Abstract:
A hydraulic turbine has a runner blade fixedly mounted to a runner hub. The runner blade has a mounting flange having a generally rectangular shape held in contact with a complementary generally rectangular shaped outside surface portion of the runner hub. The complementary rectangular shapes increases surface contact area between the blade mounting flange and the hub over that of circular shaped flanges and thereby reduces the stress levels between the blade flange and the hub. Further, the surface contact area between the blade mounting flange and the blade root is increased to thereby reduce the stress level in the blade root fillets.

Description:
RELATED APPLICATION  
       [0001]    The subject application is related to Canadian application Serial No. ______ filed concurrently herewith for “Axial Flow Hydraulic Turbine with Fixed Blades Bolted-On” (Docket No. 229650-2) for the same inventors and assignee as herein. 
       FIELD OF THE INVENTION  
       [0002]    The present invention relates to axial flow hydraulic turbines known as fixed blade propeller and diagonal turbines assembled by attaching flanges of the blades in a fixed manner to a hub of the turbine. In particular, it relates to increasing the surface area of the blade flange connection to both the hub and the root of the blade. 
       BACKGROUND OF THE INVENTION  
       [0003]    In the manufacture of hydraulic machine runners for turbines, it is known to bolt the runner blades of the turbine onto the runner hub of the turbine with fitted studs and nuts. Typically the hub is hollow and has a non-planar outer surface that is conical, cylindrical or spherical in shape. The blade is provided with a circular shaped flange which is bolted to the outer surface of the runner hub by a series of studs and nuts arranged in a single circle that pass through the runner hub and into the flange of the runner blade. The bolted connection allows for an easy adjustment of the blade angle to meet homology requirements during the assembly of the hydraulic machine and reduces runner size for transportation as the blades are not welded in place and can be removed. 
         [0004]    In some hydraulic turbine assemblies, space limitations within the runner hub prevent a sufficient number of bolting connections, arranged in the single circular pattern on a circular flange, to pass through the hub and into the circular flange. As a result it may not be possible to ensure proper fatigue life of the bolting by flange pre-loading. Further, when the space limitations result in the flange having a smaller diameter than desired, stress levels in the flange can rise over acceptable limits. In these instances the runners are usually assembled without the use of bolting and by welding the runner blades to the runner hub or with the use of segmented casting that is united with shrink rings or welding. 
         [0005]    Clearly, any improvements to the connection between the runner hub and the runner blade flange which reduce stress levels would be desirable. 
       BRIEF DESCRIPTION OF THE INVENTION  
       [0006]    The present invention relates to the use of a generally rectangular shaped mounting flange on a runner blade of a hydraulic turbine formatting to a turbine hub that provides more surface area than a circular flange so that a larger connection surface area between the flange and the hub is achieved. It is contemplated within the realm of the present invention that the blades may be attached to the hub by fastening means such as, for example, welding and, preferably, bolted connections. 
         [0007]    The increased surface area associated with the rectangular shaped flange reduces the stress levels between the blade and the flange. Further, it also increases the area between the flange and the blade root to thereby reduce the stress level in the blade root fillets. 
         [0008]    Where bolting connections are used, the additional surface area provided by rectangular shaped flanges ensures that total bolt clamp force may avoid surface separation between blade flange and hub in all operating conditions and improve fatigue life of the bolt connections. The bolting connections can be spread across the flange further from its center thereby improving bolt group inertia. 
         [0009]    In one embodiment of the present invention there is provided an axial flow hydraulic turbine with fixed blade mounting comprising a plurality of runner blades. Each of the runner blades comprises a mounting flange comprising a planar hub abutting surface portion having a first generally rectangular shape. The turbine comprises a hub for supporting the runner blades. The hub comprises a non-planar outer surface having a plurality of recesses, one recess for each of the plurality of blades. Each of the recesses has a planar flange seating surface portion for seating a corresponding planar hub abutting surface portion of the mounting flange in contacting relation therewith. The turbine further comprises fastening means for attaching in fixed position each of the runner blades to the hub where each mounting flange meets the hub. 
         [0010]    In one embodiment, the planar flange seating surface portion of each of the recesses is a second generally rectangular shape complementary to the first generally rectangular shape of the hub abutting surface portion. Further, the first and second generally rectangular shapes have a radius at corners thereof. 
