Investigation of the acoustic characteristics of the solid rocket motor combustion chamber under pulse triggering

Pyrotechnic pulse generators are critical tools for investigating combustion instability in solid rocket motors (SRMs), yet the mechanisms of acoustic oscillations under pulse triggering remain poorly understood. To address this issue, this study established an experimental setup and numerical model to characterize acoustic oscillations in a pulse-triggered combustion chamber. The model achieved excellent accuracy, with errors of <4% for the first four axial modal frequencies, <6% for the first three axial modal amplitudes, and 7.75% for damping coefficients compared to experimental results. Bicoherence analysis revealed nonlinear self-/cross-coupling of acoustic modes and their energy transfer with mean pressure under pulse triggering, demonstrating energy cascading from low- to high-order modes that drove high-frequency chamber oscillations. Standing wave and attenuation coefficient analyses demonstrated that pulse triggering could generate up to 4th-order standing waves, enabling acoustic damping measurements. A parametric study investigated throttling orifice diameter (3–6 mm), pulse direction, and location. Increasing the orifice diameter enhanced pulse triggering intensity by 4.38 times. Radial pulse triggering proved more effective than axial triggering, with head-end radial pulse triggering increasing the pulse rate by 1.99 times and modal amplitudes by >2 times for the first four modes. Mid-chamber radial pulse triggering selectively triggered even-order modes, while tail-end radial pulses triggered transverse acoustic oscillations, making tail-end radial pulses ideal for studying transverse combustion instability.