Abstract:
A hydraulic machine through which a main flow of water passes including at least one turbine blade having an upstream end and a downstream end and a channel extending an entire length of the blade for tapping flow from the main flow adjacent the upstream end of the blade and discharging the tapped flow at the downstream end of the blade in a direction of the main flow.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydraulic machine of the type traversed by a main flow of water, comprising at least one blade profile of a turbine, having an upstream end and a downstream end, in the vicinity of which is formed at least one eddy zone or a reduced-pressure zone or a cavitation zone, the machine comprising means of injecting a flow tapped from said main flow, not modified relative to the main flow, in said eddy or reduced-pressure or cavitation zone so as to locally modify the main flow or increase the pressure in this zone. 
     2. Brief Description of the Related Art 
     Such a hydraulic machine is used, for example, in a plant for producing hydroelectricity. The machine is installed in the path of the current or is supplied with water from a reservoir into which one or more water courses are discharged. 
     In these hydraulic machines, there are zones in which the main flow traversing the machine is disturbed and forms eddies or exhibits a reduced pressure or cavitation zones, because of the configuration of the machine. Such zones disrupt the general performance of the hydraulic machine because they reduce the efficiency of action of the main flow in the hydraulic machine or cause problems of operation of the hydraulic machine. 
     The document U.S. Pat. No. 1,942,995 describes a hydraulic machine of the abovementioned type, making it possible to inject a flow tapped from the main flow in the cavitation zone being formed along the blades of the turbine wheel. 
     However, the outlet orifices for the tapped flow are arranged to inject the flow in a direction roughly perpendicular to the direction of the main flow. Such orifices do not make it possible to eliminate the eddy zones that are formed in the trail of the blades and also disturb the general performance of the hydraulic machine. 
     SUMMARY OF THE INVENTION 
     One of the objects of the invention is to alleviate these drawbacks by proposing a hydraulic machine making it possible to eradicate the eddy zones that are formed in the trail of any blade profile. 
     Accordingly, the invention relates to a hydraulic machine of the aforementioned type, in which the injection means comprising a duct drawing the flow from the main flow and making it open into the downstream end substantially in the direction of the main flow. 
     The injection of a flow tapped from the main flow into the downstream end of the blade profile makes it possible to modify the main flow in the eddy zone that is formed immediately downstream of the blade profile in the trail of the latter. The eddy zone is thus eliminated, which makes it possible to effectively make good the lack of performance in the action of the main flow in this zone, which enhances the performance and the behaviour of the hydraulic machine. 
     According to other features of the hydraulic machine:
         the duct comprises an inlet drawing the flow from the main flow upstream of the blade profile and an outlet opening into the eddy or reduced-pressure or cavitation zone,   the injection means comprise a valve placed in the path of the tapped flow, the said valve being able to be moved between an open position in which it allows the tapped flow to pass from the main flow and a closed position in which it prevents the passage of the tapped flow,   the movement of the valve is controlled by suitable control means,   the blade profile is at least one blade of a plurality of blades of a Francis turbine wheel, said blades being arranged between a ceiling and a belt, the flow being tapped from the ceiling or from the belt by means of openings formed in said ceiling or in said belt, said flow opening into the downstream end of the at least one blade.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aspects and advantages of the invention will appear during the following description, given as an example and made with reference to the appended drawings in which: 
         FIG. 1  is a schematic representation in section from the top of a blade profile of a turbine according to the invention, 
         FIG. 2  is a partial schematic representation in section of a Francis turbine according to the invention, 
         FIG. 3  is a schematic representation seen from above of the Francis turbine rotor of  FIG. 2   
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention described below applies particularly to hydraulic machines of the Francis turbine type. Since these machines are known, they will not be described in detail in the present description. The invention also applies to other types of hydraulic machines in which problems of the formation of eddy, reduced-pressure or cavitation zones occur. 
     In the description, the terms “upstream” and “downstream” are defined with respect to the direction of flow of the main flow E traversing the hydraulic machine. 
     With reference to  FIG. 1 , a member of a hydraulic machine of the blade profile  1  type of a turbine is described. Such a blade profile  1  is for example a fixed guide vane, a wicket gate or a turbine blade. The blade profile  1  shown in  FIG. 1  is a fixed guide vane. 
     The function of fixed guide vanes and wicket gates is to guide a main flow E which traverses the rotor  4  of the turbine sweeping against the blades  6 , which rotates the rotor  4  about a vertical axis Z-Z′. 
     The blade profile  1  has an upstream end  8  and a downstream end  10  connected together by side walls  12  swept by the main flow E. Whether it be a fixed guide vane, a wicket gate or a turbine blade, an eddy and/or reduced-pressure zone  14  is created in the vicinity of the downstream end  10 , particularly immediately downstream of the downstream end  10 , which can cause vibrations in the hydraulic machine. 
     The blade profile  1  comprises at least one duct  16  extending inside the profile between an inlet opening  18  and an outlet opening  20 . The inlet opening  18  is placed in the vicinity of the upstream end  8  and emerges for example in one of the side walls  12  of the blade profile  1 . A portion E 1  of the main flow E sweeping the side walls  12  is therefore tapped off in the duct  16  via the inlet opening  18  and is conveyed to the outlet opening  20 . According to another embodiment, the duct  16  taps the flow E 1  on the outside of the blade profile  1  and conveys this flow to the outlet opening  20 . 
