Title: Multiscale modeling of transient flows from fire and ventilation in long tunnels
Speaker: Dr Guillermo Rein

From: Department of Mechanical Engineering at Imperial College, UK
Date: July. 30, 2014
CV of the Speaker:

Guillermo is Senior Lecturer in the Department of Mechanical Engineering at Imperial College and Editor-in-Chief of the journal Fire Technology. Guillermo joined Imperial in 2012 from a previous academic position at University of Edinburgh (2006-2012). His professional activities are centred on research in fire behaviour and combustion of solid fuels, and teaching of thermofuild sciences to engineers. He is contributing to mitigate the accidental burning of ancient carbon deposits – megafires of peatlans and coal seams (see keynote presentation). These are the largest and longest burning fires on Earth, and its study is particularly important in the context of greenhouse emissions and geoengineering. Another emphasis of his research is on fire dynamics and how engineers design safer buildings and tunnels. He pioneered the engineering concepts of 'travelling fires' and 'forecasting fire dynamics', which offer a paradigm shift in the design and protection of modern infrastructure.
Guillermo has received a number of international awards (e.g, Hinshelwood Prize, Distinguished Paper Combustion Institute, FM Global Award) and has been featured in international media (e.g. ENR, BBC Material World,GeoLog, New York Times, DotEarth). He maintains a blog, Fortune Favours the Bold, where he writes occasionally in a more informal tone on fire science and engineering.
Abstract:

This presentation applies a transient multiscale approach to model ventilation flows and fires in a tunnel domain. The multiscale model couples dynamically a Computational Fluid Dynamics (CFD) solver with a simple 1D network model, allowing for a more rational use of the computational resources without loss of accuracy. The 1D network models tunnel regions where the flow is fully developed (far field), while detailed CFD models regions where flow conditions require 3D resolution (near field). The work describes both numerical models and gives emphasis to the discussion of the coupling algorithm and the control of the numerical error. Compared to full CFD, the multiscale model provides a reduction of the required computing time by 40 times without significant loss of accuracy. The methodology has been applied to study the transient flow interaction between a growing fire and a ramping-up ventilation system in a modern tunnel of 7 m diameter section and 1.2 km in length. Different ventilation scenarios are investigated to provide the timing to reach the critical velocity at the seat of the fire, and to remove the upstream back layering. The results allow for simultaneous optimization of the ventilation and detection systems. The multiscale methodology represents the most feasible tool to conduct accurate simulations in long tunnel domains, when the limitation of the computational cost becomes too restrictive.