JPS5832903A - Axial flow turbine - Google Patents

Abstract

PURPOSE:To reduce the cascade loss due to the secondary flow by bending the wall face profile along the back side outward the passage direction and by bending the wall face profile along the belly side inward the passage direction. CONSTITUTION:The height of wall faces 28.30,29.31 at the inlet end and outlet end of a cascade is made equal at the berry and back sides. The wall face profiles 24, 26 along the back side at the middle section between the inlet and outlet sections are bent outward the passage direction, and the wall face profiles 25a, 27a along the berry side are bent inward the passage direction. The pressure at the back side near the inside wall 22 and outside wall 23 is increased and the pressure at the berry side is decreased, thereby the pressure gradient between the berry and back sides at the wall face can be alleviated, thus the secondary flow in the cascade is decreased and the loss can be reduced.

Description

[Detailed Description of the Invention] - The present invention relates to an axial flow turbine, and in particular, the present invention relates to an axial flow turbine.
The present invention relates to an axial flow turbine with a row of blades mounted on an outer wall.

The stages of an axial flow turbine are composed of annular rows of movable and stationary blades, and due to these different slopes and relatively low blade heights, losses due to secondary flows are It is known that a large proportion of the total losses are accounted for.

To explain the mechanism of generation of secondary flow in the conventional blade row shown in Fig. 1 below, the working fluid flowing in the direction i & of the arrow X flows through the 1% IO passage of the turbine blade t1m Due to the centrifugal force, the pressure on the ventral side 12 of the tube is greater than the pressure on the dorsal side 13, creating a pressure gradient across the passageway. On the other hand, the outer wall 14 of the blade row
Since a boundary layer is formed in the vicinity of the inner wall 1s, the flow velocity is low, and there is no centrifugal force sufficient to combine with the pressure gradient, so the outer wall 1s. In the vicinity of the inner wall 15, a pressure gradient causes a flow 2 in a direction across the passage from the ventral side 12 to the dorsal side 13, which is called a secondary flow. When a secondary flow exists, the energy of the working fluid is dissipated by the vortices and is not used effectively, causing blade row loss.

Various structures have been proposed in the past in order to reduce losses due to such secondary flows. For example, the shape of the outer wall 14 and the inner wall 15 is not a single cylindrical surface or a conical surface as shown in FIG.
2. There is a method of making the height different on the dorsal side 13. FIG. 2 shows an example of this, in which the inner wall 15 on the ventral side 12 is placed at the outlet of the blade row, and the inner wall 1 on the back @13 is
The inner wall 15 is sloped so as to be higher than the position 17 of 5, and the fluid near the inner wall 15 is caused to flow from the dorsal side 13 to the antral side 111!
This is an attempt to cancel out the secondary flow by creating a flow towards it. This structure of blade rows does not show any effect on non-rotating blade rows such as stationary blades, and since the positions 16 and 17 of the inner walls 15 on the ventral side 12 and the dorsal side 13 are different at the exit section of the blade row, Under the department.

Losses may occur when the ventral 12 and dorsal 13 streams merge.

An object of the present invention is to provide an axial flow turbine that reduces blade cascade loss due to secondary flow regardless of whether the stationary blades or rotor blades are busy, and which does not cause additional loss or reduction in strength. .

In the axial flow turbine according to the present invention, the positions of the wall surfaces at the inlet and outlet sections of the blade row are the same on the ventral side and the front side, while the wall surface shape is different from the middle section between the inlet section and the outlet section to the dorsal side 1fcE in the passage direction. It is characterized by being curved on the outside, and the wall surface shape on the ventral side is curved inward in the passage direction.

Hereinafter, details of the blade row of the axial flow turbine according to the present invention will be explained with reference to FIGS. 3 and 4.

FIG. 3 is a perspective view 21a of a blade row according to the present invention.

21b turbine member, 22 inner wall 23 close to the turbine shaft;
is the outer wall far from the turbine axis, 24 is the intersection line of the outer 11!3 and the back side of the turbine blade 211, 25a, 2$b are the outer wall 112
3 and turbine blade 21! l, the intersection line of the ventral aspect of 21b,
26 is the intersection line %2 between the inner wall 22 and the back side of the turbine blade 21a
7a and 27b are the inner wall 22 and the turbine blade 21R921
The lines of intersection with the ventral surface of b are shown, respectively. FIG. 4 is a sectional view of a main part of a blade row according to the present invention, and the reference numerals are the same as in FIG. 3.

According to the present invention, as shown in FIGS. 3 and 4, the intersection lines 24 and 25m where the outer wall 23 touches the dorsal and ventral surfaces of the turbine blade 21m converge at a point 28 at the tool inlet end, and They converge at point '29 at the end.

