JPH11241601A - Axial turbine - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the difference in the degree of reaction in the radial direction, reduce the flow between the rotor blades on the inner peripheral side and the secondary flow, and reduce the clearance loss due to the chip clearance flow on the outer peripheral side. Provided is an axial turbine that can be reduced and can improve energy efficiency and increase performance. SOLUTION: An inner peripheral casing 1 extends from an inner peripheral base of a leading edge 21A of a stationary blade 21 to an inner peripheral base of a trailing edge 31B of the moving blade 31.
1 has an outer diameter shape on the center axis side with respect to a straight line (reference line: B) connecting the inner peripheral base of the leading edge 21A of the stationary blade 21 and the inner peripheral base of the trailing edge 31B of the moving blade 31 in the axial section. A concave recess 11A is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fluid passage formed between an inner peripheral casing and an outer peripheral casing, in which a turbine stage composed of a stationary blade row and a moving blade row is provided. The present invention relates to an axial turbine in which kinetic energy generated by a pressure difference is guided as rotary mechanical energy by guiding the fluid to a low-pressure portion through a fluid.

[0002]

2. Description of the Related Art In an axial flow turbine, a turbine stage composed of a stationary blade row and a moving blade row is provided in a fluid passage formed between an inner casing and an outer casing, and a high-pressure turbine is provided in the fluid passage. By guiding the kinetic energy generated by the pressure difference to the low pressure part through the working fluid, the kinetic energy is extracted as rotary mechanical energy.

[0003] Since the working fluid expands in the stage due to the pressure drop, the downstream fluid passage is enlarged. At this time, if the diameter of the inner peripheral casing is reduced to increase the area of the fluid passage, the area of the fluid passage is enlarged. As shown in FIG. 11 schematically showing a longitudinal section, the shape of the inner peripheral casing 11 in the step is between the inner peripheral base of the leading edge 21A of the stationary blade 21 and the inner peripheral base of the trailing edge 31B of the moving blade 31. Are formed so as to connect diagonally and linearly (that is, to reduce the diameter at a fixed rate).

In addition, the shape of the wing also takes into account various other influencing factors in the radial equilibrium condition of the fluid, which is determined by the balance between the centrifugal force and the radial pressure gradient when the working fluid passes in recent years. A vortex-type three-dimensional twisted blade is used, which is set to maximize the geometric outflow angle of the main flow part with emphasis on the efficiency of the main flow part with little loss as shown by the broken line in FIG. Have been.

[0005]

Incidentally, especially in a low-pressure turbine, the boss ratio (ratio of inner casing diameter / outer casing diameter) is small, and therefore, the blade height is high. For this reason,
The radial pressure gradient of the working fluid increases, and as a result, the difference in the degree of reaction between the inner and outer circumferences increases.

That is, the degree of reaction is the pressure drop amount (difference between the blade inlet pressure and the blade outlet pressure) in the turbine stage and the pressure drop amount (difference between the blade inlet pressure and the blade outlet pressure) in the blade. The reaction is small on the inner peripheral side where the stationary blade outlet pressure (moving blade inlet pressure) is low, and large on the outer peripheral side where the stationary blade outlet pressure (moving blade inlet pressure) is high.

As a result, on the inner peripheral side where the degree of reaction is small, as shown in the Mach number distribution of the blade surface in FIG. As a result, the boundary layer separation shown in FIG. 14 develops, and the energy loss between the blades increases. Furthermore,
The secondary flow of the blade surface facing the inner peripheral surface (inner peripheral casing 11) shown in FIG. 13 develops, thereby increasing the energy loss.

