Investigation of a Computationally Efficient Multi-Scale Fire Modelling Method in Longitudinally Ventilated Tunnels for FDS6

To reduce the computational time for modelling large tunnel networks, we used FDS6.1 to investigate the solver’s capabilities for multi-scale modelling by combining 1D and full CFD models in the same domain. This study is to investigate the capabilities of FDS6.1 for simulating a tunnel ventilation system (cold and fire) using the multi-scale method. Firstly, we replicated the physical condition for cold flow using the multi-scale method and we validated the predictions against field measurements in the Dartford Tunnel, UK. This study demonstrated both the multi-scale and full models have good correlation with each other, and with the field measurements. Depending on the ratio of 1D and full CFD plus the scenarios modelled, the reduction in the computational time for the multi-scale method varies from 20% to 220% compared to the full CFD method. Secondly, we introduced a fire up to 75 MW in the multi-scale and full CFD models. Both models exhibit oscillatory mass flows along the tunnel similar to the pulsation effect observed in a tunnel fire. In the multi-scale method, the models significantly under or over-predicted the mass flows.