The dynamical behaviors of water drop impacting and bouncing on an inclined hydrophobic surface

Abstract

Drop impacting on an inclined surface is currently a topical research area due to its broad industrial applications. However, a comprehensive investigation of drop bouncing outcomes is relatively lacking in the literature, especially at a high (> 60°) inclined angle. In this paper, the dynamical behaviors of water drop impacting and bouncing on an inclined hydrophobic surface are investigated with a numerical method. Specifically, we examine the effects of several key impacting factors including impacting velocity (Vi = 0.5–2.0 m/s), drop diameter (D0 = 1.5–2.5 mm), and inclined angle (β = 0°–80°) on impacting outcomes, sliding lengths of drop, drop leading and trailing edges (Ld, Llea, and Ltra), spreading diameters and maximum spreading diameters in both the tangential and lateral directions (Dtan, Dlat, Dtan_max, and Dlat_max). Four distinct outcomes take place on the variations of Vi, D0, and β. For the rebound and partial rebound outcomes, drop behaviors at β = 80° are quite different from β ≤ 60°, which is mainly caused by the liquid accumulation at drop head resulting from the drastic increase in tangential inertial force. For the same reason, the temporal variations of Dlat are more stable than Dtan, especially at a high β. Both Dtan_max and Dlat_max increase with Vi and D0 but reduce with β, owing to the increased normal inertial force. More significantly, scaling laws of the nondimensionalized maximum spreading diameters with the normal Weber number Dtan_max*∝WeNα1 and Dlat_max*∝WeNα2 are discovered where α1 and α2 decrease as β increases due to the smaller variations of Dtan_max* and Dlat_max* at larger β when impacting condition changes. These new findings provide a useful supplement to the currently insufficient understanding of the complicated phenomena of post-impacting drop behaviors on an inclined hydrophobic surface.