Abstract
When a layer of particles or liquid is explosively accelerated, the dispersed material typically forms coherent jet-like structures that are aerodynamically stable. Such particle jets are observed at a range of scales in natural phenomena, from the ash jets observed during Plinian volcanic eruptions, to particle jets that form in supernova remnants at astrophysical scales. In the generic problem of a shock wave interacting with a group of particles, the non-uniform particle distribution characteristic of the resulting high-speed gas-particle flow can result from a variety of mechanisms. For weak gas shocks, particle jets may form due to a multiphase hydrodynamic instability, often denoted the shock-driven multiphase instability. This instability is related to other classical hydrodynamic interfacial instabilities (such as the Rayleigh-Taylor and Richtmyer-Meshkov instabilities), but has distinct features due to the transfer of momentum and energy between the phases. If particles or liquids are accelerated by the strong shocks (GPa pressures) characteristic of condensed explosives, particle filaments and jets are also typically formed. However, in this case, I will argue that it is not the strong shock wave, but rather the expansion wave that returns from the free particle surface, which plays the key role in the jet formation. I will illustrate some of the above phenomena from a variety of experimental studies, and highlight some of the outstanding issues that need to be resolved to model the multiphase flows.
About the Speaker
David Frost is currently a Professor in the Mechanical Engineering Department of McGill University in Montreal. Last December he was happy to finish his two terms as Associate Dean in the Faculty of Engineering and greatly reduce his number of Zoom meetings. His research interests are in the areas of metal combustion, multiphase combustion processes and shock wave physics. He joined McGill after completing his PhD at Caltech where he studied the dynamics of explosive boiling at the superheat limit. Past projects have involved steam explosions due to molten metal/water interactions, bubble detonations, shock interactions with compressible materials, and the synthesis of ballistic ceramics. For the last few decades, he has been studying the combustion of dust clouds, blast waves from metalized explosives, and the reaction of metal fuels with air and water as a carbon-free energy source. Most of what he knows about metal combustion and optical diagnostics he learned from discussions with his long-time colleagues Sam Goroshin and Jeff Bergthorson from McGill, Nick Glumac and Mike Soo from UIUC, among others, frequently over beer.
Host: Professor Taher Saif
