What does a high Rayleigh number indicate?

A high Rayleigh number indicates a strong buoyancy-driven flow. The Rayleigh number is a dimensionless quantity used in fluid dynamics that measures the ratio of buoyant forces to viscous forces within a fluid. When the Rayleigh number is high, it signifies that buoyancy forces (which arise due to temperature differences within the fluid) are dominating over the viscous forces that resist flow. In such cases, this can lead to significant convection currents as warmer, less dense fluid rises and cooler, denser fluid sinks, resulting in vigorous mixing and heat transfer within the fluid. This is particularly important in processes such as natural convection, where heat transfer is driven by buoyancy rather than mechanical means.