Large eddy simulation of two isothermal and reacting turbulent separated oxy-fuel jets

In this work, a Large eddy simulation (LES) method and a tabulated chemistry approach according to the Flamelet Generated Manifold (FGM) strategy are coupled to numerically study the interactions of turbulent isothermal and reacting flows stemming from two aligned jets providing alternately fuel (natural gas) and oxidant (pure oxygen gas). The jets feature different geometries and deliver unequal momentums at the boundaries. The effect of oxygen in comparison to air environment on the FGM tabulation and results is pointed out. In addition, the impact of combustion on the flow and mixing field evolvement is analyzed. The LES relies on a dynamic Smagorinsky subgrid scale (SGS) model and a linear eddy diffusivity ansatz to close the SGS stresses and the SGS scalar fluxes for describing the turbulent flow field and the turbulent scalar field, respectively. For model assessment, available laser-based experimental data are used for model validation. In particular the numerical results are compared with available experimental data for the flow field. The latter are gained experimentally by the Particle Image Velocimetry (PIV) and laser tomography, respectively. In the first part of this paper, the jets interaction process is studied for the isothermal case while the oxy-fuel combustion in the reacting case is analyzed in the second part. The analysis is achieved in terms of statistical quantities for the flow velocity, mixture fraction, chemical species and temperature. An overall satisfactory agreement is reported

Numerical and experimental study of central jet displacement effects on the dynamics of a coaxial burner

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Poste de professeur-e en communication Tenure track position of Assistant Professor in Communication Studies

Le Département de communication sollicite des candidatures pour occuper un poste à temps plein de professeure ou de professeur de communication au rang d’adjoint (Université de Montréal)

Numerical and experimental investigation of turbulent three separated jets

WOS:000379270400016International audienceIn this work three-dimensional turbulent and separated jets are numerically studied and compared with experimental data. The basic idea of the separated jet burner consists in separating fuel and oxidizer injection to dilute reactants with combustion products before the reactants mix. The computation is achieved using the finite-volume numerical method. The turbulence is modeled using a second order Reynolds Stress Model (RSM) by Launder Reece Rodi. A non uniform grid is applied and particularly tightened close to the exit jets in order to capture the near field mechanisms. The validation of the numerical tools is done by comparison with experimental data of the non ventilated jets. Ventilated jets are investigated only numerically. The obtained results show that mixing is improved using three jets compared to the single jet. A comparison between computed ventilated and non ventilated jets is presented. It yields a larger velocity mean value, but a decreasing of the corresponding root mean square of the turbulent velocity fluctuations (rms). (C) 2016 Elsevier Ltd. All rights reserved

Oxygen enrichment effects on CH 4 -air turbulent flow characteristics in a coaxial swirl burner

International audienceThis paper reports results on the effect of oxygen enrichment on flow and turbulent flames in a coaxial swirl burner. The investigation was performed by S-PIV in CH4-air-O2 non-reacting and reacting flows. This work is the continuation of studies carried out previously by the authors on the same burner, with different new operating conditions. The burner consists of 2 concentric tubes, with a swirler located in the annular part through which the oxidant (air-O2) is supplied. The CH4 gas is delivered into the central tube and injected radially into the combustion chamber through small holes. The burner is placed in a parallelepiped combustion chamber with a volume of 120×50×50 cm3. The paper reports detailed results on mean velocity fields, profiles of the three velocity components (U,V,W) and velocity fluctuations (U’,V’,W’) in the case of a 150 Nl/min oxidant flow rate, a swirl number Sn = 1.4 and an equivalence ratio Φ = 1. Three cases of O2 addition were investigated, 21%, 25%, and 30% (in vol.) corresponding to 9.4 kW, 11.7 kW, and 14.5 kW of combustion power, respectively. In-depth analysis of the field velocity differences between reactive and non-reactive cases was carried out and showed a significant difference in flow velocities between reacting and non-reacting flows. The profiles of the mean velocities, fluctuations and velocity decays differed, and higher values were observed in the reacting case. The enrichment of air with oxygen affected the velocity fields and their fluctuations in both distribution and values. The addition of O2 increased the flame temperature, leading to a greater radial expansion and a reduction in the size of the recirculation zone. The maximum axial velocity increased significantly as a function of the O2 rate, whereas the swirling velocity varied only slightly. The velocity fluctuation results also revealed a difference in profiles and values depending on O2 enrichments and locations along the flow

Point defect localization and cathodoluminescence emission in undoped ϵ-Ga2O3

In this study, experimental and theoretical investigations have been performed on nominally undoped ϵ-Ga2O3 films deposited on (0001)-Al2O3 substrates by metal-organic vapor phase epitaxy using different O and Ga precursor ratios. Hydrogen and helium were used as carrier gas. Low-temperature cathodoluminescence (CL) broad emissions extending over the range 1.5-3.4 eV were deconvoluted in five peaks, whose position, integrated intensity, and full width at half maximum were investigated in the temperatures range 80 K-300 K. A non-monotonic behavior of the extracted CL peaks is observed, which is attributed to localization phenomena connected with families of point defects. The behavior of two main luminescence emissions with temperature has been simulated using the localized state ensemble model. The derived parameters agree with the experimental observations and provide a new interpretation of micro-and macroscale disorder inside ϵ-Ga2O3 and related potential fluctuations

Elaboration de dépôts de TiO2 par projection plasma pour le traitement de l'eau par photocatalyse

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Combined impact of B2H6 flow and growth temperature on morphological, structural, optical, and electrical properties of MOCVD-grown B(In)GaAs heterostructures designed for optoelectronics

BGaAs/GaAs epilayers and BInGaAs/GaAs quantum well (QW) have been prepared using metal–organic chemical vapor deposition under different growth conditions, and their physical and structural properties have been examined. SEM-EDS investigation showed a dependence of surface properties of the ternary compound on the growth conditions. High-resolution X-ray diffraction evidenced a tensile strain for the ternary alloys whatever the growth condition, while the quaternary QW always shows a compressive strain state. Room temperature optical absorption allowed to follow the variation of the bandgap with boron incorporation. Photoluminescence measurements confirmed the carrier-localization phenomenon and its dependence with the growth conditions. Deposition temperature and diborane (B2H6) flow rate are with particularly significant effects on the optical properties: lower diborane flow rate and high growth temperature enhance the radiative emission. Computer simulation using localized state ensemble model quantitatively relates the lattice inhomogeneity to the optical properties and suggests a way to engineer the localization phenomenon and avoid clustering effects. Electrical investigations by current–voltage, capacitance and conductance methods have been performed for the first time on selected BGaAs samples. The ideality factor of Schottky barriers has been determined, while their height and film doping level could only be approximately estimated. Such physical properties make boron-based alloys very promising for applications in multijunction solar cells