On the outer peripheral side where the degree of reaction is large, FIG.
As shown in FIG. 16 (A), the pressure difference between the blade abdominal surface and the back surface is increased so as to show the blade tip surface static pressure distribution, and as shown in the front view and the plan view in FIG. The chip clearance flow in which the fluid flows from the abdominal surface to the back surface via the gap 14 (tip clearance) of the outer casing 12 increases. The tip clearance flow is a flow that does not contribute to the work, and its amount depends on the pressure difference between the abdominal surface and the back surface when the tip clearance is the same. Therefore, the energy loss increases due to the increase in the chip clearance flow.

That is, since the degree of reaction differs in the radial direction due to the radial pressure gradient of the working fluid, the inner peripheral side of a low-pressure turbine having a high blade height and a large radial pressure gradient is particularly preferable. However, there is a problem that the energy loss due to the deterioration of the flow between the rotor blades and the secondary flow is large, and the energy loss due to the clearance loss due to the chip clearance flow is large on the outer peripheral side.

The present invention has been made in view of the above problems, and can reduce the difference in the degree of reaction in the radial direction, reduce the flow between the inner rotor blades and the secondary flow, and reduce the outer peripheral flow. It is an object of the present invention to provide an axial turbine capable of reducing a clearance loss due to a chip clearance flow on the side, improving energy efficiency, and increasing performance.

[0011]

In the axial flow turbine according to the present invention, which achieves the above object, the axial cross section of the inner peripheral casing is reduced in size by forming a concave portion between the leading edge of the stationary blade and the trailing edge of the moving blade. It is characterized by having such a configuration.

[0012] Further, the radial distribution of the geometric outflow angle of the moving blades constituting the moving blade row is set so as to be maximum near the inner peripheral side and to be smaller on the outer peripheral side.

Further, the inner peripheral casing has a cross section in the axial direction formed with a concave portion between the leading edge of the stationary blade and the trailing edge of the moving blade to reduce the diameter.
The moving blades constituting the moving blade row are characterized in that the radial distribution of the geometric outflow angle is set to be maximum near the inner peripheral side and to be smaller on the outer peripheral side.

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an axial sectional view showing a conceptual configuration of a turbine stage which is an example of a configuration of an axial flow turbine according to the present invention.

In the illustrated turbine stage, a stationary blade row 20 (static blade 21) and a moving blade row 30 (moving blade 31) are provided in a fluid passage 13 formed between an inner peripheral casing 11 and an outer peripheral casing 12.
The energy of the high-pressure fluid flowing through the fluid passage 13 is converted into velocity energy by the stationary blade 21, and the moving blade 31 is moved by the velocity energy (converts the velocity energy into mechanical work). It is something that has become.

The area of the fluid passage 13 on the downstream side is increased by reducing the diameter of the inner peripheral casing 11. That is, the inner peripheral casing 11 has a smaller diameter on the downstream side.

Here, the diameter reduction ratio of the inner peripheral casing 11 from the inner peripheral base of the leading edge 21A of the stationary blade 21 to the inner peripheral base of the trailing edge 31B of the moving blade 31 is not constant, but the upstream is large and the downstream is small. As a result, the outer diameter of the inner peripheral casing 11 is set to
A concave portion 11A is formed on the center axis side with respect to a straight line (reference line: B) connecting the inner peripheral base of the leading edge 21A and the inner peripheral base of the trailing edge 31B of the rotor blade 31.

The amount of displacement of the recess 11A with respect to the reference line B is set to be the largest between the trailing edge 21B of the stationary blade 21 and the leading edge 31A of the moving blade 31.

As described above, the concave portion 11A is formed on the inner peripheral side (the inner peripheral casing 11) between the leading edge 21A of the stationary blade 21 and the trailing edge 31B of the moving blade 30 (reducing the diameter of the inner peripheral casing 11). Is non-linear), it is possible to suppress a decrease in static pressure on the inner peripheral side of the entrance of the rotor blade 31 and increase the degree of reaction on the inner peripheral side.

