Experimental investigation of a drop impacting on wetted spheres

• We performed experiments concerning a single drop impact on wetted spheres.
• The sphere-drop curvature ratio can greatly influence the splashing thresholds.
• The spreading factor can be increased by decreasing the curvature ratio.
• Weber number influences on the spreading factor are minor.
• A linear model for the spreading factor is proposed.

Numerous experiments were performed to investigate a heptane drop impact dynamics on wetted spheres using a high speed camera. Outcomes after impact include spreading at a low impact Weber number and splashing at a high value. Limits between the two outcomes can be greatly affected by the sphere-drop curvature ratio ranging in 0.090–0.448. Additionally, the spreading process on wetted spherical surfaces is discussed in detail. The spreading factor defined as the ratio between the spreading area and the drop surface area can be increased by increasing the curvature ratio or by reducing liquid viscosity, while the effect of the increment in the Weber number is minor. It is found that the spreading factor follows a linear law with dimensionless time, which is confirmed by the butanol drop spreading as well. Finally, concerning different curvature ratios and fluids, many coefficients with respect to the linear law are obtained to predict the spreading scale by regressing the experimental data.

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