arXiv subjects

S. She-Ming Lau-Chapdelaine

Publications and source records attributed to S. She-Ming Lau-Chapdelaine.

5 recordsLinked to original sources

arXiv2026

Quasi-Two-Dimensional Simulation of a Rotating Detonation Engine Combustor and Injector

A numerical simulation of an annular rotating detonation engine with stoichiometric hydrogen-oxygen is performed. A generic, well posed, and easily implemented approach using a quasi-two-dimensional method to model the area variations through the rotating detonation engine's injector and combustor is presented. The detonation--injector interaction is studied for the case with a ratio of four between the combustor and injector's throat areas. A shock wave is formed in the divergent portion of the injector due the high back pressure created by the detonation in the combustor. A Favre-averaged steady-state analysis of stream lines and particle paths reveals that the shock causes an irrecoverable loss of stagnation pressure. Stagnation pressure gain in the combustor is insufficient to make up for the loss and the flow leaves the engine with lower stagnation pressure than in the plenum.

physics.flu-dyn↗

arXiv2025

Estimating Energy Release in Metallized Composite Explosives Using the Taylor Model

The potential for reactive metal fuels to enhance the energetic output of high explosives has generated an enduring interest in the study of composite explosives. It has typically been demonstrated that added metal fuels can have little or even deleterious impact on the accelerating ability of composite military explosives relative to baseline performance. Often this has led to the assumption of limited reaction of the metal fuel over microsecond timescales. The widespread availability of Photonic Doppler Velocimetry has enabled time resolved measurement of accelerated confinement, ultimately demonstrating prompt reaction of metal fuels. Motivated by this observation, hydrocode modelling studies, and prior author's modifications of Taylor's tubular bomb model, we developed a differential equation form of Taylor's model in a manner where it is straightforward to add sources or phases. An afterburning version of the JWL equation of state was used to add energy to the gaseous products at a linear, time-dependent rate. The metal particles are assumed to remain in velocity equilibrium with the gaseous products and do not transfer heat or influence chemical composition. We focus exclusively on added aluminum as it remains the most ubiquitous choice of metal fuel. The model is initialized with a CJ state calculated from Cheetah 2.0 assuming the Al particles are inert in the detonation. JWL coefficients for the baseline explosive are also used. Qualitative agreement is observed between the model and previously published experiments.

physics.chem-ph↗

arXiv2020

Non-uniqueness of solutions in asymptotically self-similar shock reflections

The present study addresses the self-similar problem of unsteady shock reflection on an inclined wedge. The start-up conditions are studied by modifying the wedge corner and allowing for a finite radius of curvature. It is found that the type of shock reflection observed far from the corner, namely regular or Mach reflection, depends intimately on the start-up condition, as the flow "remembers" how it was started. Substantial differences were found. For example, the type of shock reflection for an incident shock Mach number $M=6.6$ and an isentropic exponent $γ=1.2$ changes from regular to Mach reflection between $44^\circ$ and $45^\circ$ when a straight wedge tip is used, while the transition for an initially curved wedge occurs between $57^\circ$ and $58^\circ$.

physics.flu-dyn↗

arXiv2016

Viscous solution of the triple shock reflection problem

The reflection of a triple-shock configuration was studied numerically in two dimensions using the Navier-Stokes equations. The flow field was initialized using three shock theory, and the reflection of the triple point on a plane of symmetry was studied. The conditions simulated a stoichiometric methane-oxygen detonation cell at low pressure on time scales preceding ignition, when the gas was assumed to be inert. Viscosity was found to play an important role on some shock reflection mechanisms believed to accelerate reaction rates in detonations when time scales are small. A small wall jet was present in the double Mach reflection and increased in size with Reynolds number, eventually forming a small vortex. Kelvin-Helmholtz instabilities were absent and there was no Mach stem bifurcation at Reynolds numbers corresponding to when the Mach stem had travelled distances on the scale of the induction length. Kelvin-Helmholtz instabilities are found to not likely be a source of rapid reactions in detonations at time scales commensurate with the ignition delay behind the Mach stem.

physics.flu-dyn↗

arXiv2013

Influence of hydrodynamic instabilities on the propagation mechanism of fast flames

The present work investigates the structure of fast supersonic turbulent flames typically observed as precursors to the onset of detonation. These high speed deflagrations are obtained after the interaction of a detonation wave with cylindrical obstacles. Two mixtures having the same propensity for local hot spot formation were considered, namely hydrogen-oxygen and methane-oxygen. It was shown that the methane mixture sustained turbulent fast flames, while the hydrogen mixture did not. Detailed high speed visualizations of nearly two-dimensional flow fields permitted to identify the key mechanism involved. The strong vorticity generation associated with shock reflections in methane permitted to drive jets. These provided local enhancement of mixing rates, sustenance of pressure waves, organization of the front in stronger fewer modes and eventually the transition to detonation. In the hydrogen system, for similar thermo-chemical parameters, the absence of these jets did not permit to establish such fast flames. This jetting slip line instability in shock reflections (and lack thereof in hydrogen) was correlated with the value of the isentropic exponent and its control of Mach shock jetting instability (Mach & Radulescu).

physics.flu-dyn↗