Francis-type runner for a turbine, and energy conversion plant comprising such a runner

Abstract

This Francis-type runner for a turbine includes a crown, a band and blades the number of which is not a prime number. These blades are made as one piece and extend between the crown and the band, and between a leading edge and a trailing edge each trailing edge has its concave face facing upstream over its entire length. In addition, first blades are uniformly distributed about a central axis of the runner in a number equal to a divisor of the total number of blades. Each of these first blades has a point of attachment of its trailing edge to the crown that is lowered by comparison with the point of attachment of the trailing edge to the crown of second blades, which are likewise part of the runner. Moreover, the ratio between, on the one hand, the radius of a circle centered on the central axis of the runner, perpendicular to this axis and passing through the point of attachment of the trailing edge of a first blade to the crown and, on the other hand, the radius of a circle centered on the central axis of the runner perpendicular to this axis and passing through the point of attachment of the trailing edge of the same blade to the band is less 0.15.

Claims

1. A Francis-type runner for a turbine, comprising a crown, a band and first blades and second blades, a total number of the first and second blades is not a prime number, the first and second blades extending between the crown and the band and comprising a leading edge, and a trailing edge, each trailing edge having a concave face facing upstream over an entire length, wherein: the first blades, uniformly distributed about a central axis of the runner and equal in number to a divisor of the total number of the first and second blades, have a point of attachment of the trailing edge to the crown of the second blades; and a first ratio between a radius of a circle centered on and perpendicular to a central axis of the runner and passing through the point of attachment of the trailing edge of the first blades to the crown, and a radius of a circle centered on and perpendicular to the central axis of the runner and passing through the point of attachment of the trailing edge of the first blades to the band, is less than 0.15; and wherein a second ratio between the radius of the circle centered on and perpendicular to the central axis of the runner and passing through the point of attachment of the trailing edge of the first blades to the crown and a radius of a circle centered on and perpendicular to the central axis of the runner and passing through the point of attachment of the trailing edge of the second blades to the crown is less than 0.75.

2. The Francis-type runner for a turbine as claimed in claim 1, wherein the first ratio is less than 0.1.

3. The Francis-type runner for a turbine as claimed in claim 1, wherein the points of attachment of the trailing edges to the band of the first and second blades lie on one and the same circle centered on and perpendicular to the central axis of the runner.

4. The Francis-type runner for a turbine as claimed in claim 1, wherein a third ratio between an area of a lateral surface of the first blades and an area of a lateral surface of the second blades is from 1.05 to 1.50.

5. The Francis-type runner for a turbine as claimed in claim 1, wherein a periodicity of the first blades about the central axis is higher than a periodicity of the second blades, and at least twice as high.

6. The Francis-type runner for a turbine as claimed in claim 1, wherein a periodicity of the total number of blades is 2/15 and a periodicity of the number of first blades is 2/3 or 2/5.

7. The Francis-type runner for a turbine as claimed in claim 1, wherein a periodicity of the total number of blades is 2/12 and a periodicity of the number of first blades is 2/3 or 2/4.

8. A plant for converting hydraulic energy into electrical or mechanical energy, comprising a turbine, wherein the turbine comprises a Francis-type runner as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other advantages thereof will become more clearly apparent from the following description of one embodiment of a Francis turbine runner and of an installation both in accordance with its principle, given solely by way of example and made with reference to the attached drawings in which:

(2) FIG. 1 is a schematic diagram, in axial section, of a plant according to the invention;

(3) FIG. 2 is a perspective view from beneath of the Francis turbine runner of the plant of FIG. 1, this runner being a runner according to the invention;

(4) FIG. 3 is a meridian section of the runner of FIG. 2.

DETAILED DESCRIPTION

(5) The plant 100 depicted in FIG. 1 comprises a Francis-type turbine 101 the runner 1 of which is intended to be set in rotation about a vertical axis X.sub.1 by a forced flow of water E from a water catchment not depicted. In FIG. 1, for the clarity of the drawing, the runner 1 is depicted as viewed from the outside. A shaft 103 supports the runner 1 and is coupled to an alternator 104 which delivers an alternating current to a grid, not depicted. The plant therefore allows the hydraulic energy of the flow E to be converted into electrical energy.

(6) The plant 100 may comprise several turbines 101 fed from the same water catchment.

(7) As an alternative, the shaft 103 may be coupled to a mechanical assembly, in which case the plant 100 converts the hydraulic energy of the flow E into mechanical energy.

(8) As an alternative, the turbine 101 is a turbine-pump, in which case it may also operate in pump mode, i.e. in a mode in which the runner 1 is turned by the alternator 104 in the opposite direction of rotation to the direction in which it rotates when the turbine-pump is operating in turbine mode. In pump mode, the alternator 104 then acts as a motor, to displace a quantity of water to the water catchment which has not been depicted. The water then flows in the opposite direction to the arrows E in FIG. 1. In the alternative form in which the shaft 103 is coupled to a mechanical assembly and the turbine 101 is a turbine-pump operating in pump mode, the runner 1 is driven by this mechanical assembly.

(9) A penstock 105 conveys the flow E to the runner 1 when the turbine-pump is operating in turbine mode. The penstock 105 extends between the water catchment and a tank 106 equipped with wicket gates 107 which regulate the flow E. A draft tube 108 is provided downstream of the turbine in the direction of the flow E to discharge this flow and return it to the bed of a stream, a river or a reservoir downstream.

