JPH11117703A - Axial turbine blade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial turbine blade which is capable of reducing the friction loss and the pressure loss generated due to a two-dimensional flow produced in the neighborhood of the blade end part of a three-dimensional blade profile constituting a cascade of blades, and thereby improving the turbine efficiency. SOLUTION: With the axial turbine blade, in order to relax the velocity gradient of a working fluid flowing with increasing the flow velocity in the direction crossing a blade back face 5 at right angles, which is brought about by a two-dimensional flow produced in a break away region formed between the blade back face 5 and passage eddies 7 flowing on the blade back face 5 toward the downstream side, and to reduce the friction loss generated by the blade back face 5, riblets 11, the top of each of which is formed into a sharp shape, are provided in the break away region formed between the blade end-wall 2 and the passage eddies 7. Troubles generated in conventional axial turbine blades due to the passage eddies can thus be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to a steam turbine, a gas turbine, and the like, and has a friction loss generated in a secondary flow loss region and generated near a tip end of a three-dimensional airfoil constituting a cascade. The present invention relates to an axial turbine blade capable of reducing pressure loss and greatly improving performance.

[0002]

2. Description of the Related Art Friction generated in a root region of a three-dimensional airfoil forming a cascade or a blade tip wall near a blade tip, generated in a passage vortex generated by a secondary flow and formed in a loss region. In an axial flow turbine blade in which a large cascade loss occurs due to the loss and the pressure loss, it is important for improving performance to reduce these cascade losses generated in these loss regions.

FIG. 5 is a schematic view showing the flow inside an axial flow turbine blade cascade provided with turbine blades erected in a circumferential direction on a blade end wall so as to form a blade cascade. . As shown in the figure, the flow of the working fluid F such as steam or combustion gas flowing near the blade tip wall 2 upstream of the cascade collides with the leading edge of the turbine blade 1 and sinks into the blade tip wall 2 to form a passage vortex. 7 is formed.

The vortex tube of the passage vortex 7 is formed so as to surround the leading edge of the wing near the wing tip wall 2, and is called a horseshoe vortex 3 because of its shape as shown by a dashed line. That is,
An inter-blade flow path formed in a cascade of turbine blades 1 disposed adjacent to each other and sandwiched between a blade abdominal surface 4 of one turbine blade 1 and a blade back surface 5 of the other turbine blade 1. In the vicinity of the wing tip wall 2 in the inside 8, a secondary flow 6 flowing from the wing apex surface 4 side to the wing back surface 5 side is formed by the pressure difference of the working fluid F acting on the wing apex surface 4 and the wing back surface 5. You.

[0005] Therefore, among the horseshoe vortices 3 generated when the working fluid F collides with the leading edge of the turbine blade 1, the horseshoe vortex 3 flowing toward the blade abdominal surface 4 is caused by the working fluid F in the inter-blade flow path 8. Through the secondary flow 6
While flowing through the inter-blade flow path 8 toward the blade back surface 5, the passage vortex 7
It develops into a large vortex called. The vortex tube of the passage vortex 7 crosses the corner of the inter-blade flow path 8 sandwiched between the blade back surface 5 and the blade tip wall 2 as it extends downstream, and moves along the blade back surface 5 toward the center of the blade height. Go. FIG. 6 is a cross-sectional view showing details of the flow near the blade tip wall 2 of the blade back surface 5 of the turbine blade 1 among the internal flow of the conventional axial flow turbine cascade. In the figure, reference numeral 7 denotes a passage vortex viewed in a cross section perpendicular to the flow of the working fluid F, and as shown in FIG.
The path vortex 7 flowed downstream along the blade back surface 5 flows downstream.

For this reason, the passage vortex 7 entrains the high-speed fluid 9 which accelerates the working fluid F flowing at a position distant from the blade tip wall 2 and the blade back surface 5 near the blade back surface 5. As a result, in the separation region S from the wing tip wall 2 on the wing back surface 5 to the passage vortex 7, the velocity gradient of the high-speed fluid 9 in the direction perpendicular to the wing back surface 5 becomes steep, and due to wall friction generated on the wing back surface 5 The momentum loss of the high-speed fluid 9 increases rapidly.

