Large Eddy Simulation Of Spray Combustion Research Articles

Experimental and numerical investigation of thermo-acoustic instability in a liquid-fuel aero-engine combustor at elevated pressure: Validity of large-eddy simulation of spray combustion

The feasibility of applying the large-eddy simulation (LES) of spray combustion to the investigation of the thermo-acoustic instability mechanisms in practical aero-engine combustors was examined, employing experimental data obtained from optical measurements. Single sector combustion tests using a staged fuel injector were conducted at the JAXA high temperature and pressure combustion test facility. An unstable operating condition exhibiting strong self-excited thermo-acoustic instability with a peak frequency of approximately 500Hz and an amplitude more than 40kPa was chosen for measurements of the dynamic pressure, in addition to OH-PLIF and OH∗ chemiluminescence studies. LES calculations were performed under the same conditions and the use of LES was validated based on comparisons of results with experimental data, considering the dynamic pressure and unsteady flame behaviors. In addition, a more detailed investigation was performed with the LES data, focused on unsteady characteristics such as velocity, evaporation rate, equivalence ratio and heat release rates. In general, LES was found to successfully reproduce the experimentally observed unsteady characteristics of pressure and flame structures during thermo-acoustic instability, though there were several discrepancies between LES and experimental results with regard to the oscillation amplitude and local flame behavior, such as the periodical flame flashback. In the LES data, the time evolution of the product of the flame surface area and the flame-area-averaged equivalence ratio were in good agreement with the overall heat release rate variations, suggesting a simple dominant mechanism for the thermo-acoustic instability. These results provide evidence for the feasibility of employing LES as a means of further exploring the effects of key physical parameters, such as the spatial distribution of fuel and its temporal variations, on combustion instability.

Large-eddy Simulation of Ethanol Spray-Air Combustion and Its Experimental Validation

Large-eddy simulation of spray combustion is under its rapid development. Different combustion models were used by different investigators. However, these models are less validated by detailed experimental data. In this paper, large-eddy simulation (LES) of ethanol spray-air combustion was made using an Eulerian-Lagrangian approach, a subgrid-scale kinetic energy stress model, and a filtered finite-rate combustion model, neglecting the sub-grid scale reaction rate. The simulation results are compared with experimental dada in the literature and validated in detail. The LES obtained statistically averaged gas temperature is in much better agreement with the experimental results than Reynolds averaged (RANS) modeling using the most complex probability density function (PDF) equation combustion model. The instantaneous LES results show the coherent structures of the shear region near the high-temperature flame zone and the fuel vapor concentration map, indicating that the droplets are concentrated in this shear region. The instantaneous temperature, oxygen and carbon dioxide concentration maps show the close interaction between the coherent structures and the combustion reaction.

Large-eddy simulation of spray combustion in a gas turbine combustor

The paper describes the results of a comprehensive study of turbulent mixing, fuel spray dispersion and evaporation and combustion in a gas-turbine combustor geometry (the DLR Generic Single Sector Combustor) with the aid of Large Eddy Simulation (LES). An Eulerian description of the continuous phase is adopted and is coupled with a Lagrangian formulation of the dispersed phase. The sub-grid scale (sgs) probability density function approach in conjunction with the stochastic fields solution method is used to account for sgs turbulence-chemistry interactions. Stochastic models are used to represent the influence of sgs fluctuations on droplet dispersion and evaporation. Two different test cases are simulated involving reacting and non-reacting conditions. The simulations of the underlying flow field are satisfying in terms of mean statistics and the structure of the flame is captured accurately. Detailed spray simulations are also presented and compared with measurements where the fuel spray model is shown to reproduce the measured Sauter Mean Diameter (SMD) and the velocity of the droplets accurately.

Advances in LES of Two-phase Combustion (II) LES of Complex Gas-Particle Flows and Coal Combustion

Large-eddy simulation (LES) is under its rapid development and is recognized as a possible second generation of CFD methods used in engineering. Large-eddy simulation of two-phase flows and combustion is particularly important for engineering applications. Some investigators, including the present authors, give their review on LES of spray combustion in gas-turbine combustors and internal combustion engines. However, up to now only a few papers are related to the state-of-the-art on LES of gas-particle flows and combustion. In this paper a review of the advances in LES of complex gas-particle flows and coal combustion is presented. Different sub-grid scale (SGS) stress models and combustion models are described, some of the main results are summarized, and some research needs are discussed.

Advances in Large-eddy Simulation of Two-phase Combustion (I) LES of Spray Combustion

Spray combustion is widely used in power, transportation, chemical and metallurgical, iron and steel making, aeronautical and astronautical engineering. In recent years, large-eddy simulation (LES) becomes more and more attractive, because it can give the instantaneous flow and flame structures, and may give more accurate statistical results than the Reynolds averaged Navier-Stokes (RANS) modeling. In this paper, the present status of the studies on LES of spray combustion is reviewed, and the future research needs are discussed.