Large-eddy simulation of multiphase combustion jet in cross-flow using flamelet model

In this work, large-eddy simulations of pulverized coal combustion are conducted using the flamelet model, in which the devolatilization, char surface reactions, radiation and flame-wall interactions (FWI) are all considered. The mixings between the oxidizer and the volatiles/char off-gases are described with two mixture fractions Zvol and Zchar, while the interphase heat transfer and progress of reactions are described with the manifolds of total enthalpy He and reaction progress variable YPV, respectively. The turbulence-chemistry interactions are considered with the presumed probability density functions. Standard pulverized coal combustion submodels are used to characterize the coal combustion sub-processes of devolatilization, char surface reactions, radiation, etc. Characteristics of pulverized coal combustion jet in cross-flow (JICF) are analyzed in detail. Particularly, the effects of the flame-flame interactions (FFI) and the wall heat losses (WHL) on the pulverized coal flame structure and thermo-chemical quantities distributions are studied through both qualitative and quantitative analyses. The results show that the overall flame temperature with twin jets in cross-flow (TJICF) is higher than that with single jet in cross-flow (SJICF) due to the FFI. The gas velocities in different directions have different sensitivities to the FFI, and the particle residence time/trajectory is influenced by the FFI. Three stages of FFI are identified, i.e., separated flames, merging flames and a merged flame. When the effects of WHL are neglected, the flame front becomes more wrinkling, the flame base moves towards the injectors, and the coal particles are ignited earlier. The pulverized coal flame structure at the lee-side of the flame front is more complicated than that at the leading-edge due to the different flow dynamics, and many burning pockets can be observed at the lee-side.