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National Advisory Committee for Aeronautics, Technical Notes - Impingement of Water Droplets on NACA 651-208 and 651-212 Airfoils at 4° Angle of Attack

As part of a comprehensive research program directed toward an
appraisal of the problem of ice prevention on high—speed aircraft, an
investigation of the impingement of cloud droplets on airfoils and other
aerodynamic bodies has been undertaken at the NACA.Lewis laboratory. The
investigation includes a study of the extent of impingement on low-drag
airfoils and the rate of droplet impingement per unit area of the airfoil
surface affected.

Previous investigators have calculated the water droplet
trajectories for cylinders (refs. 1 to 6) and for Joukowski air-
foils (refs. 7 and 8). An empirical method for determining area, rate,
and distribution of water-droplet impingement on airfoils of arbitrary
sections is presented in reference 9. The method is more firmly estab—
lished for lS—percent—thick airfoils resembling Joukowski airfoil sec-
tions than for low-drag airfoils, because the basic data used in devel-
oping the empirical method were obtained for four Joukowski airfoil sec—
tions but for only one low-drag section. Some impingement data for an
NACA 651-212 airfoil, which is a lZ-percent-thick low—drag section, are
presented in reference 10. Recent developments in high—speed aircraft
necessitate further water—droplet trajectory studies on low—drag air—
foils, particularly for thin sections, in order to determine the effect
of thickness ratio on droplet impingement.

The studies presented in this report are for 8-percent- and 12-
percent-thick wings designated as NACA.651-208 and 651-212 airfoils,
respectively, each placed at an angle of attack of 4°. The results pre—
sented are applicable to the NACA_651—208 airfoil and the NASA 851—212
airfoil under the following conditions: chord lengths from 2 to 20 feet;
altitudes from 1000 to 55,000 feet; airplane speeds from 150 miles per
hour to the flight critical Mach number; droplet diameters from 5 to
100 microns; and an angle of attack of 40. The flight critical Mach num-
ber is defined as the lowest flight speed which results in sonic veloc-
ity at some location on the airfoil.