96 research outputs found
Direct numerical simulation of an atomizing biodiesel jet: Impact of fuel properties on atomization characteristics
[EN] The utilization of biodiesel is an effective approach to reduce pollution from internal combustion engines and thus
has attracted steadily increasing interest in the recent years. As the viscosity of biodiesel is much higher than that of
standard diesel, the atomization characteristics of a biodiesel jet can significantly deviate from those of a standard
diesel jet under identical injection conditions. Since atomization of the injected fuel has a strong impact on fuel-air
mixing and the following combustion processes, it is important to investigate the atomization of biodiesel and in
particular to understand how the fuel properties affect the atomization process and the resulting spray characteristics.
In the present study, three-dimensional direct numerical simulations are conducted to investigate atomizing
biodiesel and diesel jets. The novel adaptive multiphase solver Basilisk is used for simulations. The statistics of
droplets formed in the biodiesel jet is compared to the diesel jet under identical injection conditions.This project has been supported by the ANR MODEMI project (ANR-11-MONU-0011) program. This work was granted access to the HPC resources of TGCC-CURIE under the allocations x20152b7325, x20162b7325 and t20162b7760 made by GENCI. We would also acknowledge support from the Academic and Research Computing Services at the Baylor University.Ling, Y.; Legros, G.; Popinet, S.; Zaleski, S. (2017). Direct numerical simulation of an atomizing biodiesel jet: Impact of fuel properties on atomization characteristics. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 370-377. https://doi.org/10.4995/ILASS2017.2017.5035OCS37037
Planar Jet Stripping of Liquid Coatings: Numerical Studies
In this paper, we present a detailed example of numerical study of flm
formation in the context of metal coating. Subsequently we simulate wiping of
the film by a planar jet. The simulations have been performed using Basilisk, a
grid-adapting, strongly optimized code. Mesh adaptation allows for arbitrary
precision in relevant regions such as the contact line or the liquid-air impact
zone, while coarse grid is applied elsewhere. This, as the results indicate, is
the only realistic approach for a numerical method to cover the wide range of
necessary scales from the predicted film thickness (tens of microns) to the
domain size (meters). The results suggest assumptions of laminar flow inside
the film are not justified for heavy coats (liquid zinc). As for the wiping,
our simulations supply a great amount of instantaneous results concerning
initial film atomization as well as film thickness.Comment: 20 pages, 20 figure
Breaking wave field statistics with a multilayer model
The statistics of breaking wave fields is characterised within a novel
multi-layer framework, which generalises the single-layer Saint-Venant system
into a multi-layer and non-hydrostatic formulation of the Navier-Stokes
equations. We simulate an ensemble of phase-resolved surface wave fields in
physical space, where strong non-linearities including wave breaking are
modelled, without surface overturning. We extract the kinematics of wave
breaking by identifying breaking fronts and their speed, for freely evolving
wave fields initialised with typical wind wave spectra. The
distribution, defined as the length of breaking fronts (per unit area) moving
with speed to following Phillips 1985, is reported for a broad range
of conditions. We recover the scaling without any
explicit wind forcing for steep enough wave fields. A scaling of
based solely on the mean square slope and peak wave phase speed is shown to
describe the modelled breaking distributions well. The modelled breaking
distributions are found to be in good agreement with field measurements and the
proposed scaling is consistent with previous empirical formulations. The
present work paves the way for simulations of the turbulent upper ocean
directly coupled with realistic breaking waves dynamics, including Langmuir
turbulence, and other sub-mesoscale processes.Comment: first submissio
Model Skill and Sensitivity for Simulating Wave Processes on Coral Reefs Using a Shock-Capturing Green-Naghdi Solver
International audienceWave flume data from published benchmark experiments were used to extensively evaluate numerical model skill and sensitivity for applying a shock-capturing Green-Naghdi (GN) model to simulate nonlinear wave transformation processes on complex coral reefs. Boussinesq-type models that utilise nonlinear shallow water equations (NSWEs) to represent wave breaking and dissipation hold significant potential for understanding coastal hazards associated with global environmental change and sea-level rise. These fully nonlinear phase-resolving models typically require a threshold condition to switch from dispersive equations to shock-capturing NSWEs in areas of active wave breaking. However, limited information exits regarding how this splitting approach influences the behaviour of different surf-zone processes that contribute to wave runup and inundation on coral reefs. This paper presents a comprehensive analysis of model sensitivity to explore how input parameters that control wave breaking and dissipation influence the behaviour of sea-swell (SS) waves, infragravity (IG) waves, wave setup, runup and solitary waves on coral reefs. Results show that each wave process exhibits unique sensitivity to the free-surface slope threshold (B) that is used to represent areas of active wave breaking by locally switching from the weakly-dispersive GN equations to the shock-capturing NSWEs. However, accurate representation of all wave processes can be achieved if the wave-face steepens to at least 35 degrees (B ≥ 0.7) before breaking is initiated. Results from this research support and encourage the use of nonlinear phase-resolving wave models as tools for academic research, coastal management, coastal engineering and hazard forecasting on atoll and fringing reef environments
Direct numerical simulation of bubble-induced turbulence
We report on an investigation of bubble-induced turbulence. Bubbles of a size larger than the dissipative scale cannot be treated as pointwise inclusions, and generate important hydrodynamic fields in the carrier fluid when in motion. Furthermore, bubble motions may induce a collective agitation due to hydrodynamic interactions which display some turbulent-like features. We tackle this complex phenomenon numerically, performing direct numerical simulations with a volume-of-fluid method. In the first part of the work, we perform both two-dimensional and three-dimensional tests in order to determine appropriate numerical and physical parameters. We then carry out a highly resolved simulation of a three-dimensional bubble column, with a set-up and physical parameters similar to those used in laboratory experiments. This is the largest simulation attempted for such a configuration and is only possible thanks to adaptive grid refinement. Results are compared both with experiments and previous coarse-mesh numerical simulations. In particular, the one-point probability density function of the velocity fluctuations is in good agreement with experiments. The spectra of the kinetic energy show a clear k(-3) scaling. The mechanisms underlying the energy transfer and notably the possible presence of a cascade are unveiled by a local scale-by-scale analysis in physical space. The comparison with previous simulations indicates to what extent simulations not fully resolved may yet give correct results, from a statistical point of view
- …