Roles of Acoustic Impedance and Acoustic Velocity Ratios on Semiconfined Detonation Propagation

A numerical study is conducted to reveal the roles of the acoustic impedance ratio Z and acoustic velocity ratio X on semiconfined cellular detonations propagating through a layer of reactant bounded by inert gas. A series of cases are simulated based on the control variate method in two initial conditions. The simulation results unveil significant differences in the roles of Z and X in the layered detonation propagation. As the Z increases (at [Formula: see text]), the layered detonation propagation regime remains in an oblique-shock-attached detonation structure whose shock wave angle generally remains the same while the interface angle slightly decreases, resulting in reduced detonation area expansion. However, as the X increases (at [Formula: see text]), the layered detonation propagation regime is more complicated, whose shock wave angle significantly increases and even becomes an overshooting detached shock to generate a compression effect on the detonation front. In cases with a high X of 3–4, the overshooting detached shock forms an inverse-Mach reflection or double-Mach reflection shock system, leading to a detonation area decrement and overdriven propagation. Furthermore, a semi-empirical prediction model for the detonation velocity deficit subject to both detonation area expansion and decrement is established in a unified manner and validated through existing experimental data. This study first clarifies the respective roles of two parameters and elucidates the underlying mechanisms, which further deepens the understanding of the layered detonation propagation.