Convection—the rising of warm, buoyant fluid through cooler, denser fluid—occurs in the oceans, the atmosphere, Earth’s core and mantle, the stars, heated beakers and pots, and uncountable other natural and industrial systems. Despite that ubiquity, our understanding of the process remains incomplete, at least when the system is driven hard enough to become turbulent. To study the problem, researchers often turn to an idealized experiment: the Rayleigh—Bénard convection cell, a container of fluid heated from below and cooled from above.
The temperature gradient drives the convection. As hot, coherent plumes of fluid rise upward due to the buoyant force, they push aside material above them. Similarly, cold plumes detached from a thin layer at the top push aside material as they fall. The deflection of material, whether in a cell the size of a soda can or a swimming pool, sets up a thermal “wind” that circulates the upwelling and...
