Comparative Analysis of Numerical Methods Regarding the Backflow Investigation in Tunnels of Zentrum am Berg

Abstract

The efficiency of tunnel ventilation systems is commonly evaluated through numerical modelling. In this survey, two CFD models were developed by means of Fire Dynamic Simulator and Ansys Fluent software. The simulation results were used to assess the model performance in studying the backflow distribution in a real tunnel. A full-scale experiment to evaluate the ventilation conditions in the western railway tunnel was carried out in Zentrum am Berg. The velocity values were obtained for 90 examined points located at 10 cross-sections along a 100-meter tunnel part. The results showed good agreement in velocity variation trends from field measurements and those predicted by numerical models. At cross-sections more distant from the fan outlets, the FDS and Fluent models overestimated the flow velocities to a different extent. The simulated backflow development corresponds well to the observed three specified regions (initial, transitional, and developed) with distinctive flow structures. The FDS calculations confirmed the registered spontaneous changes in flow direction at points with a prevailed flow direction in the vicinity of the jet fans. Despite some discrepancies in results, the comparative analysis of two numerical models showed their applicability in the backflow investigation.