Numerical Simulations Of Dynamics Of A Tunnel Fire

This book covers a wide range of issues in fire safety engineering in tunnels, describes the phenomena related to tunnel fire dynamics, presents state-of-the-art research, and gives detailed solutions to these major issues. Examples for calculations are provided. The aim is to significantly improve the understanding of fire safety engineering in tunnels. Chapters on fuel and ventilation control, combustion products, gas temperatures, heat fluxes, smoke stratification, visibility, tenability, design fire curves, heat release, fire suppression and detection, CFD modeling, and scaling techniques all equip readers to create their own fire safety plans for tunnels. This book should be purchased by any engineer or public official with responsibility for tunnels. It would also be of interest to many fire protection engineers as an application of evolving technical principles of fire safety.

Fire and combustion presents a significant engineering challenge to mechanical, civil and dedicated fire engineers, as well as specialists in the process and chemical, safety, buildings and structural fields. We are reminded of the tragic outcomes of ‘untenable’ fire disasters such as at King’s Cross underground station or Switzerland’s St Gotthard tunnel. In these and many other cases, computational fluid dynamics (CFD) is at the forefront of active research into unravelling the probable causes of fires and helping to design structures and systems to ensure that they are less likely in the future. Computational fluid dynamics (CFD) is routinely used as an analysis tool in fire and combustion engineering as it possesses the ability to handle the complex geometries and characteristics of combustion and fire. This book shows engineering students and professionals how to understand and use this powerful tool in the study of combustion processes, and in the engineering of safer or more fire resistant (or conversely, more fire-efficient) structures. No other book is dedicated to computer-based fire dynamics tools and systems. It is supported by a rigorous pedagogy, including worked examples to illustrate the capabilities of different models, an introduction to the essential aspects of fire physics, examination and self-test exercises, fully worked solutions and a suite of accompanying software for use in industry standard modeling systems. Computational Fluid Dynamics (CFD) is widely used in engineering analysis; this is the only book dedicated to CFD modeling analysis in fire and combustion engineering Strong pedagogic features mean this book can be used as a text for graduate level mechanical, civil, structural and fire engineering courses, while its coverage of the latest techniques and industry standard software make it an important reference for researchers and professional engineers in the mechanical and structural sectors, and by fire engineers, safety consultants and regulators Strong author team (CUHK is a recognized centre of excellence in fire eng) deliver an expert package for students and professionals, showing both theory and applications. Accompanied by CFD modeling code and ready to use simulations to run in industry-standard ANSYS-CFX and Fluent software

This thesis investigates experimentally, theoretically and numerically the critical ventilation velocity in longitudinal ventilated tunnels in case of a fire. The critical velocity is defined as the minimum ventilation velocity that confines the front of the backlayer of harmful buoyant gases downwind of the source of emission. The fire is first modeled by a release of light gas in ambient air. In the experiments, the light fluid is an air/helium mixture. A simple mathematical model, based on the classical plume study, is formulated to interpret the variations of the critical velocity as a function of the source conditions (momentum and buoyancy fluxes and geometry). A good agreement is observed between the experimental results and the theoretical predictions for both the momentum-driven and buoyancy-driven releases. In addition, the non-Boussinesq effects, i.e. related to large differences between the densities of the buoyant plume and the ambient fluid, could be suitably modeled. Subsequently, the difference between a buoyant plume and a fire is studied, by combining experiments and numerical simulations. The reason for the appearance of the so-called 'super-critical' velocity, a ventilation velocity that becomes independent of the heat release rate when it becomes large, is discussed. It is shown that small fires can be reliably modeled as buoyant densimetric plumes released at ground level. The dynamics induced by larger fires require instead the modeling of large flames and hence a volumetric source of heat and buoyancy within the tunnel. In the simulation of fires, when the heat release rate is increased, the volume of combustion also increases, but the critical velocity remains nearly constant, which validates the appearance of the 'super-critical' velocity. The effect of tunnel inclination on the critical velocity is then studied. The influence of slope (defined as negative when the entrance of fresh air is at a lower elevation than the source) on the movement of smoke is mainly related to the role of the component of buoyancy along the tunnel axis. A positive slope helps the formation of the backlayer, while a negative slope helps reaching the critical condition. However, this effect depends on the source condition. Our experiments and numerical simulations on densimetric plumes suggest that the dynamical condition at the source affects the critical velocity of a buoyant plume: when the buoyant plume is momentum-driven, the influence of slope is small; when the buoyant plume is buoyancy-driven, the influence of slope is large. This behavior can be well described by a theoretical model based on the previous model of the critical velocity in a horizontal tunnel. These results have been extended to the case of fires by conducting numerical simulations and there is again a good agreement between the observed results and the theoretical model. In particular, the ratio of the critical velocities obtained for an inclined and an horizontal tunnel is independent of the power of the fire. Finally, the effect of vehicular blockage on the critical velocity is studied experimentally and numerically. The vehicles are modeled by blocks of different sizes placed upstream of the buoyancy or fire source. It is shown that only the block close to the source affects the critical velocity, whereas the effect of other blocks of the same size located further upstream is negligible. As the fire-blockage distance becomes larger, the critical velocity changes and becomes close to the value in an empty tunnel. The relative position between the blocks and the fire source has large influence on the critical velocity. When the blocks are placed at the center laterally, the ventilation flow cannot reach the fire plume directly, a larger critical velocity is needed compared with that in a corresponding empty tunnel. [...].

This book aims to cast light on all aspects of tunnel fires, based on experimental activities and theoretical and computational fluid dynamics (CFD) analyses. In particular, the authors describe a transient full-scale fire test (~15 MW), explaining how they designed and performed the experimental activity inside the Morgex North tunnel in Italy. The entire organization of the experiment is described, from preliminary evaluations to the solutions found for management of operational difficulties and safety issues. This fire test allowed the collection of different measurements (temperature, air velocity, smoke composition, pollutant species) useful for validating and improving CFD codes and for testing the real behavior of the tunnel and its safety systems during a diesel oil fire with a significant heat release rate. Finally, the fire dynamics are compared with empirical correlations, CFD simulations, and literature measurements obtained in other similar tunnel fire tests. This book will be of interest to all engineers and public officials who are concerned with the nature, prevention, and management of tunnel fires.

This book contains twelve chapters detailing significant advances and applications in fluid dynamics modeling with focus on biomedical, bioengineering, chemical, civil and environmental engineering, aeronautics, astronautics, and automotive. We hope this book can be a useful resource to scientists and engineers who are interested in fundamentals and applications of fluid dynamics.

This book is served as a reference text to meet the needs of advanced scientists and research engineers who seek for their own computational fluid dynamics (CFD) skills to solve a variety of fluid flow problems. Key Features: - Flow Modeling in Sedimentation Tank, - Greenhouse Environment, - Hypersonic Aerodynamics, - Cooling Systems Design, - Photochemical Reaction Engineering, - Atmospheric Reentry Problem, - Fluid-Structure Interaction (FSI), - Atomization, - Hydraulic Component Design, - Air Conditioning System, - Industrial Applications of CFD

TRB’s National Cooperative Highway Research Program (NCHRP) 415: Design Fires in Road Tunnels information on the state of the practice of design fires in road tunnels, focusing on tunnel fire dynamics and the means of fire management for design guidance.