Abstract:
A hydro turbine assembly includes a hub configured to rotate about a center axis and configured to be mounted in a water passage. The hub includes an upstream end, a downstream end and an outer surface between the upstream and downstream ends. The hub includes at least three mounting recesses arranged in the outer surface wherein each mounting recess includes a first hub mounting surface and a second hub mounting surface, and the second hub mounting surface is downstream and radially inward of the first hub mounting surface. The assembly includes at least three runner blades each including a base configured to seat in a respective one of the mounting recesses, wherein the base includes a first blade mounting surface arranged to abut the first hub mounting surface and a second blade mounting surface arranged to abut the second hub mounting surface.

Description:
CROSS RELATED APPLICATION 
     This application is the U.S. national phase of International Application No. PCT/CA2013/000102 filed 6 Feb. 2013 which designated the U.S. and claims priority to U.S. Provisional Patent Application No. 61/596,872 filed 9 Feb. 2012, the entire contents these applications are incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to hydro turbines and in particular to coupling runner blades to a hub in a water (hydro) turbine. More particularly, the invention relates to the mounting surfaces at the base of a runner blade and the opposing mounting surfaces on the hub. 
     BACKGROUND 
       FIG. 1  illustrates a conventional axial water turbine  10  in an annular chamber  12  that may be embedded in the concrete of a water dam  13 . An example of the axial turbine of the propeller blade type shown in  FIG. 1 , and particularly the mounting of the runner blades to the hub, is shown in U.S. Patent Application Publication 2009/0092496. 
     A water turbine is typically at an elevation well below the surface of the lake or other water source behind a dam. The annular chamber  12  defines a generally vertical axial water flow passage, as indicated by the arrow labeled H2O. Water flows through passages in the dam, through the annular chamber and over the runner blades. The blades and hub  16  rotate about a vertical axis. A shaft  24  extends between the hub and a generator. The force of the water rotates the runner blades, hub and shaft to drive the electric generator which produces electricity. 
     The hub  16  is tapered in the direction of water flow and may connect to a cone  18 . The tapered surfaces of the hub and cone extend the hydraulic profile of the hub. Water flows smoothly over the hub and cone and down from the water turbine. 
     The more water flowing through the turbine, the greater the amount of power that can be delivered by the turbine to the generator. The amount of water flowing through the turbine is limited by the smallest cross-sectional area of the water passage in the turbine. This smallest cross-sectional area is typically the narrowest, e.g., the throat (T), portion of the annular water passage between the chamber  12  and hub  16 . The throat is typically at the same elevation in the turbine as are the tips of the runner blades. The diameter of the throat (T) and the diameter (H) of the hub at the throat determine the smallest annular area of the water passage. The greater the ratio of the throat to the hub (T/H) the larger the water passage. 
     Runner blades are often made of stainless steel, which provides corrosion and cavitation resistance but is expensive. Where the hub is integrally cast with the runner blades, the hub is also formed of stainless steel. If the runner blades are not integrally formed with the hub, the hub may be formed of a less expensive material such as mild steel because the hub is less exposed to cavitation of the water than are the blades. Hubs formed of mild steel may be painted to provide corrosion resistance. 
     A common runner blade type is propeller-style blades bolted to a hub. This type of runner blade has a circular base  20  that bolts to a recessed circular mount  22  in the side of the hub, as is shown in  FIG. 1 . The bottom of the base has a mounting surface that is typically flat, circular and generally perpendicular to the axis of the runner blade. 
       FIG. 2  illustrates another conventional water turbine  26  having runner blades  28  fixed to a conical hub  30 . Each runner blade  28  is integrally cast with a segment of the hub  30 . The hub segments with the blades are arranged in an annular array and held together by shrink rings  32 . 
     Water flows radially inward to the water turbine  26  and is discharged axially downward. The turbine  26  is a diagonal propeller blade turbine because the water moves diagonally across the runner blades. The chamber  34  extends cylindrically around the tips of runner blades. The conical hub  30  mounts to a head cover  36 . The shaft  38  connects to the hub  30 , extends through the head cover and connects to an electrical generator. 
