US2758815A - Hydraulic reaction turbine - Google Patents

Description

4, 1956 E. FONTAINE ETAL 2,758,815

HYDRAULIC REACTION TURBINE Filed April 15, 1954 5 Sheets-Sheet 1 ELIE FONTA/NE HENRI PE VR/N a I BY INVENTOR r ATTORNEY 4, 1956 E. FONTAINE ETAL 2,758,815

HYDRAULIC REACTION TURBINE Filed April 15, 1954 :5 Sheefs-Sheet 2 .33 I R r 40 5 I I/ I! I I \U EL/E FONTA/NE HENRI PEYR/N ATTORNEY INVENTOR E. FONTAINE ETAL 2,758,815

HYDRAULIC REACTION TURBINE Aug. 14, 1956 Filed April 15, 1954 3 Sheets-Sheet 3 oasaeo aeweoo mmase 6O0 Q69? wa e 85 o o g o 77 I oo o 00 Il lllllllllllll /v' INVENTOR ELIE FONTA/NE HENRI -PEVR/N ATTORNEY United States Patent HYDRAULIC REACTION TURBINE Elie Fontaine, Brive, and Henri Peyrin, Grenoble, France, assignors to Etablissements Neyrpic, Grenoble, France, a corporation of France Application April 15, 1954, Serial No. 427,766

Claims priority, application France April 17, 1953 15 Claims. (Cl. 253-117) The present invention relates to improvements in hydraulic reaction turbines of the Francis or of the axialflow types. The invention especially relates to improvement of the operation of such turbines under critical loads and more particularly to the stabilization of the flow in the central zone at the downstream side of the runner blades without the necessity of utilizing auxiliary means of considerable size.

It is known that at certain loads, and especially in machines of large size, hydraulic phenomena are produced which are related to the concept of central cavitation at the beginning of the draft tube that are due to the fact that the central core is not fixed. The violence of the forces thus produced provoke deformations in the members of the turbine that are transitory but may be severe. It is known that the blowing in of air centrally lessens these forces considerably but the amount of air necessary to secure the result leads to apparatus which is costly or uncertain in its behavior.

The shaft of the turbine conventionally is connected to the runner by a coupling plate which is fixed to the central part of the web of the runner in a Francis turbine or to the runner hub in an axial-flow turbine. The exterior surface of the web of the Francis runner or of the hub of the axial-flow runner that constitutes the inner surface of the water flow passage through the runner is prolonged in the direction downstream from the blades by the surface of a hollow member which is supported on the runner to rotate therewith and may be open at the downstream extremity of this hollow member. This member, which is called the runner point in the Francis turbine and the runner cap in the axialflow turbine, will be identified in each case by the term runner point in the following description in order to simplify the language. Generally in conventional machines this runner point is relatively short and its extremity in the Francis turbine does not extend to the plane of the outlet from the runner.

Moreover, in the Francis turbine the central part of the web of the runner conventionally is provided with a certain number of equalizing openings through the web which afford communication between the space at the upstream side of the web, formed between the web and the base or stationary part of the turbine, with a downstream flow space either by way of the interior of the runner point, in which case this runner point is open, or at the exterior of the runner point adjacent the zone of discharge from the blades.

The present invention has for an object the improvement in reaction turbines of the Francis or of the axialflow type which is characterized by the feature that the runner point is hollow and is provided with lateral orifices distributed regularly and in sufiicient number peripherally about the runner point, preferably in the vicinity of the discharge or downstream side of the runner blades. The downstream end of the. runner point has an opening of suitable cross section communicatingwith the interior hollow space thereof.

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In turbines of the Francis type the runner point of the invention is extended at least to the plane of the outlet from the runner, that is to say, the plane of the entrance to the draft tube, and preferably somewhat beyond this plane. By the combination of lateral orifices and the end opening of the runner point and in some cases also utilizing conventional equalizing openings, as above referred to, in the Francis turbine these equalizer openings communicating with the interior of the runner point, there are developed at the outlet from the blades in the central zone of the flow of the water through the turbine auxilary currents the influence of which surpresses or reduces to a considerable extent the forces above mentioned which may produce severe deformations of the members of the turbine.

