JPH02119602A - Turbine exhaust hood - Google Patents

Abstract

PURPOSE:To decrease exhaust loss and achieve high performance for a wide range of operating conditions by installing a guide vane capable of tracking wind directions over a range of a circular exhaust passage downstream of the final step of an axial flow fluid machine, in which the occurrence of a counterflow is anticipated. CONSTITUTION:A movable vane 16 is installed in a circular exhaust passage 15 consisting of an inner wall 13 and an outer wall 14, downstream of the final step which is made up of a static vane 11 and a dynamic vane 12, in the lengthwise direction of vane from the root of the dynamic vane and over a range in which the occurrence of a counterflow is anticipated. The movable vane 16 is supported by a rotary shaft 19 in the circular passage between the inner wall 13 and a ring guide 18 fixed concentrically therewith with a support 17. The cross-sectional shape of the vane is formed of a plate without any warping. A guide pin 20 is installed on the downstream end opposite to the upstream end on which the rotary shaft 19 is installed. The movable vane 16 is rotated over a range theta in which the guide pin 20 is engaged with a guide groove 21, making it possible for the movable vane 16 to track wind directions within the movable range theta.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention aims to improve performance by reducing exhaust loss occurring in the final stage of an axial fluid machine such as a steam turbine. This invention relates to a turbine exhaust chamber end structure for reducing exhaust loss that increases due to changes in the turbine exhaust chamber.

[Conventional technology]

In a steam turbine, exhaust losses occurring in the final stage include:
Exhaust flow path resistance loss in the high-speed range under high load, turn-up loss due to backflow phenomenon occurring at the root of the blade at low load, and movement due to increased outflow velocity component from the blade that occurs at high and low loads. There is a leaving loss corresponding to energy.

Japanese Unexamined Patent Publication No. 57-129206, Utility Model Application No. 57-63902
Although the publication attempts to reduce exhaust loss by improving the shape of the exhaust flow path downstream of the final blade, it is difficult to change the flow state over the entire three-dimensionally complex flow field in the exhaust flow path. Utility Model Application Publication No. 57-63902 is equipped with a movable guide vane to control the flow state over the entire area in the exhaust flow path, but the expected effect can only be achieved as long as there is a direction of flow from the blade. outside of this range, the guide vanes will have an adverse effect on the flow in the channel, and are not sufficient. Furthermore, although this method uses an external drive device to control the angle of the guide vane, it has the disadvantage that an enormous amount of operating force is required to overcome the steam force acting on the guide vane and operate the guide vane.

An object of the present invention is to provide an efficient structure for reducing turn-up loss and leaving loss of exhaust gas.

[Problem to be solved by the invention]

As mentioned above, the conventional technology is reluctant to develop a structure that reduces the three-dimensional backflow that occurs in the turbine exhaust chamber flow path.
It has drawbacks in terms of effectiveness and working range. Here, we will outline the flow conditions of the backflow phenomenon based on experimental data. Figure 8 shows the occurrence of backflow in the final stage of the steam turbine. In the stage consisting of the static When the exhaust speed (exhaust speed) falls below a certain limit, a backflow occurs at the root of the moving X2. As shown in FIG. 8, this reverse region is indicated by S in the blade span direction and Sa in the turbine axial direction, and as the exhaust speed decreases, S and Sa increase, and the root of the stationary blade 1 It comes to extend to. As shown in FIG. 9, the flow angle characterizing the flow situation in such a reverse region is such that the radial flow angle φ is reversed from the positive side to the negative side.

Furthermore, the circumferential flow angle δ has an axial velocity component of V a h
The velocity component decreases from Vaz to Vaz, changes greatly from +δ to -δ, and finally the axial velocity component becomes −Vaa.