The intersection lines 26 and 27Jl, where the inner wall 22 touches the dorsal and ventral side surfaces of the turbine blade 21m, converge at a point 3o at the tool inlet end,
It gathers at a point 31 at the mouth end of the tool. That is, the height of the wall surface at the inlet end and outlet end of the blade row is the same on the ventral side and the dorsal side. Next, in the present invention, the intersection line 24 where the outside @ 23 touches the back side of the turbine blade 21a is moved away from the turbine axis at the center compared to the inlet and outlet ends, as shown in the cross-sectional view of FIG. has an outwardly convex curvature, whereas the outer wall 2
The intersection 1125a where 3 crosses the ventral surface of the turbine blade 218 is closer to the turbine axis at the center than the input end and the exit end, and has a convex curvature inside the flow path. The outer wall 23 is connected to the intersection line 24
, 25b are smoothly connected to form a curved surface.

In addition, the intersection line 26 where the inner wall 22 contacts the back side of the turbine blade 21a is closer to the turbine axis at the center than at the inlet/outlet ends, and has a convex curvature outward in the flow path, so that the inner wall 22 has an inclined surface. The intersection line 271 that touches the side surface has a curvature that is farther away from the turbine axis at the center than the inlet and outlet ends and is convex toward the inside of the flow path. The inner walls 22 and 26 and 27b are smoothly connected to form a curved surface.

Next, the operation of the axial flow turbine having the blade cascade of the present invention will be explained in the fourth section.
This will be explained using figures.

Among the working fluid flowing in the direction of arrow Dorsal pressure increases by 23 Ka. On the other hand, the intersection lines 25a and 25b where the outer ll2B touches the ventral surface
The pressure in the vicinity is lower than that of the conventional blade array shown in FIG. 1 due to the wall shape of the channel having a convex curvature inward. On the other hand, considering the flow near the inner wall 22, the flow near the intersection line 26 where the inner wall 22 contacts the back surface is pushed toward the wall and flows along the inner wall 22 due to the wall shape having a convex curvature outward of the flow path. Intersection 11127 with increased dorsal pressure and opposite curvature.
The pressure on the inner wall <B abdomen/side near a and 27b decreases.

As mentioned above, the main cause of secondary flow is the pressure gradient from the ventral side to the anterior side on the wall surface, so reducing the pressure difference between the ventral side and dorsal side near the wall will dramatically reduce the secondary flow. Leads to. However, as described above, the axial flow turbine having the blade cascade of the present invention has an inner diameter of 22 mm. In the vicinity of the outer wall 23, it has the effect of increasing the pressure on the dorsal side and lowering the pressure on the ventral side compared to the conventional one, so it is possible to alleviate the pressure gradient between the ventral side, the dorsal side, and the survey on the wall surface. flow
4°, making it possible to provide an axial flow turbine with less loss. Furthermore, according to the present invention, the dorsal and ventral wall surface positions are the same at the blade row outlet.
There is no additional loss when the dorsal and ventral streams merge downstream. Further, in the present invention, there is no need to provide grooves or notches on the blade surface or wall surface, so there is no decrease in strength.

Note that FIG. 3 and FIG. 4 are one embodiment of the present invention, and the effect can be obtained even if the wall face shape shown in the figure is not applied to both the inner wall 22 @ the outer wall 23 but only to one of them. Yes, intersection 1 in Figure 4 again! 24, 2! Sa,
26, 27m, one of the intersection lines 24, 25m, and the intersection IJI26゜27
A method such as making only one of the lines 8 a curved line and making the rest a straight line also has the effect of the present invention.

As mentioned above, this design can reduce losses due to secondary flow in both the stator blades and rotor blades of the turbine, and also creates an axial flow turbine without incidental loss or deterioration in strength. can be provided.

[Brief explanation of the drawing]

1 and 2 are perspective views showing a row of blades in a known axial flow turbine, FIG. 3 is a perspective view showing an embodiment of an axial flow turbine based on the present invention, and FIG. 4 is a perspective view showing the blades of the present invention. FIG. 2 is a cross-sectional view of an axial turbine having rows taken along a plane including the turbine shaft. 21a, 21b...Turbine blade 22-...Inner wall 23...Outer wall 24...Intersecting line 25a, 2 of the outer wall and the back side of the turbine blade
5b... Intersection line 26 between the outer wall and the ventral surface of the turbine blade...
・Intersection line between the inner wall and the back side of the turbine blade 27m, 27
b...The 1st intersection line between the inner wall and the ventral surface of the turbine blade /,! ; 2nd aa 38th 411th 2nd B

Claims (1)

[Claims] In an axial flow turbine having an annular row of turbine blades with blade tips attached to the inner and outer walls, the positional relationship 1111 between the line where the turbine blade intersects with the outer wall or inner wall and the ventral surface of the turbine blade intersects with the outer or inner wall. be at the same height at the inlet and outlet of the blade row, and in the cross section KTh that includes the turbine axis, the intersection line between the back side and the outer wall should be 1 or the intersection line between the back side and the inner wall in the direction away from the turbine axis. 5. The line has a convex curvature in the direction of the turbine axis, and the line of intersection between the ventral side and the outer wall has a convex curvature in the direction of the turbine axis, or the line of intersection between the ventral side and the inner wall has a convex curvature in the direction away from the turbine axis.5.
An axial flow turbine characterized by the following characteristics: