Dynamic Response of a Liquid–Liquid Coaxial Swirl Injector Under Dual-Path Oscillations

Liquid–liquid coaxial swirl injectors in liquid-rocket engines experience oscillatory disturbances simultaneously in both propellant feed systems, which can significantly affect injector dynamic response and oxidizer-to-fuel ratio oscillations. In this study, the dynamic characteristics of a liquid–liquid coaxial swirl injector under dual-path oscillations were numerically investigated using the Volume-of-Fluid method coupled with the shear stress transport k-ω turbulence model under backpressure conditions. Different oscillation frequency combinations in the fuel and oxidizer paths were considered to investigate the dual-path coupling and its influence on the injector dynamic response and outlet oxidizer-to-fuel ratio oscillations. The results show that oscillations introduced in one propellant path can enhance the dynamic response of the other path, leading to stronger coupling behavior under dual-path excitation. Under co-frequency oscillation conditions, the oxidizer-to-fuel ratio oscillation exhibits distinct frequency-dependent characteristics. At 200 and 600 Hz, the nearly in-phase responses of the fuel and oxidizer suppress the oxidizer-to-fuel ratio oscillation relative to the corresponding single-path cases. At 1000 and 1400 Hz, the increased phase difference between the two propellant responses amplifies the oxidizer-to-fuel ratio oscillation. These results demonstrate that the relative phase between the fuel and oxidizer responses plays an important role in determining oxidizer-to-fuel ratio oscillations under dual-path oscillatory inflow conditions.