BOUNDARY-LAYER TRANSITION-DETECTION IN A CRYOGENIC WIND-TUNNEL USING INFRARED IMAGING

Cryogenic wind tunnels are currently the only option available to test models of medium to large transport air-planes at high Reynolds numbers identical to those encountered in flight. This matching in Reynolds numbers is required for reproducing the flow viscous effects, most notably the laminar to turbulent boundary-layer transition. Infrared imaging is particularly attractive for transition detection in cryogenic wind tunnels because it is nonintrusive, fast, and provides a global view of the boundary-layer status on the model. An experimental method using a commercial 8- to 12-mu infrared imaging system was developed for transition detection in cryogenic wind tunnels. So far, transition has been detected at temperatures down to 170 K. At this temperature, tunnels with a pressurization capability of only a few atmospheres can generate transonic flows at Reynolds numbers beyond 3 x 10(8) per meter.