JP6192990B2 - Axial flow turbine - Google Patents

Description

  The present invention relates to an axial flow turbine such as a gas turbine or a steam turbine used in a power plant or the like.

  In recent years, further improvement in power generation efficiency of power plants has been demanded from the viewpoint of reducing environmental load, and further improvement in performance of turbines has become an important issue. The dominant factors of turbine performance include paragraph loss, exhaust loss, mechanical loss, etc. In particular, it is considered that reducing paragraph loss is most effective for improving performance. There are various types of paragraph loss. (1) Airfoil loss caused by the blade shape itself, (2) Secondary flow loss caused by the flow crossing the flow path between blades, (3) Operation There is a leakage loss caused by fluid leaking out of the flow path between blades. Among these, the leakage loss of (3) is (a) bypass loss due to the fact that the energy of steam is not effectively used by flowing through a path other than the main flow as leakage flow, and (b) leakage flow deviating from the main flow. It consists of mixing loss that occurs when it flows into the main flow again, and (c) interference loss that occurs due to interference of the leaked leak flow with the downstream cascade. That is, it is important to reduce the amount of leakage flow and return the leakage flow to the mainstream without loss.

  Up to now, in order to reduce the leakage loss of (3), the leakage loss is reduced by reducing the gap between the stationary part and the rotating part as represented by the gap between the blade tip shroud and the seal fin embedded in the casing. Attempts have been made to keep it small. However, if this gap is made too small, the risk of contact between the stationary part and the rotating part increases, so that a certain amount of gap has to be provided. Especially for axial seal fins, the amount of thermal expansion differs depending on the temperature difference between the rotor and the casing when the turbine is started, so there is a possibility that a gap different from the assumed gap may occur, and the risk of contact increases. It was.

  In order to deal with such a problem, in Patent Document 1, an axial seal fin that can slide in the axial direction from the stationary portion and a drive device that drives the axial seal fin in the axial direction are provided in the leakage flow path on the blade front side. Installation techniques have been proposed. Since this axial seal fin and the drive device can reduce the risk of contact, the gap between the stationary part and the rotating part can be set to an appropriate size, and the radial seal fin can be omitted. Leakage loss can be kept small enough.

JP-A-61-250304

  By the way, when the mainstream steam flowing out from the trailing edge of the turbine stationary blade flows into the downstream turbine blade, the flow direction is changed by the moving blade and flows downstream. On the other hand, the leakage flow that bypasses the turbine rotor blade tip side is contracted when passing through a plurality of radial seal fins provided in the axial direction to reduce the total pressure and increase the axial flow speed. The directional velocity passes through the leakage flow path while maintaining substantially the circumferential velocity component when flowing out of the stationary blade according to each momentum conservation law. That is, since the leakage flow flows out without being redirected in the leakage flow path, a flow angle mismatch occurs when it merges with the main steam flow on the downstream side of the moving blade. This mismatch in flow angle promotes the mixing loss that occurs when the steam main flow and the leak flow merge. However, the prior art does not particularly take into consideration the problem regarding the mismatch of the flow angle when the leakage flow and the main steam flow merge.

  Therefore, the present invention aims to reduce the bypass loss by suppressing the amount of leakage flow, and reduce the mixing loss by reducing the mismatch of the flow angle when the leakage flow and the main steam flow merge.

  In order to achieve the above object, a turbine rotor rotatably supported, a turbine blade fixed to the turbine rotor, a shroud provided at a tip portion of the turbine blade, and a gap between the shroud and the shroud. The axial flow turbine includes a stationary portion opposed to each other, and a radial seal fin provided in a leakage flow path between the outer peripheral side wall surface of the shroud and the stationary portion so as to protrude in the rotor radial direction. An axial seal fin protruding in the axial direction of the rotor is provided in the leakage flow path between the downstream side wall surface and the stationary part, and the shroud, stationary part, in the leakage flow path is provided in the leakage flow path between the shroud and the stationary part. A radial seal fin provided on the most downstream side and a cavity portion surrounded by the axial seal fin are formed.

