JPH11190203A - Axial flow turbine blade cascade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial flow turbine blade cascade with an improved turbine efficiency by discouraging development of secondary flow vortices caused in the vicinity of blade ends by secondary flows, and especially by weakening the strength of the secondary flows. SOLUTION: A sectional shape in the flow direction in the vicinity of a blade inner surface 4 in a turbine blade 1 erected on a blade end wall 2 is formed into a protrusive shape such that an amount of the outward projection is made larger toward its central part in the flow direction with the blade end wall 2 bent inward while a sectional shape in the vicinity of a blade outer surface 5 is formed into a recessed shape such that an amount of the inward projection is made larger toward its central part in the flow direction with the blade end wall 2 bent outward, whereby portions of the blade end wall 2 in the vicinity of the blade inner and outer surfaces 4, 5 are smoothly connected in the circumferential direction to thereby provide the projective and recessed surfaces having an equal pitch in the circumferential direction of the blade end wall 2, and a blade-to-blade passage 8 is formed by the corresponding blade and an adjacent blade. Accordingly, the strength of a secondary flow from the blade inner surface 4 side to the blade outer surface 5 side, especially the strength of the flow in the vicinity of the blade end 2 can be weakened, resulting in restraining development of secondary flow vortices.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A large cascade loss is caused by energy loss caused by a secondary flow vortex developed by a secondary flow generated on a root of a three-dimensional airfoil forming a cascade or on a tip wall near a blade tip. In an axial flow turbine blade in which turbulence occurs, it is important to reduce these cascade losses in order to improve performance.

FIG. 3 shows a blade tip wall 2 so as to form a cascade.
FIG. 3 is a schematic diagram showing a state of a flow inside a cascade of axial flow turbine blades provided with a turbine blade 1 erected in a circumferential direction. 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. To form

[0004] The vortex tube of this passage vortex is formed so as to surround the leading edge of the wing near the wing tip wall 2, and as shown by a dashed line,
Since the shape is a horseshoe shape, the normal horseshoe vortex 3
It is called. On the other hand, of the turbine blades 1 disposed adjacent to each other, the blades formed in the cascade formed by being sandwiched between the blade abdominal surface 4 of one turbine blade 1 and the blade back surface 5 of the other turbine blade 1. In the vicinity of the wing tip wall 2 in the interflow path 8, a secondary flow flowing from the wing apex face 4 side to the wing back face 5 due to a pressure difference generated by the working fluid F acting on the wing apex face 4 and the wing back face 5, respectively. 6 are formed.

[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. From the wing abdominal surface 4 side to the wing back surface 5
The secondary flow 6 develops into a large vortex called a secondary flow vortex 7 while flowing in the inter-blade flow path 8 toward the blade back surface 5 by the secondary flow 6.

The secondary flow vortex 7 contains a fluid having a large energy loss at the center thereof, that is, a so-called pressure-loss fluid. A turbine blade that has a so-called viscous dissipation action that generates a large energy loss due to friction with a wall surface, and extracts kinetic energy of the working fluid F as work in order to increase the energy loss of the working fluid F flowing in the inter-blade flow path 8. In a row, the development of this secondary flow vortex 7 will lead to a performance degradation.

In general, the larger the pressure difference caused by the working fluid F acting on the blade flank 4 and the blade back 5, the greater
The strength of the secondary flow 6 described above increases, and the secondary flow 6 develops while flowing in the interblade flow path 8 from the blade abdominal surface 4 to the blade back surface 5.
The secondary flow vortex 7 develops more as the strength of the secondary flow 6 near the blade tip wall 2 increases, and the viscous dissipation action also increases, and the secondary flow vortex 7 significantly reduces the performance of the turbine cascade. Become.

[0008]

SUMMARY OF THE INVENTION The present invention solves the problem of the conventional axial flow turbine cascade, in which a large cascade loss is caused by the energy loss generated by the secondary flow vortex, and the performance is deteriorated. As the pressure difference between the abdominal surface and the back surface of the blade caused by the working fluid acting on the abdominal surface and the back surface of the blade decreases, the strength of the secondary flow caused by the pressure difference, in particular, the blade tip By reducing the pressure difference near the wall, weakening the intensity of the secondary flow generated near the blade tip wall, suppressing or delaying the development of the secondary flow vortex, and flowing in the inter-blade flow path An object of the present invention is to provide an axial turbine cascade in which the energy loss of a working fluid is reduced and the performance of the turbine cascade is improved.

[0009]

For this reason, the axial flow turbine cascade of the present invention has the following means.

(1) The cross-sectional shape in the flow direction near the blade abdominal surface of the turbine blade erected on the blade tip wall so as to form a blade row in the circumferential direction is such that the more the center in the flow direction, the deeper the blade tip wall becomes. (2) The cross-sectional shape in the flow direction near the blade back surface of the turbine blade increases toward the center of the flow direction with the blade end wall outwardly increasing toward the center. (3) A wing tip wall near the wing apex surface having a convex cross-sectional shape in the flow direction, and a wing tip wall near the wing back surface having a concave cross-sectional shape in the flow direction, In the circumferential direction of the blade tip wall, the cross-sectional shape that is smoothly connected in the circumferential direction and the uneven pitch surface is formed at an equal pitch adjoins the inter-blade flow path formed in the flow direction. It was formed together with the turbine blade.