[Means to solve the problem]

In the present invention, in order to satisfy such conditions, a guide vane capable of tracking the wind direction is provided in the exhaust flow path.
FIG. 1 shows an example of its structure. In Figure 1, stationary blade 1
A movable vane 16 is installed in the annular exhaust passage 15 consisting of the inner wall 13 and the outer wall 14 downstream of the final stage, which is composed of the rotor blade 1 and the rotor blade 12, from the root of the rotor blade to the blade length direction over the range where backflow is expected to occur. It is a structure that provides The movable vane 16 is supported by a rotating shaft 19 within an annular flow path between the inner wall 13 and a ring guide 18 which is concentrically fixed to the inner wall 13 by a support 17. The cross-sectional shape of the movable vane 16 is basically a flat plate shape with no warpage, and there is a rotation shaft 19 on the upstream end (front B) side.
A guide pin 20 is provided on each downstream end (trailing edge) side.

If we look at this structure on the P-P diagram, we can see that ring guide 1
The ring guide 18 can rotate around the rotating shaft 19 inserted into the ring guide 18.
This is the range in which the arc-shaped guide groove 21 concentric with the guide groove 21 is provided, and in order to regulate this, the guide pin 2o is
1 and comes into contact with the ring guide 18 at both boundaries of the movable range 0, acting as a stopper. Therefore, since the movable vane 16 does not have a driving device, within the movable range θ, there is no action to correct the flow by tracking by fluid force in the direction of the circumferential flow angle δ shown in FIG.
Since the movable vane 16 is fixed at the boundary of the movable range θ where the guide pin 20 acts as a stopper, if the flow changes further in the circumferential direction, it has the effect of guiding the flow and correcting the direction. executed. In other words, the movable guide vane structure of the present invention tracks the direction of the wind so that it does not affect the flow as long as the outflow direction from the moving blade does not adversely affect exhaust loss, and tracks the direction of the wind so that it does not affect the flow in the range where the outflow direction from the rotor blade does not adversely affect exhaust loss. In this case, the system guides the flow to reduce exhaust loss and achieve high performance over a wide range of operating conditions.

〔Example〕

The embodiment of the present invention has a structure as shown in FIG. 1, and since the structure has been explained with reference to FIG. 1, the operating state will be explained below.

In Figure 2, (a) shows the rotor blade 3 when the load changes.
1, and (b) shows the speed triangle when backflow occurs. The state of the movable vane at intermediate load in (a) is (
As shown in c), the movable vane follows the absolute speed C2, so the flow angle γ of the absolute speed and the direction η of the movable vane are in the same state. When the load in (a) increases and the flow angle of the absolute velocity becomes γ', the position of the movable vane reaches the limit of its movable range with the direction η' as shown in (d). Fixed. In this state, by setting the movable range so that η′ minus γ′, the absolute speed is 0.
2′ direction can be corrected in the axial direction,
When the load decreases and the flow angle at the absolute velocity in (a) becomes γ', the movable vane reaches the limit of its movable range in the direction of η' as shown in (e) and becomes fixed. Here, η′〉γ
By setting the range of motion so that
It is possible to modify the direction of the absolute velocity Cz' in the axial direction. In a state where a backflow occurs, the position of the movable vane 51 becomes the state (e), and the absolute velocity -02 flows from the direction of -γ, so the movable vane 51 moves at η'
This is the position where backflow is prevented in the range +1-γ1<90@ and the flow is pushed back to the downstream side.

Figure 3 shows the flow situation when the movable vane 51 is in operation. is shown to be modified in the axial direction.

In the backflow state shown in (Q), the backflow flow rate decreases.

By reducing the pressure in the space between the rotor blade and the movable vane, the backflow area is reduced, thereby significantly reducing the power loss generated in the rotor blade.

Next, although FIG. 1 shows the case where the movable vane 51 of the present invention is installed at the root of the blade length range, in the case of a long blade in the final stage, the outflow direction may be distributed in the blade direction depending on the load condition. Therefore, as another embodiment, it is possible to apply the structure of the movable vane 51 of the present invention by dividing the entire blade length into a plurality of parts as shown in FIG.

