共查询到10条相似文献,搜索用时 98 毫秒
1.
M. Sanjosé J.M. Senoner F. Jaegle B. Cuenot S. Moreau T. Poinsot 《International Journal of Multiphase Flow》2011
Large-Eddy Simulations (LES) of an evaporating two-phase flow in an experimental burner are investigated. Two different numerical approaches for the simulation of the dispersed phase are coupled to the same gaseous solver: a mesoscopic Eulerian method and a Lagrangian particle tracking technique. The spray is represented by a single droplet size owing to the locally monodisperse formulation of the employed mesoscopic Eulerian approach. Both approaches use the same drag and evaporation models. They do not take into account the atomization process and a simplified injection model is applied instead. The presented methodology, referred as FIM-UR (Fuel Injection Method by Upstream Reconstruction) defines injection profiles for the monodisperse spray produced by a pressure-swirl atomizer. It is designed so as to ensure similar spray characteristics for both approaches and allows for a direct comparison between them. After a validation of the purely gaseous flow in the burner, liquid-phase dynamics and droplet dispersion are qualitatively and quantitatively evaluated for the Eulerian and Lagrangian simulations. Results obtained for both approaches are in very good agreement and compare reasonably with experiments, indicating that simplified injection methods are appropriate for the simulation of realistic combustor geometries. 相似文献
2.
The major objective of this work is to numerically investigate the interacting physical and chemical phenomena that characterize
the flow in a stabilized cool flame diesel fuel spray evaporation system. A two-phase RANS computational fluid dynamics code
has been developed and used to predict the characteristics of the developing turbulent, multiphase, multi-component, reactive
flow-field. The code employs a Eulerian–Lagrangian approach, taking into account the mass, momentum, thermal and turbulent
energy exchange between the phases. A variety of physical phenomena, such as turbulent dispersion, droplet evaporation, droplet-wall
collision, conjugate heat transfer, drift correction, two-way coupling are taken into account by implementing respective sub-models.
Two alternative modelling approaches for the simulation of cool flame reactions have been validated and evaluated by comparing
numerical predictions with experimental data from two atmospheric pressure, evaporating Diesel spray, Stabilized Cool Flame
reactors. Both models have achieved good quantitative agreement in the majority of the considered test cases. The results
have been used to estimate the local physical and chemical characteristic time scales of the occurring phenomena, thus allowing,
for the first time, the classification of stabilized cool flames. 相似文献
3.
In this study, via an Eulerian–Lagrangian framework, the performance of two recent dispersion models, i.e. a first-order autoregressive process and the PDF model, is compared. The appropriate relations for the turbulence scales and the drift correction term are suggested and the tuned values for the constants of the models are proposed in a systematic approach by starting with the simplest case, i.e. particle-laden stationary isotropic turbulence and adding more complexities in the subsequent cases, including the homogeneous anisotropic shear flow, decaying grid turbulence, and inhomogeneous gas–solid spray. Also, the isotropic relation for the effect of inertia in the Lagrangian turbulence time scale seen by particles is extended to the anisotropic case while it remains consistent in the isotropic limit. Finally, the performance of the tuned models is evaluated for the simulation of an evaporating spray. It is observed that, the tuned constants for the evaporating spray are close to the ones obtained for the homogeneous shear flow. 相似文献
4.
Gregory Hannebique Patricia Sierra Eleonore Riber Bénédicte Cuenot 《Flow, Turbulence and Combustion》2013,90(2):449-469
Because of compressibility criteria, fuel used in aeronautical combustors is liquid. Their numerical simulation therefore requires the modeling of two-phase flames, involving key phenomena such as injection, atomization, polydispersion, drag, evaporation and turbulent combustion. In the present work, particular modeling efforts have been made on spray injection and evaporation, and their coupling to turbulent combustion models in the Large Eddy Simulation (LES) approach. The model developed for fuel injection is validated against measurements in a non-evaporating spray in a quiescent atmosphere, while the evaporation model accuracy is discussed from results obtained in the case of evaporating isolated droplets. These models are finally used in reacting LES of a multipoint burner in take-off conditions, showing the complex two-phase flame structure. 相似文献
5.
Young-Sam Shim Gyung-Min Choi Duck-Jool Kim 《International Journal of Multiphase Flow》2009,35(10):885-895
The spray–wall impingement process in gasoline direct injection (GDI) engines, which is caused by the interaction among spray, wall and air to move the air–fuel mixture near the spark plug, directly influences the engine performance and emissions. Therefore, a detailed understanding of this process is very important in designing an injection system and controlling a strategy of GDI engines. The purpose of this study is to understand the spray–wall impingement characteristics for more efficient designing of the injection system in GDI engines and to supply the fundamental data under engine operation conditions. The wall impingement processes of hollow-cone fuel spray according to ambient gas conditions and wall geometry are calculated by validated spray models. The calculated results were compared with the experimental results obtained by the laser-induced exciplex fluorescence (LIEF) technique. It was found that the spray and vortex cloud at the high ambient pressure were distributed at inner area of cavity and the more fuel film mass observed at this condition. The fuel film mass decreased with the increase of ambient temperature, while the fuel film mass increased at high cavity angles. 相似文献
6.