       FIG. 3  illustrates another exemplary conventional water turbine  40 . The propeller type runner blades  42  and hub  44  are formed as an integral metal casting. The water turbine  40  is an axial type turbine and is arranged in a chamber in a similar the chamber  12  for the water turbine  26  shown in  FIG. 2 . 
     The water turbines shown in  FIGS. 1 to 3  illustrate conventional connections between the runner blades and hubs. As shown in these figures, runner blades may be integrally cast with the hub, welded to the hub, attached by shrink rings to the hub, or bolted to the hub. Integral casting, welding and in some applications of shrink rings are manufacturing and assembly steps applied at the manufacturing location for the water turbine. The water turbine is shipped with the blades attached to the hub to the dam where the turbine is to be installed. A difficulty arises when the water turbine is too large to be shipped from the manufacturing location to the water dam or other location at which the water turbine is to be installed. 
     An advantage offered by bolting the runner blades to the hub is that one or more of the blades may be attached to the hub at the water dam or other turbine installation location. Shipping the turbine hub by itself or with fewer than all of its runner blades reduces shipping costs and difficulties. Bolting the runner blades to the hub at the installation location saves transportation costs and reduces the difficulties associated with shipping a large water turbine. Similar to bolting the blades to the hub, the runner blades may be welded to the hub or secured with shrink rings at the installation location. Bolting, applying shrink rings and welding runner blades to hubs share the advantage of reducing the costs and difficulties of transporting water turbines. 
     SUMMARY OF INVENTION 
     A runner blade mounting system has been conceived for attaching runner blades, especially propeller type blades, to a hub. The runner blades may include a long, narrow base that seats against mounting surfaces recessed in the side of a conical hub. The base of the runner blades have mounting surfaces that are stepped and shaped to abut against the mounting surfaces in the hub. 
     The stepped mounting surfaces allow the base to conform to the inward taper of the hub. Each step shifts one or more of the mounting surfaces radially inward along a downstream direction. Similarly, the mounting surfaces in the hub step radially inward in the downstream direction. Because the steps shift the mounting surfaces radially inwardly with the taper of the hub, the mounting surfaces may extend further along the hub than do conventional mounting surfaces that do not step inwardly. 
     The mounting system with stepped mounting surfaces may be used for various types of water turbines, including axial and diagonal propeller style runner blades and other turbines having fixed blades. The mounting system is particularly beneficial for diagonal turbines and where there is a desire to reduce the ratio of the throat to the hub (T/H). 
     Adding stepped mounting surfaces to a tapered hub increases the design freedom in arranging the runner blade and the pattern of mounting bolts that secure the runner blades to the hub. For example, the stepped mounting surfaces allow the base of a runner blade to be narrow and long such that it extends axially along all or nearly all the length of the hub. The stepped mounting surfaces also allow the base to better conform to a long blade root. The stepped mounting surface also allows for a relatively large area of surface contact between the base and the mounting surfaces recessed in the hub. A large surface contact area allows the bolt pattern to be optimized to sustain high load forces. 
     The stepped mounting surfaces may be used to design smaller diameter hubs for a water turbine. The hub may have a smaller diameter because the mounting stepped surfaces allow the base of the runner blade to be narrow and long which reduces the width of the mounting surfaces recessed in the hub. The hub may have a smaller diameter because the mounting recesses are relatively narrow and will fit on a small diameter hub. 
     Reducing the diameter of the hub may allow for a larger water passage through the throat. Conventional hubs tend to have a large diameter to accommodate wide flange surfaces that support the base of runner blades. 
     The stepped mounting system may be used on new water turbine systems and in retrofits of an existing water turbine system. In addition to allowing for smaller hubs and optimized bolt patterns, the stepped mounting system assists in transporting the hub and runner blades to a dam for installation. One or more of the runner blades may be shipped separately from the hub to reduce the shipping difficulties that would otherwise occur in shipping a complete water turbine with all blades attached. The blades may be bolted to the hub at the dam during the installation of the water turbine in the dam. 
