Impeller radial-axial turbines

 

(57) Abstract:

The impeller is designed to work with your device, protecting his blades from cavitation erosion during turbine operation with a significant deviation of the head from the settlement. This device has an intake channel passing through the impeller shaft connected therewith, the collector, the branching tubes that run along each blade and bring the air to the means for entering air flow part. These tools are made in the form of hollow ribs, each of which extends from the inlet edges of the blades in the direction of the streamlines in the flow part at the design mode and the rear edge has at least one hole for air release. When this edge on each blade is located with its front edge at a distance from the hub, equal to 0.2 and 0.8 of the length of the projection of the input edge of the blade to the axis of the impeller, and the edge length of 0.05 to 0.2 from the nominal diameter of the impeller. Such a device provides active suppression of cavitation during turbine operation in modes that differ significantly from those estimated. 3 Il.

The invention relates to hydromelioration and Mauro hydro or during operation in the starting period at lowered pressures.

The main cavitation destruction radial-axial wheels happen on the rear surfaces of the blades. During turbine operation at rated pressure zone of cavitation damage may appear directly behind the entrance edges of the blades of the wheel rim, when working at higher pressures the cavitation process in this area intensified, moreover, there is a zone of cavitation damage, displaced along the rim in the direction of the output edges, and when working on low pressure area is formed cavitation damage near the output edges of the blades [1].

Known means of protection against cavitation damage in the form of pairs of edges that are installed in the zone of occurrence of cavitation [2] or along the boundaries of the zone of cavitation destruction [3]. However, given the operational data, the effectiveness of such solutions is not high enough, especially during turbine operation in modes different from the calculation.

Known protection against cavitation damage in the form of a device for supplying air to the zone of cavitation. Impeller radial-axial turbines with a device containing intake channel passing through the shaft, the manifold on the wheel hub and sauasage of the invention [4]. In this known wheel cavitation erosion is most significantly decreased in area, located directly applied by means of the input air flow part, and in areas downstream, reducing erosion was observed to a lesser extent [5] . The last is particularly adversely manifests itself when the turbine at higher or lower pressures.

The present invention is the task of creating the impeller radial-axial turbines with a device for supplying air in a flow path, which would be significantly more active than the known impellers, the effect on the cavitation process, suppressing them when the modes of operation of the turbine, which differs from the calculation.

This problem is solved in the impeller radial-axial turbines, which contains the air intake channel, passing through the shaft, the manifold on the wheel hub and United with him means input air flow part on each blade and in which, in accordance with the invention, the input means of the air on each blade made in the form of hollow ribs extending from the inlet edges of the blades in the direction lineatella input edge of the blade, performed at least one opening for release of the air flow part. When this hollow edge on each blade is located with its front edge at the same distance from the hub of 0.2 - 0.8 times the length of the projection of the input edge of the blade to the axis of the impeller, and the length of each hollow rib is 0.05 to 0.2 from the nominal diameter of the impeller.

This decision created and grounded in the three-dimensional mathematical modeling of current flow in radial-axial the impeller, which has allowed to establish that the modes of operation of the turbine, which differ from the estimates, the cavitation process intensifies additional vortex flow in the stream, which originates in the area of the inlet edges of the blades at the hub. At higher pressures this eddy current occurs on the back surface of the blade and extends along the inlet edges of the blades to the rim, then turns and runs along it, leading to additional pressure drop in the zones exposed to cavitation. When working at low pressures additional eddy current occurs on the working surface of the blades and extending from the hub to the rim, the implementation of the Asti, and then passes it to the output edge.

To neutralize the negative impact of additional eddy currents was proposed to establish on the blades of the barrier ribs, preventing the passage of this vortex flow in the zone exposed to cavitation [6]. Installing the separation of edges in the path of movement of the additional eddy currents, changing their trajectory, can significantly reduce cavitation erosion, which exposed the impellers when the turbines with large seasonal deviation of the head from the settlement. However, as shown by additional experimental study on cavitation stand, also known development zones of cavitation erosion, the installation of these barrier ribs in the form of a continuous vent any further development zone of cavitation erosion on the blades at the rear ends of these ribs.

