Investigation of Aerodynamic and Icing Characteristics of a Flush Alternate-Inlet Induction-System Air Scoop Page: 9 of 44
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NACA RM E53E07 7
The effect of icing on the top-deck pressure distribution is shown
in figure 7, which presents a comparison of typical distributions dry
and after 8 minutes of icing with the ram inlet in operation. The most
significant result is the decrease in pressure recovery at the front of
the top deck. The pressures elsewhere over the top deck were fairly
uniform and showed only a slight decrease despite the presence of large
rough ice formations on the inlet lips.
Alternate-Inlet Tests
Clear air. - The average top-deck pressure recovery for the alter-
nate inlet in clear air is presented in figure 8 as a function of the
inlet mass-flow ratio. In contrast to the excellent recovery character-
istics of the ram inlet, the alternate inlet gave negative recovery over
the whole range of mass-flow ratios with values as great as 1/3 of the
test-section dynamic pressure. The poor performance of the alternate
inlet is attributed to the excessive divergence and ramp angles of the
inlet design. The negative values of the pressure recovery result from
the definition of recovery coefficient in terms of gage total pressures
and stream dynamic pressures. The negative values of the pressure recov-
ery indicate not a reverse air flow but a loss in energy which had to be
supplied by the exhauster. Considerable scatter of the data resulted
and poorer recovery was obtained at the 40 angle of attack condition than
at 00. In an effort to determine the cause of this poor recovery, tuft
studies were made over the entire alternate-inlet area. These studies
indicated considerable flow instability and separation over the inlet
ramp, particularly on the sides of the ramp and at the inlet lip. Total-
pressure rakes were also installed at three lateral stations at the
alternate-inlet lip. The results obtained from these rake measurements
are presented in figures 9 and 10 for two angles of attack at various
mass flows. The pressure surveys showed poor recovery at the inlet lip
with considerable nonuniformity in the flow existing in both the hori-
zontal and vertical planes. Only at the center of the inlet and at the
higher mass flows, particularly at an angle of attack of 00, was good
recovery obtained. For this reason only the center area of the inlet
should, in general, be used in evaluating the water-exclusion perform-
ance of the alternate inlet.
Icing. - The variation of the average top-deck pressure recovery
with icing time for the alternate inlet, is shown in figure 11 for
constant liquid-water content and droplet-size conditions at various
mass-flow ratios and tunnel-air temperatures. The rates of change in
recovery at the higher temperature were practically identical, and only
a slightly greater rate of change was obtained at the low-temperature
conditions. The poorer recovery obtained at the lower temperature prob-
ably resulted from the presence of frost on the alternate-inlet ramp
and forebody. No icing of the carburetor screen was obtained at the
higher temperature, while only a small deposit of rime ice was obtained
on the screen after 45 minutes of icing at 00 F.
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Lewis, James P. Investigation of Aerodynamic and Icing Characteristics of a Flush Alternate-Inlet Induction-System Air Scoop, report, July 24, 1953; (https://digital.library.unt.edu/ark:/67531/metadc59807/m1/9/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.