| A methodology has been developed to predict the growth of rime ice, and the resulting aerodynamic penalty, on unprotected, subcritical, airfoil surfaces. The system of equations governing the trajectory of a water droplet in the airfoil flowfield is developed and a numerical solution is obtained to predict the mass flux of super cooled water droplets impinging on the airfoil leading edge. By assuming that the droplets freeze on impact, a rime ice shape is predicted. The effect of time on the ice growth is modeled by a time-stepping procedure where the flowfield and droplet mass flux are updated periodically through the ice accretion process. A similarity analysis is performed for the rime icing problem. Two new similarity parameters, the trajectory similarity parameter and accumulation parameter, are found to govern the accretion of rime ice. In addition an analytical solution is presented for Langmuir's classical modified inertia parameter. The aerodynamic evaluation of the effect of the ice accretion on airfoil performance is determined using an existing airfoil analysis code with empirical corrections. The change in maximum lift coefficient is found from an analysis of the new iced airfoil shape. The drag correction needed due to the severe surface roughness is formulated from existing iced airfoil and rough airfoil data.; A small scale wind tunnel test was conducted to determine the change in airfoil performance due to a simulated rime ice shape. The model was tested in four configurations; clean, with leading edge roughness, with a smooth rime ice shape, and with a rough rime ice shape. The detailed pressure distributions in addition to C(, ), C(,d), and C(,m) are reported. The present method is evaluated using the experimental data from this study as well as data from the literature. The predicted droplet impingement rates, rime ice shapes, scaling analysis, and airfoil performance all agree well with experiment. This study has developed a methodology for analytically predicting rime ice effects and has identified the research needed to improve the method. |
