On the development of Doppler global velocimetry for cryogenic wind tunnels

A specially designed Doppler global velocimetry system (DGV, planar Doppler velocimetry) was tested in a high-speed cryogenic facility at Mach 0.3 to Mach 0.8 and pressures between 1.2 and 2.5 bar. The necessary seeding was achieved by injecting a mixture of gaseous nitrogen and water vapor into the dry and cold tunnel flow which then immediately formed a large amount of small ice crystals. As operational and access conditions are quite restrictive with respect to other facilities, DGV is currently considered the best choice for the non-intrusive measurement of flow fields. A comparison of DGV to the more wide-spread particle image velocimetry technique (PIV) is also given.