Numerical Study of Unstable Shock-Induced Combustion with Different Chemical Kinetics and Investigation of the Instability Using Modal Decomposition Technique

An unstable shock-induced combustion (SIC) case around a hemispherical projectile has been numerically studied which experimentally produced a regular oscillation. Comparison of detailed H-2/O-2 reaction mechanisms is made for the numerical simulation of SIC with higher-order numerical schemes intended for the use of the code for the hypersonic propulsion and supersonic combustion applications. The simulations show that specific reaction mechanisms are grid-sensitive and produce spurious reactions in the high-temperature region, which trigger artificial instability in the oscillating flow field. The simulations also show that specific reaction mechanisms develop such spurious oscillations only at very fine grid resolutions. The instability mechanism is investigated using the dynamic mode decomposition (DMD) technique and the spatial structure of the decomposed modes are further analyzed. It is found that the instability triggered by the high-temperature reactions strengthens the reflecting compression wave and pushes the shock wave further and disrupts the regularly oscillating mechanism. The spatial coherent structure from the DMD analysis shows the effect of this instability in different regions in the regularly oscillating flow field.

Automated summary

This study numerically investigates an unstable shock-induced combustion (SIC) case that exhibits regular oscillation experimentally. Detailed comparison of H-2/O-2 reaction mechanisms is made for the numerical simulation of SIC, highlighting the sensitivity of specific mechanisms to grid resolution and the generation of spurious reactions. The analysis reveals that the high-temperature reactions trigger instability in the oscillating flow field, disrupting the regularly oscillating mechanism by strengthening the reflecting compression wave and pushing the shock wave further.