Characteristics of shock-induced combustion around hypersonic cylindrical projectiles into combustible gases

Shock-induced combustion around a cylindrical projectile is numerically studied. A simplified two-step chemical reaction model is used to handle the reactions instead of realistic elementally chemical reactions. The simulations are examined with various parameters, such as projectile speed, initial pressure, projectile diameter and activation energy E₁/R in the simplified chemical model, and the unsteady mode of the large-disturbance regime, whose oscillations are less regular and low in frequency, appears in all of simulation results. The oscillation periods normalized by the induction time t_ind for the large-disturbance regime well agree with the previous experimental and numerical observations around the spherical projectile. The histories on the stagnation streamline give us the detailed oscillation mechanism with the interaction of the bow shock and the reaction front, and the unsteadiness shows different features depending on the experimental conditions. Those results with various parameters also'revealed the characteristic relation between non-dimensional oscillation period tlt_ind and non-dimensional diameter dll_ind. t/t_ind of large-disturbance regime always shows proportional relation to d/l_ind Thus, it is found that the non-dimensional diameter d/l_ind is the key factor to determine the oscillation period, and allows us to predict the oscillation periods by an arbitrary experimental condition.