Numerical analysis of smoke layer stability

International audienceThe EGSISTES project is a global reflection about risk and dangerous phenomena relative to underground infrastructures. One category of risk identified for such an infrastructure is the fire and its consequences in terms of temperature and smoke propagation. In some situations, smoke stratification is used to ensure safety of people located inside the tunnel. In such a case, it must be ensure that smoke stay stratified even in the case of an aerodynamic perturbation such as a jet fan or vehicles presence. Two ways enable the improvement of the understanding of smoke behaviour in underground infrastructure: experiments and numerical approach. Both strategies are used complementary during the project. Experiments are achieved in the INERIS fire gallery while two CFD codes, FDS and Phoenics, based on two different approaches for turbulence modelling, are used. The first step consists in a comparison between experimental and numerical results on a configuration given as a reference. This reference case was chosen as the backlayering smoke layer establishment and stability. The numerical objective was to reproduce the length and thickness of this layer. After having shown that both codes should predict with a quite good accuracy the backlayering length, those two codes are used to study the influence of perturbation on the stratification stability. This study shows firstly that a jet located upstream the backlayering smoke layer tends to modify the smoke layer front but influences slightly the smoke layer near the fire. Secondly, in case of the presence of vehicles downstream the fire in a congested tunnel, the stratification is not altered just above vehicles but can be altered downstream these obstacles

A new tunnel assessment procedure integrating smoke dispersion and evacuation models

International audienceThis paper focuses on a new risk assessment procedure for tunnel. This procedure is based on the coupling between smoke dispersion models and evacuation models. It has been developed inside the UPGRADE procedure put in place in the UPTUN project. The method is based on two heat and mass flow (HMF) models for the calculation of tenability conditions due to a fire event: NewVendis for the 1D calculation and the global equilibrium of the tunnel network and FASIT for the calculation in the vicinity of the fire. Tenability conditions are used as input data for the evacuation calculation carried out by the evacuation model CRISP . All results (smoke dispersion and evacuation) are then combined in tenability diagrams which are a superposition of HMF tenability conditions and users' location in the tunnel. This kind of presentation can then be used to help understand injuries or people casualties and to take efficient safety measures to increase safety level in tunnel

Are the tunnel ventilation systems adapted for the different risk situations ?

International audienceThe ventilation design criteria for both road and rail tunnel is based on the design fire defined by the standards and the general knowledge about smoke propagation. The problem of such an approach is that it considers only the impact on the safety ventilation of the smoke propagation and dispersion inside the tunnel excluding other possible accident. However some other situations, such as toxic gas release, are possible and even if the aim is not to design the ventilation on other dangerous phenomena with a lower occurrence frequency, it must be ensure that the ventilation system does not increase the consequences of the accident. Mainly, the problem of toxic gas dispersion is pointed out in this paper. Because of the large variety of dangerous materials that can transit in tunnel, the probability of an accident that impacts a toxic transport cannot be neglected. In the worst case scenario, such as a massive release of high toxic gases, the ventilation is useless because of the toxic quantity that induces a large number of deaths inside the tunnel. However, when the toxic release is lower and ventilation can be used, having in mind that toxic gas is generally heavy gas or a cold gas, the behaviour will of course be different than the one of smoke and the ventilation system may not be adapted for such a situation. This case has scarcely been studied yet. In this study, both experimental approach and numerical tools were used to improve the global understanding of dense gas dispersion in underground infrastructure such as road tunnels. The experimental work was achieved in the INERIS fire gallery which represents a 50 m long 1/3rd scale tunnel using Argon. It was achieved for different leaks conditions in order to appreciate the dense gas natural behaviour. This work has also enabled the comparison between experimental work and CFD calculation with FDS code for the particular application of dense gas dispersion. . The work was extended to some other configurations and geometry in order to simulate real scale situation with different kind of gases : a highly toxic dense gas such as Chlorine, a light gas stored as a liquid at a very low temperature such as Ammonia, and a gas which remains liquid at ambient temperature and pressure and is drained into an evaporating pool such as Acrolein. This work will consider the natural behaviour of the gases and the influence of longitudinal ventilation both inside and outside of the tunne