As described above, the influence of the structure and operation of the present invention on exhaust loss will be explained. Generally, exhaust loss characteristics are expressed in relation to the velocity (exhaust velocity) in the annular flow path at the exit of the final stage. FIG. 5 shows the exhaust loss characteristics. The exhaust loss is the sum of three types of losses: leaving loss, turn-up loss, and flow path loss. Among these, the reduction in exhaust loss due to the structure and operation of the present invention is achieved by reducing turn-up loss and flow path loss. In other words, in a small pumping speed range, the tar-up loss caused by backflow is LToc?・D-HNa Here, LT = power loss γ = specific weight of fluid D = Dr + H Dr'' blade root optical diameter H = radial length of reverse area (S in Figure 8) N = relationship between rotational speed Since the backflow length H of the present invention can be reduced to approximately half as shown in FIG. 6, the loss power LT is approximately halved, reducing the exhaust loss in the small exhaust speed range shown in FIG. is as shown by the line ■.Furthermore, the flow path loss is caused by the increase in flow path pressure loss due to the swirling velocity component, and this relationship is as follows:g Here, ΔP=pressure loss C in the exhaust flow path = Pressure loss coefficient (varies depending on the circumferential flow angle γ) V a n ” Pumping speed γ = Specific weight of the fluid g = Acceleration of gravity, and the pressure loss coefficient C is determined by the circumferential flow angle γ as shown in Figure 7. There are characteristics that change depending on the angle γ, but γ = 30 @ γ = 2
If corrected to 0@, C will decrease by about 30 to 40%, so in Figure 5, the exhaust loss on the high exhaust speed side is shown by the line ■
Reduce like.

As a result, when the present invention is applied, a turbine with little change in exhaust loss from a high load range to a low load range can be realized, and high performance can be achieved with respect to load changes in terms of power generation operation. In addition, the effects of the present invention are not limited to those that correspond to the load of ordinary power generation turbines that use seawater as a cold source, but in a power generation turbine that uses the atmosphere as a cold source, the atmospheric temperature changes depending on the season. It is also effective in plants where the exhaust pressure changes independently of the load and the exhaust speed fluctuates significantly.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the exhaust loss of the turbine and improve the efficiency of the turbine plant.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the operation of the present invention, and FIG. 3 is an explanatory diagram of the flow situation in the present invention.
FIG. 4 is a sectional view of another embodiment of the present invention, FIG. 5 is an exhaust loss characteristic diagram, FIG. 6 is a backflow area characteristic diagram, FIG. 7 is a pressure loss coefficient characteristic diagram of the flow path, and FIG. Flow situation explanatory diagram, FIG. 9 is an explanatory diagram of flow angle change. (C) Medium-I folding rod 30 (αn 茅 50 !=Lehi °°〉7 oke shaku t-Kusiafubune-ri (lρθ atyr exhaust 1/! ('L/S) Equivalent m8 question running surface angle and (hiko ) Potato CQ) (I)

Claims (1)

[Claims] 1. A plurality of guide vanes are arranged perpendicularly to the axis in the circumferential direction within the annular flow path of the exhaust flow path downstream of the rotor blades in the final stage of the axial flow turbomachine, and the guide vanes are arranged perpendicularly to the axis. A rotation center axis is provided at the front edge so that the guide vane can rotate around an axis perpendicular to the axis, and a convex guide pin is provided at the end surface of the guide vane at the rear edge to ensure proper flow within the flow path. Within this range, the guide pin rotates around the central axis of rotation to track the wind direction, and for wind directions beyond this range, the guide pin engages with a member that fixes the central axis of rotation of the guide vane, and the guide pin engages with a member that fixes the central axis of rotation of the guide vane. A turbine exhaust chamber characterized by being provided with a wind direction tracking type guide vane that guides the flow by regulating the rotation angle and determining the angle so as not to coincide with the flow direction. 2. The turbine exhaust chamber according to claim 1, characterized in that the guide vane is divided into a plurality of parts over the entire final blade length, and each guide vane has a structure in which it can independently track the wind direction.