Impeller radial-axial turbines

 

(57) Abstract:

The impeller is made with protivospalitionami edges on the blades, protecting the blade surfaces from cavitation destruction in operational periods in which the pressure is significantly deviates from the calculated one. In the impeller, containing the hub, rim and associated blades, ribs are located on the surfaces of the blades adjacent their inlet edges to the front edges of blades and being located between the hub and the border development zone of cavitation erosion of the blades at the inlet edges of the blades at the rim. While the ribs are set in the directions of the streamlines on the current mode of operation for the length, the components of 0.05-0.2 from nominal impeller diameter, and the distance of the input edge closest to the hub of the ribs is 0.1 to 0.8 of the length of the projection of the input edges of the blades to the axis of the impeller. This arrangement of the ribs allows dozens of times to reduce erosion destruction of the blades and to maintain high efficiency turbines. 3 Il.

The invention relates to hydromelioration and can be used in radial-axial turbines designed to operate at high colemani the district fracture radial-flow impeller occur 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, at high pressure, the cavitation process in this area intensified and, in addition, there is a zone of cavitation damage is displaced along the rim in the direction of the output edges, and with a low pressure area is formed cavitation damage near the output edges of the blades [1].

There are various ways of protection against cavitation damage, one of which is the installation of ribs on the surface of the blades.

Known impellers radial-axial turbines, in which the ribs are installed in the zone of occurrence of cavitation. The installation of such edges at the inlet edges of the blades of the turbine Krasnoyarskaya HPP allowed 6-8 times to reduce the intensity of cavitation erosion in the area outside the front edges of the blades [2].

Known impellers, in which the ribs are mounted on the rear side of the blades along the borders of the occurrence of erosive destruction [3]. According to the model tests is the arrangement of the ribs about 2 times reduces the intensity of cavitation erosion near the output crookham direct impact on formed in the zone of cavitation cavities. However, as the data reveal, the use of these solutions not effectively protects against cavitation damage.

Closest to the present invention are impellers, on the surface of blades whose edges are set for the input edges between the hub and the boundary of the zone of cavitation erosion adjacent to the wheel rim, thereby affecting the flow through the impeller [4, 5]. The closest of these is the impeller radial-axial turbines, containing the hub, rim and associated blades, the surfaces each of which ribs are installed directly behind the entrance edge of the blade (4). In these known wheels ribs generate a vortex filaments, which weaken the cavitation process. For this edge on each blade installed in pairs at an angle to each other. These solutions are intended for use in the turbines when operating at low starting pressure. The present invention laid the task of creating the impeller radial-axial gasturbine as protivoavarijnyh edges on the blades, which would be significantly more than the notes of the turbine, different from the settlement, and, however, did not reduce efficiency when working on normal modes.

This problem is solved for the impeller radial-axial turbines, containing the hub, rim and associated blades, in which on the surfaces of each blade installed ribs, located directly behind the entrance edge of the blade and passing between the hub and the boundary of the zone of cavitation erosion, and in which, in accordance with the essence of the present invention, the ribs are installed on the directions of the streamlines on the current mode for the length of 0.05 to 0.2 from the nominal diameter of the impeller, and at a distance from the hub to the input edge closest to the hub ribs, of 0.1 to 0.8 of the length of the projection of the input edges of the blades to the axis of the impeller.

This decision created and grounded in the three-dimensional mathematical modeling of current flow in radial-axial working wheel of the turbine, which has allowed to establish that the modes of operation, different from the calculated cavitation process intensifies additional vortex flow in the stream, which originates in the area of the inlet edges of the blades at Sol inlet edges of the blades to the rim, then turns and goes around it, leading to additional pressure drop in the zone 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, carries out the rotation and displacement of the working surface of the blades with the transition to the back surface of the adjacent blade, and then passes it to the output edge.

Installation of ribs in accordance with the essence of the present invention allows to change the trajectory of additional eddy currents arising from the hub, eliminating its negative impact. Thus, edges, as it follows from the data of mathematical modeling, impellers turbines for the power plant with a large seasonal increase in pressure above the estimated value, should be installed on the rear side of the blades, and are intended for hydropower plants with large seasonal reduction of pressure of the fin should be set on the working surface of the blades of the impeller Set the distance of the location of the ribs from the hub defines the ability of the ribs to reject additional eddy current from the cavitation zone. Therefore, set the range espeleologia flow and above the boundaries of the known location of occurrence of the cavitation destruction the rim at the entrance edge of the blade wheel. As shown by experimental studies and mathematical modeling results, the invention during operation of the impeller radial-axial turbines on the conditions under which the pressure is significantly different from the estimates, allows dozens of times to reduce cavitation erosion. Due to the location of edges specified length along the lines of the current calculation mode, the ribs do not have a disturbing effect or resistance to this flow, and therefore does not lead to lower efficiency on the operating mode.

The essence of the present invention is illustrated in the following further detailed description of examples of its use, accompanied by drawings, in which:

Fig. 1 is a longitudinal section of the impeller radial-axial turbines, designed to work on a hydroelectric power station with a large pressure increase above the calculated value: (a) the impeller is not equipped with means of protection against cavitation erosion, b) - impeller with protivospalitionami ribs according to the invention;

Fig. 2 - impeller radial-axial turbines, designed to work on a hydroelectric power station at a lower pressure as compared with the calculated value: (a) working cobras according to the invention;

Fig. 3 is a graphical dependence of the efficiency on the above flow turbines with protivospalitionami ribs according to the invention without them.

