| Computer simulations have the potential to viably address the design challenges of modern combustion applications, provided that adequate models for the prediction of multiphysics processes can be developed. Heat transfer has particular significance in modeling because it directly affects thermal efficiencies and pollutant formation in combustion systems. Convective heat transfer from flame-wall interaction has received increased attention in aeronautical propulsion and power-generation applications where modern designs have trended towards more compact combustors with higher surface-to-volume ratios, and in diesel engines where enclosed volumes and cool walls provide ample conditions for thermal quenching. As intense flame-wall interactions can induce extremely large heat fluxes, their inclusion is important in computational models used to predict performance and design cooling systems.;In the present work, a flamelet method is proposed for modeling turbulence/chemistry interactions in large-eddy simulations (LES) of non-premixed combustion systems with convective heat-losses. The new method is based on the flamelet/progress variable approach of Pierce & Moin (J. Fluid Mech. 2004, 504:73-97) and extends that work to include the effects of thermal-losses on the combustion chemistry. In the new model, chemical-state databases are constructed by solving one-dimensional diffusion/reaction equations which have been constrained by scaling the enthalpy of the system between the adiabatic state and a thermally-quenched reference state. The solutions are parameterized and tabulated as a function of the mapping variables: mixture fraction, reaction progress variable, and normalized enthalpy. The new model is applied to LES of non-premixed methane-air combustion in a coaxial-jet with isothermal wall-conditions to describe heat transfer to the confinement. The resulting velocity, species concentration, and temperature fields are compared to experimental measurements and to numerical results from the adiabatic model. The new method shows distinct improvement in the prediction of temperature, mixture composition, and heat flux in the near-wall regions of the combustor. |
