The present invention relates to an axial-flow turbine, and more particularly to a turbine nozzle and a moving blade forming an fluid passage of the axial-flow turbine.
A variety of techniques relating to the axial-flow turbine have been employed to improve an internal efficiency of the turbine so as to improve the performance of the same. Since a secondary flow loss among internal losses experienced with the axial-flow turbine is a loss of a type common to all stages of the turbine, a contrivance that is capable of preventing the above-mentioned loss has been required.
FIG. 19 shows cross sections of turbine stages of a usual axial-flow turbine including nozzle blades and moving blades. Referring to FIG. 19, a plurality of nozzle blades 4 are radially secured between an outer diaphragm ring 2 and an inner diaphragm ring 3 which are fit to a turbine casing 1 so that a nozzle blade passage is formed. A plurality of moving blades 6 is disposed at a downstream side of the nozzle blade passage. Each of moving blades 6 is sequentially implanted in the outer surface of the rotor wheel 5 at predetermined intervals in the circumferential direction of the rotor wheel 5. The tip of the moving blades 6 are attached to a cover 7 so that leakage of working fluid is prevented. Both the nozzle blades 4 and the moving blades 6 form a working fluid passage of this stage of the turbine.
A next (second) stage of the turbine, which is located at a downstream side of the above (first) stage, has a rapidly enlarged passage for the working fluid. This passage is composed of a nozzle blade passage and a moving blade passage as well as the above working fluid passage. The nozzle blade passage is formed by an outer diaphragm ring 8, an inner diaphragm ring 9 and nozzle blades 10. The moving blade passage is formed by both moving blades 12 implanted in a rotor wheel 11 and a cover 13 attached to the tip of the moving blades 12.
In the second stage, the working fluid expands from a high-pressure condition to a low-pressure condition trough the passage, so the specific capacity (volume) of the fluid enlarges. To correspond to such enlargement of specific capacity, the inner wall of the passage is inclined in such a manner that the area of the passage is enlarged in the downstream direction.
Through the above-mentioned passage of the two stages, the working fluid generate a secondary flow at the nozzle blades 4 and 10. This mechanism of generating the secondary flow will now be described with reference to FIG. 20.
When the working fluid, which is high-pressure steam or the like, flows in the nozzle blade passage between the nozzle blades, the working fluid is curved into a circular arc form in the nozzle blade passage as indicated with a two-dot chain line shown in FIG. 20. At this time, centrifugal components are generated in a direction from an extrados E of the nozzle blade 4 to an intrados F of another nozzle blade 4. Since the centrifugal components and the pressure in the nozzle blade passage are in equilibrium, the static pressure at the intrados F of the nozzle blade 4 is raised.
On the other hand, the pressure at the extrados E of the nozzle blade 4 is lowered because the flow velocity of the working fluid is high along the extrados E. As a result, a pressure gradient is generated in a region of the nozzle blade passage from the intrados F of the nozzle blade 4 to the extrados E of the another nozzle blades 4. As shown in FIG. 20, also a pressure gradient of the foregoing type is generated between the inner wall of the root of the nozzle blades and a layer adjacent to the outer surface of the tip of the nozzle blades in which the flow velocity is low, that is, in the boundary layer. In the portions adjacent to the boundary layer, the flow velocity is low and the acting centrifugal component is weak. Therefore, the flow of the working fluid cannot withstand the pressure gradient generated in a direction from the intrados F of the nozzle blade 4 to the extrados E of the another blade. As a result, the flows are generated in a direction from the intrados F of the nozzle blade 4 to the extrados E of the another nozzle blade, as indicated with symbols f1 and f2 shown in FIG. 20. The flows f1 and f2 collide with the extrados E of the nozzle blade 4 and curl up. As a result, secondary flow eddies 14a and 14b are generated adjacent to the inner wall of the root of the nozzle blades 4 and the outer wall of the tip of the same.
FIG. 21 is a diagram showing a mechanism of the moving blades 6 disposed downstream from the nozzle blades 4 to generate a secondary flow. Since the mechanism of the secondary flow the moving blades 6 is substantially the same as the mechanism of the nozzle blades 4 to generate eddies in the secondary flow, the same functions as those shown in FIG. 20 are given the same reference numerals and symbols. As can be understood from FIGS. 22 and 23 showing losses of the nozzle blades 4 and the moving blades 6, eddy losses are caused from the secondary flow eddies. Thus, excessive losses are produced in the portions adjacent to the inner and outer walls of the turbine blades.
