CFD modelling of vortex combustors

This dissertation examines the suitability of Computational Fluid Dynamics (CFD) modelling for the production of realistic flowfields and temperature fields within a series of vortex combustion chambers of differing geometries and operating under various conditions. Initial validation of the CFD predictions was obtained through modelling of a series of isothermal vortex chambers for which a comprehensive set of experimental data was available. It was observed that CFD did indeed produce representative flowfield predictions for chambers of various geometries and operating conditions. A vortex unit used for the incineration of sewage sludge (US Navy Waste Incinerator) was subsequently investigated, and it was shown that due to the high moisture content of the waste material used, temperature profiles obtained with a modified coal combustion model were similar to those obtained with a more straightforward and computationally less expensive spray drier model. Results from both models were similar to experimentally observed conditions. However, comprehensive validation was not possible. In order that full validation could be provided for a CFD model of a vortex combustion unit, a model was developed of a commercial thermal oxidiser used for the incineration of liquid and gaseous wastes. CFD temperature predictions for the BASF Thermal Oxidiser were validated by a series of experimental measurements obtained from the operating unit. In general, it was found that the Reynolds Stress Model for turbulence produced the most representative velocity flowfields, with the less computationally demanding k-e model being applicable only under certain limited circumstances. Furthermore, insufficient grid refinement resulted in significantly distorted velocity profiles.