The Reynolds number is a dimensionless quantity in fluid dynamics used to predict how a fluid will flow—smoothly (laminar) or chaotically (turbulent). It is calculated using properties such as the fluid’s speed, density, viscosity, and a characteristic length (like pipe diameter).
When the Reynolds number is low (typically below 2000), fluid flows in orderly layers with minimal mixing—this is laminar flow. When the number is high (above 4000), the flow becomes turbulent, with swirling vortices and chaotic movement. In between lies a transition zone where flow can fluctuate between both states.
Engineers and scientists use the Reynolds number to design systems involving air or liquid movement, such as in pipelines, aircraft, and blood flow studies. It helps in predicting pressure drops, energy losses, and overall performance of fluid systems.