JPH10318117A - Impeller of fluid machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a flow of a working fluid, enlarge the operating range, and prevent cavitation, by installing an overhang having attack angle which is equal to the incident angle of the working fluid on at least a band root of a runner vane. SOLUTION: In a runner vane 5, an overhang 20 is provided at a crown side root and a band side root of an entrance side leading edge of a water wheel. The overhang 20 has sweepback angle which is planely sharp, and side- view, which has an attack angle equal to the incident angle assumed at designing of a working fluid to a blade, is formed to be triangular or top tapered shape similar to it. During partially loaded operation, because the leading edge separating vortex like a vortex tube, which is generated on the negative-pressure surface side of the runner vane 5 around the overhand 20 caused by the change of an incident angle of a working fluid, flows down along the main stream of the working fluid, to local and rapid pressure change is prevented. In overloaded operation, because the separating vortex which is generated by the overhang 20 flows down along the pressure surface side of the runner vine 5, the separation of flow and secondary flow are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an impeller of a fluid machine such as a turbine, a pump turbine, or a turbine.

[0002]

2. Description of the Related Art FIG. 11 is a longitudinal section of a general Francis turbine, and an impeller 2 is fixed to a lower end of a main shaft 1 of the turbine. The impeller 2 has a runner crown 3 and a band 4
And a plurality of runner vanes 5 arranged in a row in the circumferential direction and fixed to the runner crown 3 and the band 4 therebetween. The upper side of the impeller 2 is covered by an upper cover 6, and the lower side is covered by a lower cover 7.

[0003] A plurality of movable guide vanes 8 for changing the opening of the water port are provided radially outward of the impeller 2, and a plurality of stay vanes 9 are further provided outside thereof. A spiral casing 10 connected to a penstock (not shown) is provided outside the stay vane 9. On the other hand, a suction pipe 11 is connected to the lower cover 7 so that water that has passed through the impeller 2 during operation of the water turbine is guided to a water discharge channel.

When the movable guide vane 8 is opened, water flows from the spiral casing 10 into the runner chamber in which the impeller 2 is disposed, flows between the runner vanes 5 of the impeller 2, and flows into the runner chamber. The car 2 is rotated. Then, the water that has passed through the impeller 2 is led out to the water discharge channel via the suction pipe 11.

FIG. 12 is a sectional view of the impeller 2 of the above-mentioned Francis turbine. A plurality of runner vanes 5 are arranged in a row in the circumferential direction between a substantially disk-shaped crown 3 and a cylindrical band 4. And are integrally fixed to the crown 3 and the band 4. Reference numeral 3a in the figure is a runner cone for rectification.

Therefore, during normal operation of the turbine, high-pressure water, which is a working fluid, flows between the runner vanes 5 in the direction of the arrow in the figure, and the impeller 2 releases the pressure to convert energy into rotational force. .

[0007]

By the way, not only such water turbines but also fluid machines such as pump turbines and turbines operate most efficiently by using the flow rate, hydraulic head (pressure) and rotational speed of the working fluid as design points. Since it is made to absorb the energy of the fluid, the efficiency is reduced in operating conditions outside the design point. Furthermore, in the high specific speed runner for water turbines, unsteady negative pressure distribution occurs at the base of the runner vane near the band due to the separation of the flow in the operating state outside the design point, causing vibration and cavitation, and There are cases of erosion.

More specifically, in a turbine having a specific rotational speed including a water turbine, when the operating state is lower than the design point and the flow rate is lower than the design point, the flow rate of the working fluid flowing between the runner vanes is relatively large. At the same time, the angle of incidence increases, and the flow is separated on the negative pressure surface of the runner vane, disturbing the pressure distribution, and the efficiency decreases. At the same time, the boundary layer develops significantly, and the flow separates near the leading edge of the runner vane, causing swirling stall or surging, which may cause vibration in the entire machine.