In a general way, depending upon the particular turbine and upon the outline of the runner and the rate of water flow, the device of the invention has the effect of blowing or sucking the boundary layer in the region of the lateral orifices, thereby to stabilize the central zone of flow downstream from the runner blades. At certain rates of flow corresponding to partial loads on the turbine, the local pressures on the exterior surfaces of the runner point as well as the pressures against the interior surface thereof due to centrifugal force determine the movement of water from the interior toward the exterior of the runner point in the form of jets flowing outwardly through the lateral orifices. The water thus ejected normally comes from downstream through the open end of the runner point under the effect of centrifugal pumping but in the case of a Francis turbine it also can come in part from the leakage through the labyrinth joint, passing through the conventional equalizing openings from which it is discharged to the interior of the hollow runner point.

The suction of water developed by rotation of the runner point with the runner at the open end of the runner point draws off a part of the water of the central core at the entrance to the draft tube which has the effect of stabilizing thecentral core. In addition, the jets flowing through the lateral orifices are turned in the downstream direction by the main flow of the water and define about the runner point a zone of mixture which contributes to stabilizing the central zone of flow downstream from the region of the outlet of the blades.

In order to favor the effect of centrifugal pumping, in some cases it is advantageous in accordance with the invention to dispose Within the runner point several vanes which may serve also as reinforcing ribs.

Under certain other conditions where the exterior pressure on the runner point in the zone of the main water flow adjacent the lateral orifices is strong, the arrangement according to the invention may operate in the reverse direction, that is, to develop flow through the orifices into the hollow runner point, and there may be produced at the level of the orifices a suction acting on the border layer which also has the eifect concurrently with the discharge from the opening at the downstream end of the runner point of stabilizing the central core at its base.

In addition in a period of exceptionally low water, if the turbine shows any signs of central cavitation and if the conventional equalizing openings discharge to the interior of the runner point, it is sufficient in operating a turbine constructed in accordance with the invention to blow only a small amount of air into the base of the turbine to eliminate the detrimental effects on the machine.

The invention will be further understood from a description thereof to follow of embodiments in a Francis turbine which are to be taken by way of example, the invention not being limited to the embodiments shown and described in connection with the drawings, in which:

Fig. 1 is a longitudinal section of a Francis vertical turbine provided with a runner embodying the invention;

Fig. 2 is a partial vertical section to enlarged scale of the runner point shown in Fig. 1;

Fig. 3 is a vertical section of a runner point of modified form suitable for the turbine of Fig. 1;

Fig. 4 is a section on line 44 of Fig. 3;

Fig. 5 is a vertical section of a Francis turbine having a runner point embodying another modification of the invention;

Fig. 6 is a section on line 6--6 of Fig. 5;

Fig. 7 is a vertical longitudinal section of a runner point embodying another modification of the invention; and

Fig. 8 is a section on line 88 of Fig. 7.

In the embodiment of Figs. 1 and 2 the driving water comes from the head race, not shown, through the distributor 1 provided with distributor vanes 3 and then flows through the runner 5 having blades 7 and i discharged therefrom downstream to the draft tube 9 of which only the inlet portion is shown in Fig. 1. The upper flask 11 of the distributor carries the base 13 of the turbine. The shaft 15 passes through the cylindrical sleeve portion 17 of the base and is provided at its lower end with a coupling flange 19.

The runner convention-ally is formed with a generally conical web portion 21 to which the blades 7 are secured and also is provided with a central web portion 23 to which the flange 19 of the shaft is secured by suitable means so that upon rotation of the runner and its web portions 21, 23 the shaft 8 is rotated. On the periphery of the web portion 21 and on the flask 11 are disposed rings 25, 27 which cooperate to form a labyrinth joint for resisting flow of the water between the flask 11 and the web 21 of the runner and between the base 13 and the runner.

The space 29 between the web portion 21 and the base 13 of the turbine may communicate with the tail race of the .installation through the openings 30 and the equalizer pipe 31. The space 29 also communicates through the equalizing passages 33 with the space within the runner point 34.