When performing in accordance with the present invention separation ribs hollow, the input of air flowing through them in part for the trailing edge of the ribs allows to eliminate the appearance of these additional development zones of cavitation erosion and even more to reduce erosion in known areas, typical modes of operation , the AK and ribs to reject the trajectory of the additional eddy currents generated by the input edges of the blades of the impeller. However, to achieve the effect ejection air supply hollow edge, according to the invention, should be set a little further from the hub.

The essence of the present invention is illustrated following example, illustrated by the drawings, in which:

Fig.1 shows the impeller radial-axial turbines in longitudinal section;

Fig. 2 is a fragment of the blade at the location of the hollow ribs according to the invention, in section along a-a in Fig. 1 in an enlarged scale;

Fig. 3 - hollow edge, according to the invention, in cross-section B-B in Fig. 2

Impeller radial-axial turbines shown in the drawings, includes a wheel hub 1, the rim 2 and associated blade 3.

To suppress cavitation impeller is equipped with an air supply system in flow part. This system includes the air intake channel 4, passing through the impeller shaft connected to the collector 5 for air distribution on the blades 3, United with him inlet tube 6, which the mouth of the input air according to the invention is made in the form of hollow ribs 8, located in the direction of flow of the main flow of water through the impeller on the current mode of operation and having in this direction streamlined hydrodynamic shape of the wing. On the rear edge of each rib is made a slot 9 for the release of the air flow part.

The rib 8 for reliable shutoff and deflect additional eddy currents must have a length l of 0.05 - 0.2 of the diameter D1the impeller and the height of t within 0,010 - 0,012 D1. While the rib 8 on each blade 3 its front edge should be located directly behind the entrance edge of the blade and defend at a distance h from the hub 1 of 0.2 - 0.8 times the length of b0the projection of the input edge of the blade to the axis of the impeller. This arrangement of the ribs 8 is determined by the results of mathematical modeling conducted in connection with the problem of eliminating additional vortex motion, emerging from the inlet edges of the blades, and due to the need for safe ejection effect for air flow in the flow part.

As it was previously installed on the edges with the corresponding functional purpose, they, with the forecast in the forecast mode of operation for seasonal low pressure should be placed on the working surface of the blades.

The invention was tested for two years on one of the HPP with radial-axial turbine is operated with a significant seasonal increase in pressure. Two blades of the impeller of this turbine D1= 4.1 m was installed hollow rib in the wing directly behind the entrance edge of the blade at a distance h from the hub, amounting to 0.72 of length b0the projection of the input edge of the blade to the axis of the impeller. The edge length l was equal to 0.05 D1and its height t was 0,01 D1. The results of the examination of these blades has shown:

to install the edge intensity of cavitation damage on the blades during operation of the turbine at higher pressures was Iv= 0,23 cm3per hour;

when applying only air the intensity of cavitation damage is Iv= 0,07 cm3per hour;

when installed on the blade edges with the air inlet of the cavitation damage is not detected.

Sources of information

1. Hydropower and auxiliary equipment of hydropower plants, so 1. M., 1988, S. 35-36, figure 4.7.

2. Hydropower and auxiliary equipment of hydropower plants, so 1. M., 1988, S. 40.

6. Patent RF N 99.100253 from 11.01.99.

Impeller radial-axial turbines, containing the intake channel passing through the shaft, the manifold on the wheel hub and United with him means input air flow part on each blade, characterized in that the input means of the air flow part made in the form of hollow ribs extending from the inlet edges of the blades in the direction of the line current flowing in part on the current mode of operation, and the rear edge of the fin is made of at least one opening for release of the air flow part, when this edge on each blade is located with its front edge at a distance from the hub, equal to 0.2 and 0.8 of the length of the projection of the input edge of the blade to the axis of the impeller, and its length is 0.05 to 0.2 from the nominal diameter of the impeller.

 

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