Impeller radial-axial turbine includes a hub 1, the rim 2 and associated blade 3 with work surfaces 3.1 (pressure side) and dorsal surfaces 3.2 (rarefaction). One of the main geometrical parameters of the turbine are the rotor diameter of D1and the height of the input flange b'0blades, defined as the projection of the input flange on the axle of the impeller or similar parameter characterizing the height of the guide vanes. Thus, the relative amount of b'0for D1characterizes the speed of the turbine.

As indicated above, development zone of cavitation erosion is investigated and their location is known [1]. These zones are marked by the dashed lines. On normally the zone of cavitation erosion is observed on the rear surfaces of 3.2 blades for input edges near the rim - zone A (Fig. 1A). Significantly reduce the intensity of the cavitation process in these modes allows testing of blade systems with optimization Pro is constructive activities, in particular the installation of ribs on the surface of the blades.

In accordance with the invention, the ribs 4 should be located so as to change the trajectory of additional eddy currents that occur when the variance of the modes of operation of the turbines from the settlement on the surface of each blade near the hub 1 at the inlet edges of the blades. Method three-dimensional mathematical modeling, it was found that when the turbine is at pressures substantially in excess of the calculated specified vortex passes over the input flange from the hub to the rim along the back surface 3.2 of the blades (Fig. 1A), increasing cavitation erosion in the area and creating A new lesion cavitation destruction, displaced along the rim 2 to the output edge area B.

When working at pressures substantially lower than estimated, additional eddy current starts to be formed on the working surface 3.1 of the blades at the entry edge near the hub, passes along the input edge, and then breaks away from the working surface and moves to the back surface 3.2 of adjacent blades, passing next to the output edges (Fig. 2A). In this mode, the zone of cavitation erosion is formed at the output of the edges on the back surface Loo vortex flow along the inlet edges of the blades ribs 4 must be installed on the blades between the place of origin of this vortex flow and the boundary of possible cavitation damage - area A. This determines the need for the location closest to the hub 1 rib 4 of its input edge distance h, constituting 0.1 to 0.8 times the height b'0the inlet edges of the blades. For more reliable overlap and change the trajectory of additional eddy currents ribs 4 should be set to its input edges directly behind the entrance edge of the blade 3, and their length should be from 0.05 to 0.2 of the diameter D1the impeller. The height of the ribs 4 (not labeled) is assigned within 0,010-0,012 of the diameter D1the impeller. The direction of the ribs 4 must match the direction of flow field in the impeller on the operating mode. Thus, edges 4 must be installed in accordance with the operating conditions of the turbine, i.e., for operation at pressures exceeding the design head - on the back surface 3.2 of the blades (Fig. 1B), and to work on the heads below the estimated head - on work surface 3.1 of the blades (Fig. 2B).

To evaluate the effectiveness of the invention by the method of mathematical modeling studies were performed on a radial-axial turbines. Studies were conducted to operating conditions of the turbine when the pressure below the estimated 30% and the pressure above the R installation on their respective sides of the blades limits of the range of 0.1 to 0.8 times the height of the inlet edges of the blades. The data obtained in the result of research showed that thanks to the invention it is possible to expect reduction of the intensity of cavitation erosion of the blades of the impeller radial-axial turbines in a few dozen times.

We also conducted model erosion testing of turbines in relation to the conditions of the HPP with the seasonal increase in pressure above the estimated value. Studies were conducted on the model of the impeller with a diameter of D1= 460 mm with a relative height of the input flange b'0= 0,22. The tests were carried out by a known method using a coating of legkomyslenogo material on the impeller without protivoavarijnyh edge control sample and on the impeller with protivospalitionami ribs. Both series of tests were conducted for 6 h on mode: the power of 25 m, the water flow 557 l/s and the speed with 61.3 min-1the cavitation coefficient of 0.085.

For the control sample size of the destruction of the covering blades in the area of offset along the rim from the inlet edges of the blades to the output amounted to 5.1 cm2.

On the model of the impeller with protivospalitionami ribs according to the invention on the back surface of the vane is mi to the input edges of the blades, the first of which, nearest to the hub, located from their input edge at a distance 0,22 height b'0the inlet edges of the blades. For test cycle demolition area covering the blades was 0.1 cm2that corresponds to the reduction of erosive destruction of approximately 50 times.

We also conducted a comparative model tests to determine effect of protivoavarijnyh ribs above the impeller on the power characteristics of the turbine. Test data of conducted in a wide range of costs and shown in Fig. 3 in the form of dependences of the relative efficiency model = /maxthe above flow Q1from which curve 1 refers to the test sample, and curve (2) to model the impeller with protivospalitionami ribs according to the invention.

Presented on Fig. 3 evidence suggests that protivokomarinye edges do not affect the energy qualities of the impeller radial-axial turbines.

Sources of information

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

2. Ibid., S. 40.

3. Auth. St. USSR N 1378492, F 03 B impeller radial-axial turbines, containing the hub, rim and associated blades, on the surface each of which has a rib adjacent its input edges to the front edges of the blades and located between the hub and the border development zone of cavitation erosion of the blades for their input edges at the rim, characterized in that the ribs are set in the directions of the streamlines on the current mode of operation for the length, the components of 0.05 - 0.2 from the nominal diameter of the impeller, and at a distance from the hub of the input edge nearest to her ribs, of 0.1 to 0.8 of the length of the projection of the input edges of the blades to the axis of the impeller.

 

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