Technical note A simple shock tunnel driver gas detector

A device has been developed to detect the arrival of the driver gas in a shock tunnel. The detector is small enough to be used in conjunction with other experiments. It works by choking a duct when the specific heat ratio is increased past a critical value. Times are given for the onset of a 7.5% contamination level in flows with freestream enthalpies ranging from 3–9 MJ/kg. These results are compared with and are shown to be in agreement with measurements made with a mass spectrometer. Results displaying the rate at which the test gas is contaminated are also given.