Cryogenic Wind Tunnels - A Brief Review

Abstract

Until recently, the problem of low test Reynolds numbers has limited the usefulness of wind tunnels, especially at transonic speeds. Perhaps the best solution to the problem of low Reynolds number comes by operating a relatively big tunnel (2 × 2 m test section or larger) at a relatively high pressure (up to 5 bar) and at cryogenic temperatures using nitrogen (or nitrogen-rich air) as the test gas. The first cryogenic wind tunnel was a low-speed tunnel built at the NASA Langley Research Center in 1972. Since then, workers at research centers around the world have started a large number of cryogenic wind-tunnel projects. The degree of success of the various projects depends on many things. The more successful cryogenic tunnels reflect a skillful combination of cryogenic technology with wind-tunnel technology. I briefly review the principles of operation and the history of cryogenic wind tunnels. I describe some of the more significant cryogenic wind-tunnel projects not covered by other papers at this conference. I also describe some of the problems we must solve before we can realize the full potential of cryogenic wind tunnels. Finally, I briefly describe the heavy-gas option for high Reynolds number testing.