Moreover, a large amount of momentum is thus lost,
The generated pressure loss fluid 10 having a large pressure loss flows downstream while being swept toward the center of the height of the turbine blade 1 by the rotational motion of the passage vortex 7, so that the blade tip wall 2
The height of the separation region 7 sandwiched between the passage vortex 7 and the turbine blade 1 in the blade width direction increases, in other words, a large portion of the blade back surface 5 is always exposed to the high-speed fluid 9,
There is a problem that it becomes a source of a large pressure loss and the turbine efficiency is greatly reduced.

[0008] Of the passage vortex 7, the passage vortex 7 flowing to the back side 5 of the turbine blade 1 provided with the leading edge that generated the passage vortex 7 is generated by the secondary flow. As a result, the vortex tube of the passage vortex 7 does not move to the inter-blade flow path 8 as it extends downstream, and therefore the blade height of the rear side 5 of the turbine blade 1 is reduced. In addition, there is little movement toward the center, and almost no problems occur due to the passage vortex 7 extending toward the rear side 5 of the adjacent turbine blade 1 as described later.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned situation, the present invention reduces the friction loss and the pressure loss occurring in the secondary flow loss region generated at the tip of a three-dimensional airfoil, thereby achieving a large turbine blade. It is an object to provide an axial turbine blade capable of improving performance.

[0010]

Therefore, the axial flow turbine blade of the present invention has the following means. (1) A separation region formed between a blade tip wall and a passage vortex flowing downstream along a blade back surface of a turbine blade forming a blade row erected in a circumferential direction on the blade tip wall. The velocity gradient of the working fluid, which is induced by the generated secondary flow and increases by increasing the flow velocity in the direction perpendicular to the back surface of the wing, is reduced,
In order to reduce the friction loss generated at the blade back, a pointed shape is formed on the blade back of the turbine blade in the separation area formed between the blade tip wall and the passage vortex generated in the cascade. The formed riblets were provided. Preferably, the riblets are provided with a plurality of pointed shapes at the tops, and the pointed shapes are formed in the same blade width direction on the blade back surface along the flow direction of the working fluid.

According to the axial flow turbine blade of the present invention, (a) the path vortex generated at the leading edge of the turbine blade and moved to the rear surface of the blade by the above-mentioned means (1) is a high-speed vortex at a position away from the rear surface of the blade. The fluid is entrained near the blade back like a conventional axial-flow turbine blade, but this high-speed fluid directly contacts the blade back due to the sharp point at the top of the riblet provided on the turbine blade back in the separation area. Area only. Further, the high-speed fluid that is entrained and accelerated by the passage vortex is decelerated by the riblets, and the velocity gradient decreases.

As a result, the wall friction generated on the back surface of the blade can be reduced, and the loss such as the movement of the high-speed fluid can be reduced. In addition, since the pressure-loss fluid having a large pressure loss caused by friction with the riblets flows downstream along the riblets without being swept toward the center of the blade height, the high-speed fluid entrained near the wall surface by the passage vortex Will flow through the fluid having a large pressure loss between the blade and the back of the blade. As described above, the velocity gradient in the vertical direction of the wing rear surface in the vicinity of the wing tip wall on the wing rear surface is moderated, and loss due to wall friction on the wing rear surface can be suppressed.

The axial turbine blade of the present invention employs the following means. (2) The passage vortex is prevented from moving from the leading edge of the turbine blade to the rear surface of the turbine blade, which flows downstream along the blade rear surface of the turbine blade forming the cascade in the circumferential direction on the blade tip wall. In order to reduce the pressure loss on the blade back surface and the pressure loss by weakening the passage vortex itself, it is generated at the leading edge of the turbine blade near the blade tip A bypass passage is provided at the leading edge of the turbine blade from a position where the vortex flowing toward the blade rear side flows downstream and crosses the blade rear surface, and penetrates from the blade abdominal surface to the blade rear surface. One or more bypass passages may be provided in the cord direction, or may be provided in multiple stages in the spanwise direction.

