3D numerical investigation of surface wettability induced runback water flow behavior

The blade icing problem seriously affects the power generation efficiency and safe operation of wind turbines. Employing a combination of active anti-icing methods combined with passive superhydrophobic surfaces has been recently proposed and shown some promise. Superhydrophobic surfaces have the capability to induce rapid breakup and shed of runback water on anti-icing surfaces, thereby preventing the runback ice formation to reduce energy consumption. This work investigates the influence of surface wettability on the flow behavior of runback water on a three-dimensional blade surface by using the Volume of Fluid (VOF) method. The flow and breakup characteristics of water film are examined on different surfaces with contact angles from 10° to 150°, and compared with experimental results. A theoretical model of liquid film flow evolution is formulated. It is found that a larger contact angle leads to a shorter evolution time from continuous water film to rivulets and beads-like flow, with earlier breakup and shedding from the surface. The chordwise location of breakup into rivulets shifts towards the leading edge with increasing contact angle, and the number of rivulets initially increases and then decreases as the contact angle rises, showing good agreement with the experimental observation. Furthermore, the velocity fluctuations of runback water along the streamwise are observed, primarily attributed to the thickness variation caused by breakup. Crucially, the breakup and shedding of runback water are closely associated with the formation of bulges at the head of the rivulets. A larger contact angle leads to a higher bulge that results in greater aerodynamic drag force exerted on the runback water, leading to easier breakup.