It is to be noted that, by increasing the amount of inward projection of the wing tip wall toward the center in the flow direction, the upstream of the wing tip wall having a convex cross-sectional shape provided in the flow direction near the wing abdominal surface,
And the downstream end side, without providing the uneven surface, project outward from the normal blade end wall where the turbine blade is installed, and the blade end wall faces outward toward the center in the flow direction By increasing the amount of protrusion, the upstream and downstream end sides of the blade end wall having a concave cross-sectional shape provided in the flow direction near the blade rear surface are made to project inward from the normal blade end wall surface. It is preferable that the cross section be shaped as described above.

According to the axial flow turbine cascade of the present invention, by the means described above, the inter-blade between the blade apex and the portion close to the blade end wall where the blade end wall on which the turbine blade is erected is made convex is provided. The working fluid flowing through the flow path is accelerated by the convex shape of the blade tip wall, and accordingly, the static pressure in this portion decreases. Also,
The working fluid flowing through the inter-blade flow path in the vicinity of the back surface of the wing and in the vicinity of the wing tip wall is decelerated by the concave shape of the wing tip wall, and the static pressure in this part increases accordingly. I do.

As a result, a pressure difference generated by the working fluid F acting on each of the blade abdominal surface and the blade back surface, that is, a pressure difference in which the static pressure near the blade abdominal surface is higher than the static pressure near the blade back surface, and a secondary flow vortex Is generated and the pressure difference in the vicinity of the developing blade tip wall is alleviated, and the strength of the secondary flow flowing from the blade abdominal surface toward the blade rear surface is reduced.

For this reason, the secondary flow vortex flowing downstream from the blade apex side to the blade back side in the blade-to-blade flow path is weakened by reducing the strength of the secondary flow near the blade tip wall. The development is suppressed, and furthermore, the speed of development is slowed down, the amount of pressure loss fluid contained in the working fluid when flowing in the inter-blade flow path is reduced, and the viscous dissipation action is also reduced, and the inter-blade flow Energy loss due to the secondary flow vortex of the working fluid flowing in the path can be reduced, the performance of the turbine cascade can be improved, and an axial turbine cascade with high turbine efficiency can be obtained.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an axial turbine cascade according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view showing a part of an axial turbine cascade as a first embodiment of the axial turbine cascade of the present invention. FIG. 2 is a flow direction blade end wall of the axial turbine cascade shown in FIG. It is a conceptual diagram of a shape. In the figure, the same members as those shown in FIG.
The same reference numerals are given and the description is omitted.

In the drawing, reference numeral 9 denotes a ventral cut line provided in the flow direction of the working fluid F flowing near the wing apex surface 4 on the wing tip wall 2, and 10 similarly flows near the wing back surface on the wing tip wall 2. It is a back side cutting line provided in the flow direction of the working fluid. Ventral-side cutting line 9 and back-side cutting line 10 provided in the flow direction near the wing abdominal surface 4 and near the wing back surface 5
End wall 2 cut in the direction of flow of working fluid 8
As shown in FIG. 2, the cross-sectional shape of the cutting line 9 in the vicinity of the blade abdominal surface 4 is such that the blade end wall 2 has a larger amount of inward (upward) projection toward the center of the flow. The cross-sectional shape of the portion along the cutting line 10 near the blade back surface 5 is a concave shape 12 in which the blade end wall 2 has a larger outward projection toward the center of the flow.

The sectional shape in the flow direction is a convex shape 11
The wing tip wall 2 in the vicinity of the wing abdominal surface 4 and the wing tip wall 2 in the vicinity of the wing back surface 5 having a convex sectional shape 12 in the flow direction are connected by a smooth curve or straight line in the circumferential direction. Then, in the circumferential direction of the blade end wall 2 on which the turbine blade 1 is erected,
A blade end wall 2 having a transverse cross-sectional shape having a uniform pitch uneven surface is formed, and an inter-blade flow path 8 for flowing a working fluid F from the leading edge side to the trailing edge side of the turbine blade 1 with the adjacent turbine blade 1. It is formed.

The upstream and downstream ends of the convex shape 11 provided in the flow direction near the blade abdominal surface 4 are provided with two normal blade tip walls on which turbine blades are erected without providing any uneven surface. 2 and a concave shape 1 provided in the flow direction near the blade back surface 5.
The upstream and downstream ends of the blade 2 are arranged so as to protrude inward from the normal surface of the wing tip wall 2.

In the axial flow turbine cascade according to the present embodiment, the blade tip wall 2 has a convex shape 11 near the blade abdominal surface 4 and a concave shape 12 near the blade back surface 5. By changing the shape in accordance with the cascade pitch, energy loss of the working fluid F due to the secondary flow vortex 7 can be reduced, and turbine efficiency can be improved.

