Macchi, Marco, Wen, Jennifer X., Volkov, Konstantin, Heidari, Ali and Chung, Yongmann M. (2016) Modeling liquid fuel cascades with OpenFOAM. Process Safety Progress, 35(2), pp. 179-184. ISSN (print) 1066-8527
Abstract
Evaporating liquid cascades resulting from gasoline and liquefied natural gas (LNG) tanks overfilling or rupture of elevated pipes create a source of flammable vapour cloud. Such phenomena were responsible for the formation of the large fuel vapour cloud, the ignition of which resulted in the large scale explosion, in Buncefield [1] on 11 December 2005 at the Hertfordshire Oil Storage Terminal, an oil storage facility located by Hemel Hempstead in Hertfordshire, England. Despite its significance, there lacks adequate models treating the underlying physics of this phenomenon. The present study numerically analyses fuel cascades which are considered as a droplet-laden system. Consideration is given to vapour production inside the cascade due to droplets evaporation and breakup. The solver used here is a modification of the sprayFoam solver which is present in the open source computational fluid dynamics (CFD) toolbox OpenFOAM® [2]. The fuel droplets evaporate during their motion and create a cloud of flammable vapour. In order to capture the characteristics of the hazardous phenomena, the CFD model needs to address the underlying physics with adequate sub-models. In the present study, the multi-phase flow is simulated with a combined Eulerian-Lagrangian approach. The governing equations of the gas phase represent the conservation equations of mass, momentum and energy including the source terms arising from the interaction with the droplets. The Reynolds Averaged Navier-Stokes (RANS) simulation approach was used for its computational efficiency. The Large-Eddy Simulation (LES) would be more robust in handling the interaction of the droplets with the flow but it would be require more computational resource. The particulate phase is simulated through a Lagrangian deterministic or stochastic tracking models to provide particle trajectories and particle concentration. