Comparison of Turbulence Modeling Methods for Evaluating GDI Sprays with Transient Needle Motion

Understanding the complex, transient spray phenomena associated with Gasoline Direct Injection (GDI) technologies continues to be key when designing injection systems to meet the stringent performance and emissions standards of modern internal combustion engines. Internal flow phenomena, such as string cavitation and hole-to-hole flow variations, are often highly transient and affected by turbulence. To better understand the current degree to which turbulence modeling influences simulations of GDI sprays, RANS and LES simulations have been performed on the multi-hole Spray G injector through the start of injection phase, with results compared to previously available X-Ray radiography data. Specifically, the k-ω SST RANS model and the k-equation LES model with a WALE sub-grid scale stress model have been tested on grids generated with the Generation 3 Spray G geometry, which includes as-produced injector dimensions based on X-Ray radiography measurements. The Homogeneous Relaxation Model (HRM) was employed to capture the effects of phase change in both simulations. A unique sealing algorithm was also included, providing the ability to accurately capture needle opening dynamics. Finally, a grid dependence study was performed to determine the resolution requirements of the LES cases and demonstrate adequate convergence. The LES model was found to achieve slightly more accurate results compared to RANS, primarily due to its ability to maintain time accuracy and resolve transient phenomena. Both turbulence models resulted in flow rates that agreed well with experimental measurements.