That is, from the leading edge 21A of the stationary blade 21 to the moving blade 31
Recess 1 in the inner peripheral casing 11 between the rear edges 31B.
By forming 1A, an increase in the fluid Mach number on the inner peripheral side of the blade entrance can be suppressed, as shown in an example of the Mach number distribution at the blade entrance in FIG.
As shown in FIG. 3, the static pressure distribution on the inner peripheral side can be locally increased to alleviate the static pressure gradient. On the other hand, the static pressure distribution at the rotor blade outlet is almost constant on the inner and outer peripheral sides with almost no change as shown in FIG. 4, and as a result, FIG. 5 shows the reaction of the turbine stage in the radial direction (blade height direction). The degree of reaction on the inner peripheral side can be increased so as to show the degree distribution, and the fluid flow in the inner peripheral part of the moving blade can be improved to improve the energy efficiency. 2 to 5
The broken line in the middle indicates the inner peripheral casing 11 as a reference line in FIG.
The case where the shape shown by B is set is shown.

Further, instead of forming the recess 11A in the inner casing 11 as described above, the geometric outflow angle distribution in the blade height direction of the moving blade 31 is reduced in the vicinity of the inner circumference to a maximum on the blade tip side. By setting so as to make it possible, the degree of reaction on the inner peripheral side can be increased.

That is, FIG. 6A is a sectional view on the inner peripheral side, and FIG.
FIG. 7 shows an outer blade tip diagram, and FIG. 7 shows a geometrical outflow angle distribution in the blade height direction. As shown in FIG. To form a three-dimensional shape that is small (θMIN) on the blade tip side (outer circumference side).

FIG. 8 shows the distribution of the static pressure at the inlet of the moving blade.
As shown in FIG.
At the entrance of No. 1, there is almost no change between the inner and outer circumferences,
At the outlet, the pressure on the inner peripheral side decreases and the pressure on the outer peripheral side increases. As a result, as shown in FIG. 10, a reaction degree distribution in the radial direction (blade height direction) of the turbine stage is shown.
The degree of reaction on the inner side is large, the degree of reaction on the outer side is small, the flow of fluid on the inner side of the moving blade 31 is improved, and the clearance flow at the outer edge can be suppressed, thereby improving energy efficiency. Can be done. 7 to 1.
The broken line in 1 shows the case of the rotor blade set so as to maximize the outflow angle of the mainstream portion.

The configuration in which the concave portion 11A is formed in the inner casing 11 and the geometrical outflow angle distribution in the blade height direction of the moving blade 31 are set so as to be maximum near the inner peripheral side and to be smaller on the blade tip side. The configuration has an effect by being implemented independently of each other, but a further synergistic effect can be obtained by implementing the two in combination.

[0025]

As described above, in the axial-flow turbine according to the present invention, the axial-flow turbine has an inner peripheral casing having an axial section depressed from the leading edge of the turbine stage to the trailing edge of the moving blade. Is formed so as to reduce the diameter, whereby a decrease in static pressure on the inner peripheral side of the blade entrance can be suppressed,
By increasing the degree of reaction on the inner peripheral side, it is possible to improve the fluid flow in the inner peripheral portion of the rotor blade and improve energy efficiency.

Further, since the radial distribution of the geometric outflow angle of the moving blade is set so as to be maximum near the inner peripheral side and smaller on the outer peripheral side, the work on the inner peripheral side of the moving blade can be reduced. As the work becomes larger, the work on the outer peripheral side becomes relatively smaller, so that the degree of reaction on the inner side can be increased and the degree of reaction on the outer side can be reduced. As a result, the flow of the fluid on the inner peripheral side of the moving blade can be improved, the clearance flow at the outer edge of the moving blade can be suppressed, and the energy efficiency can be improved.

