Cryogenic wind tunnels for high Reynolds number testing

The present investigation has the objective to provide an overview of the development of cryogenic wind tunnels and their application to high Reynolds number testing. The current need for wind tunnels reflects the fact that many complex three-dimensional flows cannot yet be adequately dealt with analytically. Imperfections of wind tunnels are partly related to the fact that for most wind tunnel tests the Reynolds number is much too low. The best solution to this problem appears to be an operation of the tunnel at cryogenic temperatures (arbitrarily defined as temperatures of 150 K or less. In addition to decreasing the temperature, there are three other approaches for increasing the Reynolds number. These approaches include the use of a heavy gas, an increase in the model size, and an increase in pressure. Attention is given to the variable density tunnel concept, problems with high dynamic pressures, low-speed cryogenic tunnel results, transonic cryogenic tunnel tests, and the injection of liquid nitrogen into the tunnel.