Design and test of mixed-flow impellers 1: aerodynamic design procedure Page: 3 of 44
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NACA RM E52E05
viscosity, parameters such as blade loading and blade-height-to-passage-
width ratio become very important. In order to investigate these param-
eters and their various effects upon over-all performance, a series of
mixed-flow impellers.is being designed and tested. An attempt is being
made to conduct the investigation in such a mlaher that the results will
lead to improved design techniques. The procedure followed in the appli-
cation of recent design and analysis methods to the design of the first
of these impellers, designated the MFI-l, is presented herein.
In the design, an attempt was made to reduce or to eliminate, wher-
ever possible, any velocity decelerations along the wetted surfaces,
especially along the blade trailing face. Theoretical analysis (refer-
ence i) and experimental investigations (references 2 and 5) indicate
that although substantial decelerations along the impeller blade driving
face (pressure surface) may be tolerated, decelerations along the blade
trailing face (suction surface) may result in severe losses.
The MFI-l impeller was designed to give a blade shape with a pre-
scribed blade surface-velocity distribution at the mean blade height by
the method of reference 4. The blade shape at all other locations was
fixed by the introduction of radial blade elements and blade taper which
were specified in consideration of stress requirements. The effect of the
hub-shroud curvature on the velocity distribution and the compromises
in geometric design necessitated by stress restrictions were investigated
by an analysis in the meridional (hub-shroud) plane by the method of
In order to allow for viscous effects, such as effective decrease
in'area, and to increase the blade-height-to-passage-width ratio, the
blade height was arbitrarily increased and splitter vanes were added for
the first test version of the experimental impeller designated the
MFI-1A. These design changes will be eliminated by successive steps in
the experimental impeller in order to obtain a better estimate of the
allowances that-should be made.
The geometric coordinates for the design (MFI-1) and the modified
(MFI-1A) impellers are given in table I and the2 experimental performance
characteristics of the MFI-1A are presented in figure 1.
In the design procedure, the design method of reference 4 and the
analysis method of reference 5, both of.which are for isentropic com-
pressible flow, were used to arrive at the design of the MFI-1. In order
to use this design procedure, complete familiarity with both references
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Osborn, Walter M. & Hamrick, Joseph T. Design and test of mixed-flow impellers 1: aerodynamic design procedure, report, September 19, 1952; (digital.library.unt.edu/ark:/67531/metadc59165/m1/3/: accessed January 16, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.