Further, the inner peripheral casing has a cross section in the axial direction having a recess formed between the leading edge of the turbine blade and the trailing edge of the moving blade to reduce the diameter, and the moving blade has a radial distribution of its geometric outflow angle. Is set to be smaller on the outer circumference side with the maximum near the inner circumference side, so that a decrease in the static pressure on the inner circumference side of the blade entrance can be suppressed, and the degree of reaction on the inner circumference side is synergistically increased. In addition, the clearance flow at the outer edge of the moving blade can be suppressed, the fluid flow at the inner peripheral portion of the moving blade can be improved, the energy efficiency can be improved, and a high-efficiency axial flow turbine can be configured. Things.

[Brief description of the drawings]

FIG. 1 is an axial cross-sectional view showing a conceptual configuration of a turbine stage, which is one configuration example of an axial flow turbine according to the present invention.

FIG. 2 is a graph showing an example of a Mach number distribution at a blade entrance.

FIG. 3 is a graph showing a blade inlet static pressure distribution.

FIG. 4 is a graph showing a static pressure distribution at a blade outlet.

FIG. 5 is a graph showing a reaction rate distribution in a radial direction of a turbine stage.

6A and 6B show a rotor blade shape, wherein FIG.
(B) is an outer peripheral wing tip view.

FIG. 7 is a graph showing a geometrical outflow angle distribution in a blade height direction.

FIG. 8 is a graph showing a blade entrance static pressure distribution.

FIG. 9 is a graph showing a blade outlet static pressure distribution.

FIG. 10 is a graph showing a reaction degree distribution in a radial direction of a turbine stage.

FIG. 11 is a longitudinal sectional view conceptually showing a turbine stage as a conventional example.

FIG. 12 is a graph showing a Mach number distribution of a rotor blade surface.

FIG. 13 is an explanatory diagram of a secondary flow.

FIG. 14 is an explanatory diagram of separation of a boundary layer on a wing surface.

FIG. 15 is a graph showing a blade tip surface static pressure distribution.

FIG. 16 is an explanatory diagram of a chip clearance flow;
(A) is a front view, (B) is a plan view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Inner peripheral casing (inner peripheral side) 12 Outer casing 13 Fluid passage 20 Stator blade row 21 Stator blade 21A Stator blade leading edge 30 Rotor blade row 31 Rotor blade 31B Rotor blade trailing edge θ Geometric outflow angle

Claims (3)

[Claims] 1. A turbine stage comprising a stationary blade row and a moving blade row is provided in a fluid passage formed between an inner peripheral casing and an outer peripheral casing, and a high pressure fluid is passed through the fluid passage to a low pressure portion. In the axial flow turbine, which guides and extracts kinetic energy generated by the pressure difference as rotational mechanical energy, the inner peripheral casing has a small diameter in which an axial cross section forms a concave portion between a leading edge of a stationary blade and a trailing edge of a moving blade. An axial flow turbine characterized in that it is configured to 2. A turbine stage comprising a stationary blade row and a moving blade row is provided in a fluid passage formed between an inner peripheral casing and an outer peripheral casing, and a high pressure fluid is passed through the fluid passage to a low pressure portion. In the axial flow turbine, which guides and extracts kinetic energy generated by the pressure difference as rotational mechanical energy, the moving blades constituting the moving blade row have a radial distribution of a geometric outflow angle which is maximum in the vicinity of the inner peripheral side. The axial flow turbine is set to be smaller on the outer peripheral side. 3. A turbine stage comprising a stationary blade row and a moving blade row is provided in a fluid passage formed between an inner peripheral casing and an outer peripheral casing, and a high pressure fluid is passed through the fluid passage to a low pressure portion. In the axial flow turbine, which takes out kinetic energy generated by the pressure difference as rotational mechanical energy by guiding the inner peripheral casing, the axial cross section of the inner peripheral casing forms a concave portion between the leading edge of the stationary blade and the trailing edge of the moving blade, and has a small diameter. An axial flow turbine, wherein the rotor blades constituting the rotor blade row are set so that the radial distribution of the geometric outflow angle becomes maximum near the inner peripheral side and becomes smaller on the outer peripheral side.