Published online by Cambridge University Press: 04 July 2016
In recent years the need for high Reynolds number wind tunnel facilities has led to the development of the Cryo-genic Wind Tunnel. In this type of tunnel, the flow is cooled to extremely low temperatures, with the result that at constant Mach number the Reynolds number is greatly increased whilst the power required to drive the tunnel is reduced. The cryogenic tunnel incorporates a means of injecting liquid nitrogen into the free stream. The evaporation of this liquid cools the flow and some or all of the tunnel structure. Once the required low temperature has been reached a steady flow of liquid nitrogen into the tunnel and gaseous nitrogen out balances the heat input through the walls and from the fan and maintains constant pressure in the circuit. In addition to providing increased Reynolds numbers at reduced drive power, the cryogenic wind tunnel possesses numerous other advantages over its ambient temperature counterpart. For a detailed theory see Ref. 1.