Description:

From raindrops striking a windshield to coffee splashing on a table, drop impact is a common occurrence in everyday life and plays a key role in many natural and industrial processes, including soil erosion, spray coating, and inkjet printing. In this work, we explore two unconventional aspects of this familiar fluid phenomenon, uncovering the fascinating physics behind what appears to be a mundane process.

First, we investigate the impact force, pressure, and shear stress distribution during drop impact, highlighting their influence on the deformation and erosion of granular surfaces. We introduce a novel technique, high-speed stress microscopy, which enables real-time imaging of the evolving shape, impact force, and stress distribution of drops across a broad range of Reynolds numbers (Re). Our measurements capture the propagation of a non-central pressure peak and the formation of a shockwave in the early stages of drop impact. Additionally, we examine the morphology of impact craters on granular surfaces and discover an intriguing parallel between drop-impact cratering and meteoroid impact cratering.

Second, we study the impact of non-Newtonian fluids, specifically shear-thinning and shear-thickening liquids, which are directly relevant to important industrial coating and printing processes. By combining experiments with numerical simulations, we reveal the rapid energy conversion that occurs during an impact event and demonstrate how the behavior of non-Newtonian drops maps onto that of Newtonian drops. Our findings establish a universal scaling law that successfully predicts the maximum spreading of non-Newtonian drops.  

Xiang Cheng, Professor, University of Minnesota

Host: Michelle Driscoll