The evaluation of radiative heat transfer effects in turbulent non-premixed flames.

摘要

This thesis is concerned with studying the effect of radiation heat transfer on turbulent combustion. While radiation heat transfer affects both temperature and species concentrations in turbulent combusting flows, this effect is often not accounted for in existing combustion models. The goal of the current research is to develop a methodology for incorporating the effect of radiation into the laminar flamelet combustion model and to assess the impact of this coupling on turbulent combusting flow predictions.; With the conventional flamelet model, the flame structures are calculated with radiative heat losses neglected, so that the radiation effects on flame structures are not accounted for in the flamelet library. A new approach based on a presumed environ mental temperature has been proposed in the current study. It is assumed that each flame is exposed to different environmental temperatures, thus exchanging a different level of radiative energy with the surroundings. Thus, a series of non-adiabatic flamelet libraries can be generated for a wide range of environmental temperatures. The non-adiabatic flamelet libraries are then validated by comparison with the experimental data, for turbulent hydrogen jet flame and a bluff body flame.; From the non-adiabatic flamelet library, the effect of radiation heat transfer on each species can be estimated, but actual effects depend on the local enthalpy defect and the strain rate of the turbulent flame considered. The results show that the species concentrations can be significantly affected by the radiative heat losses at low strain rates and high enthalpy defect regions. The inclusion of radiation heat losses in the flamelet generation generally provides improved predictions of species concentrations. Ultimately, the current study will make a contribution to the development of more sophisticated prediction models of air pollutants by providing accurate prediction for species concentrations in turbulent combustion.