Coupled/decoupled spray simulation comparison of the ECN spray a condition with the -Y Eulerian atomization model

Abstract

This work evaluates the performance of the Σ-Y Eulerian atomization model at reproducing the internal structure of a diesel spray in the nearfield. In the study, three different computational domains have been used in order to perform 3D and 2D coupled simulations, where the internal nozzle flow and external spray are modeled in one continuous domain, and 2D decoupled simulations, where only the external spray is modeled. While the 3D simulation did the best job of capturing the dense zone of the spray, the 2D simulations also performed well, with the coupled 2D simulation slightly outperforming the decoupled simulation. The similarity in results between the coupled and the decoupled simulation show that internal and external flow calculations can be performed independently. In addition, the use of spatially averaged nozzle outlet conditions, in the case of an axisymmetric (single-hole) convergent nozzle, leads to a slightly worse near-field spray predictions but to an accurate far-field ones. Finally, a novel constraint on turbulent driven mixing multiphase flows is introduced which prevents the slip velocity from exceeding the magnitude of the turbulent fluctuations through a realizable Schmidt number. This constraint increased model stability, allowing for a 4x increase in Courant number.

Modelling and validation of near-field Diesel spray CFD simulations based on the Σ -Y model

“…. TIM is related to spray dispersion, so higher TIM indicates faster mixing [18]. It is shown that RANS modelling tends to increasingly over-predict TIM from the nozzle exit and thus spray mixing, while LES calculations are closer to experimental data up to 6 mm.…”

“…Previous work has shown the Σ-Y RANS predictions compared to x-ray data [18] [29]. Figure 1 shows projected mass density (PMD) at different axial locations downstream the nozzle.…”

“…At 6 mm the PMD is over-predicted, however the spray width is well captured. Two different inlet boundary condition were used in the RANS simulations: a mapped boundary condition, where all flow variables were taken from previous nozzle flow calculations [18], and a constant radially averaged outlet profile, which will be used to compare with LES cases. [35].…”

Subgrid Liquid Flux and interface modelling for LES of Atomization

“…Regarding the geometry and the inflow condition several options may be considered, full 3D simulation with in injector flow and needle movement [10] up to a simple 2D axisymmetric configuration [11]. On both cases it has been possible to show that even with the less resolved configuration (RANS) the essential features of the injection can be captured with the ELSA family.…”

Influence of Stokes Number on Collisional Interfacial Area Production Terms within the Σ-Y Eulerian Spray Atomization Model

“…Here, τ coll is a characteristic collisional production time, depending on the relative velocity and spacing between droplets, and Σeq is the equilibrium value for interfacial area. The mathematical form in equation (5) has been adopted in several publications of other authors, see for example [2,3,4,5,6,7,8]. However, different formulations for the modeling of τ coll and Σeq exist.…”