Radulescu Gasdynamics Laboratory

Influence of Porosity on the Flame Speed inGasless Bimetallic Reactive Systems by Hesam Akbarnejad Self-propagating High-temperature Synthesis ( SHS ) is the synthesis of solid materials by a reaction wave propagating into the initial reactants, typically two metals, which can alloy exothermically . Typically, experiments are performed with the reactants in powder form, with relatively low density. Recent experiments by Bacciochini et al. revealed much larger flame speeds in densified powders near TMD, obtained by the cold spray process. The present thesis investigates why the flame speed increases dramatically with an increase in density of the powders. The investigation rests on the analytical model formulated by Makino by controlling how the variables are affected by changes in density. Flame speed measurements were performed in mixtures of nickel (Ni) and aluminum (Al) at different initial densities. The density was varied by controlling the cold-pressing of the s...

.. and onto a PhD. Numerical Simulations of Detonation Re-Initiation Behind an Obstacle by She-Ming Lau-Chapdelaine  This numerical study explored the mechanisms responsible for the re-initiation of a detonation, which quenched while diffracting over a half-cylinder obstacle. The purpose of the study was to make accurate predictions of when detonation re-initiation would occur, determine the role various re-initiation mechanisms, and compare the effect of different chemical models. The problem was modelled using the reactive Euler equations with either the one-step Arrhenius or two-step chain-branching chemical models, calibrated to post-shock conditions in order to properly reproduce the ignition delay. The simulations were validated using the stoichiometric methane-oxygen experiments of Bhattacharjee et al. Detonation failure and separation into shock-flame structure The numerical model was able to accurately predict detonation re-init...

Nick was also nominated for some fancy award - en route for the Sirmas instability and a promising PhD.   Shock Instability in Gases Characterized by Inelastic Collisions  by Nick Sirmas The current study addresses the stability of shock waves propagating through dissipative media, analogous to both granular media and molecular gases undergoing endothermic reactions. In order to investigate the stability, a simple molecular dynamics model was developed to observe shock waves and their structures with the inclusion of energy dissipation. For this, an Event Driven Molecular Dynamics model was implemented in a 2D environment, where a molecule is represented by a disk. The simulations addressed the formation of a shock wave in a gas by the sudden acceleration of a piston. Inelastic collisions were assumed to occur only if an impact velocity threshold is surpassed, representing the activation energy of the dissipative reactions. Parametric studies ...

Using the soap bubble technique, we visualize the dynamics of unconfined hydrogen-air flames using high speed schlieren video - a technique that permits to see density gradients. For sufficiently weak mixtures, i.e., low flame speeds, buoyancy effects become important, as shown in the following two photographs. As the flame begins to grow inside the soap bubble, the light products of combustion inside the flame ball begin to rise, forming a mushroom-shaped flame. The critical dimension of flame balls that will begin to rise due to buoyant forces is given by equating the time scale for flame propagation to the time scale of convection by buoyant forces. More details can be found in our arXiv paper and video , which has won one of the three Van Dyke awards for the Gallery of Fluid Motion at the 65th Annual Meeting   of the American Physical Society - Division of Fluid Dynamics . UPDATE 19-9-2013 :  The article is now available in Physics of Fl...