The invention relates to a Francis-type turbine-pump and to an energy conversion plant comprising such a turbine-pump .

Within the field of converting hydraulic energy into electrical or mechanical energy it is known practice to use a Francis turbine to turn a shaft bearing a runner of the turbine, this shaft being connected, for example, to an alternator. Certain turbines, referred to as turbine-pumps, are reversible in so far as they can be used to convert electrical energy or mechanical energy into hydraulic energy by displacing a quantity of water to a basin situated upstream of the turbine- pump. This operation in pump mode generally takes place during periods in which the energy requirements are at their lowest. During periods of high energy demand, the turbine-pump is used in turbine mode by reversing the direction in which the shaft rotates.

A constant concern with turbine-pumps is still how to optimize the operation in pump mode, over the widest possible range of hydraulic heads and throughputs. The problem is that there is a region of unstable operation, sometimes referred to as a scallop, which limits the performance of the pump below a threshold throughput value or above a limit hydraulic head value. This has a direct impact on the sizing of a turbine- pump and of an energy conversion plant comprising such a hydraulic machine. The abovementioned region of instability causes separation and areas of recirculation in the turbine-pump runner, it being possible for these phenomena to cause the pressure in the ducts that remove the water from the turbine-pump and vibration levels in the plant to fluctuate.

Installing, in the ducts between the blades of a runner of the Francis type, vanes which run perpendicular to the blades, overall in the direction in which the water flows along each duct, is known from FR-A-2 811 718. While these vanes which extend continuously from the leading edge to the trailing edge of each blade improve the stability of the flow under certain operating conditions, they decrease the energy efficiency of the plant. Further, when a turbine equipped with such a runner is operating at zero or near-zero resistive torque, i.e. under conditions close to runaway, the flow passing through the turbine is highly unstable.

It is these disadvantages that the invention more particularly seeks to address by proposing a new turbine - pump the operating stability of which is improved over a wide range of throughputs and hydraulic heads in pump mode. To this end, the invention relates to a Francis-type turbine-pump comprising a runner rotating about a vertical axis, this runner itself comprising a runner crown, a runner band, blades, which extend between the runner crown and the runner band and which between them define water flow ducts, and vanes each arranged in a flow duct, each vane being overall parallel to the elementary direction in which the water flows along the duct and overall perpendicular to the blades defining this duct, each blade extending between a first edge, that forms a leading edge when the turbine is operating in pump mode and a trailing edge when it is operating in turbine mode, and a second edge, that forms a trailing edge when the turbine is operating in pump mode and a leading edge when it is operating in turbine mode. According to the invention, each vane extends, measured parallel to the direction in which the water flows through the corresponding duct, that represents less than 80% of the distance between a point of attachment of the first edge to the runner band and a point of attachment of the second edge to the runner band, measured parallel to the direction in which the water flows along the duct.

By virtue of the invention, the presence of a vane in each flow duct makes the flow more stable when the turbine is operating in pump mode because the flow entering the runner is channeled toward the elementary ducts defined on each side of the vane, between two adjacent blades. Furthermore, the vane has practically no influence on the incoming flow of water entering the ducts between the blades when the turbine-pump is operating in turbine mode because the vane does not extend as far as the vicinity of the region that is the inlet for the flow in turbine mode, given its relatively short length in comparison with the distance between the first edge and the second edge of the blades .

According to advantageous but non-compulsory aspects of the invention, such a turbine-pump may incorporate one or more of the following features, considered in any technically permissible combination:

The length of the vane is less than 50% of the distance between the points of attachment of the first edge and of the second edge to the runner band.

The length of each vane is greater than 5%, preferably greater than 30%, of the distance between the points of attachment of the first edge and of the second edge to the runner band.

Just one vane is arranged in each flow duct.

The ratio between, on the one hand, the distance, measured along the first edge, between the vane and the point of attachment of the first edge to the runner band and, on the other hand, the length of the first edge, is comprised between 5% and 95%, preferably between 10% and 50%, and more preferably still, equal to around 30%.

At least two vanes are arranged in each flow duct. - Each vane comprises a part projecting beyond the first edge of the two blades between which it extends.

Each vane lies flush with the first edges of the blades between which it extends.

Each vane begins set back toward the inside of the flow duct in which it is situated, by comparison with the first edges of the blades between which it extends.

The invention also relates to a plant for converting hydraulic energy into electrical or mechanical energy or for converting mechanical or electrical energy into hydraulic energy, and which comprises a turbine-pump as mentioned hereinabove together with ducts for conveying water to the turbine-pump and for removing water therefrom.

