Sand’bubbles’flow like liquid

摘要

Gravitational instabilities in granular particles of different densities could help us understand how structures such as mudslides and volcanoes formed.A Columbia University team layered two types of sand horizontally,with lighter granules at the bottom and heavier granules at the top.When subject to vertical vibration and upward gas flow,the lighter sand formed”fingers”before rising further and breaking off into bubbles.Chris Boyce,Assistant Professor of Engineering at Columbia University,said:”We think our discovery is transformational.We have found a granular analog of one of the last major fluid mechanical instabilities.”