JP2000204908A - Axial turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease diffuser outlet pressure on an opposite side of a fluid outlet, and equalize pressure distribution of an outlet casing in a circumferential direction. SOLUTION: In an axial turbine 1 which leads a fluid F passing through a moving blade 2 in the direction of a turbine axis C using a circular diffuser 3 in the radial direction outside, and discharges the one from a fluid outlet 5 through an outlet casing 4, the circular diffuser 3 is leaned to a side of the fluid outlet 5 against the turbine axis C. A passage length for an opposite side of the fluid outlet 5 of the circular diffuser 3 becomes shorter than that for the side of the fluid outlet 5, a pressure increasing rate on the opposite side worsens intentionally, diffuser outlet pressure decreases, and diffuser inlet pressure decreases. Also, the diffuser outlet pressure is differentiated in each circumferential direction position, and pressure distribution of the outlet casing 4 is equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an axial turbine applied to a gas turbine, a marine turbocharger, and the like.

[0002]

2. Description of the Related Art Generally, there is known an axial flow turbine provided with a radially outflow type diffuser, that is, an annular diffuser. As shown in FIG. 5, the fluid F that has passed through the rotor blades 51 in the direction of the turbine axis C is transferred to an annular diffuser 52.
At the fluid outlet 54 through the outlet casing 53.

[0003]

However, with this structure, in the outlet casing 53, the fluid on the opposite side (lower side in the figure) of the fluid outlet 54 with respect to the turbine shaft C is discharged to the fluid outlet 5
Since it is far to 4, it is difficult to discharge, and there is a problem that the pressure at that position is increased.

That is, at the position on the opposite side, the fact that the pressure in the exit casing 53 is high means that the annular diffuser 52
This means that the pressure is high at the outlet and thus at the inlet.
In a turbine, the higher the inlet pressure of the moving blade 51 and the lower the outlet pressure, the better. Therefore, if the moving blade outlet pressure or the diffuser inlet pressure is high, a large differential pressure cannot be obtained and a large turbine work cannot be obtained. .

The outlet casing 53 is a passage orbiting around the turbine axis C, and a passage having a constant cross section, generally called a chamber type, is used. Since the flow velocity is sufficiently reduced at the outlet of the annular diffuser 52, the outlet casing 5
The pressure distribution of No. 3 is almost constant in the circumferential direction, and the pressure loss due to the circumferential flow is said to be slight. However, strictly speaking, as described above, the pressure increases on the side opposite to the fluid outlet 54 side. Then, a circumferential pressure distribution occurs in the outlet casing 53, and the flow is disturbed in the outlet casing 53, resulting in a loss.

Heretofore, there have been many studies on conventionally used axial inflow / outflow diffusers, and maps and the like showing the performance have already been established. However, there are not many studies on the radial outflow diffuser as described above.

[0007]

According to the present invention, there is provided an axial flow turbine for guiding a fluid passing through a blade in an axial direction of a turbine radially outward by an annular diffuser and discharging the fluid from a fluid outlet through an outlet casing. Is eccentric to the fluid outlet side with respect to the turbine shaft.

According to this, the length of the passage of the annular diffuser on the side opposite to the fluid outlet can be made shorter than that of the fluid outlet. This intentionally worsens the rate of pressure rise on the other side,
The diffuser outlet pressure can be reduced, the diffuser inlet pressure can be reduced, and the diffuser outlet pressure can be varied for each circumferential position, so that the pressure distribution in the outlet casing can be equalized in the circumferential direction.

[0009]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an axial turbine according to the present invention.
In this axial flow turbine 1 as well, the fluid F that has passed through the rotor blade 2 in the direction of the turbine axis C is guided radially outward by the annular diffuser 3 and discharged from the fluid outlet 5 at one circumferential position through the outlet casing 4, as in the prior art. It has become.