FIG. 13 is a view showing the flow on the band side inlet side in the runner vane. During normal load operation, as shown in FIG. 13 (a), the working fluid flows into the runner vane according to a predetermined design. It flows in at an angle and produces a smooth flow over the surface of the runner vane. But,
During the partial load operation of the turbine, the flow path of the water flowing between the runner vanes is relatively reduced because the flow path is narrowed by the guide vanes 8, while the inlet area and the rotation speed of the impeller itself are constant, so that the water flow to the runner vanes is reduced. Incident angle increases. Therefore, the flow of water itself loses stability, and FIG.
As shown in (b), a flow separation area is generated on the negative pressure side of the runner vane 5, which causes vibration and cavitation.

In particular, in the impeller of the Francis turbine, the joint between the band 4 and the runner vane 5 forms a flowing water surface having a large curvature due to geometrical interference between the curvatures of the respective curved surfaces. Due to the shape of the sharply curved flow channel that flows down almost vertically on the band 4 side, the incident angle of the runner vanes 5 near the band 4 becomes relatively larger than other portions, and the flow tends to be unstable.

Also, during overload operation, FIG.
As shown in (1), since the incident angle of the working fluid to the runner vane is smaller than the incident angle assumed at the time of design, contrary to the partial load, flow separation and cavitation tend to occur on the pressure surface side.

FIG. 14 shows a state in which the flow at the band-side entrance is separated during the partial load operation of the conventional impeller.

In view of the above, the present invention stabilizes the flow of working fluid mainly at the time of partial load operation in a fluid machine such as a water turbine, a pump turbine, an axial turbine, etc., thereby expanding the operating range and cavitation. An object is to obtain an impeller with improved characteristics.

[0014]

According to a first aspect of the present invention, a runner vane in a Francis type water turbine or a Francis type pump turbine having a plurality of runner vanes fixed in a row in the circumferential direction between a crown and a band is operated as a water turbine. At least at the root of the working fluid inlet side leading edge at the band side when
It is characterized in that it has an angle of attack substantially equal to the incident angle of the working fluid in the operating state assumed at the time of design, and has a tapered overhang having a sharp receding angle.

According to a second aspect of the present invention, a movable runner van in a Kaplan type turbine or a tubular turbine in which a plurality of runner vanes are radially arranged around a boss is provided at a root on a boss side at a front edge of a working fluid inlet side and a tip end on a casing side. And a projection similar to that of the first invention is provided.

In a third aspect of the present invention, in a mixed flow turbine in which a plurality of runner vanes are radially arranged around a boss, a movable fluid runner vane has a boss-side root and a casing-side tip at a front edge of a working fluid inlet side. It is characterized in that an overhang similar to that of the first invention is provided.

Further, a fourth invention provides a radial turbine in which a plurality of blades are radially arranged around a rotation axis, at least at a tip side of a working fluid inlet side leading edge of the blades. It is characterized by providing an overhang similar to that described above.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a longitudinal sectional view of an impeller of a Francis turbine showing an embodiment of the present invention.
A plurality of runner vanes 5 are arranged in a row in the circumferential direction between the runner vane 5 and the band 4, and each runner vane 5 is fixed to the runner crown 3 and the band 4. The runner vane 5 has a sharp receding angle at the crown-side root and the band-side root at the leading edge on the inlet side of the turbine, and has an angle of attack equal to the incident angle assumed at the time of designing the working fluid to the blade. A protruding portion 20 having a triangular shape or a tapered shape similar thereto is provided. That is, the overhang portion 20 is formed such that the amount of overhang decreases as the distance from the crown-side root portion or the band-side root portion increases.

FIG. 2 is a diagram showing the state of the flow of the working fluid near the overhanging portion in the case where the overhanging portion 20 is provided on the runner vane 5 as described above.
When the flow is near the design as described above, the overhang portion 20 is basically parallel to the flow of the working fluid, and no separation vortex is generated on the downstream side of the overhang portion 20 of the runner vane 5. The sharp flow shape has little effect on the flow intended at the time of design, and the sharp and local pressure rise at the root portion of the blade due to the impact of the working fluid is reduced, and the pressure loss is reduced.

