EXPERIMENTAL-TECHNIQUES FOR THE INVESTIGATION OF RELAXATION PROCESSES BEHIND STRONG SHOCK-WAVES IN AIR

The conditions in the flow around reentry vehicles are characterized by strong detached shock waves which cause real gas effects. Shock tubes are very suitable instruments for investigating these phenomena in detail over a wide range of reentry conditions. In the present paper experimental techniques for the investigation of different relaxation processes in air behind strong incident shock waves are presented. Since all thermodynamic properties of the gas as well as the flow velocity change very rapidly behind the shock wave, it is necessary to employ different measuring techniques simultaneously for obtaining results for the time dependence of these quantities. The shock tube used in these experiments was equipped with several pressure gauges, with Langmuir probes and with an infrared tunable diode laser absorption spectrometer (IR-TDLAS) operated in the spectral range near 5 mu m. Evaluating the signals of these instruments the velocities of the shock front and of the contact surface and ionization relaxation times have been determined; the pressure, the ion concentration and the rotational-vibrational excitation of the NO-molecule can be determined as functions of time.