  According to the present invention, the bypass flow is reduced by suppressing the leakage flow amount, the circumferential velocity component of the leakage flow is reduced, the mismatch of the flow angle when the leakage flow and the main steam flow are merged, and the mixing loss is reduced. The leakage loss can be effectively reduced.

It is sectional drawing which represents roughly the principal part structure of the steam turbine stage part which concerns on one Example of this invention. It is explanatory drawing showing the condition of the wing | blade space | interval and the leakage flow in the blade front end side which concerns on one Example of this invention. FIG. 3 is an enlarged cross-sectional view schematically showing a rotor blade tip leakage flow path shape according to an embodiment of the present invention. FIG. 3 is an enlarged cross-sectional view schematically showing a rotor blade tip leakage flow path shape according to an embodiment of the present invention. It is a graph showing the influence which the clearance gap of the axial seal fin which concerns on one Example of this invention has on a rotor blade outflow angle distribution. It is a graph showing the influence which the clearance gap of the axial direction seal fin which concerns on one Example of this invention has on a blade loss coefficient distribution. It is a graph showing the relationship between the mixing loss which concerns on one Example of this invention, and a shaft and radial direction seal fin clearance ratio. It is an expanded sectional view showing roughly the shape of a bucket tip leak channel concerning another example of the present invention. It is explanatory drawing showing the condition of the flow in the cavity of the rotor blade front end downstream which concerns on another Example of this invention. It is a graph showing the influence which the clearance gap of the axial seal fin which concerns on another Example of this invention has on a rotor blade outflow angle distribution. It is a graph showing the influence which the clearance gap of the axial direction seal fin which concerns on another Example of this invention has on a blade loss coefficient distribution. It is an expanded sectional view showing roughly the shape of a bucket tip leak channel concerning another example of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, the same code | symbol is attached | subjected to the equivalent component through each drawing. Each example described below is an example in which the present invention is applied to a steam turbine rotor blade. The operation principle of the present invention is the same even in a gas turbine having a different working medium, and this patent can be applied to an axial flow turbine in general. In order to facilitate understanding of the structure of the present invention, some dimensions are exaggerated.

A first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing a steam turbine stage structure according to this embodiment. As shown in FIG. 1, the turbine stage of the steam turbine according to this embodiment includes a turbine rotor blade 5 installed in the circumferential direction of a turbine rotor 3, and a turbine circumferential direction between a diaphragm outer ring 1 and a diaphragm inner ring 2. And a plurality of turbine stationary blades 4 installed on the turbine. A shroud 6 is provided at the tip of the turbine rotor blade 5 on the outer peripheral side in the turbine radial direction. Further, the gap between the rotating body and the stationary part is minimized between the outer peripheral side wall surface of the shroud 6 provided on the tip side of the turbine rotor blade 5 and the stationary part facing the outer peripheral side wall surface, thereby suppressing leakage flow. A plurality of radial seal fins 7 are provided in the rotor axial direction. Further, axial seal fins 8 are provided between the downstream side wall surface of the shroud 6 and the stationary part facing the downstream side wall surface, and the shroud 6, the stationary part, and the most downstream side in the leakage flow path. A cavity 9 is formed between the radial seal fins 7 provided on the surface of the substrate. Further, the axial seal fin 8 is connected to a drive device for driving it in the axial direction, and is configured to be driven in the axial direction.
The main steam 12 that is the working fluid flows out of the turbine stationary blade 4 provided upstream of the turbine rotor blade 5 in the steam flow direction, and most of the main steam 12 that flows out flows into the turbine rotor blade 5, It flows into a leak channel formed between the stationary part and the shroud 6 that is a rotating body. Then, after passing through the plurality of radial seal fins 7 as the leakage flow 13, it rejoins the mainstream steam 12 downstream of the turbine rotor blade 5. The steam turbine rotates the turbine rotor 3 together with the turbine rotor blade 5 by causing the steam main flow 12 flowing out from the turbine stationary blade provided on the upstream side of the turbine rotor blade 5 to flow into the turbine rotor blade 5. Electricity is generated by converting rotational energy and electrical energy via a generator (not shown) connected to the end. For this reason, the leakage flow 13 that bypasses the turbine rotor blade 5 and passes through the leakage flow path is not converted into the rotational energy of the turbine rotor 3, resulting in a loss.

