Large Eddy Simulation of cavitation effects on reacting spray flames using FGM and a new dispersion model with multiple realizations

Abstract

In the present study Large Eddy Simulations (LES) are performed to investigate the ignition behavior of cavitating and non-cavitating n-dodecane flames. Inspired by the work of Tsang et al. (2019) [1] an LES specific dynamic dispersion model, that evaluates the dispersion velocity locally, is proposed. Although the model discards tuning of global model constants, excellent mixing predictions are obtained for all cases. The resulting model is extensively validated using inert Spray A conditions as defined by the Engine Combustion Network (ECN). Subsequently, it is applied to the larger orifices of Spray C and Spray D. A Flamelet Generated Manifolds (FGM) approach that takes the effect of scalar dissipation into account is adopted for combustion modeling. The coupling of the turbulence modeling approach and FGM shows excellent predictions of ignition characteristics on Spray C and Spray D, suggesting a minor effect of cavitation on ignition development. For the sake of understanding the injection-to-injection variations of LES, multiple realizations are performed. Based on the analysis of structure similarity index (SSI), it is found that a single realization is sufficient for global parameters such as ignition delay time (IDT) and lift-off length (LOL). However, different number of realizations are needed for different scalar fields. It is suggested that the temperature-based IDT is preferred for a single realization while a radially integrated intensity is needed for an OH-based IDT or LOL.