On the other hand, as shown in FIG. 2B, during the partial load operation, the overhang portion 20 functions as a vortex generator due to a change in the incident angle of the working fluid, and a vortex tubular leading edge separation vortex that winds up the flow is formed. It is generated on the runner vane negative pressure side near the place where the overhang is formed. This vortex tube flows down along the main flow of the working fluid and suppresses local and rapid pressure fluctuations, so that erosion due to cavitation that adheres to the base of the runner vane and collapses is reduced.

In the overload operation, the incident angle of the working fluid to the cascade is smaller than the incident angle assumed at the time of the design, contrary to the partial load operation, as shown in FIG. Separation of the flow or cavitation occurs on the pressure surface side, but the separation vortex generated by the overhanging portion flows down along the pressure surface side of the runner vane, so that separation of the flow, secondary flow, cavitation and erosion associated therewith And the operating range of the water turbine is expanded without losing efficiency.

FIG. 3 shows the state of generation of a vortex tubular separation vortex at the band-side entrance at the time of partial load operation in a runner vane provided with an overhang.

FIG. 4 is an iso-efficiency curve (eyeball curve) based on a conventional turbine model test. The horizontal axis represents the rotation speed per unit head indicating the operating state of the model turbine corresponding to the operating head of the actual turbine. The axis is the flow rate per unit head, and each line is a characteristic curve of each guide vane opening. On the other hand, FIG. 5 is an iso-efficiency curve of a water turbine to which the present invention is applied.

By comparing the iso-efficiency curves in both figures, it can be seen that the range in which the iso-efficiency is applied is wider and the operating range is expanded when the present invention is applied.

FIG. 6 is a diagram showing the results of verification by a model test of a water turbine, and shows a performance curve of one guide vane opening. Here, the horizontal axis is the rotation speed per unit head representing the operating state of the model turbine corresponding to the operating head of the actual turbine, the vertical axis is the efficiency η (%), the dotted line is the conventional type, and the solid line is the actual one. 3 shows the efficiency of a water turbine to which the invention is applied.

Therefore, it can be seen from this graph that the provision of the overhang improves the characteristics during partial load operation. Naturally, this effect is obtained at all guide vane openings, and the maximum efficiency point is slightly increased.

FIG. 7 shows a Francis type pump-turbine in which a projecting portion 20 is provided on the crown-side and band-side root of the runner vane front edge at the turbine-side inlet. The basic structure of the pump turbine runner is the same as that of the turbine dedicated machine, but in order to give priority to the pump performance at the time of design, the camber line (warp line) of the runner vane has a concave surface on the negative pressure side, contrary to the turbine dedicated during turbine operation Therefore, fluid loss and cavitation erosion occurred on the suction surface side of the runner vane front edge at the turbine-side inlet, thereby limiting the operating range. However, by providing the overhanging portion 20, FIG. It has the same effect as shown. further,
This overhang exerts the same streamline effect as the fillet at the junction between the aircraft fuselage and the wings when the fluid flows out of the cascade even during pump operation, reducing pressure loss and flow separation. Also improves pump performance.

FIG. 8 is a diagram showing another embodiment of the present invention, in which the present invention is applied to a runner of a Kaplan turbine. In other words, the movable runner vane 12 of the Kaplan turbine runner is formed with a projecting portion 20 similar to that shown in FIG. And this overhang 2
0 has the same effect as in the embodiment shown in FIG. 1, and the operating range at each opening of the runner vane 12 can be expanded.

FIG. 9 is a view showing an application of the present invention to a mixed flow turbine having movable runner vanes. Also in this case, the tip side of the front edge of each runner vane 12 and the boss 1 are shown.
An overhang 20 similar to that described above is formed at the base of 3. In this case, the same effects as those of the above-described embodiments can be obtained.

In each of the above embodiments,
FIG. 10 shows an example applied to a water turbine or a pump water turbine.
As shown in the above, the present invention can also be applied to a large-diameter reaction radial turbine used for a steam turbine or the like.

That is, in FIG. 10, reference numeral 14 denotes a rotor blade radially provided on a rotor shaft 15 of the radial turbine. A similar overhang 20 is formed.

