University of Osaka researchers discover why high-speed particles rebound more strongly from wet surfaces

University of Osaka scientists find that cavitation in wet collisions reduces liquid drag, causing high-speed particles to rebound with more energy.

By: AXL Media

Published: Apr 28, 2026, 9:34 AM EDT

Source: Information for this report was sourced from EurekAlert!

The Counterintuitive Physics of High Velocity Impacts on Wet Walls

Researchers at the University of Osaka have identified a surprising phenomenon where particles traveling at high speeds bounce off wet surfaces with more kinetic energy than expected. Traditionally, liquid films are used as a cushioning agent to absorb impact energy and protect internal components from debris damage. However, the study published in the International Journal of Multiphase Flow demonstrates that at speeds reaching tens of meters per second, the liquid film fails to act as a traditional brake, instead allowing for a much stronger rebound that could affect the structural integrity of high speed machinery.

A Morphological Shift from Liquid Bridges to Protective Domes

The investigation utilized a combination of experimental high speed photography and advanced numerical simulations to visualize the behavior of the liquid during the millisecond of impact. The team observed that as the impact speed increases, the post collision liquid film undergoes a dramatic structural change. While slower impacts result in a stringy bridge of liquid that pulls the particle back, high speed collisions cause the fluid to form a dome shape that encapsulates the gap between the particle and the wall. This transition is fundamental to the change in rebound strength observed in the trials.

Cavitation as the Primary Driver for Enhanced Rebound Strength

The catalyst for this structural change is cavitation, a process triggered by an intense drop in pressure within the particle wall gap immediately following the collision. When the internal pressure falls below the saturated vapor pressure, a vapor cavity rapidly forms. According to lead author Hironori Hashimoto, this cavitation is what gives rise to the dome shape and fundamentally alters the collision dynamics. By creating this vapor pocket, the physical interaction between the particle and the liquid is severed before the liquid can exert a significant slowing force.