In the axial turbine blade of the present invention, by means of the above (2), a passage vortex generated at the leading edge of the turbine blade is provided with a bypass passage penetrating from the blade abdominal surface to the blade back surface. In the bypass passage, a bypass flow that flows from the blade abdominal surface to the blade back surface is generated by the pressure difference, so that the movement to the blade back side is suppressed and the vortex strength is also weakened.

That is, the direction of the bypass flow is opposite to the direction of the secondary flow and the direction of the vortex tube of the passage vortex when viewed in terms of components in the blade pitch direction near the blade tip wall.
The bypass flow suppresses the development of the passage vortex and the movement of the passage vortex onto the back surface of the blade. As a result, the passage vortex moves from the blade tip wall at the leading edge of the turbine blade to the rear surface of the turbine blade adjacently arranged, and moves downstream of the blade rear surface. The region where the wall friction is large on the blade back surface generated by entraining the high-speed fluid near the blade back surface is reduced, and the frictional resistance is reduced, thereby reducing the pressure loss of the working fluid. further,
The vortex strength of the passage vortex itself due to the bypass flow is also weakened,
This also reduces the friction and pressure losses on the wing back.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an axial turbine blade according to the present invention will be described below with reference to the drawings. FIG. 1 is a partial perspective view showing a first embodiment of an axial flow turbine blade of the present invention,
FIG. 2 is a cross-sectional view of the flow inside the axial turbine cascade according to the first embodiment shown in FIG. The same or similar members as those of the axial turbine blade shown in FIGS. 5 and 6 described above are denoted by the same reference numerals, and description thereof will be omitted.

In FIGS. 1 and 2, reference numeral 11 denotes a plurality of riblets provided in parallel with the flow, and a notch such as a V-shape of about 0.05 mm parallel to the flow direction of the high-speed fluid 9; Passage vortex 7 and wing tip wall 2 extending on wing back surface 5
And is disposed in a triangular separation area S formed on the trailing edge side of the turbine blade 1.

In FIG. 2, as shown in detail, the top of the riblet 11 is formed with a plurality of sharply pointed shapes, and the sharply pointed shapes are arranged at equal pitches at substantially constant positions in the spanwise direction. In this way, a plurality of blades are provided in the separation area of the blade back surface 5. Further, in a groove (notch) sandwiched between the riblets 11, a pressure-loss fluid 10 having a large pressure loss exists, and flows to the downstream side in parallel with the riblets 11.

According to the axial turbine blade of the present embodiment,
As in the case of the conventional axial flow turbine blade, the passage vortex 7 extending to the blade back surface 5 entrains the high-speed fluid 9 at a position away from the blade tip wall 2 and the blade back surface 5 near the blade back surface 5. High-speed fluid 9 that has been accelerated and has a large velocity gradient
However, only the sharp region at the top of the riblet 11 comes into direct contact with the blade back surface 5, the wall friction due to the friction of the high-speed fluid 9 with the blade back surface can be reduced, and the loss of momentum of the high-speed fluid 9 can be reduced.

That is, the velocity gradient in the direction perpendicular to the wing back surface 5 generated near the wing end wall 2 of the wing back surface 5 is alleviated by the riblets 11, and the contact area is reduced, so that the velocity gradient in the wing back surface 5 is reduced. By reducing the wall friction, the occurrence of pressure loss of the high-speed fluid 9 can be suppressed.

The pressure loss fluid 10 having a large pressure loss caused by friction with the riblet 11 flows downstream along the notch of the riblet 11 without being swept toward the center of the blade height. The high-speed fluid 9 caught in the vicinity of the wall is suppressed from being mixed with the pressure-loss fluid 10.
, And flows out downstream without pressure loss.

As described above, in the axial flow turbine blade according to the present embodiment, the riblet 11 is provided in the separation region S sandwiched between the blade end wall 2 and the passage vortex 7 on the blade back surface 5, so that the separation region 2 The velocity gradient of the high-speed fluid 9 in the direction perpendicular to the blade back surface induced by the next flow vortex is alleviated, the loss due to wall friction can be suppressed, and the mixing of the high-speed fluid 9 and the pressure-loss fluid 10 is suppressed. However, the pressure loss of the high-speed fluid 9 can be reduced, and the turbine efficiency can be greatly improved.

