Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

Abstract

<jats:p>In this study, various mixing and evaporation modeling assumptions typically considered for large-eddy simulation (LES) of the well-established Engine Combustion Network (ECN) Spray A are explored. A coupling between LES and Lagrangian particle tracking (LPT) is employed to simulate liquid n-dodecane spray injection into hot inert gaseous environment, wherein Lagrangian droplets are introduced from a small cylindrical injection volume while larger length scales within the nozzle diameter are resolved. This LES/LPT approach involves various modeling assumptions concerning the unresolved near-nozzle region, droplet breakup, and LES subgrid scales (SGS) in which their impact on common spray metrics is usually left unexplored despite frequent utilization. Here, multi-parametric analysis is performed on the effects of (i) cylindrical injection volume dimensions, (ii) secondary breakup model, particularly Kelvin–Helmholtz Rayleigh–Taylor (KHRT) against a no-breakup model approach, and (iii) LES SGS models, particularly Smagorinsky and one-equation models against implicit LES. The analysis indicates the following findings: (i) global spray characteristics are sensitive to radial dimension of the cylindrical injection volume, (ii) the no-breakup model approach performs equally well, in terms of spray penetration and mixture formation, compared with KHRT, and (iii) the no-breakup model is generally insensitive to the chosen SGS model for the utilized grid resolution.</jats:p>

Large eddy simulation of diesel spray–assisted dual-fuel ignition: A comparative study on two n-dodecane mechanisms at different ambient temperatures

“…In the present study, Navier-Stokes equations for gas phase compressible turbulent flow are solved using the LES approach. The present numerical strategy has been thoroughly validated in our previous publications for the SF ECN Spray A case 17,[36][37][38] and SF/DF cases 2,3 . The solver provides results in a very good agreement with the ECN data in terms of the liquid length, vapor penetration, radial mixture fraction profiles, and ignition characteristics.…”

“…The governing equations are solved using the finite volume library OpenFOAM 39 . Here, a second order time integration method is utilized whereas the pressure-velocity coupling is treated using the PIMPLE algorithm 2,3,17,38 .…”

“…Here, we choose k = 0.3 for the momentum equation whereas k = 1.0 is selected for the scalars ensuring a bounded total variation diminishing solution. These k values are selected based our previous studies 2,3,17,38 . We note that recently Gadalla et al 38 compared the ILES approach against different SGS models in the ECN Spray A context, while Kaario et al 2020 42 studied effects of multiple flow realizations on LES results.…”

Fast reactive flow simulations using analytical Jacobian and dynamic load balancing in OpenFOAM

“…The simulations are performed for 4 reacting cases with varied ambient temperature (900, 1000, 1100, and 1200 K), and a single non-reacting case at 900 K. The domain is discretized with static mesh of 62 µm cell size in the inner most refinement layer to resolve the turbulent mixing and the quasi-steady lifted flame, as shown in Figure 7, resulting in total amount of 25-39 million cells depending on the particular case. Moreover, the implicit LES (ILES) approach is employed for turbulent subgrid-scale (SGS) modeling, consistent with our previous spray combustion works [25, 34-37, 40, 41], while the no-breakup model approach is used for droplet atomization which is further discussed in [41]. The volume-rendered spray flame shown in Figure 7 for ambient T = 900 K indicates the mixing and evaporation zone, the low-temperature combustion zone, and the ignition and high temperature combustion region wherein fully developed diffusion flame is observed.…”

Development of a Eulerian Multi-Fluid Solver for Dense Spray Applications in OpenFOAM

“…All of the mentioned approaches are still being actively researched [18,19,[24][25][26][27][28][29][30][31], and the academic and engineering community is constantly re-evaluating which approach gives the best trade-off between the cost and accuracy for each problem. This work presents the development of a Eulerian multi-fluid framework for predicting dynamic spray behavior in OpenFOAM.…”