  FIG. 2 shows a blade shape and a speed triangle when viewed from the front end side of the turbine blade. In FIG. 2, the broken line indicated by reference numeral 17 represents the rotor blade peripheral speed. The mainstream steam 12 flowing out from the trailing edge of the turbine stationary blade 4 at an absolute speed 15 flows into the turbine blade as a relative speed 16. Thereafter, the turbine blade 5 turns and flows out as a relative speed 19. At this time, the flow is turned to the flow absolute velocity 18 close to the axial direction, and the pressure and temperature are reduced by the amount of energy recovered by the turbine rotor blade, and flow into the next stage.

  On the other hand, the leak flow 13 that bypasses the turbine rotor blade 5 is contracted when passing through a plurality of radial seal fins 7 provided in the axial direction, and the total pressure decreases and the axial flow speed increases. The circumferential speed passes through the leakage flow path while substantially maintaining the circumferential speed component when flowing out of the turbine vane 4 according to each momentum conservation law. That is, as shown in FIG. 2, the leakage flow 13 flows out without being turned in the leakage flow path, and a flow angle mismatch occurs when it merges with the steam main flow 12. This mismatch in flow angle promotes mixing loss that occurs when the steam main flow 12 and the leak flow 13 merge.

  Details of the configuration and operation of this embodiment will be described.

  An enlarged view of the leak channel shape of the present invention is shown in FIG. A plurality of radial seal fins 7 are provided in the axial direction between the diaphragm outer ring 1 and the blade shroud 6. The radial seal fin 7 has a rotationally symmetric cross-sectional shape around the rotation axis of the turbine, and has a wedge shape with a sharp tip. A gap width Cr is provided between the radial seal fin 7 and the outer peripheral side wall surface of the shroud 6 in order to prevent contact between the stationary portion and the rotating portion. The leakage flow 13 is contracted and expanded when passing through this gap, and the total pressure is reduced by the thermal diffusion of velocity energy. This contracted flow expansion phenomenon becomes a resistance to the leakage flow, and the leakage flow amount can be reduced. In the case of the present embodiment, the radial seal fin 7 is fixed to the diaphragm outer ring 1 and its tip is directed to the shroud 6 side of the moving blade, but conversely, the radial seal fin 7 is shroud. The effect is not changed even if it is fixed to 6 and its tip is directed toward the diaphragm outer ring 1 side. In the case of the present embodiment, the shape of the shroud outer peripheral side wall has a step shape, but the effect of the present invention does not change even if it has another shape such as a flat shape.

  An axial seal fin 8 is provided downstream of the radial seal fin 7. The axial seal fins 8 are fins that protrude in the axial direction of the rotor in the leakage flow path between the downstream side wall surface of the shroud and the stationary part. The axial seal fin 8 forms a cavity 9 with a shroud 6, a stationary portion, and a radial seal fin 7 provided on the most downstream side in the leakage flow path. A strong circulating flow 20 is formed. The leakage flow 13 is affected by viscosity from the wall surface in the process of circulating in the cavity, and the circumferential velocity component is attenuated. When the radial seal fin is not provided and the cavity is not formed, the leakage flow and the main steam flow strongly interfere and the flow is disturbed, so that it is not possible to form a strong pair of circulating flows as shown in this embodiment. Further, since the area of the radial seal fins is reduced as compared with the present embodiment, the swirl velocity component of the leakage flow cannot be sufficiently attenuated. Therefore, in this embodiment, when the leakage flow 13 flows out of the cavity 9 and merges with the main steam flow 12, the flow angle mismatch is alleviated and the mixing loss can be effectively reduced. Furthermore, the axial seal fin 8 has an effect of preventing the high-pressure main steam flow 12 from flowing back into the cavity 9, and this effect can further reduce the mixing loss.

