Phase Step Holographic Interferometry in Hypervelocity, High Temperature Flows

Abstract

A holographic interferometer with a 300 mm field of view for the flow visualisation in the high enthalpy shock tunnel (HEG) has been installed and upgraded. This world's largest free piston driven shock tunnel is located at the German Aerospace Research Esstablishment (DLR) in Goettingen. Ist interferometer applies the phase step technique. This method enables computerized evaluation of the holograms to create high quality interferograms by increasing the signal to noise ratio. Complete flow field density gradients around two dimensional models are calculated from the interferograms.Because of the high spatial resolution of the holograms, large optical enlargements and Hologram-Schlieren is made possible. Typicalresults which are presented, demonstrate is feasibility and underlinethe demand on optical techniques like the holographic interferometry to study the complex flow phenomena of high temperature reacting flows produced by the tunnel. Thus it is shown that the tunnel works in the desired flow range of nonequilibrium gas state.