A Reevaluation of Appendix C Ice Roughness Using Laser Scanning

Many studies have been performed to quantify the formation and evolution of roughness on ice shapes created in Appendix C icing conditions, which exhibits supercooled liquid droplets ranging from 1-50 µm. For example Anderson and Shin (1997), Anderson et al. (1998), and Shin (1994) represent early studies of ice roughness during short-duration icing events measured in the Icing Research Tunnel at the NASA Glenn Research Center. In the historical literature, image analysis techniques were employed to characterize the roughness. Using multiple images of the roughness elements, these studies of roughness focused on extracting parametric representations of ice roughness elements. While the image analysis approach enabled many insights into icing physics, recent improvements in laser scanning approaches have revolutionized the process of ice accretion shape characterization. Additionally, McClain and Kreeger (2013) demonstrated a two-dimensional self-organizing map approach 1) to characterize the mean ice shape, 2) to unwrap a three-dimensional laser scan of an iced airfoil, and 3) to evaluate the ice roughness variations along the surface by employing a multi-variate statistical approach. For this study, the ice roughness developed on a 21-in. NACA 0012 at 0° angle of attack exposed to short duration Appendix C icing events similar to those used in the earlier studies were characterized using laser scanning. The resulting Appendix C roughness parameters are then compared to the historical measurements of Appendix C roughness.