The runner point 34 is of generally truncated conical form and to facilitate assembly is composed of two sections 35, 36 connected by flanges 37 secured together by bolts 38, these flanges being formed within the interior of the hollow runner point. The upper section 36 is provided with an inturned flange 39 secured by bolts 40, Fig. 2, to the central web portion 23 of the runner. In accordance with the invention the runner point is provided with a series of orifices 41 through the wall of the runner point in the portion thereof adjacent the outlet of the water from the runner blades 7, these orifices being formed in the upper section 36 in the embodiment of Figs. 1 and 2. The orifices 41 are distributed, preferably uniformly, peripherally about the runner point .in a plurality of parallel planes perpendicular to the axis of the runner, the orifices in the different planes being staggered in relation to each other.

Tests carried out on a Francis turbine having a runner of 4.4 meters diameter embodying the invention have shown that a good result is obtained in providing about a hundred orifices of 30 millimeters diameter in each of three or four rows, that is in three or four planes perpendicular to the axis, the spacing of the orifices in each of the rows in these planes being about 60 millimeters.

The lower end 42 of the runner point is disposed below the plane of the outlet end 43 of the runner 5 and within the entrance of the draft tube 9. The lower end of the runner point 34 has a diameter suflicient toprovide an opening 45 in suitable proportion to the size of the central core of the water flow of the turbine.

In Fig. 2 there is shown by lines carrying arrows the lines of the current flowing at the exterior of and within the runner point. The shape of the runner point is such in this embodiment that it provides an impelling means moving the water upwardly within the runner point along the lines 47 under the effect of centrifugal pumping produced by rotation of the runner point 34 with the runner. This water, as well as a part of the water leaking through the labyrinth joint and arriving within the space 29 and flowing through the equalizer passages 33 along lines 48, flows outwardly through the orifices 41 in the form of jets which are turned in the downstream direction by the main flow of the water represented in Fig. 2 by the lines 49. The water issuing from the jets thus turned downwardly defines along and about the runner point a mixing zone 50.

The suction of water passing the lower extremity of the runner point as well as the ejection of the water laterally through the orifices 41 modify the central zone of flow in the region of the runner point and in the region immediately downstream thereof, giving to this flow a stable form. The overall effect is particularly efficient at critical loads when this central zone of flow assumes an importance which often is great and disturbs by its instability the main flow at the outlet of the runner blades and throughout the draft tube.

In Figs. 3 and 4 is shown a modification of the runner point disclosed in Figs. 1 and 2. In the embodiment of Figs. 3 and 4, instead of the full opening 45, Fig. 1, at the lower end of the runner point, the area for flow into the interior of the runner point is provided by a large number of holes formed in a partition or plate extending across the interior of the runner point transverse to the axis thereof. The effect of providing this perforated plate with the holes therein distributed over the area thereof is to subdivide into a plurality of flow paths the secondary current of water which is established to flow, as described in connection with Fig. 2, from the exterior of the runner point into the interior and through the interior of the runner point and outwardly through the orifices 41, to be returned downwardly with the main flow of Water from the blades. This subdivision of the water flow passing upwardly into the interior of the runner point is favorable to the separation within the interior of the runner point of the air dissolved or entrained in the water. Separation tends to be produced at the outlet of the blades in the central zone of flow where the pressure is a minimum and often less than atmospheric pressure. The air thus separated within the runner point is mixed with the currents of Water which flow from the interior to the exterior of the runner point and secure the effects of stabilizing the flow of the turbine water at the outlet of the runner.

Due to the deaerating effect which is accentuated by the division of the secondary currents by the provision at the lower end of the runner point of the plate forming a strainer instead of a large opening, it is found that in certain cases it is no longer necessary to introduce air either through the equalizing passages provided in the web of the runner or by pipes fixed in the draft tube and discharging at the center of the draft tube immediately below the runner.

In addition to the efiect of stabilizing the flow at the outlet of the runner the compressible fluid, such as air, which the runner point contains as well as that which is contained within the space between the web of the runner and the base of the turbine, constitutes a surge dampener which logically is situated at the core of the turbine. This dampener has the effect of totally suppressing the strong central cavitation which is encountered in all turbines at certain critical loads and which is translated into dull but violent detonations which are not periodic.