By the way, even in this type of turbine, at the time of partial load operation, although the flow is swirled at the tip due to the centrifugal force and the interference of the boundary layer, a pressure loss is caused. This can produce the same effects as described above. Also, on the rotor shaft side, the overhang 20 can reduce the pressure loss and the collision loss of the narrow portion.

[0034]

According to the present invention, as described above, the root of a runner vane of a water turbine, the tip side of a moving blade of a radial turbine, etc., in which flow separation or secondary flow is likely to occur during partial load operation or overload operation, is described. Since the overhanging portion is provided, a vortex tube is generated by the overhanging portion, the separation of the flow in the portion is delayed, and the rapid pressure change is reduced,
Vibration and other adverse effects are suppressed. Furthermore, the secondary flow of the surrounding main flow is also suppressed and stabilized, so that the operable range can be greatly expanded without impairing the efficiency.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an impeller of a Francis type water turbine showing a first embodiment of the present invention.

FIGS. 2 (a), (b), and (c) show the flow states of the working fluid at the band-side inlet of the impeller of the present invention near the design point, during partial load operation, and during overload operation, respectively. FIG.

FIG. 3 is a schematic diagram showing a state in which fluid is separated from a band-side inlet of a runner vane during partial load operation of an impeller according to the present invention.

FIG. 4 is an iso-efficiency diagram of a conventional Francis turbine.

FIG. 5 is an iso-efficiency diagram of the Francis type water turbine of the present invention.

FIG. 6 is a performance curve diagram in a model test.

FIG. 7 is a diagram showing another embodiment of the present invention.

FIG. 8 is a diagram showing still another embodiment of the present invention.

FIG. 9 is a diagram showing another embodiment of the present invention.

FIG. 10 is a diagram showing still another embodiment of the present invention.

FIG. 11 is a sectional view showing a schematic configuration of a conventional Francis type water turbine.

12 is a vertical sectional view of the impeller of the Francis type water turbine shown in FIG.

FIGS. 13A, 13B, and 13C are diagrams showing states of flow of a working fluid at a band-side inlet of a runner vane, respectively.

FIG. 14 is a schematic view showing a state in which a fluid is separated from a band-side inlet of a runner vane when a partial load is applied to a conventional impeller.

[Explanation of symbols]

 Reference Signs List 3 runner crown 4 band 5 runner vane 6 upper cover 7 lower cover 8 movable guide vane 11 suction pipe 12 runner vane 13 boss 20 overhang portion

Claims (4)

[Claims] 1. A working fluid inlet side leading edge of a runner vane in a Francis type water turbine or a Francis type pump turbine in which a plurality of runner vanes are fixed in a row in a circumferential direction between a crown and a band when the turbine is operated as a water turbine. At least at the base of the band, a fluid having an angle of attack substantially coincident with the incident angle of the working fluid in the operating state assumed at the time of design, and provided with a tapered overhang having a sharp receding angle. Machine impeller. In a Kaplan type water turbine or a tubular water turbine in which a plurality of runner vanes are radially arranged around a boss, the movable runner vane is provided at the root on the boss side at the leading edge on the working fluid inlet side and at the tip of the casing side at the time of design. An impeller for a fluid machine, wherein the impeller has an angle of attack substantially equal to the incident angle of the working fluid in the operating state and has a tapered overhang having a sharp receding angle. 3. An operating state assumed at the time of design at a boss-side root and a casing-side tip of a working fluid inlet side front edge of a movable runner vane in a mixed flow turbine in which a plurality of runner vanes are radially arranged around a boss. An impeller for a fluid machine, characterized in that it has an angle of attack substantially equal to the incident angle of the working fluid in (1), and has a tapered overhang having a sharp receding angle. 4. A working fluid in an operating state assumed at the time of design at least at a tip side of a working fluid inlet side leading edge of the working blade in a radial turbine in which a plurality of moving blades are radially arranged around a rotation axis. An impeller for a fluid machine, characterized in that the impeller has an angle of attack substantially coinciding with the angle of incidence and has a tapered overhang having a sharp receding angle.