Characteristics of runback ice accretions on airfoils and their aerodynamic effects

The initial results of a research program to investigate runback ice accretions due to hot-air ice protection systems, scaling of external flow parameters for testing thermal systems and the resulting aerodynamic effects are presented. The scaling of external flow parameters for testing thermal anti-icing systems in icing tunnel investigations was developed and tested. An icing tunnel test was conducted at the NASA Glenn Icing Research Tunnel to evaluate three scaling methods developed to match thermodynamic and droplet impingement parameters. A typical business jet wing section with a hot-air anti-icing system was used for the test. Data collected from the test included surface temperatures (using both thermocouples and an IR camera), photographs, high definition video, tracings and molds. Results of the scaling analysis showed that a useful and qualitatively accurate scaling method was developed for scaling thermal anti-icing systems for ground testing. However, further development and investigation of the method and governing equations is required, including generating full-scale runback ice accretions for quantitative evaluation of the scaling methods. A wind tunnel test was also conducted to evaluate the aerodynamic performance effects of simulated ice shapes based on the shapes observed in the icing tunnel test. Aerodynamic testing revealed significant aerodynamic penalties for all flight conditions tested.