     The outlet opening  20  emerges in the downstream end  10 . Therefore, the tapped flow E 1  from the main flow E travels in the duct  16  and is injected into the zone  14  via the outlet opening  20 . The effect of this is to modify the properties of the flow E in the zone  14  and thereby to prevent the vibration phenomena. 
     In the case of a blade  6 , there is also a problem of the creation of cavitations on the profile of the blades  6  of the rotor  4  in a zone in the vicinity of the inlet edges or upstream end  8  and/or of the outlet edges or downstream end  10  of the blades. In order to alleviate this drawback, the blade  6 , shown in  FIG. 2 , comprises other ducts (not shown) extending inside the blade between an inlet opening  22  and an outlet opening  24 ,  26 . The inlet openings  22  of the ducts are placed in the vicinity of the upstream end  8  of the blade  6  so as to tap off a flow from the main flow E upstream of the blade. The outlet openings  24 ,  26  of the ducts are arranged to inject the tapped flow on the side walls of the blades  6  in the vicinity of the upstream end  8  and/or of the downstream end  10  of the blade  6 . The effect of the tapped and injected flow is to locally modify the main flow E and thereby to prevent the phenomena of forming cavitation on the profile of the blades. Certain ducts therefore comprise an outlet opening  24  leading into a side wall of the blade  6  in the vicinity of the upstream end  8  in order to prevent the phenomena of forming cavitation on the blades in the vicinity of the upstream end  8 . Other ducts comprise an outlet opening  26  opening into a side wall of the blade  6  in the vicinity of the downstream end  10  in order to prevent the phenomena of forming cavitation on the blades in the vicinity of the upstream end  10 . 
     According to various embodiments, the inlet and outlet openings may be placed in series along the upstream end  8  and the downstream end  10  of the blade  6  in a direction which may be perpendicular to the direction of the main flow E, as shown by the outlet openings  24  of  FIG. 2 . 
     According to a particularly advantageous embodiment, the outlet openings are arranged so as to open into the downstream end  10  of the blade  6  in the direction of the main flow E. The openings open, for example, into the base of the blade  6 . The injection of the flow tapped into the downstream end makes it possible to eliminate the eddy zone that is formed in the zone of turbulence of the blades  6 . 
     The blades  6  of the rotor  4  are placed between a ceiling  28  and a belt  30 . 
     According to one embodiment, the phenomena of cavitation on the blades may also be prevented by openings  31  made in the ceiling  28  opposite the blades  6 , as shown in  FIG. 3 . These openings  31  communicate with the outlet openings  24 ,  26  and/or with the outlet openings  20  opening into the downstream end  10  by means of channels not shown. In this embodiment, a flow E 2  is tapped off from the main flow E and passes through the spaces between the fixed part of the turbine and the moving blades  6 . The tapped flow E 2  is tapped off in the annular space  34  situated above the ceiling  28 . This flow E 2  enters the openings  31  and is then guided to the outlet openings  24 ,  26  and/or  20 . 
     In addition to the cavitation phenomena on the blades, there may also be phenomena of forming a vortex in the space  33  between the blades  6 . These phenomena may be alleviated by means of ducts, the inlet and outlet orifices of which are placed between the upstream and downstream ends of the blades and open into the space  33  between the blades. According to one embodiment, the problem of forming a vortex between the blades  6  is solved by means of orifices  32  made in the ceiling  28 , as shown in  FIG. 2 . 
     In this embodiment, the flow E 2  tapped off upstream of the blades  6  in the annular space  34  travels into the openings  32  and supplies the spaces  33  between the blades  6 , as shown in  FIG. 3 . The openings  32  are distributed in the ceiling  28  facing the spaces  33  separating the blades  6 . Therefore, the tapped flow E 2  is injected between the blades  6  and modifies the properties of the flow E in order to prevent the phenomena of forming a vortex between the blades  6 . 
     As a variant, instead of or in addition to travelling via the ceiling  28 , the tapped flow E 2  can travel through the belt  30  by means of openings (not shown) made in the latter. 
     According to an embodiment that can be applied to all the injection means described above, the injection means comprise a valve  72  placed in the path of the tapped flow, as shown in  FIGS. 2 and 5 . The valve  72  can be moved between an open position in which it allows the tapped flow to pass and a closed position in which it prevents the passage of the tapped flow. The valve  72  is for example placed in the vicinity of each inlet opening of the injection means and makes it possible manually or automatically to control the injection of the tapped flow. In the case of the Francis turbine, the valve  72  is provided in the vicinity of each opening  32  arranged in the ceiling  28 . 
     The movement of the valve  72  is controlled by control means (not shown) which are mechanical or electric in a manner known per se. Therefore, during operating conditions of the hydraulic machine causing the formation of eddy or reduced-pressure or cavitation zones, an automatic system or an operator of the machine switches the valve(s) to the open position which makes it possible to inject the tapped flow in the said zones and to prevent the formation of these zones, as described above. 
     It should be noted that the tapped flow is not modified relative to the main flow E, that is to say that the water does not sustain any operation to modify its composition during the tapped flow.