Performance of Twin-Duct Variable-Geometry Side Inlets at Mach Numbers of 1.5 to 2.0 Page: 5 of 34
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4 4 NACA RM E56KL5
In addition, second-ramp angles of 0 and 300 were tested as a means of
obtaining low stable mass-flow ratios at high Mach numbers.
Compression-surface boundary layer could be removed through perfora-
tions in the second ramp just ahead of the cowl. The perforations were
alined in successive rows in the flow direction for the-00-cant inlet
and staggered so that alternate rows were alined for the -50-cant inlet.
In addition, a flush slot in the second ramp just inside the cowl and a
combination of this slot and the perforations were investigated with the
o0-cant inlet. This configuration can be seen in figure 1(c). Bleed air
entered the fuselage cavity and was exhausted at the base of the model.
The effect of second-ramp angle on subsonic-diffuser area variation
is shown in figure 2. Duct cross sections are also indicated.
Instrumentation and Data Reduction
To determine the local flow conditions just upstream of the inlets,
two rakes with static- and total-pressure instrumentation (see figs. 3 and
4) were mounted on the fuselage at model station 34.78 ahead of-one of the
inlets, and two 60-half-angle wedges with total- and surface static-pressure
instrumentation were mounted at the same model station ahead of the other
inlet. The Pitot and static-pressure profiles obtained from the rake data
were used to compute the local total-pressure profile. The wedge data
were used to determine local Mach number ahead of the inlets and local
flow angularity with respect to the plane of the wedges. This plane was
normal to the fuselage surface and parallel to the fuselage centerline.
Some data were obtained with two total-pressure rakes just inside each
cowl at model station 41.00 with wall static-pressure orifices at the
ends of each rake. These rakes were used to obtain the total-pressure
profile at the entrance of the duct to aid in selecting a position for-a
Mach number sensor for second-ramp control. Each duct was instrumented
at model station 48.91 to record the static-pressure variation during
At the compressof-face station (model station 64.97), six equally
spaced rakes were employed. Each rake consisted of four total-pressure
tubes arranged for area-weighted averages and an additional tube located
immediately adjacent to the outer wall. Air distortion was computed from
all the total tubes, and pressure recovery was obtained from an average
of those tubes arranged for area-weighted averages. Downstream of these
rakes at model station 71.11 were located eight static-pressure orifices,
four in the outer wall and four in the centerbody. Mass-flow calculations
were made using the average static pressure obtained from these orifices
with the assumptions of a choked geometrical minimum area determined at
the duct exit by plug position and a plug discharge coefficient of 0.99.
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Yeager, Richard A.; Beheim, Milton A. & Klann, John L. Performance of Twin-Duct Variable-Geometry Side Inlets at Mach Numbers of 1.5 to 2.0, report, January 21, 1957; (https://digital.library.unt.edu/ark:/67531/metadc63208/m1/5/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.