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National Advisory Committee for Aeronautics, Technical Notes - Impingement of Water Droplets on an Ellipsoid with Fineness Ratio 10 in Axisymmetric Flow

The presence of radomes and instruments that are sensitive to water
films or ice formations in the nose section of all-weather aircraft and
missiles necessitates a knowledge of the droplet impingement character-
istics of bodies of revolution. Because it is possible to approximate
many of these bodies with an ellipsoid of revolution, droplet trajecto-
ries about an ellipsoid of revolution with a fineness ratio of 10 were
computed for incompressible axisymmetric air flow. From the computed
droplet trajectories, the following impingement characteristics of the
ellipsoid surface were obtained and are presented in terms of dimensions
less parameters: (1) total rate of water impingement, (2) extent of
droplet impingement zone, and (5) local rate of water impingement. These
impingement characteristics are compared briefly with those previously
reported for an ellipsoid of revolution with a fineness ratio of 5.

The data presented herein are a continuation of the study reported
in reference 1 on the impingement of cloud droplets on a prolate ellips-
oid of revolution. The calculations discussed in reference 1 for an
ellipsoid with a fineness ratio of 5 (20 percent thick) were extended
for this report to an.ellipsoid of fineness ratio of 10 (10 percent
thick). As mentioned in the reference cited, a prolate ellipsoid of
revolution is a good approximation in the determination of cloud-droplet
impingement for many body shapes used for radomes, rocket pods, and
bombs. The data presented herein, along with the results presented in
reference 1, permit the estimation of impingement characteristics on
many of these bodies.

The traJectories of atmospheric water drOplets about a prolate
ellipsoid of revolution with a fineness ratio of 10 moving at subsonic
velocities at zero angle of attack were calculated with the aid of a
differetial analyzer at the NACA Lewis laboratory. From the computed
trajectories, the rate, the distribution, and surface extent of impinging
water were obtained and are summarized in this report in terms of dimen—
sionless parameters.