Large Eddy Simulation of High-Velocity Fuel Sprays: Studying Mesh Resolution and Breakup Model Effects for Spray A

Wehrfritz, Armin; Vuorinen, Ville; Kaario, Ossi; Larmi, Martti

doi:10.1615/atomizspr.2013007342

Cited by 65 publications

(51 citation statements)

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“…As shown in Figure 5, the model shows fairly good qualitative agreement, but underpredicts the fuel mass fraction on the spray centerline. Similar results have been reported by Wehrfritz et al [12,15] for comparable grid resolutions using Lagrangian spray models that rely on parameter tuning. In reference [15], the mixture field prediction could be improved by increasing the spatial resolution, which has not been targeted in this study due to the high computational cost.…”

Section: Inert Casesupporting

confidence: 88%

“…Similar results have been reported by Wehrfritz et al [12,15] for comparable grid resolutions using Lagrangian spray models that rely on parameter tuning. In reference [15], the mixture field prediction could be improved by increasing the spatial resolution, which has not been targeted in this study due to the high computational cost. Nevertheless, considering the fact that no model parameter tuning has been performed, the overall agreement is in an acceptable range.…”

Section: Inert Casesupporting

confidence: 88%

“…Hence, Lagrangian spray models are usually only valid in a limited range of operating conditions. Especially, the initial droplet sizes and breakup model parameters vary significantly in the literature [15,16].…”

Section: Spray Modelmentioning

confidence: 99%

“…Further breakup models have not been applied in this study, since no major effect had been seen in previous simulations. The momentum exchange was modeled by a high velocity drag formulation for spherical droplets [15], while the evaporation model by Miller et al [19] is employed for computing the heat and mass transfer.…”

Section: Spray Modelmentioning

confidence: 99%

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LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Davidovic

Falkenstein

Bode

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-A single-hole n-dodecane spray flame is studied in a Large-Eddy Simulation (LES) framework under Diesel-relevant conditions using a Multiple Representative Interactive Flamelets (MRIF) combustion model. Diesel spray combustion is strongly affected by the mixture formation process, which is dominated by several physical processes such as the flow within the injector, break-up of the liquid fuel jet, evaporation and turbulent mixing with the surrounding gas. While the effects of nozzle-internal flow and primary breakup are captured within tuned model parameters in traditional Lagrangian spray models, an alternative approach is applied in this study, where the initial droplet conditions and primary fuel jet breakup are modeled based on results from highly resolved multiphase simulations with resolved interface. A highly reduced chemical mechanism consisting of 57 species and 217 reactions has been developed for n-dodecane achiving a good computational performance at solving the chemical reactions. The MRIF model, which has demonstrated its capability of capturing combustion and pollutant formation under typical Diesel conditions in Reynolds-Averaged Navier-Stokes (RANS) simulations is extended for the application in LES. In the standard RIF combustion model, representative chemistry conditioned on mixture fraction is solved interactively with the flow. Subfilter-scale mixing is modeled by the scalar dissipation rate. While the standard RIF model only includes temporal changes of the scalar dissipation rate, the spatial distribution can be accounted for by extending the model to multiple flamelets, which also enables the possibility of capturing different fuel residence times. Overall, the model shows good agreement with experimental data regarding both, low and high temperature combustion characteristics. It is shown that the ignition process and pollutant formation are affected by turbulent mixing. First, a cool flame is initiated at approximately stoichiometric mixture and propagates towards the rich side. Hence, heat and radicals are transported away from the most reactive mixture and thus the ignition is delayed. At the same time, the transported heat and radicals increase the reactivity of rich mixtures, which strongly affects the CO formation. NO was found to increase compared to the no transport case due to enhanced mixing, which is related to a broader high-temperature zone and the additional transport of oxygen from lean into high-temperature regions.