Furthermore, in this embodiment, the axial seal fin 8 is connected to a drive device having a pressure receiving head 10 and an elastic body 11 for driving the seal fin 8. The driving device is provided in a groove 23 formed in the stationary part, and receives a vapor pressure and moves in the radial direction. The pressure receiving head 10 is moved by the pressure receiving head 10 and moved in the rotor axial direction. The member 24 and the elastic body 11 which is an urging means for urging the fin support member 24 in a direction opposite to the pushing direction by the pressure receiving head.
The pressure receiving head 10 is a segment structure that is continuous in an annular shape around the rotor central axis, and serves as a piston that reciprocates in the groove 23 in the radial direction. The contact surface 10a with the fin support member on the inner circumferential side of the pressure receiving head has a gradient in the rotor axial direction.

  The fin support member 24 is an annular member and has a contact surface 24a parallel to the contact surface 10a. Since the pressure receiving head 10 and the fin support member 24 are in contact with each other at the contact surface 10a and the contact surface 24a inclined in the axial direction, the acting direction of the pressing force from the pressure receiving head 10 is applied to the fin supporting member as the axial pressing force. Works. An elastic body 11 is provided between the other axial end of the fin support member 24 and the groove 23, and the elastic body 11 is fixed to the fin support member 24 or the groove wall surface. Furthermore, a convex portion that protrudes in the inner circumferential direction is formed on the inner circumferential side of the fin support member 24. The convex portion protrudes from the opening of the groove 23 on the steam main flow path side, and the axial seal fin 8 is supported at the tip of the convex portion.

  The drive device converts the steam force of the high-pressure steam 14 obtained by extracting from the upstream stage or passing the pipe directly from the boiler as the axial force via the pressure receiving head 10 when the turbine is started. The axial seal fin is driven in the axial direction, and the gap width Ca between the axial seal fin 8 and the shroud 6 can be increased. Therefore, even if the gap width Ca is narrowed due to the difference in thermal expansion due to the temperature difference between the turbine rotor and the casing at the time of startup, the shroud 6 and the axial seal fin 8 can be started up safely without contact. By stopping the supply of steam when entering the steady operation state, the axial clearance width Ca can be reduced to a value equivalent to that when the turbine is stopped by the reaction force of the elastic body 11 connected to the axial seal fin 8. it can. That is, the gap width Ca of the axial seal fin can be controlled using the driving device, and the appropriate axial gap width Ca can be maintained at all times, so that the leakage flow loss can be further reduced.

  The present embodiment shows a structure in which the axial seal fin is driven in the axial direction by using the vapor pressure acting on the driving device in the radial direction as a driving source. However, the present invention is based on the linear expansion coefficient of the turbine rotor and the casing. The same effect can be obtained with other drive mechanisms such as a drive device that uses a metal expansion / contraction force with a large linear expansion coefficient or a reaction force to return to the original shape of the shape memory alloy as a drive source. The effect of the present invention is not affected by the drive mechanism.

  Therefore, this embodiment reduces the bypass flow by suppressing the amount of leakage flow, prevents the main flow from flowing into the cavity, and the flow angle mismatch when the leakage flow and the main steam flow merge by removing the circumferential velocity component. By suppressing the mixing loss, the mixing loss can be reduced, and the leakage loss can be effectively reduced.

  Furthermore, the flow angle distribution in the blade height direction is made uniform by suppressing the mismatch of the flow angle when the leakage flow and the main steam flow are merged. As a result, the flow toward the stationary vane is rectified in the blade height direction. can do. As a result, the interference loss can be reduced, and the leakage flow loss can be effectively reduced.

  By the way, as shown in FIG. 4, when the width of the gap Ca between the axial seal fins when the turbine is stopped is set too wide, the backflow of the high-pressure mainstream steam 12 cannot be prevented and the mixing loss is sufficiently reduced. You may not be able to. In addition, when the axial gap Ca is wide, the cavity 9 becomes a semi-open region, and recirculates to the steam main flow 12 without forming the circulation flow 20, and the circumferential velocity component cannot be sufficiently removed, and mixing is performed. There is a possibility that the loss reduction effect cannot be obtained sufficiently. FIG. 5 shows the difference in the absolute flow angle distribution downstream of the rotor blade due to the influence of the gap between the axial seal fins. The outflow angle is based on the axial direction, and the absolute value of the flow angle approaches 90 degrees as the circumferential speed increases with respect to the axial speed. As described above, by providing the axial seal fin, the circumferential velocity component is also reduced due to the effect of the circulation flow even in the case of leaking flow that rejoins while leaving the strong circumferential velocity component originally given by the stationary blade. It can be merged with the mainstream downstream of the rotor blade in a suppressed state. As a result, the flow angle distribution in the vicinity of the blade tip can also approach the axial outflow, and the change in the flow angle distribution in the vicinity of the blade tip can be suppressed, so that the mixing loss caused by the mixing of the main flow and leakage flow is reduced. Get smaller. This effect is significant when the gap between the axial seal fins is narrowed as shown in FIG. As a result, as shown in FIG. 6, the blade loss including the mixing loss of the leakage flow and the main flow can be reduced at the blade tip portion, and the stage efficiency of the stage to which the present invention is applied is improved.

