Experimental Investigation of Flow in the Rotating Passages of a 48-Inch Impeller at Low Tip Speeds Page: 4 of 38
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NACA IM E51D20
The same type instrumentation was installed at station 3 in the
single discharge duct, 12 diameters from the collector flange as
recommended in reference 2.
CE0 Static pressure was measured along the stationary front shroud and
M3 along the front and rear diffusers at various radii along a diametral
line.
Impeller instrumentation. - A schematic diagram of the instrument
locations in the impeller passages is shown in figure 3. The total and
static pressures were measured at each circled intersection of radius
and geometric-streamline. The total-pressure probes were distributed
throughout the 18 passages so that any one passage had no more than
three probes.
The total-pressure probes were of the Kiel type and were set at
the mean height of the blade at any given radius. A calibration of
the probes showed a negligible error for a flow-angle range of 400,
so the probes were set as nearly parallel to the blades as possible.
The static pressure was measured through 0.030-inch-diameter ori-
fices in the impeller hub. In addition to these static measurements,
the pressure along both the driving and the trailing blade faces
(defined in fig. 3(a)) was measured at the mean height at each radius,
and at five equally spaced heights at radii of 14, 18, and 221 inches
2
as shown in figure 3(a). A static pressure was measured in the center
of the passage at the 19-inch radius in alternate passages. Altogether,
148 pressures were measured an the impeller.
Pressure-transfer device. - In order to transfer the pressures
from the rotating impeller to the stationary measuring station, a
pressure-transfer device was necessary. The device used with the
48-inch compressor was a 21-cell, sealed ball-bearing type; figure 4
shows a sketch of a section of the pressure-transfer device. Each
pressure-transfer unit consists of a cavity around the shaft at each
pressure-tube outlet; an inner and outer spacer and two sealed ball
bearings are used to form this cavity. The pressure is transferred from
the rotating shaft through a hole in the inner spacer to the cavity and
thence to the stationary outer spacer. The neoprene seals of the bear-
ing prevent leakage from one transfer unit to the next; the rubber seal
rings around the inner and outer races of the bearings also prevent
leakage around the outer surfaces of the bearings. The whole unit is
surrounded by a water jacket, which keeps the bearings cool during
operation. Preliminary checks of each transfer unit showed no leakage
with vacuums up to 26 inches of mercury in the cavity.3
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Michel, Donald J.; Ginsburg, Ambrose & Mizisin, John. Experimental Investigation of Flow in the Rotating Passages of a 48-Inch Impeller at Low Tip Speeds, report, June 26, 1951; (https://digital.library.unt.edu/ark:/67531/metadc58806/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.