Design and test of mixed-flow impellers 1: aerodynamic design procedure Page: 2 of 44
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NASA Technical ary
NAC RM ES2E05
3 1176 01435 5904
NATIONAL ADVISORY CCWITTEE FOR AERONAUTICS
DESIGN AND TEST OF. MIXED-FLOW IPEEJRS
I - AERODYNAMIC DESIGN PROCEDURE
By Walter M. Osborn and Joseph T. Hamrick
A mixed-flow impeller was designed using recently available tech-
niques with special emphasis on the reduction or elimination of velocity
deceleration along the wetted surfaces, especially along the blade suc-
tion surface. With a given hub-shroud profile, the blade shape at the
blade mean height was determined from a prescribed velocity distribution
on the blade surface for isentropic flow with the aid of the preliminary
assumption of uniform flow conditions frm hub to shroud. 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
In order to determine the velocities throughout the passage from
the hub to the shroud, the over-all flow configuration was investigated
by the use of an analysis in the hub-shroud plane in which axially
symmetrical isentropic flow was assumed. The analysis method was
extended to obtain the blade surface velocity distribution throughout
the passage and to make comparisons at the blade mean height.
Impellers designed for an average velocity acceleration from inlet
to outlet have relatively low outlet blade heights which may result in
losses due to secondary flow and clearance effects. In order to allow
for viscous effects (such as effective decrease in flow area) and to
increase the blade-height-to-passage-width ratio, the blade height was
arbitrarily increased. Splitter vanes were added to increase further
the blade-height-to-passage-width ratio. Preliminary experimental
results show that an impeller designed by this procedure had higher than
average efficiency and good operating characteristics.
Research on centrifugal ccgpressors at the NACA Lewis laboratory is
being conducted to evolve reliable design procedures which will eliminate
the large amount of experimental development now necessary on new designs
anti will increase the centrifugal-compressor efficiency. In the develop-
ment of design procedures it is necessary to investigate certain param-
eters that affect the flow when viscosity is considered. Because of
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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/m1/2/: accessed October 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.