Layered detonation propagation subject to bilateral expansion: Role of the air layer height

A two-dimensional numerical study was conducted to reveal the role of air layer height on cellular detonations propagating through a layer of vaporized kerosene/air reactant bounded by inert gas (upper side) and air (lower side). A series of cases with different reactive layer heights (h) and air layer heights (h2) are simulated and analyzed. The results indicate that the detonation propagation structures and ignition regimes at the interface between the reactive and air layers are significantly affected by h2. At h2 = 5.8λCJ (λCJ is theoretical cell width), the bottom oblique shock wave propagated as regular reflection structures, and the ignition regime relied on transverse detonations. As the h2 decreases below 2.9λCJ, the bottom oblique shock forms a Mach reflection structure with the bottom wall, and the detonation front ignition regimes can be divided into three types based on h2. The first ignition regime is also through transverse detonation (at h2 = 2.9λCJ). The second ignition regime is the collision between the reflected triple point, the downward triple point, and the Mach stem (at h2 = 0.72λCJ). However, at h2 = 1.45λCJ, in addition to the above two regimes, the ignition regime also relies on the collision between the downward transverse detonation and the Mach stem. Moreover, it was found that when the h/λ is larger than 5.6, layered detonation affected by bilateral expansion can propagate successfully, which is significantly closer to the rotating detonation experimental values compared with detonations subject to unilateral expansion.