JP2000045703A - Axial flow turbine cascade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial flow turbine cascade which can restrain the occurrence of a secondary flow vortex in the axial flow turbine cascade for reducing a secondary flow ross. SOLUTION: In this axial flow turbine cascade having a plurality of blades so as to form a cascade 1 in a peripheral direction, the turbine cascade is formed so that the width of a passage A at the upper and lower blade ends of each blade may be narrower than the width A of the passage at the center of a blade height H, and moreover the width of a throat at the upper and lower blade ends 10 of each blade may not be smaller than the width of the throat at another blade height position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial turbine cascade such as a steam turbine and a gas turbine.

[0002]

2. Description of the Related Art FIG. 5 is a schematic diagram showing a flow inside a conventional axial flow turbine cascade. In FIG. 5, reference numeral 2 denotes a wing tip wall. When the working fluid 3 passes through the axial-flow turbine cascade 1 (hereinafter simply referred to as “cascade 1”), the flow of the working fluid 3 in the vicinity of the blade tip wall 2 generates kinetic energy by friction with the blade tip wall 2. lose. The lost kinetic energy cannot be taken out as power and is called loss.

The high-loss fluid near the tip wall 2 forms a secondary flow vortex 4. The secondary flow vortex 4 is composed of the wing apex surface 5 and the wing back surface 6
It develops further due to the cross-flow 7 created by the pressure difference between and flows downstream of the cascade 1 with increasing losses. The loss generated by the action of the wing tip wall 2 and the secondary flow vortex 4 is called secondary flow loss.

[0004]

SUMMARY OF THE INVENTION In view of the above problems in the axial turbine cascade, the present invention provides an axial turbine cascade capable of suppressing generation of secondary flow vortices and reducing secondary flow loss. The task is to provide.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and is directed to an axial flow turbine cascade having a plurality of blades so as to form a blade cascade in a circumferential direction. The width of the flow path at the upper and lower wing ends of each wing is smaller than the flow path width at the center of the wing height, and the throat width at the upper and lower wing ends of each wing is not smaller than the throat width at other wing height positions. The present invention provides an axial flow turbine cascade characterized by being formed as follows.

That is, according to the present invention, in the cascade, the flow rate of the working fluid near the blade tip wall is reduced to suppress the generation of the secondary flow vortex, the secondary flow loss is reduced, and the throat is reduced. The flow rate of the working fluid can be made uniform in the blade height direction so that the working fluid can flow uniformly into the downstream cascade.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. FIG. 1A is a perspective view showing a partial blade arrangement of an axial flow turbine cascade according to an embodiment of the present invention, and FIG. 1B is an airfoil cross section of the blade shown in FIG. FIG. FIG. 2A is a perspective view showing a throat portion in a partial blade arrangement of an axial flow turbine cascade according to an embodiment of the present invention, and FIGS. 2B and 2C are diagrams showing another throat portion. It is explanatory drawing of the example of.

As shown in FIGS. 1 (a) and 1 (b), the cascade 1 according to the present embodiment has a channel width A on the leading edge 11 side of the blade because the upper and lower blade tips 10 are thick. Has a narrow wing shape,
The blade height center portion 12 has a thin airfoil shape having a wide flow path width A on the blade leading edge 11 side, and has a shape in which these airfoils are smoothly joined in the blade height H direction. .

As shown in FIG. 2A, a throat portion 14 formed between the trailing edge 13 of each wing in the cascade 1 and the back surface 5 of the adjacent wing has a throat width B. It is larger at the upper and lower wing tips 10 than at the average throat width obtained by (throat area S / wing height H) and smaller at the center 12 of the wing height. However,
The throat width B is not limited to this, and another example of the throat portion 14 is shown in FIG.
Alternatively, as shown in (c), the throat width B may be constant in the wing height H direction. That is, as shown in FIG. 3, the distribution of the throat width B in the direction of the wing height H has a shape of a constant straight line C or a valley D, as shown in FIG.

[0010] The axial turbine cascade according to the present embodiment comprises:
With the configuration described above, as shown in FIG. 1, when the working fluid 3 flows into the cascade 1 from the blade leading edge 11 side, the flow path width A between the blades near the blade leading edge 11 is Upper and lower wing tips 10
And narrow at the wing height center 12, so that the cascade 1
As shown in FIG. 4 showing the streamlines of the working fluid 3 in the meridional plane of FIG. 4, the flow rate of the working fluid 3 is concentrated near the blade height center 12 on the blade leading edge 11 side. As a result, the flow rate of the working fluid 3 near the blade tip wall 2 is reduced, the generation of the secondary flow vortex is suppressed, and the secondary flow loss is reduced.

On the other hand, near the trailing edge 13 at the exit of the cascade 1,
As shown in FIGS. 2A, 2B, and 2C, the throat width B is constant in the wing height H direction or is smaller than the average throat width defined by (throat area S / wing height H). The throat width B is large at the upper and lower wing tips 10 and smaller at the wing height center 12.

That is, since the throat width at the upper and lower wing tips of each wing is not smaller than the throat width at the other wing height positions, as shown in FIG. Part of the flow rate of the working fluid 3 biased toward the center 12 is the throat width B
, The flow rate distribution of the working fluid 3 in the direction of the blade height H is made uniform throughout. As a result, the working fluid 3 can be uniformly supplied to the downstream cascade in the blade height H direction.

[0013]

As described above, according to the present invention, in an axial turbine cascade provided with a plurality of blades so as to form a blade cascade in the circumferential direction, the axial turbine cascade is formed at the upper and lower blade tips of each blade. The width of the channel is smaller than the width of the channel at the center of the blade height, and the throat width at the upper and lower wing tips of each wing is formed so as not to be smaller than the width of the throat at other wing height positions. Therefore, in the cascade, the flow width at the blade tip is narrower than the flow width at the center of the blade height, so that the flow rate of the working fluid near the blade tip wall is reduced, and the generation of the secondary flow vortex is suppressed. The flow loss is reduced, and in the throat portion, the flow rate of the working fluid is made uniform in the blade height direction by the shape of the throat portion, so that the working fluid can be uniformly supplied to the downstream cascade.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a partial blade arrangement of an axial flow turbine cascade according to an embodiment of the present invention, and FIG. 1B is an airfoil sectional view of the blade shown in FIG. It is.

FIG. 2A is a perspective view showing a throat in a partial blade arrangement of an axial flow turbine cascade according to an embodiment of the present invention, and FIGS. 2B and 2C are diagrams showing another throat. It is explanatory drawing of the example of.

FIG. 3 is a diagram showing a relationship between a blade height position and a distribution of a throat width.

FIG. 4 is an explanatory diagram showing streamlines of a working fluid in a meridional plane of a cascade.

FIG. 5 is a schematic diagram of a flow inside a conventional axial flow turbine cascade.

[Explanation of symbols]

 Reference Signs List 1 cascade 2 wing tip wall 3 working fluid 4 secondary flow vortex 5 wing apex surface 6 wing back surface 7 cross flow 10 wing tip 11 wing leading edge 12 wing height central part 13 wing trailing edge 14 throat

Claims (1)

[Claims] In an axial flow turbine cascade provided with a plurality of blades so as to form a blade cascade in a circumferential direction, a flow path width at upper and lower blade tips of each blade is narrower than a flow path width at a blade height center. ,
And a throat width at upper and lower blade tips of each blade is formed so as not to be smaller than a throat width at another blade height position.