Effect of Co- and Counterswirl Air on Swirl Airblast Atomization

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For swirl-stabilized gas turbine combustor, liquid fuel distribution in the near field dictates local equivalence ratio, volumetric heat release, and heat transfer to the chamber wall, and hence its understanding is essential. The effect of inlet air aerodynamics on spray characteristics in a primary zone of a simulated gas turbine burner is studied using a phase Doppler particle analyzer, high-speed Mie scatter imaging, and an orthogonal decomposition method. By employing intense coswirl air, the luminous spray region shifts upstream to the burner exit, where lower mass flux can be observed in the central region and higher mass flux in the outer region of the spray due to the recirculation zone formation. Based on the size velocity joint probability distribution functions (JPDFs) and the individual droplet transport with acquisition time, we conclude that the recirculation zone entraps the smaller droplets and transports them from the downstream to the upstream spray region. Compared to coswirl, counterswirl air exhibits torsion instability, intensifies the concentration of drops in the central region, and improves secondary atomization. Finally, five distribution functions are curve-fitted to the experimental data to capture the atomization process accurately.