Abstract
Numerical simulations of one-dimensional and two-dimensional detonations have been performed with two-step chemical reaction mechanisms for a stoichiometric hydrogen-air mixture at initial conditions of 42.7 kPa and 293 K. One-dimensional overdriven detonations are initiated by solutions of steady ZND detonations for degree of overdrive 1.1-2.0, and by shock compression with a piston for degree of overdrive 1.2. Shock pressure histories developing from steady detonations indicate high frequency oscillations for degree of overdrive 1.6-2.0 and low frequency oscillations for 1.1-1.5. In the piston initiation case, post-shock pressure is temporally led in a highly overdriven condition by penetration of an interior detonation and is gradually attenuated by incident rarefaction waves. In this decaying process of the overdriven detonation, both high frequency and low frequency oscillations are observed for the fixed degree of overdrive 1.2. The relation between the shock pressure and the oscillation characteristics such as period and pressure amplitude agrees with results of steady detonation initiations. An initiation process of a two-dimensional detonation from high pressure and temperature conditions is also numerically investigated. Oscillation characteristics on the center line of the cell in two-dimensional detonation indicate a similar transition to one-dimensional detonations in the decay process of initial overdriven conditions but do not depend on the shock pressure very much.
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