         [0011]    It should be understood that the planar hub abutting surface portion of the mounting flange presents the rectangular shape when viewed normal to this surface. Similarly the planar flange seating surface portion presents a rectangular shape when viewed normal to this surface. The surfaces may be vertically orientated or orientated at an angle to the vertical whereby surfaces that are angled with respect to the vertical appear trapezoidal in shape when viewed along a horizontal orientation. 
         [0012]    In one embodiment the first and second generally rectangular shapes are square shapes. 
         [0013]    In another embodiment, the plurality of recesses are machined into the non-planar outer surface of the hub and form a lip that at least partially surrounds each of the mounting flanges. 
         [0014]    In another embodiment, the mounting flange comprises a plurality of threaded flange apertures extending from the planar hub abutting surface portion into the mounting flange. The plurality of threaded flange apertures are grouped spread across the planar hub abutting surface portion in a first array like pattern. The hub is hollow and comprises a central opening. Each of the recesses has a flange seating surface portion for seating a corresponding planar hub abutting surface portion of the mounting flange. The recess has a plurality of hub apertures extending from the planar flange seating surface portion through the hollow hub and opening into the central opening. The plurality of hub apertures are grouped spread across the planar flange seating surface portion in a second array like pattern. Each of the hub apertures in the second array like pattern align with a corresponding one of the threaded flange apertures of the first array like pattern whereby the first and second array like patterns are complementary. The fastening means comprises a plurality of bolting connections, one for each aligned hub aperture and threaded flange aperture, for securing the plurality of blades to the hollow hub. Each bolting connection has a bolt head-like portion located within the central opening of the hollow hub and has a threaded shaft portion extending through a corresponding aligned hub aperture and threaded flange aperture for threading engagement with the threaded flange aperture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]    For a better understanding of the nature and objects of the present invention reference may be had to the following detailed description when taken in conjunction with the accompanying diagrammatic drawings in which: 
           [0016]      FIG. 1  is a sectional assembly view of the turbine runner hub and runner blades; 
           [0017]      FIG. 2  is a front view of a portion of the outer surface portion of the hub of the turbine; 
           [0018]      FIG. 3  is an isometric view of one of the turbine blades; and 
           [0019]      FIGS. 4 and 5  illustrate alternative aperture patterns. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Referring to the Figures, the present invention relates to a hydraulic turbine  10  having runner blades  34  assembled to a hollow runner hub  12  for a fixed blade axial flow turbine. In the figures shown, the blades  34  form part of a diagonal turbine runner. It should be understood that the fixed blades  34  may form part of a propeller turbine runner (not shown). The hub  12  is connected by studs and nuts  14  to a prime mover or shaft  16 . The hub  12  has a central opening  18  and a non-planar outer surface portion  20  that is generally conical, in shape and may be cylindrical or spherical depending on the turbine design. The hub  12  comprises a plurality of recesses  22 , one for each blade  34 , which recesses  22  are machined into the surface  20  of the hub  12  and define a protruding lip  25  that at least partially, if not fully, surrounds the recess  22 . 
         [0021]    Referring to  FIGS. 1 and 2 , the hub recess  22  is shown to comprise a planar flange seating surface portion  24  having a generally rectangular shape in the form of a square with corners  21  machined with a small radius. The flange seating surface portion  24  acts as a seat for the a mounting flange  36  of the runner blade  34  ( FIGS. 1 and 3 ). The recess  22  has a plurality of hub apertures  26  that are bored to extend from the flange seating surface portion  24  through the hub  12  and open into the central opening  18 . The hub apertures  26  are grouped spread across the planar flange seating surface portion  24  in an array like pattern  42 . In the preferred embodiment shown the array like pattern is shown as two concentric circular patterns  28 ,  30  ( FIG. 2 ) and in an alternative embodiment may comprise a single circular pattern. As seen in  FIGS. 4 and 5  other array-like patterns for the hub apertures  26  may comprise concentric rectangular patterns  25   a  in  FIG. 4  and a matrix array pattern  25   b  as in  FIG. 5 . Further, it should be understood that these patterns may be incomplete in that an aperture in the pattern may be omitted (such as shown at designation  100  in  FIGS. 2 ,  4  and  5 ) due to space limitations discussed hereinafter. 