Next, FIG. 3 is a partial perspective view showing a second embodiment of the axial flow turbine blade of the present invention, and FIG. 4 is a flow chart showing the flow inside the axial turbine blade cascade according to the second embodiment shown in FIG. It is sectional drawing.

Also in these figures, the same members as those of the axial flow turbine blades shown in FIGS. 5 and 6 or similar members are denoted by the same reference numerals and description thereof will be omitted. 3 and 4, reference numeral 12 denotes a bypass passage, and reference numeral 13 denotes a bypass flow. The bypass passage is formed from the leading edge of the turbine blade 1, and the vortex tube of the passage vortex 7 extending onto the blade back surface 5 of the adjacent turbine blade 1 by the secondary flow 6 forms a vortex tube between the blade end wall 2 and the blade back surface 5. From the position crossing the line of intersection to the leading edge to the turbine blade 1, one or more chords are provided near the blade tip wall 2 in the chord direction so as to penetrate the turbine blade 1 from the blade abdominal surface 4 to the blade back surface 5.

As shown in FIG. 4, the passage vortex 7 flowing out of the portion where the bypass passage 12 is provided is substantially on the wing end wall 2,
A bypass flow 13 is generated in the bypass passage 12 provided in the turbine blade 1 so as to penetrate from the blade front surface 4 to the blade rear surface 5 due to a pressure difference between the blade front surface 4 and the blade rear surface 5. The direction of the bypass flow 13 is, in terms of components in the blade pitch direction near the blade tip wall 2, the direction of the secondary flow 6 and the passage vortex 7
Of the bypass flow 1
Numeral 3 reduces the vortex strength of the passage vortex 7, suppresses the development of the passage vortex 7, and suppresses the movement of the passage vortex 7 generated at the leading edge of the adjacent turbine blade 1 onto the blade back surface 5.

As a result, the passage vortex 7, which is generated on the blade tip wall 2 at the leading edge of the turbine blade 1 and moves onto the blade back surface 5 of the turbine blade 1 disposed adjacently, is in the blade width direction, that is, in the blade width direction. Instead of moving toward the center of height, the blade moves toward the downstream side near the wing tip wall 2 of the wing back surface 5. At the wing back surface 5, the passage vortex 7 entrains the high-speed fluid 9 described above near the wing back surface 5. As a result, the separation area S where the wall friction at the blade back surface becomes large is reduced, and the friction loss is reduced. As a result, the pressure loss of the working fluid F is reduced. Further, the weakening of the vortex strength of the passage vortex 7 itself due to the above-mentioned bypass flow 13 also reduces the friction loss and the pressure loss on the blade back surface 5, reduces the pressure loss of the high-speed fluid 9, and greatly increases the turbine efficiency. Improvement can be achieved.

[0027]

As described above, according to the axial flow turbine blade of the present invention, the axial flow turbine blade is generated in the separation region formed between the blade tip wall and the passage vortex flowing downstream on the blade back surface. In order to reduce the velocity gradient of the high-speed fluid accelerated by the working fluid flowing by increasing the flow velocity in the direction orthogonal to the blade back surface induced by the secondary flow to reduce the friction loss generated at the blade back surface, A riblet having a sharpened top is provided in a separation region formed between the blade tip wall and the passage vortex.

As a result, the passage vortex that has moved onto the back of the wing entrains the high-speed fluid, in which the working fluid flowing away from the back of the wing is accelerated, near the back of the wing. The only contact is in the sharpened area of the top of the riblet provided on the blade back surface of the turbine blade in the separation area, and the high-speed fluid accelerated by the passage vortex is
The speed is reduced by the riblets, and the speed gradient is reduced. Therefore, it is possible to reduce the wall friction generated on the back surface of the blade, and to reduce the loss of the momentum of the high-speed fluid.

