windtunnels

Windtunnels are facilities designed to study the aerodynamic properties of objects by generating a controlled airstream over models. They enable measurement of forces, moments, pressure distributions, and flow characteristics under repeatable conditions. A typical wind tunnel consists of an air-moving system, a contraction to accelerate and direct the flow, a test section where the model is placed, and a diffuser and return system to recover energy. Instrumentation such as a six-component force balance, pressure taps, hot-wire anemometers, and flow visualization tools are used to collect data.

Operation and modeling: The wind tunnel creates a steady, uniform flow in the test section. Researchers select flow speed (Mach number) and Reynolds number to achieve similarity with the real object. Models are often scaled, and sometimes with active flow control. Data include lift, drag, moment coefficients, pressure distributions, and flow separation locations.

Types and ranges: Subsonic wind tunnels operate at Mach numbers below about 0.3–0.5; transonic, supersonic, and hypersonic tunnels handle higher speeds, often using different shock management and nozzle designs. Open-circuit (open-return) tunnels draw air from the room and exhaust it back; closed-circuit (recirculating) tunnels loop air through a closed path. There are also specialized wind tunnels for indoor airflows, turbulence studies, or water tunnels for marine engineering.

Applications and limitations: Wind tunnels are essential in aerospace, automotive, civil engineering, and sports equipment design. They provide controlled, repeatable testing but can be expensive to build and operate, and numerical simulations may be needed to supplement scaling and extrapolation to full size.