Stochastic sub-grid scale acceleration model (SSAM) for LES of primary atomization using iso-advector VOF method for ECN Spray-A

Abstract

Primary atomization at high Weber numbers evolves in highly sheared gas flow. The latter is characterized by energetic intermittent turbulent structures on small length-scales. Although the effects of turbulent flow dynamics on small scales may strongly correlate with wrinkling of the liquid/gas interface, the residual scales are usually discarded in reduced simulations. In this paper, we present the large eddy simulation (LES) of primary atomization of a diesel spray jet using VOF method accounting for intermittency effects on sub-grid scale liquid/gas interface. The principal idea of this approach is to force the filtered Navier Stokes equation by the subgrid acceleration, which is modelled in a way to represent the main statistical properties of intermittency in the high Reynolds number flows. Earlier, this approach was referred to as LES-SSAM (stochastic subgrid acceleration model). In this approach, the statistics of acceleration on residual scales is modelled by two independent stochastic processes i.e., one for the norm and the other for the unit orientation vector. The both are modelled by Ornstein-Uhlenbeck process: while the norm is modelled by a long-correlated log-normal process, the acceleration orientation vector is modelled by diffusion on the unit sphere with relaxation towards the local vorticity field, and with correlation on the short Kolmogorov time. The resulting stochastic velocity field is then used for reconstruction of the liquid/gas interface in the framework of iso-advector geometrical VOF method. The approach is applied to simulate the primary atomization of ECN Spray-A injector. A qualitative comparison of liquid/gas interface evolution with the under-resolved LES-VOF approach is provided.