That is, in the vicinity of the wing apex surface 4, the wing tip wall 2 has a convex shape 11 in the flow direction of the working fluid F, so that the flow velocity of the working fluid F flowing along the wing tip wall 2 increases,
The static pressure, which varies in proportion to the square of the flow rate, decreases. For this reason, the static pressure is lower at the blade tip surface 4 at the blade tip of the turbine blade 1 than at the blade tip surface 4 at the center of the blade height.

On the other hand, in the vicinity of the blade back surface 5, the blade end wall 2 has a concave shape 12 in the flow direction of the working fluid F, so that the flow velocity of the fluid flowing therethrough decreases, and the static pressure is accordingly reduced. Rises. For this reason, the static pressure is higher at the blade back 5 at the blade tip than at the blade back 5 at the center of the blade height.

As a result, at the blade tip of the turbine blade 1, the pressure difference between the blade abdominal surface 4 and the blade back surface 5 becomes smaller than the pressure difference between the blade abdominal surface 4 and the blade back surface 5 at the center of the blade height. Wing vent surface 4
The strength of the secondary flow 6 flowing from the side toward the blade back surface 5 is weakened, and particularly the secondary flow 6 generated near the blade tip wall 2 at the leading edge of the turbine blade 1 and near the blade tip wall 2. Developed by 2
The development of the secondary flow vortex 7 is suppressed, and the development of the secondary flow vortex 7 that develops while flowing in the inter-blade flow path 8 is delayed. The pressure loss fluid contained in the fluid F is reduced, and the viscous dissipation action is also reduced. The energy loss due to the secondary flow vortex of the working fluid F flowing in the interblade flow path 8 is reduced, thereby improving the performance of the turbine cascade. And an axial turbine cascade with high turbine efficiency can be obtained.

[0023]

As described above, according to the axial turbine cascade of the present invention, the flow near the blade abdominal surface of the turbine blade erected on the blade end wall so as to form the blade cascade in the circumferential direction. The cross-sectional shape in the direction is a convex shape with the blade tip wall inwardly projecting inward toward the center in the flow direction and the amount of protrusion is increased.The cross-sectional shape in the flow direction near the back of the blade of the turbine blade is the center in the flow direction. The wing tip wall has a concave shape with the projection amount increased toward the outside, and the wing tip wall near the wing abdominal surface and the wing tip wall near the wing back face,
The cross-sectional shape, which is smoothly connected in the circumferential direction and has an uneven pitch at the same pitch in the circumferential direction of the blade tip wall, forms an inter-blade flow path formed in the flow direction together with the adjacent turbine blade. It was taken.

In the axial flow turbine cascade according to the present invention, the inter-blade flow path in the vicinity of the blade tip surface where the blade tip wall on which the turbine blade is erected is formed in a convex shape and near the blade tip wall is thereby formed. The flowing working fluid is accelerated by the convex shape, and the static pressure in this portion decreases accordingly, and the working fluid flows through the inter-blade flow passage near the concave back surface of the blade and near the blade tip wall. The more the fluid, the more the speed is reduced by the concave shape, and the static pressure in this portion increases accordingly.

Therefore, the pressure difference generated by the working fluid F acting on the blade apex surface and the blade back surface, that is, the pressure difference in which the static pressure near the blade aft surface is increased by the static pressure near the blade back surface, and the secondary flow vortex The pressure difference in the vicinity of the generated and developed blade tip wall is alleviated, and the intensity of the secondary flow flowing from the blade abdominal surface toward the blade back surface is reduced.

Therefore, the secondary flow vortex generated near the blade tip wall at the leading edge of the turbine blade and developing while flowing from the blade abdomen side to the blade back side in the blade-to-blade flow path is generated by the blade. The development is suppressed by the strength of the secondary flow near the end wall being weakened, the development is further delayed, and the pressure drop fluid contained in the working fluid when flowing in the inter-blade flow path is reduced,
The viscous dissipation effect is also reduced, the energy loss due to the secondary flow vortex of the working fluid flowing in the inter-blade flow path is also reduced, and the performance of the turbine cascade can be improved. can do.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a part of an axial flow turbine cascade as a first embodiment of an axial flow turbine cascade according to the present invention;

2 is a conceptual diagram of a cross-sectional shape of a flow direction blade end wall of the axial flow turbine cascade shown in FIG.

FIG. 3 is a schematic diagram showing a state of a flow inside a conventional axial flow turbine cascade.

[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 Secondary flow vortex 8 Blade flow path 9 Ventral cut line 10 Back cut line 11 Convex shape 12 Concave shape F Working fluid

Claims (1)

[Claims] 1. An axial flow turbine cascade provided with turbine blades erected on a blade tip wall so as to form a blade cascade in a circumferential direction, wherein the blade tip wall near a blade abdominal surface of the turbine blade is provided. The cross-sectional shape in the flow direction has a convex shape protruding inward toward the center in the flow direction, and the cross-sectional shape in the flow direction of the blade end wall near the blade back surface of the turbine blade is more outward toward the center in the flow direction. The concave shape that protrudes toward
The convex shape and the concave shape are smoothly connected to each other in the circumferential direction, and an inter-blade flow path having a cross-sectional shape in which uneven surfaces having equal pitches are formed in the circumferential direction on the blade tip wall is provided. Axial turbine cascade.