windtunnel

A wind tunnel is a research facility that produces a controlled stream of gas, typically air, used to study aerodynamic forces and flows around solid bodies such as aircraft, cars, or buildings. By placing a model in the flow and measuring forces, pressures, and flow characteristics, engineers can assess performance, optimize shapes, and predict in-service behavior.

Wind tunnels are categorized by speed regime: subsonic, transonic, supersonic, and hypersonic, corresponding to Mach numbers. They can be open-jet, open-return, or closed-loop (recirculating) in which the flow is directed back through a return path. Some facilities are cryogenic or pressure-fed to achieve higher Reynolds numbers or to simulate dense gases.

Key components include the test section where the model is mounted on a balance or force-measurement system; flow conditioning devices such as honeycomb and screens to straighten the flow; a drive system with a blower or compressor; and instrumentation for pressure taps, force and moment measurements, and flow diagnostics such as hot-wire anemometry or particle-image velocimetry. In a closed-loop tunnel, a contraction and settling chamber improve uniformity; in a cryogenic tunnel, the air is cooled to raise density.

Historically, wind tunnels emerged in the late 19th century, with early work by Francis Wenham and later developments culminating in the 20th century. They have been central to aerospace design, automotive engineering, architectural wind-load analysis, sports equipment development, and various research fields. A major consideration is achieving dynamic similarity, using Reynolds and Mach numbers to relate model behavior to real-scale objects; designers may use corrections or specialized facilities to address wall effects and scale limitations.