Shock tube experiments are a primary means of obtaining ground test data for the hypersonic regime. Accurate characterisation of the test gas is crucial to understanding experimental results. However, characterisation of the flows produced behind the shockwave has historically proven challenging. This paper applies a methodology to calculate the shocked test gas properties using the experimentally recovered shock speed profile. Static pressure, Pitot pressure and heat transfer predictions are found to closely match the experimental data for a range of shock trajectories with both Argon and Air test gases. Thermochemical variations in the test gases are found to depend strongly upon variations in shock speed along the tube, and it is shown that characterisation of the test gases requires accommodating the influence of wave effects associated with the varying shock speed. Tube diameter is found to influence test time significantly, and also the magnitude of nonuniformities in the test gas. Location and number of shock timing stations in experimental facilities are found to play a vital role in the ability to accurately characterise the test gas of a given experiment.

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The T6 Stalker Tunnel is a multi-mode, high-enthalpy, transient ground test facility. It is the first of its type in the UK. The facility combines the original free-piston driver from the T3 Shock Tunnel with modified barrels from the Oxford Gun Tunnel. Depending on test requirements, it can operate as a shock tube, reflected shock tunnel or expansion tube. Commissioning tests of the free-piston driver are discussed, including the development of four baseline driver conditions using piston masses of either 36 kg or 89 kg. Experimental data are presented for each operating mode, with comparison made to numerical simulations. In general, high-quality test flows are observed. The calculated enthalpy range of the experimental conditions achieved varies from $$2.7\hbox { MJ kg}^{-1}$$ 2.7 MJ kg - 1 to $$115.0\hbox { MJ kg}^{-1}$$ 115.0 MJ kg - 1 . Graphical abstract

Shock tubes are a crucial source of experimental data for the aerothermodynamic modelling of atmospheric entry vehicles. Notably, many chemical-kinetic and radiative models are validated directly against optical measurements from these facilities. Typically, the incident shock speed at the location of the experimental measurement is taken to be representative of the test slug; however, the shock velocity can vary substantially upstream of this location. These variations have been long posited as a source of disagreement with computational predictions, although a definitive link has proved elusive. This work describes a series of experiments which aim to isolate and confirm the importance of the shock deceleration effect. This is achieved by generating different shock trajectories and comparing the post-shock trends in atomic oxygen emission and electron density. These trends are shown to be directly linked to the upstream shock speed variations using a recently developed numerical tool (LASTA). The close agreement of the comparisons confirms the importance of shock speed variation for shock tube experiments; these findings have direct and potentially critical relevance for all such studies, both past and present.