ANNULAR FLOW REGIME CHARACTERISTICS OF AN INTERNAL IMPINGING EFFERVESCENT ATOMIZER

Liquid fuels for sustained supersonic scramjet flight demand rapid atomization for efficient combustion. This study introduces a simple internal impinging effervescent atomizer, achieved by modifying the internal geometry of a scramjet ramp injector to incorporate an atomizing gas for effervescent action. Spray characteristics under annular flow regimes (Re<sub>l</sub> 5395, GLR 5% to 10%) were experimentally investigated using high-speed shadowgraph imaging, Mie-scattering particle image velocimetry (PIV) and phase Doppler techniques. Shadowgraph and Mie-scattering revealed the spray structure, spread, cross-sectional spray pattern and distribution, while PIV captured velocity vector fields. Phase Doppler measurements quantified droplet sizes and velocities. The results show finely atomized sprays at short distances downstream of injection, where the two-phase mixture is initially clustered before rapid atomization occurs. In the annular flow regime, high-velocity gas occupies the core of the jet, while liquid clusters dominate the periphery. During initial injection, the gas shifts slightly toward the impingement direction, penetrating the liquid phase further downstream. Velocity vectors confirm the characteristic annular flow, with a faster inner core compared to the outer regions. Phase Doppler analysis also indicates finely atomized droplets, confirming the atomizer's capability to produce stable, efficient sprays under annular flow conditions.