Runner for francis type hydraulic turbine

Abstract

There is disclosed a runner for a Francis-type hydraulic turbine where each runner blade has a outlet edge comprising a deflected edge portion. The deflected edge portion is located adjacent to the junction or attachment point of the outlet edge to the band of the runner to define a stress reducing tip extension portion of the blade adjacent the band. This tip extension portion reduces stress concentration adjacent where the outlet edge joins the runner band.

1 . A runner for a Francis-type hydraulic turbine, comprising a band, a crown and a number of blades having a curved shape and being attached to the band and the crown, each blade comprising an inlet flow dividing edge adapted to face upstream in the turbine and an outlet edge adapted to face downstream from the turbine towards a draft tube, the outlet edge comprising a continuous edge extending between the crown and the band and the outlet edge comprising a deflected edge portion located adjacent the band that meets the band at a first junction point, the deflected edge portion defining a stress reducing tip extension portion of the blade adjacent the band, and the first junction point (B) being downstream in the direction of rotation of the runner from an expected junction point (B′) of the band and the outlet edge without the deflected edge portion.  
     
     
         2 . The runner according to claims  1  wherein a second junction point (A) of the blade inlet edge at the band is located forwardly of an inlet edge junction point (C) at the crown, and that the first junction point (B) of the blade outlet edge at the band, is located forwardly of an outlet edge attachment point (D) at the crown, as seen in the rotational direction of the runner.  
     
     
         3 . The runner according to  claim 1  wherein the tip extension portion of the blade is integrally formed therewith.  
     
     
         4 . The runner according to  claim 2  wherein the tip extension portion of the blade is integrally formed therewith.  
     
     
         5 . The runner according to  claim 1  wherein the deflected edge portion has a length shape selected from the group of straight, convex and serpentine.  
     
     
         6 . The runner according to  claim 2  wherein the deflected edge portion has a length shape selected from the group of straight, convex and serpentine.  
     
     
         7 . The runner according to  claim 3  wherein the deflected edge portion has a length shape selected from the group of straight, convex and serpentine.  
     
     
         8 . The runner according to  claim 4  wherein the deflected edge portion as a length shape selected from the group of straight, convex and serpentine.  
     
     
         9 . The runner according to  claim 1  wherein the tip extension portion forms an acute angle (α) where the deflected edge portion meets the band when viewed looking into the runner from its exit opening.  
     
     
         10 . The runner according to  claim 2  wherein the tip extension portion forms an acute angle (α) where the deflected edge portion meets the band when viewed looking into the runner from its exit opening.  
     
     
         11 . The runner according to  claim 3  wherein the tip extension portion forms an acute angle (α) where the deflected edge portion meets the band when viewed looking into the runner from its exit opening.  
     
     
         12 . The runner according to  claim 4  wherein the tip extension portion forms an acute angle (α) where the deflected edge portion meets the band when viewed looking into the runner from its exit opening.  
     
     
         13 . The runner according to  claim 1  wherein the defected edge portion has a radial displacement (dR) from the band that is at least 3% of an exit diameter (DE) for the band.  
     
     
         14 . The runner according to  claim 13  wherein the outlet edge of the blade comprises a curving non-deflected edge portion and the deflected edge portion continues from the curving non-deflected edge portion at a deflection point.  
     
     
         15 . The runner according to  claim 14  wherein the deflection point is displaced by the radial displacement (dR) from the band.  
     
     
         16 . The runner according to  claim 2  wherein the defected edge portion has a radial displacement (dR) from the band That is at least 3% of an exit diameter (DE) for the band.  
     
     
         17 . The runner according to  claim 16  wherein the outlet edge of the blade comprises a curving non-deflected edge portion and the deflected edge portion continues from the curving non-deflected edge portion at a deflection point.  
     
     
         18 . The runner according to  claim 17  wherein the deflection point is displaced by the radial displacement (dR) from the band.