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National Advisory Committee for Aeronautics, Technical Notes - Effects of Axial Plane Curvature and Passage Area Variation on Flow Capacity of Radial Discharge Impeller with Conventional Inlet Buckets

An experimental radial-discharge impeller was designed to have,
by comparison with conventional impellers, a long radius of axial-
plane curvature, a large axial depth, and a small inlet-blade root
diameter. The impeller had conventional inlet-bucket bending and
inlet and discharge diameters similar to an existing commercial
hapeller. This experimental impeller was tested as part of an
investigation to improve the flow capacity of radial impellers.

The performance effect of impeller passage area was investigated
by tests of a series of three impeller front- shroud profiles. The
impeller passages of profile 1 had constant area along the mean flow
path taken in an axial plane. Profiles 2 and 3 had uniforndy con-
verging areas along the mean flow path.

The best performance for the experimental impeller was obtained
with impeller blade profile 1, but the advantages over profiles 2
and 5 was apparently diminishing with increasing impeller tip speed.
A comparison of specific flow capacity with that of a conventional
radial-discharge impeller of approximately equal inlet and discharge
diameters and with that of a mixed-flew impeller at an impeller tip
speed of 1200 feet per second showed the experimental impeller to
have a specific capacity 47 percent greater than the conventional
radial-discharge impeller and 2 percent greater than the mixed-flew
impeller. Mbst of the increase in volume flow capacity of this
impeller, as compared with the'conventional radial-discharge impel-
ler, may be attributed to the gradual change in direction of the
impeller passage resulting from the rear shroud profile of large
radius of curvature and the large axial depth. A small increase in
volume flow capacity was due to a slightly larger impeller-inlet
annular area.

The volume flow capacity of the radial-discharge centrifugal
impeller must be improved to meet the increasing air-flow require-
ments of aircraft power plants. The volume flow capacity of a
radial-discharge centrifugal impeller would be expected to depend,
for fixed inlet and discharge diameters, on the entrance angle, the
blade curvature that determines the rate of change of angular veloc—
ity of the air, the curvature of the passage in the axial plane, and
the area and area variation along the passages.