Cloud-droplet ingestion in engine inlets with inlet velocity ratios of 1.0 and 0.7 Page: 3 of 53
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NACA TN 3593
reasonable approximations to those found on aircraft. The results of
the studies on the two simple shapes lead to important general con-
cepts on water ingestion into inlets of this type.
DESCRIPTION OF CONFIGURATIONS
In order to make a study of impingement on inlets, it is necessary
to devise a model configuration for which the air-flow field can be ob- w
tained and which reasonably represents the actual case of an inlet on 0
an airplane. The models chosen for this study are basically dependent
on the air velocity flow field surrounding a prolate ellipsoid of revo-
lution. Both inlet configurations consist of an annulus surrounding an
ellipsoid of revolution as the forebody.
The inlets differ somewhat in physical appearance as well as in
the entrance velocity of the air. In one inlet configuration, the cowl,
or outer wall, is infinitely thin and conforms to the shape of an air
streamline. With this inlet there are many possible locations of the
outer wall with respect to the ellipsoid forebody. A possible configura-
tion is shown in figure 1. The cowl of the other inlet configuration
has a slight thickness, as shown in figure 2. This outer wall has a
fixed configuration with respect to the ellipsoid forebody AB. The
inner surface of the cowl and the inlet inner wall are straight and
parallel. Either of the inlets shown in figures 1 and 2 may be a com-
plete annulus surrounding the forebody or a sector of an annulus such
as would be found in side ram-scoop inlets.
The ellipsoid chosen for this study is 10-percent thick (fineness
ratio of 10). The problem is limited to an angle of attack of 00 be-
tween the major axis of the ellipsoid and the free-stream air, because
the facile methods of calculating the flow field and trajectories are
limited to 00,
Each of the two configurations has an associated inlet velocity
ratio, which is defined as the ratio of the velocity at the inlet en-
trance to the free-stream velocity. For configuration 1 (fig. 1), the
inlet velocity ratio is nominally 1.0. (Precise calculations show that
the inlet velocity ratio may vary from 0.98 to 1.02, depending on the.
location of the inlet entrance.) The inlet velocity ratio for config-
uration 2 (fig. 2) is nominally 0.7 (0.714, actually). A particular
air-flow field is associated with each velocity ratio. The methods used
in calculating the two flow-field patterns produced a cowl and inner
wall with a slight difference in geometrical shape for the two inlets.
In spite of this, the difference in velocity ratio is not caused princi-
pally by the difference in geometry, but rather by differences in flow
requirements. As will be discussed further, the slight cowl thickness
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Brun, Rinaldo J. Cloud-droplet ingestion in engine inlets with inlet velocity ratios of 1.0 and 0.7, report, January 1956; (digital.library.unt.edu/ark:/67531/metadc55936/m1/3/: accessed July 22, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.