  On the other hand, if the width of the gap Ca between the axial seal fins when the turbine is stopped is set too narrow, the risk of contact between the shroud and the axial seal fins during steady operation increases. Further, in the present invention, the main effect of the axial seal fin is not reduction of the leakage flow amount but reduction of mixing loss by preventing the backflow of the mainstream steam and removing the circumferential velocity component of the leakage flow. Therefore, it is not necessary to narrow the gap as much as the gap width Cr of the radial seal fin. FIG. 7 shows a graph of mixing loss and axial and radial seal fin gap ratios obtained by performing numerical analysis under conditions of a plurality of axial gap widths Ca. Here, the gap ratio is obtained by making the axial seal fin gap Ca dimensionless with the radial seal fin gap Cr. As shown in FIG. 7, when the gap ratio Ca / Cr is about 3.0 or less, the mixing loss can be effectively reduced, and when the gap ratio is higher than that, the mixing loss reducing effect is gradually increased. When the gap ratio is about 9.0 or more, the mixing loss reduction effect of the axial seal fin can hardly be obtained.

  From the above results, it can be said that it is effective to configure the axial seal fin gap width to satisfy Cr ≦ Ca ≦ 3Cr.

  Another embodiment of the present invention is shown in FIG. In this embodiment, a rib 21 is provided in the cavity 9 between the radial seal fin 7 and the axial seal fin 8. Details of the configuration and operation of the present embodiment will be described focusing on differences from the first embodiment.

  FIG. 9 shows the flow state in the cavity on the downstream side of the blade tip. As described in the first embodiment, the leakage flow 13 that has flowed into the leakage flow path from the main flow passes through the leakage flow path with almost no loss of the circumferential velocity component. Thereafter, it flows into the cavity 9, forms a circulating flow 20, and the circumferential velocity component is attenuated while being influenced by the viscosity from the wall surface. In this embodiment, a rib 21 for further reducing the circumferential speed is provided in the cavity. The ribs 21 are thin plates that extend in the cavity in the axial direction of the rotor, and are fixed to the stationary part. Further, as shown in FIG. 9, the ribs 21 are arranged at equal intervals in the circumferential direction at the same circumferential pitch as the moving blades (that is, the number of ribs is the same as that of the moving blades). In addition, although the installation direction of a rib may be installed along a rotor axial direction, you may incline in the circumferential direction with respect to a rotor axial direction toward the same direction as a steam main flow. By inclining the arrangement, the leakage flow can be directed in the same direction as the main steam flow, and more effects can be obtained.

  The leakage flow 13 that has flowed into the cavity collides with the rib 21 and is turned in the axial direction, and forms a circulation flow 20. As a result, the leakage flow 13 can be discharged in the axial direction, and the mixing loss can be further reduced.

  FIG. 10 shows the difference in absolute outflow angle distribution downstream of the rotor blade depending on the presence or absence of ribs. When the rib is provided, the circumferential velocity component can be made substantially zero, and the change in the flow angle distribution in the vicinity of the blade tip can be further suppressed. Therefore, the mixing loss caused by mixing the main flow and the leak flow is reduced. As a result, as shown in FIG. 6, the blade loss including the mixing loss of the leakage flow and the main flow can be reduced at the blade tip portion, and the stage efficiency of the stage to which the present invention is applied is improved. Furthermore, since a uniform outflow distribution can be maintained near the blade tip, the incidence to the next stage is also improved. As a result, the stage efficiency in the next stage can also be improved.