If secondary flow eddies 14a and 14b are generated, a portion of energy of the working fluid is dispersed. Moreover, nonuniform flows of the working fluid are formed, thus causing a problem to arise in that losses of the nozzle blades and the moving blades are enlarged and the performance of the stages to deteriorate excessively.
To prevent the secondary flow loss caused from the secondary flow eddies 14a and 14b generated in the above-mentioned passage (stages), a variety of techniques have been researched and developed. For example, a nozzle blade having a reduced outer surface has been employed. This reduced outer surface has a irregularities formed in the tip of the nozzle blade to reduce the height of the flow passage in the downstream direction. FIG. 24 is a cross sectional view showing a turbine nozzle having the nozzle blade 15 having a reduced outer surface. The nozzle blade 15 having the reduced outer surface causes flows along the outer surface of the nozzle blade 15. Thus, the flow line is shifted toward the inside portion (toward the central portion) of the nozzle blade passage as indicated with an arrow ft. It leads to a fact that the flow lines in the central portion and the root (inside) portion, similarly to those along the outer surface, are shifted inwards (toward the central portion), as indicated by arrows fp and fr. As a result, the flow lines pushes the flows to the inner wall of the nozzle blade 15 in portions adjacent to the root of the nozzle blade 15. Thus, enlargement of the boundary along the inner wall can be prevented so that enlargement of the loss caused from the secondary flow eddies is prevented.
FIG. 25 shows a distribution of losses reduced attributable to an effect of the conventional nozzle blade 15 having the reduced outer surface to prevent enlargement of losses caused from eddies in the secondary flow. As can be understood from FIG. 25, losses can significantly be reduced in the portions adjacent to the root of the nozzle blade. Improvement in the performance has been confirmed also in overall efficiency experiments of the turbine stages.
The fact that the nozzle blade 15 having the reduced outer surface is able to improve the performance has been confirmed in the above-mentioned stage efficiency experiments. However, local separation of the flow at the tip of the nozzle blade takes place attributable to a rapid shift of the flow line, as shown in the distribution of losses in the trailing edge of the nozzle blade. Therefore, the secondary flow cannot satisfactorily be improved.
Moreover, a great portion of the working fluid flows adjacent to the root of the nozzle blade. Therefore, considerable change in the flow rate occurs in the direction of the height of the nozzle blade.
Therefore, the stage performance realized by the nozzle blade 15 having the reduced outer surface can furthermore be improved. That is, a nozzle blade passage is required which is capable of preventing separation of flows of the working fluid and improving the flow rate characteristic at the tip of the nozzle blade.
In view of the foregoing an object of the present invention is to provide a turbine nozzle and a turbine moving blades of an axial-flow turbine capable of reducing a loss in the secondary flow with a simple structure.
This object can be achieved according to the present invention by providing an axial-flow turbine comprising: an outer diaphragm ring and an inner diaphragm ring forming together an annular fluid passage; and a plurality of nozzle blades disposed in the annular passage, each of the nozzle blades being formed into a warped shape such that a central portion in a lengthwise direction of the nozzle blade maximally projects in a downstream direction.
In preferred embodiments, the annular fluid passage has a stepped portion at an inner surface of the outer diaphragm ring and an outer surface of the inner diaphragm ring, the stepped portion having a curvature surface so that the height of the fluid passage is reduced in a downstream direction thereof.
The stepped portion has a height in a radial direction of the fluid passage, the height being described by the relationships:
0xe2x89xa6h1/L1 less than 0.05
0.1 less than h2/L1 less than 0.2
where L1 is the height of an leading edge of the nozzle blades, h1 the height of the stepped portion provided for the inner diaphragm ring and h2 is the height of the stepped portion provided for the outer diaphragm ring.
Each of said turbine blades has an axial distance from the leading edge of the diaphragm to the trailing edge of the nozzle blades, the distance being described by the relationships:
Zt less than Zr less than Zp
where Zt is the distance at the outermost end of the nozzle blades, Zr is the distance at the innermost end of the same and Zp is the distance at the central portion of the same.
