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High-fidelity simulations for polydispersed sprays in the Eulerian–Lagrangian framework need to incorporate subgrid-scale effects in the particle evolution equations. Although the quasi-linear evaporation rate formulation captures evaporating droplet statistics, further improvement is required when subgrid-scale velocity effects become essential. The subgrid dispersion model strongly affects droplets spatial distribution, and subsequently net evaporation rate, depending on how rapidly they are dispersed into the dry air region. The main original contribution of this study is to assess the performances of a number of commonly used dispersion models in a consistent manner, against a reference direct simulation results. The models considered are (i) discrete random walk, (ii) approximate deconvolution method, (iii) stochastic model based on the Langevin equation, and (iv) combined approximate deconvolution method with the Langevin equation. Mass and enthalpy transfer source terms together with droplet diameters and particle distributions were compared against corresponding direct numerical and large-eddy simulations without a model as reference cases. Numerical results at low Stokes and moderate Reynolds numbers indicate that the dispersion model choice does not affect Eulerian field averages or fluctuations. However, proper dispersion models are essential to capture droplet distributions in the far-field region after jet breakup for Stokes number smaller than unity. The unclosed Lagrangian momentum equation without any dispersion model most accurately reproduces direct numerical simulation in the near field. [ABSTRACT FROM AUTHOR]

The study is aimed at demonstrating a methodology for the time-scale characterization of the chemistry-wall-heat-transfer interaction. The driving chemical time-scale is estimated by means of the tangential stretching rate, and a proper thermal timescale for the temperature-time variation due to wall heat flux is presented. A thermal Damköhler number, Dath, is proposed as the ratio of the two. The methodology is applied on a prototypical laminar methane-oxygen diffusion flame impinging on an isothermal cold wall. Non-adiabatic effects are described qualitatively and a CSP-TSR analysis is performed to obtain topological information and physical insights. The thermal Damköhler number field is computed and discussed to highlight the interplay between chemical and diffusive processes and to a-priori assess the accuracy of the steady laminar flamelet assumption under non-adiabatic conditions. [ABSTRACT FROM AUTHOR]