Evaluation of Turbulence Models in Gas Dispersion

Abstract

Several earlier model validation studies for predicting gas dispersion scenarios have been conducted for the three RANS two-equation eddy viscosity turbulence models, the standard k-ε (SKE), Re- Normalisation group k-ε (RNG) and Realizable k-ε (Realizable). However, these studies have mainly validated one or two of the models, and have mostly used one simulation case as a basis for determining which model is the best suited for predicting such scenarios. In addition, the studies have shown conflicting results as to which model is ideal for dispersion simulations. The aim of the study was therefore to assess three well-known RANS two-equation eddy viscosity models, in four different gas dispersion cases. The purpose was to evaluate the models' behaviour compared to experimental data, in order to see which of the models was best suited for predicting dispersion scenarios. The cases used in the thesis were: CO2 dispersion in a cross- wind, neutral dispersion in an urban environment, hydrogen jet impinging on a surface, and a dense jet dispersion on an industrial site. All simulations were conducted with a CFD software that partially resolved the geometry, and was designed for large complex multiscale flow scenarios. The most important parameters for assessing the turbulence models were accuracy of the simulation results and computational time used. Overall, SKE seemed to be the best-suited model for 3 out of 4 cases, and provided good results for all the scenarios. However, RNG also provided reasonably results in all cases, in a practical timeframe. Realizable was the model that commonly used longest computational time, and was found least suitable for 3 out of 4 cases.