A conjugate axisymmetric model of a high-pressure shock-tube facility

Abstract

Purpose -An axisymmetric shock-tube model of the high-pressure shock-tube facility at the Texas A&M University has been developed. The shock tube is non-conventional with a non-uniform cross-section and features a driver section with a smaller diameter than the driven section. The paper aims to discuss these issues. Design/methodology/approach -Computations were carried out based on the finite volume approach and the AUSM þ flux-differencing scheme. The adaptive mesh refinement algorithm was applied to the time-dependent flow fields to accurately capture and resolve the shock and contact discontinuities as well as the very fine scales associated with the viscous effects. The incorporation of a conjugate heat transfer model enhanced the credibility of the results. Findings -The shock-tube model is validated with simulation of the bifurcation phenomenon and with experimental data. The model is shown to be capable of accurately simulating the shock and expansion wave propagations and reflections as well as the flow non-uniformities behind the reflected shock wave as a result of reflected shock/boundary layer interaction or bifurcation. The pressure profiles behind the reflected shock wave agree with the experimental results. Originality/value -This paper presents one of the first studies to model the entire flow field history of a non-uniform diameter shock tube with a conjugate heat transfer model beginning from the bursting of the diaphragm while simultaneously resolving the fine features of the reflected shock-boundary layer interaction and the post-shock region near the end-wall, at conditions useful for chemical kinetics experiments. An important discovery from this study is the possible existence of hot spots in the end-wall region that could lead to early non-homogeneous ignition events. More experimental and numerical work is needed to quantify the hot spots.

Methane Ignition in a Shock Tube with High Levels of CO2 Dilution: Consideration of the Reflected-Shock Bifurcation

“…The work of Lamnaouer et al 31 provided insight into the nature of the nonuniform conditions, showing temperature and pressure gradients behind reflected shock waves when bifurcations were present. As observed from the color schlieren images of Kleine et al, 28 all features of the bifurcation were seen in simulations done by Lamnaouer et al 31 These include features such as the bifurcated foot of the reflected shock wave; the separation bubble from the boundary layer under the oblique shocks; and, critical to the understanding of hotspots, swirling fluid of the shear layer and wall jet. Lamnaouer et al also showed the presence of local hotspots in the wall jet after the passage of the bifurcation.…”

“…Ever since bifurcation was first observed by Mark in 1958, much work has been conducted to investigate bifurcation from experimental and numerical perspectives. ,− Of some of the insights gained from these works, a couple to note are the change in bifurcation length with changing mixture composition and the presence of nonuniform conditions after passage of the bifurcated reflected shock wave. The work of Lamnaouer et al provided insight into the nature of the nonuniform conditions, showing temperature and pressure gradients behind reflected shock waves when bifurcations were present.…”

“…Ever since bifurcation was first observed by Mark in 1958, much work has been conducted to investigate bifurcation from experimental and numerical perspectives. ,− Of some of the insights gained from these works, a couple to note are the change in bifurcation length with changing mixture composition and the presence of nonuniform conditions after passage of the bifurcated reflected shock wave. The work of Lamnaouer et al provided insight into the nature of the nonuniform conditions, showing temperature and pressure gradients behind reflected shock waves when bifurcations were present. As observed from the color schlieren images of Kleine et al, all features of the bifurcation were seen in simulations done by Lamnaouer et al These include features such as the bifurcated foot of the reflected shock wave; the separation bubble from the boundary layer under the oblique shocks; and, critical to the understanding of hotspots, swirling fluid of the shear layer and wall jet.…”

Asymmetric characteristics of the shock bifurcation in the reflected shock/boundary layer interaction

“…Quasi-one-dimensional and axial numerical simulations of reflected shock and boundary layer interactions reproduced the shock bifurcation by Wilson et al (1995). Lamnaouer et al (2014) developed an axisymmetric shock-tube model with a non-uniform cross-section, which can capture the detailed bifurcation structure with very good resolution, and they discovered a possible existence of hot spots in the end-wall region triggering early non-homogeneous ignition events. The numerical results by Gamezo et al (2001Gamezo et al ( , 2005 showed that the bifurcation creates a recirculation region attached by the shock that could act as a flame holder, which leads to an increase in energy release rate, and is in favor of triggering deflagration-to-detonation (DDT).…”

Effects of High Fuel Loading and CO2 Dilution on Oxy-Methane Ignition Inside a Shock Tube at High Pressure

“…To elaborate on consequential nonuniformities that are presented in bifurcating systems, previous numerical work of Lamnaouer et al [38] revealed temperature and pressure gradients behind reflected shock waves, as well as hotspots in the wall jet after the passage of the bifurcation. In addition, Yamashita et al [35] provide support for localized hotspots in bifurcated flows, and with recent work of Lipkowicz et al [36] it was shown that various gas dynamic and fluid dynamic structures occurred at a distance from the end wall supporting these localized nonuniformities due to the bifurcated shock.…”