ID#: 131
Abstract Title: Effects of Boundary Layers on Ignition Behind Reflected Shocks
Session Title: Shock Ignition
Session Date: 7/31/01
Session Start Time: 11:20 AM
Contributing Author: Gamezo, V.N.
Organization: Naval Research Laboratory
Country: USA
Authors: Vadim N. Gamezo, Alexei M. Khokhlov, Elaine S. Oran
Short Abstract: Two-dimensional Navier-Stokes numerical simulations were used to study ignition phenomena behind reflected shocks in a stoichiometric ethylene-air mixture. The simulations were performed for a series of Mach numbers of the incident shock, Ms, and two channel widths. The results show that the flow nonuniformities resulting from the interaction of the reflected shock with boundary layers created by the incident shock may strongly affect the ignition process. The reflected shock develops a bifurcated structure consisting of an oblique leading shock, secondary shocks, and a number of vortices. This structure grows substantially before the ignition occurs. For relatively weak incident shocks, or in narrow channels, the leading oblique shock reaches the center of the tube and creates several secondary shocks. Interactions of these shocks with each other and with vortices intensify mixing and create hot spots far from the reflecting wall. Some of these hot spots ignite and produce flames that interact with vortices and generate additional weak shocks and compression waves. This leads to new hot spots and flames, and eventually creates conditions that allow a transition to detonation. Ignitions occur closer to the end wall for stronger incident shocks and larger channels where the influence of bifurcated structures is less pronounced. For the same Ms, weak ignition producing a flame in a narrow channel occurs sooner than strong ignition at the end wall in a wider channel.