Flamelet Table Research Articles

Flamelet LES of a semi-industrial pulverized coal furnace

The goal of this work is to introduce the flamelet model into large eddy simulation (LES) of realistic coal furnaces. A flamelet table based on two mixture fractions (for volatile and char off-gases) and enthalpy is generated and used in a massively parallel LES of the semi-industrial IFRF coal furnace (Weber et al. 1992 [1, 2]) for which comprehensive experimental data is available enabling the validation of the flamelet model under realistic conditions. Comparison between experiment and simulation is shown by means of averaged quantities of velocities, species concentrations and temperature. Overall good agreement between experiment and simulation could be obtained, giving evidence for the suitability of the flamelet model. The results of the LES are further analyzed, focussing on instantaneous particle and gas phase data to gain additional insight into the coal conversion process inside the furnace.

One-Dimensional H2/O2 Counterflow Diffusion Flame Simulation for Flamelet Table Construction at Supercritical Pressure

Supercritical fluid properties are implemented in a one-dimensional counterflow flame simulation code using the Soave-Redlich-Kwong equation of state and modifying the transport properties for high-pressure, low-temperature conditions. Examination of a GH2/LOX diffusion flame at supercritical pressure reveals an extremely fine structure at the edge of the oxygen diffusion layer, indicating that a DNS-like approach to simulation of such flames is not practical in the near term, and flame modeling must be used. To investigate flamelet table construction, we compare simulations that use supercritical fluid and standard temperature and pressure (STP) gas properties. Both types of simulations are shown to produce almost identical flame structures when we parameterize the flame with the scalar dissipation rate at its stoichiometric position. The results show that the use of STP gas property simulation is expected to be an effective means of greatly reducing the computational cost of constructing flamelet tables at supercritical pressures.

Molecular diffusion effects in LES of a piloted methane–air flame

Molecular diffusion effects in LES of a piloted methane–air (Sandia D) flame are investigated on a series of grids with progressively increased resolution. The reacting density, temperature and chemical composition are modeled based on the mixture fraction approach combined with a steady flamelet model. With a rationale to minimize interpolation uncertainties that are routinely introduced by a flamelet table look-up, quadratic splines relationships are employed to represent thermochemical variables. The role of molecular diffusivity in effecting spatial transport is studied by drawing a comparison with the turbulent diffusivity and analyzing their statistics conditioned on temperature. Statistical results demonstrate that the molecular diffusivity in the near-field almost always exceeds the turbulent diffusivity, except at low temperatures (less than 500 K). Thus, by altering the jet near-field, molecular transport plays an important role in the further downstream jet development. Molecular diffusivity continues to dominate in the centerline region throughout the flow field. Overall, the results suggest the strong necessity to represent molecular transport accurately in LES studies of turbulent reacting flows.