Design and test of mixed-flow impellers I :aerodynamic design procedure

Osborn, Walter M., Hamrick, Joseph T.

A mixed-flow impeller was designed with special emphasis upon the reduction or elimination of velocity decelerations along the wetted surface, especially along the blade suction surface. With the use of a provisional hub-shroud profile, the blade shape at the blade mean height was determined from a prescribed velocity distribution. The blade shape at all other locations was fixed by the introduction of radial blade elements and blade taper which were specified in consideraiton of stress requirements. The variation in flow conditions from hub to shroud and changes in the hub-shroud profile required to obtain the desired flow rate wre investigated by an analysis in the hub-shroud plane in which axially symmetrical flow was assumed. The method was extended to obtain the blade surface-velocity distribution for a finite number of blades. In order to allow for viscous effects and to increase the blade-height-to-passage-width ratio, the blade height was arbitrarily increased and splitter vanes were added. Preliminary experimental results show that an impeller designed by this procedure with allowances for viscous effects had higher than average efficiency and good operating characteristics.

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