Effervescent Atomizer with Inflow Oscillation: Internal Flow and Spray Characteristics

Effervescent atomizers are widely used in propulsion systems. However, the response of their internal flow structures and spray characteristics to inflow oscillations in the liquid supply is not fully understood. This study experimentally investigates the impact of liquid inflow oscillations on the internal two-phase flow and external spray characteristics of effervescent atomizers in atmospheric conditions. In the low-frequency range (30–80 Hz), resonance-like amplification causes the oscillation amplitude to vary nonmonotonically with frequency. At comparable amplitudes, lower frequencies promote bubble growth and coalescence, producing large-bubble-dominated or slug flow, whereas higher frequencies suppress these effects. While the macroscopic spray characteristics are predominantly influenced by liquid flow rate and gas-to-liquid ratio (GLR), the impact of inflow oscillations is relatively weak. The spray cone angle increases with liquid flow rate and GLR, while the Sauter mean diameter decreases. Analysis using proper orthogonal decomposition and fast Fourier transform reveals that the spray field does not synchronize with the inflow oscillation frequency, indicating an inherent filtering effect in the atomizer. Intrinsic spray cone angle oscillations persist near the nozzle exit, mainly governed by fluctuations in the instantaneous exit gas holdup. These findings provide new insights into the dynamic modulation of spray behavior under oscillating inflows.