DES and RANS Modeling of Primary Atomization in a Coaxial Swirling Liquid-Gas Jet

This study assesses different turbulence modeling approaches for simulation of two-phase coaxial annular swirling jet flows. The problem selected from literature for comparison involves an analytical inlet profile for an annular liquid sheet sandwiched between two coaxial annular gaseous jets. The liquid-gas interface is resolved using the volume-of-fluid model with continuum surface force approximation. Reynolds-averaged Navier-Stokes simulations and detached eddy simulations (DES) are conducted to obtain transient multiphase numerical solutions. Different turbulence models explored include the <i>k-&epsilon;</i> renormalization group (RNG) with swirl modification, the Reynolds stress model (RSM), RSM with scale-adaptive simulation (RSM-SAS), and DES. Comparisons with the direct numerical results from literature suggest that the <i>k-&epsilon;</i> RNG and RSM approaches simulate only the streamwise shear of the liquid jet and are inadequate in capturing the swirling aspect of the jet flow and expected instabilities. DES can predict several expected features such as radial asymmetry, surrounding gas vortices causing jet instabilities, and eventual jet breakup with reasonable accuracy. While RSM-SAS predicts radial asymmetry, some jet instability, and is much more accurate than <i>k-&epsilon;</i> RNG and RSM, it fails to predict instabilities as good as DES and does not predict a complete jet breakup. RSM-based methods are found to be computationally very expensive compared to the <i>k-&epsilon;</i> RNG model, suggesting DES as the better alternative than RSM methods for such applications if resources are available.