An Experimental Investigation of SLD Impingement on Airfoils and Simulated Ice Shapes

This paper presents experimental methods for investigating large droplet impingement dynamics and for obtaining small and large water droplet impingement data. Droplet impingement visualization experiments conducted in the Goodrich Icing Wind Tunnel with a 21-in chord NACA 0012 airfoil demonstrated considerable droplet splashing during impingement. The tests were performed for speeds in the range 50 to 175 mph and with cloud median volumetric diameters in the range of 11 to 270 microns. Extensive large droplet impingement tests were conducted at the NASA Glenn Icing Research Tunnel (IRT). Impingement data were obtained for a range of airfoil sections including three 36-inch chord airfoils (MS(1)-0317, GLC-305, and NACA 65₂-415), a 57-inch chord Twin Otter horizontal tail section and 22.5-minute and 45-minute LEWICE glaze ice shapes for the Twin Otter tail section. Small droplet impingement tests were also conducted for selected test models. The impingement experiments were performed with spray clouds having median volumetric diameters (MVD) of 11, 21, 79, 137 and 168 microns and for a range of angles of attack. All the impingement experiments were conducted at an air speed of 175 mph corresponding to a Reynolds number of approximately 1.6 million per foot. The maximum difference in the peak impingement efficiency from the average of repeated test runs ranged from 0.2% to 11% for 96% of the experimental cases presented. In addition to the experimental impingement provided in this paper, analysis impingement data obtained with the LEWICE-2D computer code for all configurations tested are also presented. In general, good agreement was observed between experiment and analysis for the small droplet cases. For all the large droplet cases, however, the analysis produced higher impingement efficiencies and larger impingement limits than the experiment. This discrepancy was attributed to water mass loss due to splashing experienced by the large droplets during impingement.