The height L2 of the nozzle blades at a trailing edge is made to be smaller than the height L1 of the nozzle blades at a leading edge (that is L1 greater than L2).
The fluid passage is structured such that the inner surface of the outer diaphragm ring and the outer surface of the inner diaphragm ring are outwards inclined in the downstream direction.
An angle of inclination of said fluid passage is descried by the relationships:
0xc2x0xe2x89xa6xcex81 less than xcex83 less than xcex82
where xcex81 is an angle of inclination of the outer surface of the inner diaphragm ring, xcex82 is an angle of inclination of the inner surface of the outer diaphragm ring in the leading edge of the nozzle blades and xcex83 is an angle of inclination of a portion of the inner surface of the outer diaphragm ring following the tailing edge of the nozzle blades.
The height L2 of the nozzle blades at an trailing edge is made to be larger than the height L1 of the nozzle blades at an leading edge (that is, L1xe2x89xa6L2).
The fluid passage is structured such that the inner surface of the outer diaphragm ring is outwards inclined in the downstream direction and the outer surface of the inner diaphragm ring is inwards inclined in the downstream direction.
An angle of inclination of said fluid passage is descried
xcex81 less than 0xc2x0 less than xcex83 less than xcex82
where xcex81 is an angle of inclination of the outer surface of the inner diaphragm ring is, xcex82 is an angle of inclination of the inner surface of the outer diaphragm ring in the leading edge of the nozzle blades and xcex83 is an angle of inclination of a portion of the inner surface of the outer diaphragm ring following the trailing edge of the nozzle blades.
The fluid passage is structured such that the cross sections of the nozzle blades at the tip and the root of the nozzle blades are shifted in the circumferential direction of the annular fluid passage.
A throat width between adjacent two nozzle blades is determined by the relationships:
Spxe2x89xa6Sr less than St
where Sp is the throat width at the central portion in the lengthwise direction of the nozzle blades, Sr is that at the root and St is that at the tip.
In other side of the present invention, an axial-flow turbine comprising: an outer diaphragm ring and an inner diaphragm ring forming together an annular fluid passage; and a plurality of nozzle blades disposed in the annular passage, wherein said annular fluid passage has a stepped portion at an inner surface of the outer diaphragm ring and an outer surface of the inner diaphragm ring, the stepped portion having a curvature surface so that the height of the fluid passage is reduced in a downstream direction thereof.
In preferred embodiments, the fluid passage is structured such that the cross sections of the nozzle blades at the tip and the root of the nozzle blades are shifted in the circumferential direction of the annular fluid passage.
A throat width between adjacent two nozzle blades is determined by the relationships:
Spxe2x89xa6Sr less than St
where Sp is the throat width at the central portion in the lengthwise direction of the nozzle blades, Sr is that at the root and St is that at the tip.
In other side of the present invention, the axial-flow turbine comprising: an outer diaphragm ring and an inner diaphragm ring forming together an annular fluid passage; and a plurality of nozzle blades disposed in the annular passage,
wherein the height of the nozzle blades at a trailing edge is made to be larger than the height of the nozzle blades at a leading edge,
the annular fluid passage having a stepped portion at an inner surface of the outer diaphragm ring, the stepped portion having a curvature surface so that the height of the fluid passage is reduced in a downstream direction thereof, the height of the fluid passage being enlarged at a position adjacent to he trailing edge of the nozzle blades,
the inner trailing edge of the nozzle blades being positioned in the most downstream position and the outer trailing edge being positioned in the most upstream position.
In preferred embodiments, the stepped portion has a height in a radial direction of the fluid passage, the height being described by the relationships:
0.1 less than h2/L1 less than 0.2
where L1 is the height of a leading edge of the nozzle blades and h2 is te height of the stepped portion provided for the outer diaphragm ring.
The above object can be achieved according to the present invention by providing an axial-flow turbine comprising: a rotor wheel; a plurality of moving blades disposed on an outer surface of the rotor wheel; and an annular cover attached to a tip each of the moving blades, the annular cover and the rotor wheel forming a annular fluid passage,
wherein the moving blades are formed into a warped shape in such a manner that the lengthwise directional central portion of the moving blades at the trailing edge of the moving blades is lower than a straight line connecting an trailing edge at the root and a trailing edge at the tip to each other.