     The mechanical arrangement of mounting surfaces stepped along an axial direction provides greater freedom in designing the shape of the runner blade and the pattern of bolts that secure the base of the blade to the hub. For example, the arrangement of stepped mounting surfaces allows for longer bases for runner blades and narrower hubs. Decreasing the diameter of the hub reduces the ratio of hub diameter to throat diameter which increases the cross-sectional area of the water flow passage without changing the throat diameter. 
     An increase in the cross-sectional area of the water flow passage substantially increases the water flow rates through the water flow passage. An increase in the water flow rate provides a corresponding increase in the power generated by a water turbine. Moreover, the throat diameter is typically fixed for existing water turbine installations and is proportional to the cost of a water turbine at a new installation. Increasing the cross-sectional area of the water flow passage without increasing the throat diameter yields a significant power increase by a water turbine without incurring the high costs associated with expanding the throat diameter. 
     The stepped mounting surfaces on the base of a runner blade may have a length dimension align with the hub axis which allows the length of the base to be substantially greater than its width. The stepped mounting surfaces also allow the base to mount to an inclined or tapered outer surface of the hub. Further, the stepped mounting surfaces provide design freedom in arranging the pattern of connecting bolts on the base of the runner blades. The pattern of bolts may be arranged to, for example, concentrate the bolts at the regions of the base subjected to high force loads. 
     A hydro turbine assembly has been conceived comprising: a hub configured to rotate about a center axis and configured to be mounted in a water passage, wherein the hub includes an upstream end, a downstream end and an outer surface between the upstream and downstream ends, and further wherein the hub includes at least three mounting recesses arranged in the outer surface and the mounting recess includes a first hub mounting surface and a second hub mounting surface, wherein the second hub mounting surface is downstream and radially inward of the first hub mounting surface, and at least three runner blades each having a base configured to seat in one of the mounting recess, wherein the base includes a first blade mounting surface adapted to abut the first hub mounting surface and a second blade mounting surface adapted to abut the second hub mounting surface. The at least three mounting recesses may be arranged symmetrically around the center axis. 
     The mounting recess in the hub may have a longitudinal axis parallel to the center axis. The first and second hub mounting surfaces may each form a run in a stair step pattern where a riser extends between each pair of mounting surfaces. The riser may be perpendicular to the center axis and to the first and second hub mounting surfaces. Further, the first and second hub mounting surfaces may be planar, as may be the first and second blade mounting surfaces. 
     The base of the runner blade may include a center key that seats in a key slot of a mounting recess in the hub. The key may be a post extending radially inward from the bottom of the base of the runner blade. The key is configured to seat in a key slot of the mounting recess in the base. The key slot may be adjacent to the first and second hub mounting surfaces of the runner blade. 
     A method has been conceived to install a replacement hydro turbine, the method comprising: removing an existing hydro turbine from a water passage; replacing a narrow hub having a narrower diameter than an existing hub for the existing hydro turbine, wherein the narrow hub includes an upstream end, a downstream end and an outer surface between the upstream and downstream ends, and the narrow hub includes at least three mounting recesses arranged in the outer surface wherein the mounting recess each include a first hub mounting surface and a second hub mounting surface, and the second hub mounting surface is downstream and radially inward of the first hub mounting surface; mounting three runner blades each to a corresponding one of the mounting recesses, wherein each of the runner blades comprises a base including a first blade mounting surface that abuts the first hub mounting surface and a second blade mounting surface that abuts the second hub mounting surface, and mounting the narrow hub with the mounted runner blades in the water passage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 to 3  are side views, shown partially in cross-section, of conventional water turbines for hydro-electric power generation. 
         FIG. 4  is a side view, shown partially in cross-section of a water turbine having stepped mounting surfaces on the runner of blades and corresponding mounting surfaces in recesses in the hub. 
