Modelling of non-premixed swirl burner flows using a Reynolds-stress turbulence closure

In this computational study, the performance of a differential Reynolds-stress turbulence model has been assessed in predicting a turbulent, non-premixed combusting swirling flow of the type frequently found in practical combustion systems. Calculations are also performed using the widely employed eddy-viscosity based k-ε turbulence model in order to examine the relative performances of these two closure models. The predictions are compared against the experimental data of mean axial and tangential velocities, turbulence quantities, gas temperatures and oxygen concentration collected in a 400 kW semi-industrial scale combustor fired with coke-oven gas using an industry-type swirl burner at the International Flame Research Foundation [17]. Computations of a corresponding non-combusting flow are also carried out and the predictions are compared with limited data available. The overall agreement between the measurements and the predictions obtained with both the k-ε and Reynolds-stress turbulence models are reasonably good, in particular, the flame properties. However, some features of the isothermal and combusting flow fields, and the flame are better predicted by the Reynolds-stress model. The subcritical nature of the isothermal flow and the effects of combustion on the size and shape of the swirl-induced internal recirculation zone in the corresponding combusting flow are well simulated by this model. The k-ε model fails to reproduce the subcritical nature of the isothermal flow. The predictions of this model erroneously show a general trend of the mean tangential velocity distribution to assume a forced-vortex profile. The levels of gas temperature and oxygen concentration in the internal recirculation zone and the enveloping shear region are on the whole better predicted by the Reynolds-stress model.