Fig. 3 shows a vertical section through a turbine runner point similar to that of Fig. 1 but in which in this embodiment adjacent the lower end a plate 53 extends transversely of the axis and closes this end of the runner point except for the orifices 55 which are formed therein and are distributed in more or less uniform arrangeg ment as shown in Fig. 4. Although the plate 53' is planar, this plate may be of convex or concave form about the axis relative to the interior of the runner point. If desired also, additional lateral holes 57 may be provided in the annular wall of the runner point 34 adjacent the lower end of the runner point.

In the embodiment of Figs. and 6 showing in vertical section a Francis turbine, the runner point 60 is of similar form to those of Figs. 1 and 3 in the provision of an annular wall. The runner point 60 in the embodiment of Fig. 5 comprises a lower section 61 and an upper section 62 connected together at flanges 63 by bolts 64. The runner point is connected to the web 21 of the runner at flanges 65 by means of bolts 66 in a manner similar to that described in connection with Figs. 1 and 2.

In the upper section 62 of the runner point a series of orifices 67 in a plurality of planes and distributed in each plane peripherally about the axis in the same manner as described in connection with Fig. l is provided to produce circulation of the water upwardly through the runner point and outwardly through the orifices 67, to be turned downwardly in the manner described in connection with Fig. 2.

In the embodiment of Figs. 5 and 6 at the lower end of and within the runner point 60 a plurality of vanes 69 are supported extending, as shown in Fig. 6, from the peripheral wall 60 inwardly to and connected to a hub 71 disposed upon the axis of rotation of the runner, this hub being or double conical contour in the embodiment of Fig. 5 to provide for smooth flow of the water upwardly into and through the lower section 61 of the runner point. The vanes may serve to effect disbution of the water through the cross section of the run ner point.

The vanes 69 are of helical contour as shown in Figs. 5 and 6 and may be secured to the peripheral wall 60 and to the hub 71, for example, by welding. The number and inclination of these vanes is determined as a function of the speed of rotation of the turbine and these inclined vanes constitute a pump which is particularly suitable when the speed of rotation is low or when the diameter of the runner or of its hub at the outlet of the turbine blades is itself small. These conditions lead in general to only a small degree of inclination of the cone of the runner point because the downstream extremity would occupy a large space at the center of the entrance to the draft tube.

Figs. 7 and 8 show another modification of the means disposed at the lower end of the runner point for distributing the water flowing upwardly into the interior of the runner point. In this embodiment certain features of this distributing means provided in the embodiments of Figs. 3 and 4 and of Figs. 5 and 6 are combined.

As shown in Figs. 7 and 8 within the lower entrance cross section of the runner point 75 a tubular member 77, preferably cylindrical, is disposed concentric with the axis of the runner and supported by vanes 79 connected to the wall of the runner point 75 and to the tubular member 77, the diameter of the member 77 being less than that of the inlet opening of the runner point. These vanes 79, as shown in Fig. 8, may be planar in vertical planes containing the axis and may be secured to the wall of the runner point and to the tubular member 77 by welding. Within the scope of the invention, however, these vanes may be of different forms and, if .desired, in the form of the propeller vanes 69 of Figs. 5 and 6 in order to secure distribution as well as propulsion of the water to flow upwardly in the annular space about the tubular member 77 and between this member and the wall of the runner point 75.

Transversely across the space within the tubularmember 77 a partition wall or plate 81 is disposed which is supported by the tubular member 77, being joined thereto in any suitable manner, for example,- by welding.

Similarly to the embodiment of Figs. 3 and 4, the plate 81 provides a plurality of holes 83 distributed over the area of this plate for distributing the upward flow of the water through the interior cross section of the tubular member 77. In some cases, however, if desired, the plate 81 may be omitted and the structure then becomes similar to that of Figs. 5 and 6, especially when the vanes 79 are of helical form, except that the central hub 71 is replaced by the open tubular member 77. In this further modification in which the parition wall 81 is omitted, the water may flow through the central tube as Well as through the annular space between the wall and the tubular member 77 in which it is distributed by means of the vanes 79.

The embodiment of Figs. 7 and 8 may be used to advantage whenever at critical loads on the turbine, on the one hand, the conditions of pressure immediately downstream from the runner point and, on the other hand, at the interior of this runner point are such that flow at the end of the runner point may be produced at the periphery in the direction from the interior towards the exterior, due account being taken of the centrifugal effect which is particularly intense at the internal periphery of the runner point. With the means provided in the embodiment of Figs. 7 and 8 thewater continues to be drawn towards the interior of the runner point in the central zone at its end.

