Research on Pulse Excitation in High-pressure Acoustic Chambers with Different Length-to-diameter Ratios

For the dynamic combustion stability assessment of rocket engines, a pulse gun is developed to investigate the acoustic response characteristics of high-pressure acoustic chamber under pulse excitation. Axial and radial pulse excitation experiments are conducted on five acoustic chambers ( L/D ratios: 0.6-5.1) under 10 MPa back pressure. A prediction method for initial shock wave amplitude is established based on the theory of ideal shock tube. The effects of excitation direction and chamber L/D ratio on the shock amplitude, the eigenfrequency of acoustic chamber and the attenuation coefficient of the first-order longitudinal (1L) mode are also analyzed. The pulse gun produces a maximum shock amplitude of 1.63 MPa under 10 MPa back pressure, which is correlated with chamber L/D ratio. As the L/D ratio decreases, the dominant oscillation mode transitions from longitudinal mode to tangential and high-frequency superposition mode. Two average sound speed estimation methods are developed based on cross-correlation analysis and energy conservation. The theoretical eigenfrequencies calculated from reverse-derived temperatures deviate by up to 6.24% from experimental values. The attenuation coefficient ( α_1L ) deviations of 1L mode under different excitation directions are less than 8.8%, and α_1L demonstrates a linear correlation with 1L eigenfrequency.