In the axial flow turbine 1, a blade casing 7 is formed inside a turbine casing 6.
The impeller 8 is rotatably housed in the housing. A plurality of moving blades 2 are mounted on the outer periphery of the impeller 8 in multiple rows in the axial direction. When the moving blade 2 is driven by the fluid F, the impeller 8 is rotated around the turbine axis C. A nose cone 9 is disposed axially forward (right side in the figure) or upstream of the impeller 8, and is fixed to the turbine casing 6 via a plurality of stationary blades 10.
A plurality of stationary blades 11 attached to the inner wall of the blade casing 7 are also provided between the moving blades 2 in the axial direction.

The annular diffuser 3 is a curved passage that changes the direction of flow from the axial direction to the radial direction, is formed by the turbine casing 6, and has an inlet 12 axially rearward (left side in the figure) of the moving blade 2, An outlet 13 facing the outside in the radial direction and opening to the outlet casing 4. The annular diffuser 3 is continuous along the entire circumference around the axis, and the passage area is enlarged in an annular shape around the axis as going radially outward or downstream. As a result, the high-speed fluid F flowing from the inlet 12 is gradually decelerated to a high pressure, and the outlet casing 4
Drain.

The outlet casing 4 is a so-called chamber type similar to the conventional one, and is a fluid passage coaxial with the turbine shaft C and orbiting around the shaft. The passage cross section is constant. The outlet 13 of the annular diffuser 3 is connected to the rear of the outlet casing 4 in the axial direction. The outlet casing 4 is defined inside the turbine casing 6 and surrounds the vane casing 7 from a radial outside with a predetermined thickness.

The fluid outlet 5 is provided at one location in the circumferential direction of the outlet casing 4 and discharges fluid to the outside of the outlet casing 4 in the radial direction. The fluid outlet 5 is open to the atmosphere through an exhaust duct, and thus the pressure in the fluid outlet 5 and the interior of the outlet casing 4 directly facing the fluid outlet 5 is slightly higher than the atmospheric pressure. In the illustrated example, the fluid outlet 5 is provided directly above the outlet casing 4.

Conventionally, the annular diffuser 52 was coaxial with the turbine axis C as shown in FIG. Accordingly, the length of the passage and the radial positions of the inlet and the outlet were also axially symmetric and equal to the entire circumference.

On the other hand, in the present embodiment, as shown in FIG. 1, the annular diffuser 3 is eccentric with respect to the turbine shaft C toward the fluid outlet 5. FIG. 2 shows these positional relationships. The center of the annular diffuser 3 after eccentricity is indicated by Ce,
The amount of eccentricity is e. In this figure, the passage cross section of the outlet casing 4 seems to be smaller on the fluid outlet 5 side (upper side) and larger on the opposite side (lower side) of the fluid outlet 5 due to the eccentricity of the annular diffuser 3. Actually, as shown in FIGS. 1 and 5, the outlet side partition wall 14 of the annular diffuser 3 is extended by eccentricity and the opposite outlet side partition wall 15 is shortened (cut off) by eccentricity. No significant changes.

Due to the eccentricity of the annular diffuser 3, the passage length of the annular diffuser 3 along the radial direction becomes longer toward the fluid outlet 5 and becomes shorter toward the opposite side of the fluid outlet 5.

Next, the operation of the present embodiment will be described.

FIG. 3 is a general diagram showing the pressure recovery coefficient of an annular diffuser. The pressure recovery coefficient is represented by Cp, and the greater this value, the greater the degree of pressure rise in the annular diffuser. That is, this is a preferable characteristic for an annular diffuser. The horizontal axis dimensionless passage flow L / H is the vertical axis area ratio (A ₂ / A ₁₎ -1 is are taken. As shown in FIG. 4, L is a passage length along the radial direction of the annular diffuser 3, H is a radial length of an inlet end of the annular diffuser 3, and A ₁ and A ₂ are an inlet end of the annular diffuser 3 and The annular area at the exit end. When an experiment is performed while changing the dimensions of the annular diffuser 3, a mountain-shaped line with a constant pressure recovery coefficient can be drawn. If the size of the annular diffuser 3 is determined so as to be on a straight line connecting the peaks of these lines, a compact diffuser in which the passage length and the area ratio are balanced can be obtained.

