Radulescu Gasdynamics Laboratory

Brian Maxwell just published  his results of DDT modelling with the Linear Eddy Model, where compressible dynamics of reactive gases and turbulence are explicitly taken into account.  Nicely done! Here, a detonation passes through a perforated plate, generating a turbulent flame headed by a shock. For a while, the reaction front propagates as a CJ deflagration while getting ready for transition.  Pressure fronts build up internally, favouring local auto-ignition events within the turbulent structure. We now have a tool to predict DDT in turbulent flames where compressible gas dynamics play an important role (always!).

July 2017, She-Ming Lau-Chapdelaine and I attended the International Symposium on Shock Waves in Nagoya Japan.   Shem presented his paper on shock reflections in low-gamma gases, which earned him a best paper award!  We showed how the slip line jets forward with decreasing gama and increase in shock Mach number.  Clearly relevant for Mach reflections in detonations.

From left, Maxime La Fleche, Nick Sirmas, She-Ming Lau-Chapdelaine, me, Willstrong Rokotoarison, Qiang Xiao, Wentian Wang, Brian Maxwell and Ramki Murugesan Fun times in and out of the technical sessions: Julian and John Lee with Jenny Chao mike drop? awsome Edyta the karaoke-queen Road trip on the way back, pit stop in Magog, for 70% done Steak-Frites (WW)

Today marks the final submission of Nick's seminal PhD thesis on shock instability in gases with non-elastic collisions.  cheers to the Radulescu-Sirmas (Sirmas-Radulescu?) instability! very proud of this guy! The shock instability captured via molecular dynamics in gases with inelastic collisions (bottom) can only be recovered at the continuum scale if molecular fluctuations are included in a Navier Stokes (middle).  Absence of viscous terms (top) cannot dissipated the fluctuations, and unphysical mixing ensues.   

Thanks to Scott Jackson and Maha Manoubi, all the past proceedings of the International Colloquium on the Dynamics of Explosions and Reactive Systems since 1999 are now available online .

The dynamics of cellular detonations are simpler to illustrate using Lagrangian trackers. The video was obtained from a simulation using James Quirk's AMRITA by Bijan Borzou.

Earlier in the week, some of us were in Waterloo, ON, at the Canadian Section of the Combustion Institute yearly technical meeting , where we presented progress in our reactive gasdynamics work. Wentian, Bijan, Nick, Matei, Brian and Mohamed Thermal ignition revisited with molecular dynamics: role of fluctuations in activated collisions N. Sirmas & M.I. Radulescu Nick Sirmas, in true form, presented his study on the role of molecular fluctuations in self-ignition in gases. He tackled thermal ignition problem with molecular dynamics. He found that non-equilibrium effects during thermal runaway occurs via hot-spots.  These are spontaneously generated by molecular fluctuations, and preferred in systems with high activation energies and heat release.  Reactive collisions are preferred in the neighborhood of previous reactive collisions, as common sense dictates.  The result is that at sufficiently low temperatures, hot spots are responsible for drastic r...

Mohamed Saif just completed his MaSc thesis on the CJ deflagrations and their transition to detonation. Also, check out our Proceedings of the Combustion Institute pre-print paper . Run-Up Distance From Deflagration to Detonation In Fast Flames Abstract In the process of deflagration-to-detonation transition (DDT) in reactive gases, the flame typically accelerates first to the choked flame condition (known as a Chapman-Jouguet deflagration), where it propagates at the sound speed with respect to the product gases. Subsequently, the choked flame may transit to a detonation. In the present study, the transition length from choked flames to detonations was measured experimentally in laboratory-scale experiments in methane, ethane, ethylene, acetylene, and propane with oxygen as oxidizer. The choked flames were first generated following the quenching of an incident detonation after its interaction with cylindrical obstacles with two different blockage ratios, 75\% and 90\%. Compari...

Kadeem Dennis has defended his thesis on the mechanism of cellular damage by shock waves, titled " Mechanical Modification of Cells by Pressure Waves and its Application to Traumatic Brain Injury ". The preliminary study addresses the mechanism by which shock waves damage cells and may lead to traumatic brain injury (TBI). Fibroblasts (3T3) cell cultures were exposed to pressure waves produced by reacting thermite powder in water with different pressure amplitudes, ranging from 0.04 to 1.4 MPa peak pressures. Fluorescent images of the cells before and after pressure wave exposure were used to determine the type of damage suffered by the cells and whether the cells have died.   Immediately after the exposure to the pressure waves, the cells were found to have their actin filament de-polymerized for all pressure waves tested. If allowed to recover for 60 minutes the 3T3 cells were found to have their actin re-polymerized. While the link ...

Yesterday, Brian Maxwell succesfully defended his PhD thesis, making him my first PhD student. His thesis titled " Turbulent Combustion Modelling of Fast-Flames and Detonations using Compressible LEM-LES " was very well received by his examiners.   Brian is on his way to the University of Victoria for a NSERC PDF postdoc. Congratulations Brian!  I'm very proud. Thesis abstract A novel approach to modelling highly compressible and reactive flows is formulated to provide high resolution closure of turbulent-scale reaction rates in the presence of very rapid transients in pressure and energy. For such flows, treatment of turbulent microscales are generally unattainable through traditional modelling techniques. To address this, the modelling strategy developed here is based on the Linear Eddy Model for Large Eddy Simulation (LEM-LES); a technique which has only previously been applied to weakly compressible flows. In the current formulation of the Compressible LE...

The last card was placed and the ICDERS 2015 program is now ready.  Thanks to everyone who helped out with the paper review and selection, and hope to see you in Leeds. ( update 5/8/2016 - The 2015 proceedings are now available on line in their permanent repository at  icders.org ) Les jeux sont faits, rien n'va plus ! Proceedings25ICDERS.html Message from the Program Committee Monday 3 August 2015 - AM 8:30 Welcome 13:00 Lunch 8:50 Plenary Lecture Paul Clavin Non linear theory for the dynamics of shock fronts and cellular detonations in gases ( PL1 ) F. Williams (Chair) Room M1 Room M1 ...