  In this embodiment, it is assumed that they are installed at equal intervals with the same circumferential pitch as the moving blades (that is, the number of ribs is the same as that of the moving blades), but depending on the circumferential speed given by the stationary blades, Even if it is reduced, the same effect as this patent can be exhibited.

  Another embodiment of the present invention is shown in FIG. In this embodiment, the abradable material 22 is coated on the downstream side wall surface facing the axial seal fin 8 of the shroud 6. Details of the configuration and operation of the present embodiment will be described focusing on differences from the first and second embodiments.

  As described in the first embodiment, the main effect of the axial seal fin 8 is not the reduction of the leakage flow amount, but while avoiding the danger due to the contact between the axial seal fin 8 and the opposed shroud 6, If the gap Ca between the axial seal fins can be further narrowed, the amount of leakage flow can be reduced, leading to a reduction in bypass loss. Of course, since the reverse flow of the high-pressure steam main flow can be more effectively prevented, the mixing loss can also be reduced. In this embodiment, the surface of the shroud 6 facing the axial seal fin 8 is coated with the abradable material 22 so that the axial gap width Ca is narrowed. Abradable material is a material with excellent machinability. Even when the turbine blades vibrate in the axial direction and come into contact with the axial seal fin during steady operation, the abradable material is simply cut off at the contact part. The direction seal fin 8 and the shroud 6 are not damaged. Therefore, the leakage loss can be further reduced by applying this embodiment, which leads to an improvement in stage efficiency.

DESCRIPTION OF SYMBOLS 1 Diaphragm outer ring | wheel 2 Diaphragm inner ring | wheel 3 Turbine rotor 4 Turbine stationary blade 5 Turbine rotor blade 6 Shroud 7 Radial direction seal fin 8 Axial direction seal fin 9 Cavity 10 Pressure receiving head 10a Contact surface 11 Elastic body 12 Steam main flow 13 Leakage flow 20 Circulation flow 21 Rib 22 Abradable material 23 Groove 24 Fin support member 24a Contact surface

Claims (6)

A turbine rotor rotatably supported;
A turbine blade fixed to the turbine rotor;
A shroud provided at the tip of the turbine blade,
A stationary part facing the shroud with a gap between them;
An axial flow turbine comprising a radial seal fin provided to protrude in a rotor radial direction in a leakage flow path between an outer peripheral side wall surface of the shroud and the stationary part,
A leakage flow path between the downstream side wall surface of the shroud and the stationary portion includes an axial seal fin that protrudes in the rotor axial direction and is located radially inward from the outer peripheral side wall surface of the shroud, and the shroud and the stationary portion A cavity surrounded by the downstream side wall surface of the shroud , the stationary part, the radial seal fin provided on the most downstream side in the leak flow path, and the axial seal fin An axial flow turbine characterized in that a part is formed. An axial turbine according to claim 1,
The stationary turbine includes a driving means for moving the axial seal fin in the axial direction of the rotor in accordance with an operating state of the axial turbine. An axial turbine according to claim 1 or 2,
An axial turbine having Cr ≦ Ca ≦ 3Cr when the gap width between the axial seal fin and the shroud is defined as Ca and the gap width between the radial seal fin and the shroud is defined as Cr. . An axial turbine according to any one of claims 1 to 3,
An axial-flow turbine characterized in that a rib that is supported by the stationary part and extends in the rotor axial direction is disposed in the cavity part. An axial-flow turbine according to claim 3, wherein claim 2 is referred to, claim 3 is referred to, or claim 2 is referred to .
The driving means is provided in a groove formed in the stationary part, receives a vapor pressure and moves in a radial direction, a pressure receiving head that is pushed by the pressure receiving head and moves in a rotor axial direction, and Urging means for urging the fin support member in a direction opposite to the pushing direction by the pressure receiving head;
The axial-flow turbine is supported by the fin support member. An axial flow turbine according to any one of claims 1 to 5,
Axial flow turbine, characterized in that coated with abradable material on the downstream side wall surface of the shroud facing the axial seal fins.