High speed flow visualization at HEG

The High Enthalpy Shock Tunnel Gottingen (HEG) of the German Aerospace Center (DLR) is one of the largest free piston driven shock tunnels capable of simulating high temperature effects in re-entry flows. Full utilization of such a ground based high enthalpy impulse facility, with typical test times in the order of a few milliseconds, requires detailed knowledge of the test section flow, and its starting process. Further, the temporal development of the model flow must be known in order to assure that a steady flow field has developed during the test time window. Therefore, in addition of time resolved model surface property measurements such as pressure and heat transfer, a high speed shadowgraph and schlieren system was implemented at HEG. For the first tests with the new system a cylinder flow was chosen. The large shock stand-off distance of the cylinder flow allows high spatially resolved optical measurements. Due to the sensitivity of the shock stand-off distance to the gas composition, the measurements are also a valuable aid in detecting driver gas contamination in the test section. The results presented in this paper are related to HEG operating condition III (h(0) = 13.4 MJ/kg, p(0) = 48.3 MPa, Ma = 8.7, u(infinity)=4776 m/s, T-infinity=694 K, p(infinity)=687 Pa, rho(infinity) = 3.255 g/m(3)).