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Section: Inert Casesupporting

confidence: 88%

Section: Inert Casesupporting

confidence: 88%

Section: Spray Modelmentioning

confidence: 99%

Section: Spray Modelmentioning

confidence: 99%

See 2 more Smart Citations

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Davidovic

Falkenstein

Bode

et al. 2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

View full text Add to dashboard Cite

show abstract

“…The main reason for this test is that the scheme is very popular in both LES [34,35] and Monotone Integrated Large Eddy Simulation (MILES) [36] simulations. The numerical results obtained by two simulations with and without turbulent viscosity can be distinguished in Figure 2.…”

Section: Turbulent Viscosity In Dissipative Schemesmentioning

confidence: 99%

Investigation of Numerical Effects on the Flow and Combustion in LES of ICE

Nguyen

Kempf

2017

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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-This work investigates the influence of numerical dissipation on the modeled combustion in Large Eddy Simulations (LES). It is well known that capturing the dynamics of the in-cylinder flow is crucial for engine simulations, as it strongly affects flame propagation. The flame propagation during the power-stroke highly depends on the turbulence level that is developed throughout compression. This turbulence level will be strongly influenced by the accuracy of the numerical schemes employed. Even a small extent of upwinding, filtering, low-order implicit time-stepping, cell-stretching or mapping between grids may affect the flow field, the turbulence level, and hence the turbulent flame speed and the pressure curve. To provide a reference, the LES in-house code PsiPhi is used, which ensures a minimum of dissipation due to high order explicit time-stepping, homogeneous and isotropic filters and cells. Good stability of the code permits the use of a second-order Central Differencing Scheme (CDS) for the transport of momentum, avoiding numerical dissipation. To analyse the effect of numerical dissipation, simulations of a fired engine are performed using different numerical schemes for the convection of momentum. Physical quantities including the total kinetic energy, the velocity gradient, the turbulent viscosity, the in-cylinder pressure, the flame propagation or the burning rate of different test cases are evaluated and compared to each other to show the numerical effects on combustion. Furthermore, the suitability of common LES quality criteria including an energy criterion and viscosity ratio is discussed based on the comparison of simulations with less and more accurate numerics. It is shown that these LES quality indicators can be highly misleading.

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Influence of mesh deformation on the quality of large eddy simulations

Keskinen

Vuorinen

Kaario

et al. 2016

Numerical Methods in Fluids

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SUMMARYThe influence of mesh motion on the quality of large eddy simulation (LES) was studied in the present article. A three-dimensional, turbulent pipe flow (Re D 360) was considered as a test case. Simulations with both stretching and static meshes were carried out in order to understand how mesh motion affects the turbulence statistics. The spatial filtering of static and moving mesh direct numerical simulation (DNS) data showed how an ideal LES would perform, while the comparison of DNS cases with static and moving meshes revealed that no significant numerical errors arise from the mesh motion when the simulation is fully resolved. The comparison of the filtered fields of the DNS with a moving mesh with the corresponding LES fields revealed different responses to mesh motion from different numerical approaches. A straightforward test was applied in order to verify that the moving mesh works consistently in LES: when the mesh is stretched in the streamwise direction, the moving mesh results should be in between the two extremal resolutions between which the mesh is stretched. Numerical investigations using four different LES approaches were carried out. In addition to the Smagorinsky model, three implicit LES approaches were used: linear interpolation (non-dissipative), the Gamma limiter (dissipative), and the scale-selective discretisation (slightly dissipative). The results indicate that while the Smagorinsky and the scale-selective discretisation approaches produce results consistent with the resolution of the non-static mesh, the implicit LES with linear interpolation or the Gamma scheme do not.

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Large Eddy Simulation of High-Velocity Fuel Sprays: Studying Mesh Resolution and Breakup Model Effects for Spray A

Cited by 65 publications

References 0 publications

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

LES of n-Dodecane Spray Combustion Using a Multiple Representative Interactive Flamelets Model

Investigation of Numerical Effects on the Flow and Combustion in LES of ICE

Influence of mesh deformation on the quality of large eddy simulations

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