         [0022]    Referring to  FIGS. 1 and 3 , the hub mounting flange  36  of the runner blade  34  comprises a planar hub abutting surface portion  38  having a generally rectangular shape in the form of a square machined with a small radius corners  47 . The shape of the flange seating surface portion  24  and that of the hub abutting surface portion  38  are preferably complementary to each other so as to provide for good seating of the mounting flange  36  within the recess  22  with the lip  25  of the recess  22  at least partially surrounding sides of the mounting flange  36 . The runner blades  34  comprise a plurality of threaded flange apertures  40  formed by drilling, reaming and tapping to final size. The threaded apertures  40  extend from the hub abutting surface portion  38  into mounting flange  36  of the runner blade  34 . The plurality of threaded flange apertures  40  are grouped spread across the hub abutting surface portion  38  in an array-like pattern  42  of two concentric circular or array patterns  46 ,  48  ( FIG. 3 ). The array-like pattern  25  of the hub apertures  26  is arranged to align with array-like pattern  42  of the corresponding threaded flange apertures  40 . It should be understood that if the array-like patterns  25   a  and  25   b  of  FIGS. 4 and 5  for the hub apertures  26  are used, then complementary array-like patterns (not shown) would be found on the hub abutting surface portion  38  for the threaded flange apertures  40 . 
         [0023]    As shown in  FIG. 1 , the inner surface of the hub  12  is provided with relatively flat surface portions  49  which are surfaces located on the opposite side of the planar flange seating surface portion  24  of the recess  22 . 
         [0024]    Bolting connections  32  shown in  FIG. 1  pass through a corresponding aligned hub apertures  26  and threaded flange apertures  40  so as to secure the runner blades  34  to the hub  12 . Each bolting connection  32  has a bolt head portion or nut  33  that is located within the central opening  18  of the hollow hub  12  and is tightened against a flat surface portion  48 . Each bolting connection  32  has a stud  37  with threaded shaft portion  35  that extends through a corresponding aligned aperture  26  and into threaded flange aperture  40  for threading engagement with the threaded flange aperture  40 . The threaded shaft portion  35  of the stud  37  may be continuous or have a middle portion not threaded allowing a wrench to be used against the non threaded portion to secure the stud  37  into the threaded aperture  40  of flange  36 . Otherwise two nuts can be threaded onto the stud together, locked and temporarily used to secure the studs  37  in the flange  36 . As shown in  FIG. 1 , the bolting connections  32  are arranged in two concentric circular patterns  60 ,  62  for each blade  34 . Other array bolting patterns may be used which would correspond to patterns shown in  FIGS. 4 and 5 . 
         [0025]    In some instances, due to space limitations inside of the hub  12 , there may be insufficient area for a bolting connections  32  to be used where adjacent flat surface portions  49  meet. Accordingly, no bolting connection  32  is used and associated apertures through the hub  12  and into the mounting flange  36  are not required leading to the aperture patterns through the hub  12  and into the flange  36  being incomplete. 
         [0026]    The generally square shape of the planar hub abutting surface portion  38  and the complementary square shape of the planar flange seating surface portion  24  allow for additional bolts, if required, to be passed through apertures (not shown) located in the corners or adjacent to the corners  21  and  47  respectively of the flange seating surface portion  24  and the hub abutting surface portion  38 . 
         [0027]    The nuts  33  and studs  37  are installed from inside the hollow hub  12 . Tightening of the nuts  33  or stud  37  brings the planar hub abutting surface  38  of the mounting flange  36  into direct flat abutting contact with the planar flange seating surface portion  24  of the recess  22 . The nuts  33  are tightened such that the contact pressure between the mounting flange  36  of the runner blades  34  and the recess  22  of the hollow hub  12  is a predetermined force leading to the highest forces in moments occurring on the bolting connections  32  in the two concentric bolting circles  60 ,  62  to prevent face separation. Blade angle is not adjustable. 
         [0028]    Referring to  FIG. 3 , a circle  66  is shown in broken line. Circle  66  represents the area of the prior circular flange as compared to the larger area of the generally square shape of the hub mounting flange  36 . The increased surface area provided by the square rectangular shape of mounting flange  36  of  FIG. 3  is shown in the corner areas as  68 . It should be understood that if the rectangular shape shown in  FIG. 3  had a height twice that of its width, then additional surface area above and below circle  66 , and not just in the corners, would be present. 
         [0029]    While the invention has been described in terms of very specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification that fall within scope of the appended claims.