An experimental investigation on the dynamic ice accretion and unsteady heat transfer over an airfoil surface with embedded initial ice roughness

In the present study, a comprehensive experimental study was conducted to evaluate the effects of initial ice roughness formed around the leading-edge of an airfoil model on the dynamic ice accretion and unsteady heat transfer processes over the airfoil surface. The experimental study was performed in the Icing Research Tunnel at Iowa State University, Two airfoil models with the same airfoil shape were manufactured by using a rapid protype machine for a comparative study, i.e., one test model was designed to have embedded initial ice roughness around the airfoil leading-edge and the other model having smooth airfoil leading-edge as the comparison baseline. During the experiments, while a high-speed imaging system was used to record the early-stage icing morphologies over the airfoil surfaces with and without the initial leading-edge roughness, an infrared (IR) thermal imaging system was also utilized to map the corresponding surface temperature distributions over the airfoil surfaces to quantify the unsteady heat transfer and dynamic icing, i.e., phase changing, processes under different test conditions. It was found that, the initial ice roughness formed around the airfoil leading-edge would affect the characteristics of local airflow, impingement of supercooled water droplets, collection and transport of impacted water mass, unsteady heat transfer and subsequent ice accretion processes dramatically. The initial ice roughness formed around the airfoil leading-edge would redistribute the impacted water mass, with more impacted water mass being captured and frozen over the roughness region. In addition, the initial ice roughness was also found to produce span-wise-alternating low- and high-momentum pathways (LMPs and HMPs, respectively), which can significantly affect the convective heat transfer and subsequent ice accretion processes over the airfoil surface.