Large eddy simulation of turbulent spray combustion

Abstract

The two-phase filtered mass density function (FMDF) method is employed for large eddy simulation (LES) of high speed evaporating and combusting nheptane sprays using simple (global) and complex (skeletal) chemical kinetic mechanisms. The resolved fluid velocity and pressure fields are obtained by solving the filtered compressible Navier-Stokes equations with high-order Eulerian finite difference methods. The liquid spray and gas scalar (temperature and species mass fractions) fields are both obtained by Lagrangian stochastic models. The chemistry calculation is accelerated by incorporating the parallel in situ adaptive tabulation (ISAT) method. There are two-way interactions among Eulerian and Lagrangian fields. Simulations of evaporating sprays with and without combustion indicate that the two-phase LES/FMDF results are consistent and compare well with the available experimental data at different gas temperatures and oxygen concentrations. The spray controlled flame tends to move away from a diffusion flame structure toward a premixed one as the oxygen concentration decreases and/or the ambient gas temperature increases because of changes in spray-induced turbulence and mixing. The LES/FMDF results for ignition delay show more sensitivity to the chemical kinetic model at lower gas temperatures due to slower reaction and stronger turbulence-chemistry interactions. The liftoff length is less sensitive to the kinetics.

A semi-Lagrangian transport method for kinetic problems with application to dense-to-dilute polydisperse reacting spray flows

“…It is also a well established approach in mechanical engineering problems such as gas turbines [87,60], solar concentrators [96], and chemical engineering risers [17]. For internal combustion engines with direct fuel injection, DSMC descriptions of the spray have allowed Reynolds Average Navier-Stokes (RANS) simulations with multiple physical phenomena like a moving piston [90] or a detailed turbulent-chemistry interaction model [77] as well as Large Eddy Simulations (LES) [58,93]. But stochastic Lagrangian simulations are difficult to converge leading to statistical noise and to spurious correlation patterns.…”

Turbulent mixing in non-isothermal jet in crossflow

“…(12)). In this procedure, the FMDF is represented by an ensemble of computational ''stochastic elements'' or ''Monte Carlo particles'' [58]. These notional particles evolve through a ''stochastic process'', described by a set of stochastic differential equations (SDEs) [59,60].…”

Comparative study on chemical kinetic schemes for dual-fuel combustion of n-dodecane/methane blends

“…Various SGS models have been introduced in the literature and previous spray studies include e.g. dynamic Smagorinsky type models [147,184], dynamic structure models [185,186] and one-equation eddy models [31,187]. In principle, models introduce explicitly additional dissipation into the system.…”