Airflow

Airflow refers to the movement of air relative to a surrounding environment. It arises when there is a pressure difference, temperature or density differences causing buoyancy, or when external forcing such as fans, wind, or mechanical ventilation drives air through spaces or around objects. Airflow can be characterized by velocity fields, direction, and volumetric flow rate, typically measured in meters per second for velocity and cubic meters per hour or cubic feet per minute for flow rate.

The flow can be laminar, where air layers glide smoothly, or turbulent, where motion is chaotic and mixing is enhanced. The likelihood of turbulence is described by the Reynolds number, a dimensionless quantity that depends on flow speed, characteristic length, and air viscosity. In ducts and openings, boundary layers form near surfaces, reducing velocity and influencing heat and mass transfer.

In built environments, airflow governs ventilation, temperature control, and indoor air quality, affecting comfort and pollutant dispersion. In outdoor settings, airflow shapes weather patterns, cloud formation, and the transport of aerosols and heat.

Engineers study airflow using experimental methods such as wind tunnels and tracer gases, and numerical techniques like computational fluid dynamics, which solve the governing Navier-Stokes equations to predict velocity and pressure fields. Applications span HVAC design, aerospace, automotive aerodynamics, and environmental science. Understanding airflow helps optimize energy use, health outcomes, and the performance of systems interacting with the atmosphere.