         FIGS. 5 to 8  are perspective views of an exemplary runner blade having a base with stepped mounting surfaces. 
         FIG. 9  is a perspective view of an exemplary hub having recesses with stepped mounting surfaces to receive the mounting surfaces of the base of the blade shown in  FIGS. 5 to 8 . 
         FIGS. 10 to 12  are views of a runner blade and hub assembly, shown partially in cross-section. 
         FIG. 13  is a perspective view of a portion of a water runner blade having an alternative base design. 
         FIG. 14  is a perspective view of a portion of a hub with a mounting recess to receive the alternative base of the blade shown n  FIG. 13 . 
         FIG. 15  is a perspective view of the hollow interior of a blade and hub assembly, shown partially in cross section. 
         FIG. 16  is a perspective view of a hub and blade assembly being transported on a flatbed trailer to be hitched to a truck or other motorized vehicle. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 4  is a side view of a water turbine  50  in accordance with an embodiment of the present invention. In the embodiment depicted in  FIG. 4 , a portion of the runner blades  52  and hub  54  have been cut away to show the stepped mounting surfaces  56 ,  58  on the hub which receive similar mounting surfaces on the radially inner surface of the base of the runner blade. The hub is attached to a vertical shaft  60  which may drive the rotor of an electrical generator. The water turbine  50  is mounted in an annular chamber, such as shown in  FIGS. 1 to 3 , that may be in the wall of a dam. 
     The hub is not integral with the runner blades. As such, the runner blades may be attached, mounted, fastened or otherwise connected to the hub. The hub may be formed of a mild steel or other suitable material. The runner blades may be formed of a stainless steel or other material providing good corrosion protection and which can withstand cavitation from the water flowing over the runner blades. The hub and/or blades may optionally have a wear-resistant coating. 
     Each runner blade  52  has a base  64  and blade region  63 , e.g., a propeller blade. The root  62  of each blade region  63  is integral with or attached to the base  64 . The base  64  supports and attaches the runner blade to the hub  54 . The base transfers the forces from the blade region  63  to the hub. These forces include torsion forces imparted by the water applied to the blades. 
     The base  64  has radially inwardly facing blade mounting surfaces  68 ,  70 . These surfaces may be generally planar and parallel to the axis  71  of the hub  54 . The mounting surfaces  68 ,  70  are stepped such that the upper mounting surface  68  is radially outward of the lower mounting surface  70 . The radial position of each of the mounting surfaces is with respect to the axis  71  of the hub. The upper mounting surface is aligned with a portion of the hub  54  having a larger diameter than the diameter of the portion of the hub aligned with the lower mounting surface. A riser  73  of the base extends between the mounting surfaces  68 ,  70 . 
     The mounting surface  68 ,  70  allow the base  64  of the runner blade to conform to the taper of the hub  54 . By stepping the mounting surfaces radially inwardly in a downward direction, the base may be extended further along the length of the tapered hub. Without the steps in the mounting surfaces, the base would have a single mounting surface parallel to the shaft axis. A base having an entirely straight surface does not conform to a tapered hub and does not provide the design freedom to extend the base the length of the hub. 
     The base  64  with stepped mounting surfaces  68 ,  70  may extend more than half of the length of the hub, as is shown in  FIG. 4 . The length, width and shape of the base  64  are design parameters for the runner blade and hub. By stepping the mounting surfaces  68 ,  70 , the range of lengths available for the base increases. The increase in available base lengths also allows for more freedom on the other design parameters such as the width and shape of the base, and the arrangement of bolt holes for the bolts connecting the base to the hub. For example, increasing the length of the base of the runner blade allows for a narrower base because the needed contact area can have a length much greater than its width. 
     The mounting surfaces  68 ,  70 , in this embodiment, are parallel to the hub axis  71  due to the centrifugal forces acting radially on the hub and blades. The bolts  72  that secure the base to the hub extend radially such that the centrifugal forces primarily place the bolts under tension. Bending moments, shear and torsional forces are other forces applied to the bolts and the base. The bolts and surface area of the mounting surfaces should be sized sufficiently to withstand the bending, torsion and shear forces to be applied to the bolts and interface between the base and hub. 
