Effects of Water Vapor on Cryogenic Wind Tunnels

Abstract

Cryogenic wind tunnels are capable of testing at flight equivalent conditions on scaled models to obtain full size results. To reach cryogenic temperatures the gas and much of the tunnel mass is cooled by injecting liquid nitrogen into the tunnel. During the cooling from ambient to cryogenic temperatures the thermal stress, liquid nitrogen consumption, time, and test gas dew point are critical to insure uniform and good flow quality in the test section. The dew point is critical because it shows the amount of water vapor within the tunnel circuit. A cooldown is not a problem if the gas dew point is low (< 233K) before the gas temperature drops below the dew point. If the dew point is not low while cooling, frost will from on the model and sections of the tunnel. This paper examines the sources of water vapor in a cryogenic wind tunnel, the effects it has on the tunnel operation, and the methods to manage the water vapor. The tunnel used in this study is the U.S. National Transonic Facility located at NASA Langley. Research Center.