LARGE SECOND GENERATION OF CRYOGENIC TUNNELS.

Ten years ago, at NASA's Langley Research Center, began an R&D program that has led to a series of new and unique transonic wind tunnels that provide high-Reynolds-number simulation of viscous flow effects including the critical interactions between shocks and boundary layers encountered on advanced aircraft and spacecraft designs. In October of 1971 a small group of researchers and technicians at Langley began developing an approach that was to offer a new option: operating at very low temperature. During the next four years, an extensive program evolved at Langley on technology for a fan-driven, continuous-flow cryogenic wind tunnel. This work culminated in an approach - selected over several competing ambient-temperature intermitter-type tunnel concepts - for the construction of a NASA Transonic Research Tunnel (TRT) to be constructed at Langley. However, events were beginning to take place both in the U. S. and in Europe, that would broaden interest in the concept until today at least a dozen cryogenic tunnels are operating or under construction throughout the world. They cover a range of sizes, stagnation pressures, and types of drive.