This paper presents a detailed numerical analysis of diesel engine spray structure induced by the Engine Combustion Network (ECN) Spray A at different injection pressures. The non-reacting simulations are performed using OpenFOAM where an Eulerian–Lagrangian model is adopted in the large eddy simulation (LES) framework. Effects of the LES mesh resolution as well as the spray model parameters are investigated with the focus on their impact on spray structure as the injection pressure varies. The predicted liquid and vapour penetration lengths agree well with the measurements at different injection pressures. The mixture fraction is well captured for the injection pressure of 100 and 150 MPa while a slight deviation from the measurements is observed for the injection pressure of 50 MPa near the nozzle. The parametric analysis confirms that the LES mesh resolution has significant effects on the results. A coarser mesh leads to higher liquid and vapour penetration lengths where the deviation from the measurements is larger, resulting in the highest error at the lowest injection pressure. As the mesh size increases, the droplet size distribution becomes narrower, its pick moves to the smaller droplet size and the probability of droplets with higher temperature increases. On the other hand, with increasing the mesh size, the carrier gas velocity decays slower and its radial dispersion decreases. It is found that the droplet characteristics are more affected by the mesh resolution when the injection pressure is the lowest while the opposite is true for the carrier phase. The number of Lagrangian particles also affects the droplet characteristics and the fuel-air mixing but their effects are not as significant as the mesh size. The results become less sensitive to the number of Lagrangian particles as the pressure injection decreases. Finally, the importance of the initial droplet size distribution is investigated, confirming its impact is marginal, particularly on the liquid length. It is observed that the initial droplet size is only important at very close to the nozzle and its impact on the spray structure becomes quickly insignificant due to the high rates of breakup and evaporation. This trend is consistent at different injection pressures. 相似文献
7.
Simulations of a pilot-stabilised flame in a uniformly dispersed ethanol spray are performed using a Doubly Conditional Moment Closure (DCMC) model. The DCMC equation for spray combustion is derived, using the mixture fraction and the reaction progress variable as conditioning variables, including droplet evaporation and differential diffusion terms. A set of closure sub-models is suggested to allow for a first, preliminary application of the DCMC model to the test case presented here. In particular, the DCMC model is used to provide complete closure for the Favre-averaged spray terms in the mean and variance equations of the conditioning variables and the present test case is used to assess the importance of each term. Comparison with experimental data shows a promising overall agreement, whilst differences are related to modelling choices. 相似文献
8.
A computationally efficient spray model is presented for the simulation of transient vaporizing engine sprays. It is applied to simulate high-pressure fuel injections in a constant volume chamber and in mixture preparation experiments in a light-duty internal combustion engine. The model is based on the Lagrangian-Particle/Eulerian-Fluid approach, and an improved blob injection model is used that removes numerical dependency on the injected number of computational parcels. Atomization is modeled with the hybrid Kelvin–Helmholtz/Rayleigh–Taylor scheme, in combination with a drop drag model that includes Mach number and Knudsen number effects. A computationally efficient drop collision scheme is presented, tailored for large numbers of parcels, using a deterministic collision impact definition and kd-tree data search structure to perform radius-of-influence based, grid-independent collision probability estimations. A near-nozzle sub-grid scale flow-field representation is introduced to reduce numerical grid dependency, which uses a turbulent transient gas-jet model with a Stokes–Strouhal analogy assumption. An implicit coupling method was developed for the Arbitrary Lagrangian–Eulerian (ALE) turbulent flow solver. A multi-objective genetic algorithm was used to study the interactions of the various model constants, and to provide an optimal calibration. The optimal set showed similar values of the primary breakup constants as values used in the literature. However, different values were seen for the gas-jet model constants for accurate simulations of the initial spray transient. The results show that there is a direct correlation between the predicted initial liquid-phase transient and the global gas-phase jet penetration. Model validation was also performed in engine simulations with the same set of constants. The model captured mixture preparation well in all cases, proving its suitability for simulations of transient spray injection in engines. 相似文献
9.
10.
The objective of the present work is to provide, through the association of optical diagnostics on a well-chosen experimental
configuration, new insights into the coupling of a vortical gaseous flow with a polydisperse evaporating spray representative
of practical injections. A cloud of droplets is injected in an inert laminar round jet, axisymmetric and pulsated, enabling
the study of the interaction of strong-vorticity structures with a polydisperse spray. The experiment is a laboratory-scale
representation of realistic injection configurations such as in engine combustion chambers or industrial burners. The chosen
set-up leads to a well-controlled configuration and allows the coupling of two optical diagnostics, particle imaging velocimetry
(PIV) and interferometric particle imaging (IPI), which leads to the study of both the flow dynamic and the droplet size distribution.
The behaviour of droplets is analysed regarding their relaxing and evaporating properties. Size-conditioned preferential concentration
of both weakly evaporating and strongly evaporating sprays is investigated. Droplet trajectories are also analysed by means
of high-rate tomographic visualizations. The time history between their ejection from the nozzle and their interaction with
the vortex is strongly related to the droplet preferential concentration and the observed heterogeneous repartition in the
gas flow. 相似文献