University of Arizona engineers are installing three 20-foot-long tubes for a new high-speed wind tunnel in the Aerospace and Mechanical Engineering Building. The Office of Navy Research (ONR) funded them with $2 million to study problems of instability and materials failure for aircraft and missiles flying at highly supersonic, or hypersonic, speeds of Mach 5 and above.
The wind tunnel under construction, expected to be ready for testing in spring 2018, is a low-disturbance, or quiet, Mach 4 tunnel. A second quiet tunnel, slated for completion in 2020, will shoot bursts of air at Mach 5, five times the speed of sound — about 3,800 mph. These new facilities will supplement the UA's existing wind tunnels, where researchers conduct experiments at subsonic and supersonic speeds.
Tubes for the new high speed wind tunnel are in front of one of the Arizona researchers
Hypersonics on the Edge
At speeds of Mach 5 and higher, the air begins to change chemically and becomes an electrically charged field. Craig, Fasel and Tumin are studying the complex (and still poorly understood) phenomena that occur at the boundary layer between laminar and turbulent airflows at such high speeds.
"Whenever you've got anything flying through the air, a thin layer of air forms over its surface," Craig explained. "That layer may flow in a smooth or laminar fashion, like honey pouring from a jar, or in a chaotic, turbulent way, like turning on a faucet at full blast."
When vehicles traveling at hypersonic speeds encounter airflows at the laminar-turbulent boundary, they experience significantly increased drag and become dangerously hot. Such aerothermodynamic heating is why rockets require deep layers of thermal insulation to keep them from burning up upon re-entering Earth's atmosphere.