When the conditions of pressure are such that the reverse flow through the orifices which has been mentioned'above in connection with the embodiment of Figs. 1 and 2 may occur, such reverse flow will not be impeded unduly by the disposition and arrangement of the tubular member 77 and the vanes 79 in the embodiment of Figs. 7 and 8. This is likewise the case in the embodiment of Figs. 3 and 4 and may be true to some extent in the embodiment of Figs. 5 and 6, depending on the form and inclination of the vanes.

Similarly to the embodiments of Figs. 1-6, inclusive, the runner point of Figs. 7 and 8 is constructed with two parts. The distribution means comprising the tubular member 77 and vanes 79 is secured within the lower end of the runner point as by welding of the vanes to the wall 85 of the lower part. The wall 87 of the upper part is pierced with a plurality-of rows of orifices 89 similar to those of Fig. l and disposed in distributed relation peripherally about the circumference of the runner point in the portion thereof which in the runner assembly is adjacent the outlet from the runner blades. The upper part 87 may be secured to the web of the runner in any suitable manner, such as that shown in connection with Figs. 1, 2 and 5.

Within the scope of the invention in the embodiment of Figs. 7 and 8, the plate 81 may be supported within the member 77 in such a manner as to be removable so as to provide for access to the interior of the runner point through the tubular member 77 in order to reach the bolts 91 which serve to secure the cooperating flanges 93 provided on the lower and upper parts 85, 87, and access to the means for securing the upper part 87 to the web of the runner. The plate 81 in such a case may be secured in place by a certain number of spot welds 95 peripherally disposed along the wall of the tubular. member 77 and at the downstream side of the plate 81. It thus will be possible to melt the welds at these points in order to remove the plate 81 when it is necessary to have access to the interior of the runner point.

In certain cases, if the runner point is of relatively small dimensions, it may be necessary to make the tubular member 77 removable whether or not this member is provided with a perforated plate 81 in order to gain access to the interior of the runner point.

The invention is not limited to the particular embodiments above described and disclosed in the drawings and modifications thereof may be made within the scope of the invention whileproviding the featureof the orifices in the annular peripheral wall of a hollow runner point, these orifices being disposed in peripherally spaced relation in the portion of the runner point upstream from the downstream end of the runner point, to secure under centrifugal action, or if desired by the action of positive circulating means, movement of the water through the orifices to modify the conditions of flow of the main mass of water moving through the turbine and especially along the boundary layer adjacent the surface of the runner point. As above set forth, such movement may be in either direction through the orifices and the distribution means as well as the circulation producing means may be disposed in any suitable position but preferably adjacent the downstream end of the runner point to secure distribution of the flow and other beneficial effects which have been set forth above.

What is claimed is:

1. In a hydraulic turbine having a runner provided with runner blades and rotatable on an axis of rotation, the combination with said runner of a runner point supported by said runner for rotation therewith on the axis of rotation, said runner point having a wall extending peripherally with respect to said axis of rotation about a hollow space therewithin and in the downstream direction from the runner blades, said wall being provided with orifices therethrough disposed adjacent and downstream of said runner blades and distributed peripherally about the axis of rotation, said runner point having an opening disposed downstream with respect to said orifices and communicating between the space exterior to said runner point and the interior hollow space within said runner point, and impelling means carried by said runner and engaging the water flowing from said blades for developing flow of water within said hollow space and through said opening and through said orifices upon rotation of said runner.

2. In a hydraulic turbine having a runner provided with runner blades and rotatable on an axis of rotation, said runner having a web member providing an exterior surface extending about the axis of rotation and generally defining a surface of the water passage through the blades of said runner, the combination with said runner of a runner point supported by said runner for rotation therewith on the axis of rotation, said runner point having a wall extending peripherally with respect to said axis of rotation about a hollow space therewithin and providing an exterior peripheral surface generally continuous with said web surface and extending therefrom in the downstream direction, said wall being provided with orifices therethrough distributed peripherally about the axis of rotation in a portion of said wall adjacent the blades of said turbine runner at the downstream side thereof, said nlnner point having an opening disposed downstream with respect to said orifices and communicating between the space exterior to said runner point and the interior hollow space within said runner point, and impelling means carried by said runner and engaging the water flowing from said runner blades for developing flow of water within said hollow space and through said opening and through said orifices upon rotation of said runner.

