leading edge LE1 with the wing shape being tapered
with an elliptical shape, the combustion gas F flowing into the
leading edge LE1 can flow along a smoothly curved surface of the
leading edge LE1. As indicated by the dashed line a shown in FIG.
3, it can prevent the Mach number at the leading edge LE1 from
rapidly increasing (the continuous line b indicates Mach number
when the leading edge has the conventional obtuse head shape).
Since forming of strong shock wave caused by high Mach number can
be prevented, reduction of turbine efficiency due to shock
formation can be reduced or prevented.
[0027] In the present embodiment, the trailing edge TE1 has a wing
shape as well as the leading edge LE1, however, the shape of the
trailing edge TE1 is not limited, the trailing edge TE1 may have
the obtuse head shape or rectangle as if curved portion is simply
cut off.
[0028] Furthermore, the outer shape of strut cover 102 may be an
NACA blade in a cross-section thereof in addition to the shape
shown in FIG. 2.
* * * * *