Browsing by Author "Vasilopoulos, Konstantinos"

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    Accidents caused by hazardous materials released in an urban environment: a numerical and experimental approach.
    (2019-04) Vasilopoulos, Konstantinos; Tsoutsanis, Panagiotis
    This research studies the transport and dispersion of hazardous materials after a fire accident in an urban setting and the unpredictable threats provoked for the population and the environment. A fire accident may result, inter alia, from industrial activity or during the transportation of hazardous materials, such as diesel, petrol or kerosene liquids. In the current research, mineral oil pool fire accidents are examined in order to define the toxic smoke zones at different urban scale geometries. Three different urban scale geometries are examined: a) an isolated building, b) a street canyon and c) a staggered array of urban blocks. The fluid flow, the hazardous dispersion and the safety limits are studied using the Computational Fluid Dynamics (CFD) techniques and wind tunnel experiments. The Computational simulations were conducted using the CFD solver of Fluent and the Fire Dynamic Simulator (FDS). Both Reynolds-average Navier-Stokes (RANS) modes and Large Eddy Simulations (LES) methods were applied. Wind tunnel experiments were conducted in order to better understand the flow around these geometries and evaluate them with LES models. The numerical models were validated with wind tunnel experiments and with additional experimental data selected from the bibliography. The numerical results defined the toxic smoke limits and allowed the creation of simplified risk maps. The latter can define the mitigation measures after a fire accident.
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    Assessment of air flow distribution and hazardous release dispersion around a single obstacle using Reynolds-averaged Navier-Stokes equations
    (Elsevier, 2019-04-09) Vasilopoulos, Konstantinos; Sarris, Ioannis E.; Tsoutsanis, Panagiotis
    The flow around a cubical building, with a pollution source at the central point of the top of the cube, is studied. The Reynolds-averaged Navier-Stokes and species concentration equations are solved for Reynolds number, Re = 40,000, is based on the height of the cube. The predictions obtained with the standard, the Kato-Launder, and the low-Reynolds number k-epsilon models are examined with various wall functions for the near wall treatment of the flow. Results are compared against Martinuzzi and Tropea measurements (J. of Fluids Eng., 115, 85–92, 1993) for the flow field and against Li and Meroney (J. of Wind Eng. and Industrial Aerodynamics, 81, 333–345, 1983) experiments and Gaussian models for the concentration distribution. It is found that the present unstructured mesh model performs similarly to the structured mesh models. Results from the Kato-Launder model are closer to the experimental data for the flow patterns and contaminant distribution on the cube's roof. However, the Kato-Launder model has an over-prediction for the recirculation zone and the contaminant distribution windward of the cube. The standard k-epsilon and the low-Reynolds number k-epsilon models predict similar flow patterns and are closer to the experimental data of the cube's windward and side face.
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    Computational assessment of the hazardous release dispersion from a diesel pool fire in a complex building’s area
    (MDPI, 2018-12-13) Vasilopoulos, Konstantinos; Mentzos, Michalis; Sarris, Ioannis E.; Tsoutsanis, Panagiotis
    A hazardous release accident taking place within the complex morphology of an urban setting could cause grave damage both to the population’s safety and to the environment. An unpredicted accident constitutes a complicated physical phenomenon with unanticipated outcomes. This is because, in the event of an unforeseen accident, the dispersion of the hazardous materials exhausted in the environment is determined by unstable parameters such as the wind flow and the complex turbulent diffusion around urban blocks of buildings. Our case study focused on a diesel pool fire accident that occured between an array of nine cubical buildings. The accident was studied with a Large eddy Simulation model based on the Fire Dynamics Simulation method. This model was successfully compared against the nine cubes of the Silsoe experiment. The model’s results were used for the determination of the immediately dangerous to life or health smoke zones of the accident. It was found that the urban geometry defined the hazardous gasses dispersion, thus increasing the toxic mass concentration around the buildings.
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    Large eddy simulation of dispersion of hazardous materials released from a fire accident around a cubical building
    (Springer Verlag, 2021-05-06) Vasilopoulos, Konstantinos; Lekakis, Ioannis; Sarris, Ioannis E.; Tsoutsanis, Panagiotis
    The turbulent smoke dispersion from a pool fire around a cubical building is studied using large eddy simulation at a high Reynolds number, corresponding to existing experimental measurements both in laboratory and field test scales. Emphasis of this work is on the smoke dispersion due to two different fuel pool fire accident scenarios, initiated behind the building. For the setup of fire in the first case, crude oil was used with a heat release rate of 7.8 MW, and in the second, diesel oil with a heat release rate of 13.5 MW. It is found that in both fire scenarios, the downstream extent of the toxic zone is approximately the same. This is explained in terms of the fact that the smoke concentration and dispersion are influenced mainly by the convective buoyant forces and the strong turbulence mixing processes within the wake zone of the building. It is suggested that wind is the dominating factor in these accident scenarios, which represent the conditions resulting in the highest toxicity levels.