In preferred embodiments, the annular fluid passage has a stepped portion at an outer surface of the rotor wheel and an inner surface of the cover, the stepped portion having a curvature surface so that the height of the fluid passage is reduced in a downstream direction thereof.
The stepped portion has a height in a radial direction of the fluid passage, the height being described by the relationships:
0xe2x89xa6h3/L3 less than 0.05
0.1 less than h4/L3 less than 0.2
where L3 is the height of the leading edge of the moving blades, L4 is the height of the trailing edge of the moving blades, h3 is the height of the stepped portion provided for the rotor wheel and h4 is the height of the stepped portion provided for the cover.
Each of said moving blades is structured such that an axial distance from points on a line connecting an trailing edge of a root of the moving blades to a trailing edge at the tip to points on a curved line forming a trailing edge of the moving blades are longest in the central portion of the lengthwise direction of the moving blades at the trailing edge of the moving blades.
The fluid passage is structured such that the inner surface of the cover and the outer surface of the rotor wheel are outwards inclined in the downstream direction.
An angle of inclination of said fluid passage is descried by the relationships:
0xc2x0xe2x89xa6xcex81 less than xcex83 less than xcex82
where xcex81 is an angle of inclination of the outer surface of the rotor wheel, xcex82 is an angle of inclination of the inner surface of the cover at the leading edge of the moving blades and xcex83 is an angle of inclination of a portion of the inner surface of the cover following the trailing edge of the moving blades.
The height L4 of the moving blades at the trailing edge is made to be larger than the height L3 of the moving blades at the leading edge (L3xe2x89xa6L4).
The fluid passage is structured such that the inner surface of the cover is outwards inclined in the downstream direction and the outer surface of the rotor wheel is inwards inclined in the downstream direction.
An angle of inclination of said fluid passage is descried by the relationships:
xcex81 less than 0xc2x0 less than xcex83 less than xcex82
where xcex81 is an angle of inclination of the outer surface of the rotor wheel is, xcex82 is an angle of inclination of the inner surface of the cover at the leading edge of the moving blades and xcex83 is an angle of inclination of a portion of the inner surface of the cover following the trailing edge of the moving blades.
The fluid passage is structured such that the cross sections of the outer and inner portions of the moving blades are shifted in the circumferential direction of the rotor wheel.
A throat width between adjacent two moving blades is determined by the relationships:
Sr greater than Sp less than St
where Sp is the width of the central portion in the lengthwise direction of the moving blades, Sr is that at the root and St is that at the tip.
In other side of the present invention, an axial-flow turbine comprising: a rotor wheel; a plurality of moving blades disposed on an outer surface of the rotor wheel; and an annular cover attached to an outer end each of the moving blades, the annular cover and the rotor wheel forming a annular fluid passage,
wherein said annular fluid passage has a stepped portion at an outer surface of the rotor wheel and an inner surface of the cover, the stepped portion having a curvature surface so that the height of the fluid passage is reduced in a downstream direction thereof.
In preferred embodiments, the fluid passage is structured such that the cross sections of the outer and inner portions of the moving blades are shifted in the circumferential direction of the rotor wheel.
A throat width between adjacent two moving blades is determined by the relationships:
Sr greater than Sp less than St
where Sp is the width of the central portion in the lengthwise direction of the moving blades, Sr is that at the root and St is that at the tip.
The turbine nozzle or the turbine moving blades having the above-mentioned structure of the present invention causes the working fluid introduced to the portions adjacent to the tip and root portions of the fluid passage by the nozzle blade or the moving blade to be narrowed by the stage of the wall of the fluid passage. Thus, eddies in the secondary flow between blades can be prevented and the secondary loss can be reduced.
Since the trailing edge of the nozzle blade and that of the moving blade are disposed downstream in the central portion of the blade, the flow lines of the portions of the working fluid in each of the nozzle blade and the moving blade are shifted to the tip and root portions. As a result, the distribution of the flows in the lengthwise direction of the blade can be uniformed. Thus, energy can effectively be converted by the moving blades. Therefore, the above-mentioned functions improve the performances of the turbine stages.