     The blade mounting surfaces  68 ,  70  on the base seat on stepped hub mounting surfaces  56 ,  58  recessed into the hub. The hub mounting surfaces  56 ,  58  may be within a recess  66  in the hub, as is shown in  FIG. 4 . The hub may have a recess  66  corresponding to the base of each runner blade. Each recess  66  may have a perimeter conforming to the perimeter of the base  64  of the runner blade. 
     The hub mounting surfaces  56 ,  58  may have openings to receive the shaft of bolts or threaded rods  72  that extend radially out from the hub mounting surfaces and into the base of the runner blades. A bolt head or nut may be affixed to a radially inner end of the rod  72  shaft and secure the shaft to the inside surface of the hollow hub. 
     The hollow hub  54  may include a center chamber  75  aligned with the hub axis  71 . The center chamber  75  is the hollow interior of the hub and provides access to insert the bolts  72  that secure the base of the runner blades to the hub.  FIG. 4  shows the heads or nuts of the bolts  72  arranged on an inner sidewall of the center chamber  75 . The inner side wall of the center chamber  75  may be stepped to conform to the steps  56 ,  58  in the recesses  66  on the outside surface of the hub. The corresponding steps on the inner sidewall of the center chamber  75  and in the recess  66  may be such that the thickness of the hub between the stepped mounting surfaces  56 ,  58  and the inner sidewall of the center chamber  75  remain substantially constant. 
     A key  77  on the base of each runner blade may protrude radially inward from the base into a key slot or hole  79  in the corresponding hub recess  66 . The key  77  may have a cross sectional shape of rectangular, trapezoidal, racetrack, oval or other shape. The key slot or hole has a cross-sectional shape corresponding to the cross-sectional shape of the key  77 . The key  77  seats in the key slot or hole  79  when the base of the runner blade is inserted into the recess  66  of the hub. The seating of the key  77  in the key slot or hole  79  provides support to the runner blade, especially support for the torsion loading of the runner blade due to the flow of water over the blade. 
     Shear pins (not shown) may be substituted for the key  77  or provide supplemental support to the support provided by the key  77 . The shear pins may extend radially with respect to the axis  71  and seat in corresponding recesses in the base of the runner blade and the recess of the hub. 
       FIG. 5  is a top down view of a runner blade  52  in which the tip portion of the blade portion has been removed and shown in cross-section to better illustrate the root  62  and base  64 . The root  62  of the blade portion is affixed to an upper surface of the base  64 , such as by welding, casting or bolts. The root  62  may extend substantially the entire length of the base. The root and blade portion may be askew on the base, as is shown by way of example in  FIG. 5 . The front edge of the blade portion may be offset to the left side, for example, of the base and the trailing edge may be offset to the right side of the base. 
     The base  64  of the runner blade may be generally rectangular or trapezoidal as shown in  FIG. 5 . The upper corners  74  of the base may be rounded while the lower corner  76  may have a relatively sharp ninety degree corner. 
       FIG. 6  is a side view of the runner blade  52 . The upper surface  86  of base  64  may be inclined to conform to a taper of the hub. The thickness of the base, in a radial direction, varies with the steps formed by the three mounting surfaces  80 ,  82 ,  84 . As shown in  FIG. 6 , the trailing edge of the blade portion  63  may extend beyond the lower end of the base  64 . 
     The mounting surfaces  80 ,  82  and  84  may have irregular lengths, and the lengths of each surface may be based on a design selection made in determining the mounting of the runner blades to the hub. The risers  87  at the leading edge of each mounting surface  80 ,  82  and  84  may have a radial length selected during the design of the mounts for the blades to the hub. The risers may be planar and conform to corresponding risers in the recesses of the hub. 
