How Does a Wind Tunnel Work?

Wind tunnels simulate flight conditions on the ground by moving air past a fixed object rather than moving the object through still air. Large fans or compressors drive air through a contraction cone that accelerates and smooths the flow before it reaches the test section. Instruments measure lift, drag, and side forces on the model via strain-gauge balances, while smoke, tufts, or laser-based techniques visualise airflow. Subsonic tunnels test at speeds below Mach 1; supersonic and hypersonic tunnels can reach Mach 5–20+. NASA's National Transonic Facility can test at flight-realistic Reynolds numbers with cryogenic nitrogen-cooled air.