Instrumentation techniques of the Aachen shock tunnel TH2

Abstract

High enthalpy short-duration facilities are mainly used to simulate the hypersonic flow during a reentry into an atmosphere. The special operational features of these facilities put somewhat different requirements on the instrumentation compared to usual supersonic or hypersonic blow down tunnels. The short running times of the order of some milliseconds require sensors with a very fast response and rise time. To avoid time lags by tubings, usually the sensors are installed flush into the model wall or a very short distance behind it. This implies that they have to withstand the impact of small particles of high energy, which are transported by the flow. This is the most important reason why for heat flux measurement at severe flow conditions very robust coaxial thermocouples are used. To allow also for a pressure measurement almost at the same location a pressure tap is drilled through the thermocouple. From the measurement of the stagnation point heat flux and the Pitot pressure some information can be found about the free stream. More detailed free stream measurements are possible with a mass flux gauge an a static pressure probe. Due to their complexity the development of these gauges require intensive testing and the support of numerical calculations. The same holds for the development of a force balance which meets the requirement of a shock tunnel application.