The invention will be better understood and other advantages thereof will become more clearly apparent in the light of the description which will follow of two embodiments of a Francis-type turbine-pump and of a plant in accordance with the principle of the invention, given solely by way of example and made with reference to the attached drawings in which: figure 1 is a schematic outline depiction, in axial section, of a plant according to a first embodiment of the invention, figure 2 is a meridian cross section of the runner of the turbine-pump of the plant of figure 1 when this turbine-pump is being used in pump mode,

figure 3 is a meridian cross section similar to figure 2 when the turbine-pump is being used in turbine mode, and

figure 4 is a meridian cross section similar to figure 2 for a turbine-pump according to a second embodiment .

The plant 100 depicted in figure 1 comprises a Francis- type turbine-pump 1 the runner 2 of which is intended to be rotated about a vertical axis X2 by a forced flow of water E from a water catchment that has not been depicted. This mode of operation is depicted in figures 1 and 3. In figure 1, for the sake of clarity of the drawing, the runner 2 is depicted as an external view. A shaft 3 supports the runner 2 and is coupled to an alternator 4 which delivers alternating current to a network that has not been depicted. The plant is therefore able to convert the hydraulic energy of the flow E into electrical energy when the turbine-pump 1 is used in turbine mode, as depicted in figures 1 and 3.

The plant 100 may comprise several turbine-pumps 1 fed from the same catchment of water.

As an alternative, the shaft 3 can be coupled to a mechanical assembly in which case the plant 100 converts the hydraulic energy of the flow E into mechanical energy when the turbine-pump 1 is operating in turbine mode.

The turbine-pump 1 may also operate in pump mode i.e. in a mode in which the runner 2 is turned by the alternator 4 in the opposite direction of rotation to the direction of rotation in which it turns when the turbine-pump 1 is operating in turbine mode. In pump mode, the alternator 4 therefore operates as a motor, to displace a quantity of water to the water catchment that has not been depicted. The water therefore flows in the direction of the arrows E' in figure 2, i.e. in the opposite direction to the arrows E of figures 1 and 3. In the alternative form in which the shaft 3 is coupled to a mechanical assembly, the runner 2 is driven by this mechanical assembly when the turbine- pump 1 is operating in pump mode. In figures 2 and 3, the lines L indicate imaginary stream lines along which the flow E or E' travels, notably through the runner 2.

A penstock 5 conveys the flow E to the runner 2 when the turbine-pump is operating in turbine mode. The penstock 5 extends between the water catchment and a tank 6 equipped with wicket gates 7 which regulate the flow E. A draft tube 8 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 downstream reservoir. When the turbine-pump is operating in pump mode, the tube 8 is used to supply the runner 2 with water while the penstock 5 is used to remove the water to the water catchment.

The runner 2 comprises a runner crown 202, a runner band 204 and several blades 206 distributed about the axis X2 which is an axis of symmetry for the crown 202 and the band 204.

The blades 206 all have the same geometry and each comprise a first edge 208 and a second 210. The first edge 208 of each blade 206 is closer to the axis X2 than the edge 210 of this blade. The first edge 208 of a blade 206 constitutes its leading edge when the turbine-pump 1 is being used in pump mode as depicted in figure 2, whereas it constitutes the trailing edge of this blade when the turbine-pump 1 is being used in turbine mode as depicted in figure 3. Conversely, the second edge 210 of a blade 206 constitutes its trailing edge when the turbine-pump 1 is being used in pump mode, as depicted in figure 2, whereas it constitutes the leading edge of this blade when the turbine-pump 1 is being used in turbine mode as depicted in figure 3.

A duct 10 for the circulation of water within the runner 2 is defined between the runner crown 202 and runner band 204, in the plane of figures 2 and 3 and between two adjacent blades 206 in a direction that is orthoradial with respect to the axis X ₂ .

Each duct 10 is divided, near the edges 208 of the blades 206 which delimit it, into two elementary ducts lOi and IO ₂ by a vane 12 that stretches between the blades 206 while being locally parallel to the direction of the flow E when the turbine-pump is being used in turbine mode and/or to the reverse flow E' when this turbine-pump is being used in pump mode. The vane 12 is overall perpendicular to the blades 206 between which it extends, at least in the region in which it joins these blades. In this particular instance, each vane 12 is overall parallel, i.e. inclined at an angle smaller than 20° in relation to the runner band 204.

As is more particularly apparent from figures 2 and 3, the vane 12 is more or less aligned with one of the imaginary stream lines L along which the flow E or E ' of water passing through the runner 2 flows within the duct 10 in which this vane is situated.

In the configuration of figure 2, the incoming flow E' is divided by the vane 12 into two secondary flows E Ί and E' ₂ passing respectively along the elementary ducts lOi and IO ₂ . Thus, the water of the flow E' is effectively channeled, on the one hand, through the elementary duct 10i between the crown 202 and the vane 12 and, on the other hand, through the elementary duct IO ₂ between the vane 12 and the band 204, in the region in which the water enters the runner 2. This splitting of the duct 10 into two elementary ducts lOi and IO ₂ in what, when operating in pump mode, is its inlet region, prevents water from recirculating in the direction of the arrow Fi in figure 2 because the presence of the vane reduces the bore section for the flow E' in the region in which it enters the channel 10. This leads to a localized increase in the speed of the flow E ' . Thus, when the turbine-pump is operating in pump mode at low throughput and/or with high hydraulic head, the speed of the flow E' ₂ in the region of entering the elementary channel IO ₂ is high enough to attenuate the amplitude of a recirculation.

