Impact of shock-tube facility-dependent effects on incident- and reflected-shock conditions over a wide range of pressures and Mach numbers

Abstract

In real shock tubes, deviations from the ideal gas-dynamic behavior can affect experiments and complicate data analysis and interpretation. These non-ideal effects depend on the shock-tube geometry and therefore, results (e.g., ignition delay times) may vary between different experimental facilities. To clarify the influence of geometry and operating procedures, these effects were investigated in four geometrically different shock tubes located in two laboratories, Texas A&M University and the University of Duisburg-Essen. Incident shock-wave attenuation and pressure rise (dp*/dt) were measured behind reflected shock waves over a 2.1–4.1 Mach number and a 0.1–3.0 MPa post-reflected-shock pressure range. A strong influence of the Mach number on dp*/dt was observed for all facilities and conditions, whereas only a slight influence was found for shock-wave attenuation. Both dp*/dt and attenuation were higher by about a factor of two for the shock tubes with approximately half the inner diameter (8.0 vs. 16.2 cm). These findings are analyzed through correlations with initial pressure, inner diameter, Mach number, and specific heat ratio. The implication of non-ideal effects on experiments with reactive mixtures and related combustion experiments is discussed. Extreme conditions of dp*/dt were derived from the correlations and used to understand the effects of an equivalent dT*/dt on simulated ignition delay times of two reactive systems (CH4/air and C7H16/air). It was found that smaller shock-tube diameters with respectively larger dp*/dt show shorter ignition delay times (especially at temperatures below 1000 K for the C7H16/air case). Therefore, the geometry constraints must be considered in simulations through dp*/dt inputs in the chemical kinetics simulation for the extreme cases to account for non-ideal effects.