       FIG. 7  is a view of the leading edge  88  of the blade portion  53  of the runner blade  52 . The blade portion includes a trailing edge  90  and a tip  92 . The base  64  is attached to the root  82  of the blade portion. A fillet  94  may extend along the outer edge of the joint between the base and root. The base may be welded or otherwise attached to the root of the blade. The root  62  may extend diagonally across the upper surface  86  of the base. A portion of the bottom of the root  62  may extend beyond the upper surface of the base. 
     The mounting surfaces  80 ,  82  and  84  may be parallel with each other and parallel to a longitudinal axis of the hub. The mounting steps may not be aligned with a surface of the blade portion. The mounting surfaces  80 ,  82  and  84  are shown as steps with risers  87  between each surface. Alternatively, the mounting surfaces may be inclined with respect to the axis of the hub, such as a single surface generally parallel to the taper of the hub. 
       FIG. 8  is a bottom view of the runner blade  52  which shows the radially inward surfaces of the base  64  and root  62 . The mounting surfaces  80 ,  82  and  84  are shown as having perimeters with rectangular shapes. The shapes of the perimeters of the mounting may have other shapes, such as convex or concaved, curved or triangular, provided that the shape of the mounting surface or surfaces mates with the opposing mounting surfaces on the hub. The mounting surfaces  80 ,  82  and  84  may have embedded plates or flanges  96  each having one or more openings  98  for the bolts that secure the blade  52  to the hub. 
       FIG. 9  is a side view of another embodiment of a tapered hub  100  with recesses  102  to receive runner blades. The hub has a large diameter upstream end  104  and a narrow diameter downstream end  106 . The hub may be circular in cross-section, except for the recesses. The hub may be hollow. The taper of the conical hub may be linear, convex, concave or other suitable shape. The taper of the hub may conform to the taper of the annular chamber for the turbine in the wall of the dam. The recesses  102  may extend a majority of the length of the hub, such as more than half the hub length, more than three quarters the hub length and more than four fifths of the hub length. A trailing cone is not illustrated and may be attached, e.g., welded or bolted, to the downstream end  106  of the hub. 
     The recesses  102  in the hub may be aligned with, e.g., parallel to, the longitudinal axis  108  of the hub  100 . The number of recesses may conform to the number of runner blades to be attached to the hub. The cross-sectional shape of each recess  102  may conform to the cross-sectional shape of the perimeter of the base of each runner blade. 
     Each recess  102  in the hub has a cross-section which conforms generally to the cross-section of the base of a runner blade. The recesses may each have the same cross-sectional shape and internal geometry. Alternatively, the recesses may each have a different cross-sectional shape or internal geometry to conform to variations in the bases of the runner blades. For example, each recess may have a cross-sectional shape which conforms to only one of the bases. These variations in the shape of the recess may be used to ensure that each runner blade is fitted to the proper recess. 
     The hub mounting surfaces  110 ,  112  and  114  in each recess  102  conform to the blade mounting surfaces on the base. The hub mounting surfaces may be planar and parallel to the axis  108  of the hub. The hub mounting surfaces  110 ,  112  and  114  have holes  116  through which extend the shafts of bolts which secure the runner blades to the hub. The hub mounting surfaces are stepped in an opposing manner to the steps of the mounting surfaces on the runner blades. The hub mounting surfaces abut against the blade mounting surfaces to provide a secure and rigid support by the hub for the runner blade. Bolts extending through the holes  116  bias the hub mounting surfaces against the mounting surfaces of the blades. 
     The stepping of the hub mounting surfaces  110 ,  112  and  14  allows the mounting surfaces to extend much of the length of the tapered hub. As the diameter of the hub decreases, each successive hub mounting surface is stepped radially inwardly. The risers  118  between the hub mounting surfaces and the length of each mounting surface may be selected based on the taper of the hub. 
       FIG. 10  shows runner blades  120  attached to a hub  100 . One of the recesses  102  in the hub is left open for purposes of illustration. The other hub recesses are shown as seating the bases  122  of their respective runner blades  120 .  FIG. 10  illustrates that the leading portion of the root a blade portion of a runner blade may extend outside of the base and over the surface of the hub. The lower portion of the root extends outside of the base and conforms to the outer surface of the hub. The lower surface of the root of the blade portion may abut against the outer surface of the hub. 
