Fluid reaction surfaces (i.e. – impellers) – With heating – cooling or thermal insulation means – Changing state mass within or fluid flow through working...
Reexamination Certificate
1999-02-04
2001-02-20
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
With heating, cooling or thermal insulation means
Changing state mass within or fluid flow through working...
C416S09700R, C416S22300B, C416S239000, C416S248000
Reexamination Certificate
active
06190128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a cooled moving blade for a gas turbine, and more particularly to a cooled moving blade formed in such a geometrical configuration that thermal stress induced between a base portion of the blade and a platform can be reduced.
2. Description of the Related Art
FIG. 5
is a perspective view showing a conventional cooled moving blade for a gas turbine. Referring to the figure, a moving blade
1
is mounted on a platform
2
disposed around a rotor (not shown), wherein a cooling air passage
3
is formed inside of the moving blade
1
between a leading edge thereof and a trailing edge in a serpentine pattern that sequentially extends upward and downward in a repetitious and continuous manner. The cooling air is introduced into the cooling air passage
3
from a port located on the inner side of the leading edge of the moving blade
1
by way of a blade root (not shown) portion and is discharged from holes formed in the trailing edge portion of the blade after having blown through the cooling air passage
3
. In the figure, reference numeral
4
denotes a curved surface forming a blade surface of the moving blade
1
and numeral
5
designates a fillet ellipse portion R formed in the blade base portion, which will be described below.
FIG. 6
is a schematic diagram showing the portion B shown in
FIG. 5
in detail, and more specifically it shows a blade profile of the base portion of the moving blade
1
. The base portion of the moving blade
1
is shaped in a curved surface conforming to an ellipse
6
, wherein the fillet ellipse portion R
5
is formed so as to extend continuously with a curved surface of the top portion of the moving blade. The elliptical portion mentioned above is formed over the entire circumference of the base portion of the moving blade
1
, and the base portion thus has a form that is capable of reducing thermal stress which is caused by high-temperature combustion gas.
Here, it should be mentioned that thermal stress of an especially large magnitude occurs between the base portion and the platform
2
. The reason for this can be explained by the fact that since the moving blade
1
has a smaller heat capacity than the platform
2
, the temperature of the moving blade
1
increases at a higher rate and within a shorter time period than that of the platform
2
upon start of the gas turbine. On the other hand, the temperature of the moving blade
1
falls at a higher rate and within a shorter time than that of the platform
2
, whereby a large temperature difference occurs between the moving blade
1
and the platform
2
. This in turn generates thermal stress. Consequently, the base portion is shaped in the form of a curved surface conforming to the fillet ellipse R to thereby reduce the thermal stress.
Recently, however, there is an increasing tendency to use a high temperature combustion gas to enhance the operating efficiency of the gas turbine. As a result, it becomes impossible to sufficiently suppress the thermal stress with only the base portion structure shaped in the form of the above mentioned fillet ellipse portion R, and cracks develop more frequently in the base portion where large thermal stress is induced. Under these circumstances, there is a demand for a structure of the blade base portion that is capable of reducing the thermal stress more effectively.
OBJECT OF THE INVENTION
In light of the state of the art described above, it is an object of the present invention to provide a cooled moving blade for a gas turbine which has a blade shape capable of reducing thermal stress more effectively than a conventional moving blade by adopting a partially improved shape of the fillet ellipse portion R which is formed between a base portion of the moving blade and a platform.
SUMMARY OF THE INVENTION
To achieve the object mentioned above, the present invention proposes the following means.
(1) A cooled moving blade for a gas turbine according to the present invention is mounted on a platform disposed circumferentially around a rotor and has an internal cooling air passage, wherein the cooled moving blade for the gas turbine has a blade profile which is constituted by a blade surface with an elliptical profile formed around a base portion of the moving blade which is in contact with the platform, a rectilinear blade surface portion formed in continuation with the elliptical blade surface over a predetermined length, and a curvilinear shaped blade surface extending continuously from the rectilinear blade surface portion to an end of the blade with a predetermined curvature.
The peripheral surface of the base portion of the moving blade which is in contact with the platform is formed as a curved surface conforming to an elliptic curve and the blade surface having a rectilinear surface portion is formed so as to extend continuously from the curved surface. Thus, the blade surface which is shaped in the form of a curved surface in the conventional moving blade is replaced by the rectilinear surface portion. In other words, the arcuate profile portion protruding convexly inward in a conventional moving blade is shaped in the rectilinear form. Consequently, the cross section of the blade is correspondingly enlarged outward with the cross-sectional area of the blade having the rectilinear surface portion being increased when compared with that of the conventional blade. As a result, the blade according to the present invention has a greater heat capacity than that of the conventional type blade, whereby temperature difference relative to the platform decreases in proportion to the increase of the heat capacity of the blade. Thus, the thermal stress due to the temperature difference between the blade and the platform is decreased when compared with the conventional blade. Moreover, since the cross-sectional area of the blade increases, the thermal stress decreases and it is possible to reduce the frequency at which cracks occur. Additionally, the length of the rectilinear surface portion should preferably be selected so as to cover a hub portion where thermal stress tends to be large, thereby ensuring a more advantageous effect.
(2) In the cooled moving blade for the gas turbine according to the present invention, cooling air holes communicated with the cooling air passage of the moving blade are additionally formed inside the platform. More specifically, the cooling air holes should preferably be formed at both sides of the platform so as to extend from a leading edge side of the moving blade to a trailing edge side thereof, while being communicated with the cooling air passage on the leading edge side of the moving blade.
A portion of the cooling air flowing through the cooling air passage formed inside the moving blade is introduced into the cooling air holes formed in the platform, and the cooling air is discharged into a combustion gas passage from an end portion of the platform after cooling the platform. Thus, in addition to the effect provided by the inventive structure (
1
) described above, the cooling effect is increased because the platform is also cooled, whereby cracks can be prevented from developing.
(3) Additionally, in the cooled moving blade for the gas turbine according to the present invention, the blade surface of the moving blade and the surface of the platform are coated with a heat-resisting material.
By coating the surface of the moving blade and that of the platform with a heat-resisting material, e.g., ceramics and the like, the moving blade and the platform can be protected against the effect of the heat of the high-temperature combustion gas. Thus, the thermal stress due to the heat of the high-temperature combustion gas can be reduced, whereby the effects provided by the inventive structures (
1
) and (
2
) mentioned above can be further enhanced.
REFERENCES:
patent: 3890062 (1975-06-01), Hendrix et al.
patent: 4244676 (1981-01-01), Grondahl et al.
patent: 4563128 (1986-01-01), Rossmann
patent: 5340278 (1994-08-01), Magowan
patent:
Fukuno Hiroki
Hashimoto Yukihiro
Maeda Shigeyuki
Suenaga Kiyoshi
Tomita Yasuoki
Look Edward K.
Mitsubishi Heavy Industries Ltd.
Nguyen Ninh
Sughrue Mion Zinn Macpeak & Seas, PLLC
LandOfFree
Cooled moving blade for gas turbine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cooled moving blade for gas turbine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cooled moving blade for gas turbine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2606218