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Abstract: In this paper, lean premixed flames featuring local extinction are simulated numerically by Large Eddy Simulations (LES) and investigated experimentally by one-dimensional, spatially resolved Raman scattering. Two unconfined piloted lean premixed natural gas/air flames with equivalence ratios ϕ =0.71 and 0.65 are studied. The Reaction–Diffusion Manifold (REDIM) technique is employed together with the presumed joint Filtered Density Function (FDF) to carry out the LES. In the present work, two reduced coordinates, the CO2 and N2 mass fractions, are considered in the REDIM look-up table, and the joint FDF of them is modelled in terms of two statistically independent FDFs. Good overall agreement between the experimental data and the LES results is obtained. Scatter plots from measurements and instantaneous data from LES show states with local extinction, mainly in the leaner flame. The results demonstrate the capability of the proposed REDIM-presumed joint FDF method to deal with the phenomenon of local extinction in lean premixed flames. [Copyright &y& Elsevier]

Abstract: For the first time the Reaction–Diffusion Manifold (REDIM) technique is implemented together with a presumed Filtered Density Function (FDF) to carry out Large Eddy Simulation (LES) of lean premixed swirling flames in the well-known PRECCINSTA burner. The REDIM approach reduces detailed chemical kinetics based on low-dimensional reaction–diffusion manifolds in composition space, so that many species can be accurately estimated at a relatively low computational cost via a look-up table. In the present work, only one reduced coordinate, the CO2 mass fraction, is considered in the REDIM look-up table. Implementation of the REDIM/FDF model is performed with two presumed FDF shapes, top-hat and clipped Gaussian. Two premixed flames are simulated, with equivalence ratios 0.75 and 0.83, respectively. Velocity, temperature and species concentration profiles are discussed and compared to the experimental data. The results are in good overall agreement with the corresponding experiment. It is also shown that the LES results obtained with the two presumed FDFs are very similar and the reason for this is analysed. [Copyright &y& Elsevier]

In this paper we present detailed Euler–Euler Large Eddy Simulations (LES) of dispersed bubbly flow in a rectangular bubble column. The motivation of this study is to investigate the potential of this approach for the prediction of bubbly flows, in terms of mean quantities. The physical models describing the momentum exchange between the phases including drag, lift and wall force were chosen according to previous experiences of the authors. Experimental data, Euler–Lagrange LES and unsteady Euler–Euler Reynolds-Averaged Navier–Stokes results are used for comparison. It is found that the present model combination provides good agreement with experimental data for the mean flow and liquid velocity fluctuations. The energy spectrum obtained from the resolved velocity of the Euler–Euler LES is presented as well. [ABSTRACT FROM AUTHOR]

This paper presents detailed Euler–Euler Scale-Adaptive Simulations of the dispersed bubbly flow in a square cross-sectioned bubble column. The main objective is to investigate the potential of this approach for the prediction of bubbly flows with anisotropic liquid velocity fluctuations. The set of physical models describing the momentum exchange between the phases was chosen according to previous experiences of the authors. Experimental data and Euler–Euler Large Eddy Simulation are used for comparison. It was found that the presented combination of sub-models provides good agreement with experimental data for the mean flow and liquid velocity fluctuations. The energy spectra of the resolved velocity obtained from the simulations are presented and compared to the experimental spectra. [ABSTRACT FROM AUTHOR]