(10) The runner 1 depicted in FIG. 1 comprises blades 2 distributed about the central axis X.sub.1 of rotation of the runner 1. A crown 3 is provided in the internal radial upper part of the runner 1, whereas a band 4 borders the lower, radial and external part of the blades 2. A flow duct 5 is thus defined between each pair of two adjacent blades 2, this duct being bordered by the crown 3 and the band 4. The total number of blades 2 of the runner 1 depicted in FIGS. 1, 2 and 3 is fifteen, with the knowledge that there could be a different total number of blades, not a prime number, such as 12, 18 or 24 blades.

(11) The blades 2 are of two kinds, namely first blades 2A and second blades 2B. The number of first blades 2A is a divisor of the total number of blades 2, as likewise the number of second blades 2B is a divisor of the total number of blades 2. The blades 2A are identical to one another, as are the blades 2B. The blades 2A and 2B are uniformly distributed about the axis X.sub.1, something made possible by the fact that the number of blades 2A and 2B can be divided into the total number of blades.

(12) In the example, the runner 1 comprises five first blades 2A and ten second blades 2B, with a succession of like groups each comprising one first blade 2A and two second blades 2B.

(13) As depicted in FIG. 3, the first blades 2A each comprise a leading edge 6A and a trailing edge 7A, whereas the second blades 2B each comprise a leading edge 6B and a trailing edge 7B. The leading edges 6A and 6B and the trailing edges 7A and 7B stretch between the crown 3 and the band 4, with no point of inflexion. The concave face of these edges faces upstream into the flow E over their entire length.

(14) The points of attachment of a leading edge 6A to the crown 3 and to the band 4 are denoted M.sub.A and N.sub.A respectively. The points of attachment of a leading edge 6B to the crown 3 and to the band 4 are denoted M.sub.B and N.sub.B respectively. The leading edges 6A and 6B have the same geometry and the points M.sub.A and M.sub.B of attachment are arranged on one and the same geometric circle centered on the axis X.sub.1 and perpendicular to this axis, and the radius of which is denoted R.sub.N. Likewise, the points N.sub.A and N.sub.B of attachment are arranged on one and the same circle centered on and perpendicular to the axis X.sub.1, and the radius of which is denoted R.sub.N.

(15) The points of attachment of a trailing edge 7A to the crown 3 and to the band 4 are denoted P.sub.A and Q.sub.A respectively. The points of attachment of a trailing edge 7B to the crown 3 and to the band 4 are denoted P.sub.B and Q.sub.B respectively. The points Q.sub.A and Q.sub.B of attachment are arranged on one and the same geometric circle C.sub.Q centered on and perpendicular to the axis X.sub.1, and the radius of which is denoted R.sub.Q.

(16) The points P.sub.A of attachment are situated on one and the same geometric circle C.sub.PA centered on and perpendicular to the axis X.sub.1, and the radius of which is denoted R.sub.PA.

(17) The points P.sub.B of attachment are situated on one and the same geometric circle C.sub.PB centered on and perpendicular to the axis X.sub.1, and the radius of which is denoted R.sub.PB.

(18) The circles C.sub.Q, C.sub.PA, C.sub.PB are visible in FIG. 2, whereas the radii R.sub.Q, R.sub.PA and R.sub.PB are visible in FIG. 3.

(19) The magnitude of the radius R.sub.PA is chosen to be less than the magnitude of the radius R.sub.PB. Thus, a point P.sub.A of attachment of a blade 2A is situated, in relation to a point P.sub.B of attachment of a blade 2B, closer to the axis X.sub.1 and lower down in the configuration in which the runner 1 is used. In other words, the first blades 2A have their points P.sub.A of attachment lowered and closer to the axis X.sub.1 than the points P.sub.B of attachment of the blades 2B.

(20) The geometry of the blades 2A is such that they guide the flow E into close proximity to the axis X.sub.1, thus stabilizing this flow.

(21) It will be noted that the area A.sub.A of a lateral surface of a first blade 2A is greater than the area A.sub.B of a lateral surface of a second blade 2B. In addition, the ratio between the area A.sub.A of a lateral surface of a first blade 2A and the area A.sub.B of a lateral surface of a second blade 2B is chosen so that it is comprised between 1.05 and 1.50 and preferably between 1.20 and 1.50. In practice, the magnitude of this ratio is advantageously of the order of 1.30.

(22) To confer sufficient effectiveness on the first blades 2A of the runner 1, the ratio between the radius R.sub.PA and the radius R.sub.Q is chosen to be less than 0.15. In practice, this ratio can be chosen to be less than 0.1 and even less than 0.05.

(23) It is further possible to plan for the ratio between the radii R.sub.PA and R.sub.PB to be less than 0.75 and preferably comprised between 0.25 and 0.50.

(24) Moreover, the fact that there is an alternation of first blades 2A and second blades 2B as depicted in FIG. 2 makes the operation of welding the blades 2 to the crown 3 easier because, if there were only first blades 2A, the welding operation would be extremely difficult because there would be a great many blades to weld to a small surface area.

(25) Furthermore, the first blades 2A and the second blades 2B are distributed uniformly about the central axis X.sub.1 of the runner 1, making it possible to maintain static equilibrium of the runner 1. In FIG. 2, the periodicity of the total number of blades 2 is 2/15 and the periodicity of the number of first blades 2A is 2/5. This figure merely shows one possible choice, it would be equally possible to have a periodicity of 2/3 for the first blades 2A.

(26) As an alternative, the total number of blades may be other than 15, and for example equal to 9, 12, 18 or 24. The distribution between first blades 2A and second blades 2B is then adapted. For example, in the case of a 12-bladed runner, i.e. a runner for which the periodicity of the total number of blades 2 is equal to 2/12, the periodicity of the number of first blades 2A is equal to 2/3 or 2/4.

(27) The periodicity of the number of first blades 2A is chosen to be higher than that of the total number of blades 2, preferably at least twice as high.