3. In a hydraulic turbine the combinations as defined in claim 1 in which said wall of said runner point has a form capable of developing by centrifugal action said flow of water through said opening and through said orifices.

4. In a hydraulic turbine the combination as defined in claim 1 in which said means carried by said runner for developing said flow through said opening and through said orifices comprises propeller means supported withinsaid runner point for rotation with said runner point for developing said flow of water through said opening and said orifices in a selected direction.

5. In a hydraulic turbine the combination as defined in claim 1 in which said opening of said runner point is disposed at the downstream end of said runner point and is substantially that of the internal cross section of said runner point at said downstream end thereof.

6. In a hydraulic turbine the combination as defined in claim 1 in which adjacent the downstream end of said runner point a partition Wall is disposed extending transversely of the axis of rotation and supported by the annular wall of said runner point, said partition wall having a plurality of openings therethrough to provide a composite area for water flow between the space exterior to said runner point and the interior hollow space Within said runner point.

7. In a hydraulic turbine the combination as defined in claim 2 in which said web member of said runner is provided with an equalizer passage therethrough communicating from a space between said web member and a stationary part of the turbine to the interior space within the runner point to provide for mixture of water leaking between the runner and said part of the turbine with the water circulating through the interior hollow space of said runner point and through said orifices.

8. In a hydraulic turbine the combination as defined in claim 2 in which said surface of said wall of said runner point in the portion thereof in which said orifices are formed is of generally conical contour in the plane of said axis of rotation and is inclined to said axis, said conical contour being generally an extension of the contour of the web of the turbine runner in said plane, whereby the main flow of water along said surfaces of said runner and of said runner point serves to deflect along said surfaces water discharged through said orifices from within the runner point.

9. in a hydraulic turbine the combination as defined in claim 1 in which adjacent the downstream end of and within said runner point a distributing element is supported by said runner point, said element providing a plurality of vanes disposed in spaced relation about the axis of rotation and extending inwardly toward the axis from the peripheral wall of said runner point for effecting distribution of water flowing within the interior of said runner point.

10. In a hydraulic turbine the combination as defined in claim 9 in which said vanes are connected at their outer ends to said peripheral wall of said runner point and at their inner ends to a hub having its axis coincident with the axis of rotation of said runner for confining at least a part of the water to flow through the annular spaces between said vanes.

11. In a hydraulic turbine the combination as defined in claim 9 in which said vanes are of curved contour and are connected to the peripheral wall of said runner point for rotation therewith to produce a pumping action of the water through the interior of said runner point upon rotation of the runner.

12. In a hydraulic turbine the combination as defined in claim 1 in which adjacent the downstream end of and within said runner point a distributing element is disposed, said element providing a plurality of vanes disposed in spaced relation about the axis of rotation and extending inwardly toward the axis from and supported by said peripheral wall of said runner point for effecting distribution of water flowing within the interior of said runner point, and a tubular member disposed within said runner point adjacent said downstream end thereof and in concentric relation to the axis of rotation, said vanes being connected to the wall of said tubular member for supporting said tubular member for rotation with said runner point.

13. In a hydraulic turbine the combination as defined in claim 12 which comprises a partition wall extending transversely of said axis of rotation across the space within said tubular member.

14. In a hydraulic turbine the combination as defined in claim 13 in which said partition wall is provided with a plurality of openings distributed over the area thereof and extending therethrough to provide a composite area of flow therethrough and through the space within the tubular member between the space exterior to and the interior of said runner point.

15. In a hydraulic turbine the combination as defined in claim 1 in which said runner point adjacent the downstream end thereof is provided with a plurality of auxiliary openings through the peripheral wall thereof disposed in peripherally spaced relation about the axis of rotation for flow of water through said auxiliary openings between the space exterior to and the interior of said runner point.

References Cited in the file of this patent UNITED STATES PATENTS Biggs Jan. 9, 1934 Biggs Mar. 13, 1934 Biggs June 12, 1934 Kerr May 4, 1937 Terry Dec. 12, 1939 Martin May 16, 1950

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