Unsteady combustion around a spherical projectile in supersonic flows is numerically studied using the simplified two-step chemical reaction model consisting of the induction and the exothermic reactions. A series of simulations indicates that the intensity of the concentration of the heat release is a key parameter to determine the regime of the unsteady flowfield. Flow features of the unsteady combustion with low-frequency and high-amplitude oscillation, which is called the large-disturbance regime, are reproduced when the concentration of the heat release of the chemical reaction is high. Mechanism of the large-disturbance regime is clarified based on the histories of the density and pressure profiles on the stagnation streamline and the flowfield in front of the projectile body. The period and amplitude of the oscillation corresponding to the shock pressure behind the bow shock agree with experimental observations, and the reproduction of the large-disturbance regime in the present simulation is confirmed.
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