Wind tunnel testing services provide test facilities and technical staff for aerodynamic testing. Tests may be performed on prototype aircraft, helicopters, trains, cars, or buildings. Wind tunnel testing services also perform general research and development (R&D) involving aerodynamics and aeromechanics. A wind tunnel is a tube-shaped or tunnel-like chamber that contains a test platform and a large fan. The fan blows a steady stream of air through the chamber in order to determine the effects of wind pressure on the test object, which remains fixed to the platform. Aerodynamics, the study of how air flows around an object, enables wind tunnel testing services to predict the effects of lift, drag, weight, and thrust. Lift is a measure of the aerodynamic force on an object perpendicular to the direction of the air flow. Drag is the aerodynamic force parallel to the relative airflow. Weight is the force due to gravity. Thrust is the forced generated by an object, such as an engine, under test.
Types of Wind Tunnels Used
Wind tunnel testing services use four basic types of wind tunnels: subsonic, transonic, supersonic, and hypersonic. Subsonic wind tunnels can achieve speeds up to 400 km/h and have an open return or return flow structure. Air is moved by a large, axial fan that overcomes viscous losses by increases in dynamic pressure. Transonic wind tunnels are similar in design to subsonic wind tunnels, but can achieve speeds close to the speed of sound (Mach 1). The highest speed is achieved in the test section. Because transonic testing reflects powerful shock waves, perforated or slotted walls are required. Wind tunnel testing services that use supersonic wind tunnels can perform tests at speeds greater than the speed of sound. Hypersonic wind tunnels can achieve speeds more than five times the speed of sound (Mach 5). Typically, wind tunnel testing services that offer supersonic testing or hypersonic testing specialize in military or aerospace applications.