       FIG. 11  is a side and cross-sectional view of the hub  100  and runner blades  120 . The figure shows a portion of the hub in cross-section to illustrate its hollow interior  123  which includes planar interior sidewalls  124  opposite the to the hub mounting surfaces shown in  FIGS. 9 and 10 . The interior sidewalls  124  may be stepped in a manner similar to the steps of the hub mounting surfaces. The interior sidewalls may also be parallel to the axis  108  of the hub. Alternatively the interior sidewalls may be tapered in a manner similar to the taper of the hub, especially if the hub mounting are taped. 
       FIG. 12  is an enlarged cross-sectional view of an upper region of the assembly of the hub  100  and runner blades  120 . The interior sidewalls  124  have holes through which extend the threaded shafts  128  from the base of the runner blades. The threaded shafts are seated in threaded holes extending radially into the base of the runner blades. The shafts extend from the base into the hub and protrude through the interior sidewalls  124  of the interior  123  of the hub. Nuts or other fasteners  132  are attached to the ends of the shafts to secure the runner blade to the hub. 
     The mounting surfaces  80 ,  82  and  84  on the base of the runner blade seat, e.g., abut against, the hub mounting surfaces  110 ,  112  and  114  of the hub  100 . The threaded shafts  128  and fasteners  132  bias the mounting surfaces of the base against the hub mounting surfaces. 
       FIG. 13  shows a perspective view of the side of a runner blade  140  having an alternative base  142  with stepped mounting surfaces  144 ,  146 . The mounting surfaces  144 ,  146  are arranged around the perimeter of a center key  148  that extends radially inwardly from the base. The key  148  may be a raised section of the base having a racetrack cross-section. The mounting surfaces  144 ,  146  may be U-shaped sections that extend around the key. 
       FIG. 14  is a perspective view of a portion of a hub  150  which receives the runner blade  140  having the base with a key. The hub  150  includes recesses  152  with hub mounting surfaces  154 ,  156  which receive the mounting surfaces  144 ,  146  of the base of the runner blade. The recess includes an opening  158  or a deep recess in the hub to receive the key of the base. The opening or deep recess is shaped to conform to the sidewall of the key and thereby prevent rotation of the runner blade with respect to the hub. 
       FIG. 15  is a cross-sectional view of the hollow interior of the hub  150  which illustrates the key  148  of a runner blade  140  seated in the deep recess or opening  158  of the hub. The fastener holes  160  in the sidewalls of the hub allow shafts and nut assemblies  162  to secure the runner blades to the hub. 
       FIG. 16  illustrates a hub  170  with some but not all runner blades  172  attached to the hub  170 . Because not all of the runner blades are attached, the hub and turbine assembly may be mounted on and transported by a flatbed of truck trailer  174 . The remaining runner blades may be separately transported to the dam and attached to the hub at the dam. 
     While threaded shafts and nuts have been shown to secure the blade to the hub, the base of the runner blade may be welded or otherwise fastened to the hub without use of threaded shafts and nuts. 
     The number, size and shape of the runner blades on a hub are dependent on the hydraulic design of the turbine. The number of runner blades is at least three for all of the embodiments disclosed herein. The blades may be arranged to extract the maximum of energy from the water flow that passes through the turbine. The force loads resulting from the water flow and extracting energy by the turbine are transmitted by the runner blades, through the base to the hub. The contributors to the load are gravity which applies a downward force on the base and hub due to the weight of the runner blades. Another force contributor is due to the water pressure difference between the upstream and downstream portions of the turbine. During operation of the turbine, the water flow applies a tangential force to the runner blades which is transmitted through the base to the hub. In addition, a rotational force, e.g., centrifugal force, arises due to the rotation of the runner blades and hub. The designer of the runner blade will take these forces into account in designing the runner blades and hubs. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.