Investigation of Liquid Film Atomization from the Trailing Edge of an Airfoil in a High-Speed Flow- Effect of Trailing Edge Thickness

Abstract This study investigates the effect of trailing edge thickness on liquid sheet breakup using NACA0012 airfoils with rounded trailing edges of 0.5 mm, 1.0 mm, and 2.0 mm, in high-speed airflow. Water was introduced on the airfoil surface through 26 holes, each 0.5 mm in diameter and spaced 1 mm apart. These holes were located at 65 mm upstream of the trailing edge along the approximately 100 mm chord length. A variety of experimental techniques were implemented to analyze liquid film breakup and droplet behavior. High-speed video imaging captured film flow on the surface, the accumulation of liquid, ligament formation, and breakup at the trailing edge. Microscopic high-speed imaging was used to observe droplet behavior as a function of distance downstream of the trailing edge. The results show that thicker trailing edges and higher liquid mass flow rates promote liquid accumulation at the trailing edge. This, in turn, leads to increased ligament length and sheet breakup time. In the region just downstream of the ligament breakup, droplet sizes increase with increasing trailing edge thickness and liquid volume flow rate. Once the secondary atomization is complete (~70 mm from the trailing edge), the drop sizes were found to be less affected by the trailing edge thickness and liquid flow and mainly determined by the air velocity. An analysis of variance was performed to predict SMD as a function of weber number, air to liquid mass flow rate, downstream distance and trailing edge thickness.