Experimental Techniques for Hypersonic FLows

Abstract

Hypersonic research needs various experimental techniques in order to cover the requirements of different flow conditions of hypersonic flight. The lecture will treat those techniques which are necessary if important flow conditions of a re-entry as well as a hypersonic transport vehicle are simulated in ground based facilities. At altitudes of more than 120 km, when free molecular flow conditions are dominant, not only the measurement of the overall flow quantities like forces and pressure but also the composition of the gas, the state of the internal degrees of freedom of the molecules, and the interaction of the molecules with the surface have to be considered. Hence temperatures and species concentration, using LIF and CARS and other spectroscopic techniques, are important. More or less the same is true if hypersonic flight at lower altitudes is simulated, meaning at more continuum but still high Mach number flow conditions. In addition to force and pressure measurements, heat flux measurements by means of various gauges have to be performed. A quite new aspect arises if advanced hypersonic transporter flight has to be simulated in wind tunnels. The so called "hot experimental technique" requires new kinds of model techniques and instrumentationfar from being develped. Examples of application of the techniques, partly related to the high enthalphy wind tunnels HEG and LBK and to the low density wind tunnel VXG of the DLR, will be given.