Modélisation des effets thermiques et aérauliques dans les stations de métro

This work aims at the physical and the numerical modelling of air motion and heat transport phenomena in subway stations. The study is based on an approach described by the unsteady three-dimensional Euler's equations completed by source terms. These equations are discretized with a finite volume method and solved by a SIMPLE algorithm coupled with a scheme as proposed by Van Leer. The spatial discretization is made by a cartesian grid. In order to take the relative motions of the coaches inside the station into account, a sliding grid method is implemented. To validate the model, calculations are compared to measurements of the flow generated by mixed convection in a rectangular open duct equipped with an heated plate in its central part. The study ends by some applications of the numerical code in the case of a typical Parisian subway station.Ce travail porte sur la modélisation physique et numérique des écoulements d'air et des échanges de chaleur dans les stations de métro. L'étude se base sur une description des écoulements par les équations d'Euler tridimensionnelles instationnaires auxquelles sont ajoutés des termes source. Ces équations sont discrétisées par une formulation de volumes finis et résolues par un algorithme de type SIMPLE couplé à un schéma de Van Leer. La description de la géométrie du domaine de calcul est assurée par un maillage cartésien. Afin de prendre en compte le déplacement des rames dans la station, une technique de maillage glissant est élaborée. Le modèle est validé sur des écoulements générés par convection mixte dans un canal de section rectangulaire contenant une plaque chauffante dans sa partie centrale. L'étude se termine par quelques applications du code de calcul dans une station de métro type du métro parisien

Etude numérique de l'influence des véhicules sur la destratification des fumées d'un incendie en tunnel

International audienceThis article show the results of four CFD simulations made with FDS software [1]. This numerical study deals with the influence of vehicle on stratification loss phenomena in tunnel fire. First evaluations on this influence are then proposed. A comparison is systematically established between the case with vehicles and the case without vehicle. The results shown here after concern two different heat release rate currently used in French hazard studies for road tunnels. Thèse first results have shown that vehicles stopped in the near field upstream improve the stratification by reducing theé rebound of smoke plume on the roof. In opposite, vehicles in the far field upstream fire increase the size of turbulent structures, which induces a speed up of stratification loss phenomena.Cet article présente les résultats de quatre simulations CFD réalisées à partir du code de calcul FDS [1]. Cette étude numérique permet de mettre en avant le phénomène de déstratification lié à la présence de véhicules dans un tunnel et de donner une première quantification sur ce niveau de déstratification. Une comparaison est établie de façon systématique entre la configuration tunnel avec obstacle et celle sans obstacle. Les résultats sont présentés pour deux puissances d'incendie type généralement retenues dans le cadre des études spécifiques des dangers des tunnels routiers. Ces premiers résultats ont permis de montrer que la présence de véhicules situés en aval proche de l'incendie favorise la stratification des fumées en limitant le phénomène de rebond des fumées au plafond. Par contre, plus en aval, les structures tourbillonnaires engendrées par ces véhicules accroissent le taux de déstratification

UPTUN : a risk assessment methodology for fires in tunnels

International audienc

Modélisation des effets thermiques et aérauliques dans les stations de métro

Ce travail porte sur la modélisation physique et numérique des écoulements d'air et des échanges de chaleur dans les stations de métro. L'étude se base sur une description des écoulements par les équations d'Euler tridimensionnelles instationnaires auxquelles sont ajoutés des termes source. Ces équations sont discrétisées par une formulation de volumes finis et résolues par un algorithme de type SIMPLE couplé à un schéma de Van Leer. La description de la géométrie du domaine de calcul est assurée par un maillage cartésien. Afin de prendre en compte le déplacement des rames dans la station, une technique de maillage glissant est élaborée. Le modèle est validé sur des écoulements générés par convection mixte dans un canal de section rectangulaire contenant une plaque chauffante dans sa partie centrale. L'étude se termine par quelques applications du code de calcul dans une station de métro type du métro parisien.This work aims at the physical and the numerical modelling of air motion and heat transport phenomena in subway stations. The study is based on an approach described by the unsteady three-dimensional Euler's equations completed by source terms. These equations are discretized with a finite volume method and solved by a SIMPLE algorithm coupled with a scheme as proposed by Van Leer. The spatial discretization is made by a cartesian grid. In order to take the relative motions of the coaches inside the station into account, a sliding grid method is implemented. To validate the model, calculations are compared to measurements of the flow generated by mixed convection in a rectangular open duct equipped with an heated plate in its central part. The study ends by some applications of the numerical code in the case of a typical Parisian subway station.VALENCIENNES-BU Sciences Lettres (596062101) / SudocSudocFranceF