Thermodynamic Non-Uniformities Behind Incident and Reflected Shocks in a Single-Diaphragm Shock Tube

TL;DR

This study investigates the thermodynamic non-uniformities behind incident and reflected shocks in a single-diaphragm shock tube using combined experimental diagnostics and numerical simulations, revealing gas-dependent gradients affecting chemical kinetics measurements.

Contribution

It introduces a coupled RANS-LES simulation framework validated against experimental data to quantify thermodynamic gradients behind shocks in a shock tube.

Findings

Argon maintains a nearly uniform core with modest gradients.

Nitrogen and carbon dioxide exhibit substantial axial gradients.

Incident shock attenuation significantly influences the thermodynamic state.

Abstract

Shock tubes provide well-controlled high-temperature and high-pressure conditions for chemical kinetics studies, yet the region behind the reflected shock is seldom perfectly homogeneous. Axial and radial gradients arise from shock formation, attenuation, and the interaction of the reflected shock wave with the boundary layer, and these variations influence chemical kinetic measurements such as ignition delay time. The present study combines experimental diagnostics and numerical simulations to quantify these gradients in a single-diaphragm shock tube. A coupled RANS-LES framework implemented in CONVERGE CFD incorporates realistic diaphragm opening profiles and is validated using pressure histories and shock velocity profiles for argon, nitrogen, and carbon dioxide. The results show that incident shock attenuation strongly influences the thermodynamic state of the reflected-shocked region, with test gas-dependent differences: a nearly uniform core with modest axial gradients is maintained in argon, whereas substantial axial gradients due to reflected-shock and boundary-layer interactions is seen in nitrogen and carbon dioxide. The analysis provides a foundation for quantifying test-gas homogeneity in shock-tube experiments and potential extrapolation to improving interpretation of ignition data acquired under non-ideal flow conditions.