Furthermore, the vane 12 opposes recirculation of water from the elementary duct lOi to the elementary duct 10 ₂ .

Now, if such a vane were not present, these recirculations would have a tendency to create a region of disturbance referred to as a region of "separation" near the point Pi of attachment of the first edge 208 of a blade 206 to the band 204.

When the turbine-pump is operating in turbine mode, as depicted in figure 3, the flow E enters and is distributed inside the duct 10 continuously at the edge 210 which then constitutes the leading edge of the blades 206. Thus, the flow E is not disturbed in the region of entry into the duct 10 because the vane 12 does not extend as far as near the edge 210. What this means is that the efficiency of the turbine-pump when used in turbine mode is entirely satisfactory, without introducing the limitation of vanes extending continuously between the edges 208 and 210 as envisioned in FR-A-2 811 718.

The point of attachment of the second edge 210 to the band 204 is labeled Ch . The distance between the points Pi and Ch measured along the band 204, i.e. parallel to the flow E or E' and to the lines L near the band 204, is labeled D ₂ 04 -

The length of the vane 12, measured parallel to the lines L, i.e. parallel to the flow E or E ' , is labeled L iz .

To give the vane 12 sufficient effectiveness when the turbine-pump is operating in pump mode, without reducing the overall efficiency of the turbine-pump when it is operating in turbine mode, the length L 12 is chosen to represent less than 80% of the distance D ₂ 04 - In practice, the length L 12 may be chosen to be less than 50% of the distance D ₂ 04, preferably to be equal to 30% of this distance. Moreover, the length L 12 is chosen to be greater than 5% of the distance Ό204, preferably greater than 25% of this distance. Thus, the elementary ducts l O i and I O 2 extend over just part of the length of the duct 10 in the direction of the flow E or E ' , namely between 5% and 80% depending on the choice made for the value of the ratio L i ₂ / D ₂ 04 -

As can be seen in figures 2 and 3, each vane 12 has a rounded tip 122 projecting out beyond the edge 208 with respect to the duct 10 in which this vane 12 is installed, i.e. toward the upstream side of this edge 208 when the turbine-pump 1 is operating in pump mode. This tip 122 begins to confine the flows E Ί and E'2 toward the elementary ducts lOi and IO ₂ even before the water has entered the duct 10.

As an alternative, the vane 12 may lie flush with the edges 208, or even begin set back toward the inside of the duct 10 in relation to the first edges 208 of the blades 206 between which it extends.

The point of attachment of the edge 208 of a blade 206 to the crown 202 is labeled P2. The curved length of the edge L ₂ o8, i.e. its length measured between the points Pi and P2 along this edge, is labeled L ₂ os · The distance between the vane 12 and the point Pi is moreover labeled D ₁ 2, this distance being measured along the edge 208. The ratio D ₁ 2/L208 is comprised between 5% and 95%, preferably between 10% and 50%, and more preferably still is equal to around 30%. This allows the vane 12 to be positioned in a region in which it effectively limits the recirculation of water when the turbine-pump is operating in pump mode, even at low throughput or high hydraulic head.

In the embodiment of figures 1 to 3 just one vane 12 is positioned in each duct 10 near the edge 208 of the blades 206.

As an alternative, and as depicted in figure 4 in the case of the second embodiment in which elements analogous to those of the first embodiment bear the same references, two vanes 12i and 12 ₂ may be provided in each duct 10, thereby thus defining three elementary ducts 10i, IO ₂ and IO ₃ between which the flow E' can be split on inlet into elementary flows ΕΊ, E'2, and E'3 when the turbine-pump 1 is operating in pump mode. As depicted in figure 4, the vanes 12 ₁ and 12 ₂ may be of different lengths. In other respects, this embodiment is comparable to the previous one and works in the same way. In particular, the length L ₁₂ of each vane 12 ₁ and 12 ₂ is comprised between 5% and 80% of the minimum distance D ₂ 04 between the edges 208 and 210 of a blade.

As an alternative, more than two vanes of the type of vane 12 ₁ and 12 ₂ can be provided in each duct 10.

Whatever the embodiment, the vanes 12, 12i, 12 ₂ and equivalent are fixed with respect to the other constituent parts of the runner 2. In particular, these vanes are advantageously welded to the blades 206 between which they are arranged within a duct 10. It will be noted that implementation of the invention is independent of the number of blades 206, which may be an odd number as in the example, or an even number.