From this figure, it can be said that, generally, the longer the passage length and the larger the area ratio, the larger the pressure recovery coefficient.

In the case of the present embodiment, the passage length L of the annular diffuser 3 is longer on the fluid outlet 5 side and shorter on the opposite side of the fluid outlet 5. Therefore, for example, as shown in FIG. 2, in the outlet casing 4, the pressure recovery coefficient Cp is determined at the positions of the upper portion Pu closest to the fluid outlet 5, the lower portion Pd farthest from the fluid outlet 5, and the middle horizontal portion Ph. As shown in FIG. 3, the pressure recovery coefficient Cp gradually decreases in the order of the upper portion Pu, the horizontal portion Ph, and the lower portion Pd, and the pressure rise rate deteriorates.
This is the position of the lowermost Pd farthest from the fluid outlet 5,
This means that the outlet pressure of the annular diffuser 3 can be minimized. Therefore, at that position, the inlet pressure of the annular diffuser 3 can also be reduced, and the blade outlet pressure can be reduced to increase the work load of the turbine.

Further, the pressure recovery coefficient Cp increases as the fluid outlet 5 is approached from the position right below Pd, and the outlet pressure of the annular diffuser 3 gradually increases. This is a direction in which the pressure gradient decreasing from the lower portion Pd of the exit casing 4 to the upper portion Pu of the exit casing 4 is conventionally canceled. Thus, the annular diffuser 3
The diffuser characteristic (performance) can be continuously changed for each circumferential position, so that the circumferential pressure distribution of the entire outlet casing 4 can be made uniform, and the pressure loss in the outlet casing 4 can be reduced. As described above, the loss of the entire turbine is reduced, and the work of the turbine can be increased.

The present embodiment can be considered as follows. That is, in the area directly below, the diffuser has conventionally decelerated the flow too much, so that the flow has stayed at that position, making it difficult to reach the fluid outlet. In the present embodiment, the velocity can be left as much as the diffuser cannot convert the velocity of the flow into the pressure, so that the fluid can reach the fluid outlet quickly, and the pressure increase immediately below can be prevented.

In the present embodiment, since the fluid outlet 5 is substantially at atmospheric pressure, the entire circumference of the outlet casing 4 can be made substantially at atmospheric pressure. Conventionally, the position immediately below is higher than the atmospheric pressure. FIG.
As shown in the figure, the upper part Pu, the lower part Pd, and the horizontal part Ph
It is preferable that the dimensions of the annular diffuser 3 corresponding to are set so as to be on the peak line.

In this embodiment, only the change of the annular diffuser portion is different from the conventional case. Therefore, there is an advantage that the performance can be improved at low cost without any significant change.

As described above, the embodiments of the present invention are not limited to those described above. Further, the present invention can be applied to all axial flow turbines such as gas turbines and marine turbochargers.

[0027]

The present invention exhibits the following excellent effects.

(1) On the opposite side of the fluid outlet, the diffuser inlet pressure can be reduced and the turbine work can be increased.

(2) The pressure distribution in the outlet casing can be equalized in the circumferential direction, and the turbine loss can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view showing an axial flow turbine according to an embodiment of the present invention.

FIG. 2 is a schematic longitudinal sectional front view showing a position of an annular diffuser.

FIG. 3 is a diagram showing a pressure recovery coefficient of an annular diffuser.

FIG. 4 is a diagram for explaining each dimension of the diagram of FIG. 3;

FIG. 5 is a longitudinal sectional side view showing a conventional axial flow turbine.

[Explanation of symbols]

 Reference Signs List 1 axial flow turbine 2 rotor blade 3 annular diffuser 4 outlet casing 5 fluid outlet C turbine shaft F fluid

Claims (1)

[Claims] 1. An axial flow turbine in which a fluid that has passed through a rotor blade in an axial direction of a turbine is radially outwardly guided by an annular diffuser and discharged from a fluid outlet through an outlet casing, the annular diffuser is connected to the fluid outlet with respect to a turbine shaft. An axial turbine characterized by being eccentric to the side.