The pressure loss fluid having a large pressure loss caused by friction with the riblets flows downstream along the riblets without being swept toward the center of the blade height, and is drawn into the vicinity of the wall surface by the passage vortex. The high-speed fluid flows through the fluid having a large pressure loss between the high-speed fluid and the blade back surface. The turbine efficiency can be improved by alleviating the velocity gradient in the direction perpendicular to the blade rear surface near the blade tip wall on the blade rear surface and suppressing the loss due to wall friction at the blade rear surface.

According to the axial flow turbine blade of the present invention, (2) the passage vortex flowing downstream from the leading edge of the turbine blade to the downstream side along the back surface of the blade is prevented from moving. In order to reduce the pressure loss on the backside of the blade and reduce the pressure loss by weakening the passage vortex itself, extend from the leading edge of the turbine blade near the blade tip wall to the backside of the blade in the cascade. A bypass passage penetrating from the blade abdominal surface to the blade back surface is provided at a position where the flowing passage vortex flows downstream and crosses the blade back surface of the turbine blade. As described above, the bypass passage is provided in the turbine blade from the blade abdominal surface to the blade back surface, and a bypass flow flowing from the blade abdominal surface to the blade back surface is generated in the bypass passage, so that the passage vortex moves to the blade back side. And the vortex intensity is also reduced.

As a result, the passage vortex moves from above the blade tip wall at the leading edge of the turbine blade to the back of the blade, and moves downstream of the back of the blade. The separation area where the wall friction at the blade back surface, which is generated by entrainment, becomes smaller, and the friction loss is reduced, whereby the pressure loss of the working fluid is reduced. Furthermore, the vortex strength of the passage vortex itself due to the bypass flow is also weakened, which also reduces the friction loss and pressure loss on the blade back surface. Thus, the turbine efficiency can be improved by reducing the friction loss and the pressure loss.

[Brief description of the drawings]

FIG. 1 is a partial perspective view showing a first embodiment of an axial flow turbine blade of the present invention,

FIG. 2 is a cross-sectional view of the flow inside the axial turbine cascade according to the first embodiment shown in FIG. 1,

FIG. 3 is a partial perspective view showing a second embodiment of the axial flow turbine blade of the present invention,

FIG. 4 is a cross-sectional view of the flow inside the axial turbine cascade according to the second embodiment shown in FIG. 3;

FIG. 5 is a schematic view showing a state of a flow inside a cascade of conventional axial flow turbine blades provided on a blade tip wall with turbine blades erected in a circumferential direction;

FIG. 6 is a cross-sectional view showing details of a flow near a blade tip wall on a back surface of a turbine blade among internal flows of the conventional axial flow turbine cascade shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Turbine blade 2 Blade end wall 3 Horseshoe vortex 4 Blade surface 5 Blade back surface 6 Secondary flow 7 Passage vortex 8 Blade passage 9 High-speed fluid 10 Pressure loss fluid 11 Riblet 12 Bypass passage 13 Bypass flow F Working fluid S Separation area

Claims (2)

[Claims] 1. An axial flow turbine blade provided with a turbine blade standing upright on a blade tip wall so as to form a blade row in a circumferential direction. The velocity gradient of the working fluid flowing perpendicular to the blade back surface, induced by the secondary flow vortex generated in the separation region, is reduced in the separation region on the blade back surface of the turbine blade sandwiched by the passage vortex An axial flow turbine blade provided with a riblet having a pointed top so as to reduce frictional loss generated at the blade rear surface. 2. An axial flow turbine blade provided with a turbine blade standing upright on a blade tip wall so as to form a blade row in a circumferential direction, formed at a leading edge of the turbine blade near the blade tip wall. The passage vortex that flows out of the cascade and suppresses the movement of the passage vortex onto the back surface of the blade at a front edge portion ahead of a position crossing the back surface of the turbine blade. An axial flow turbine blade provided with a bypass passage that penetrates from a blade abdominal surface to the blade back surface to reduce pressure loss and to weaken the passage vortex itself to reduce pressure loss and reduce friction loss.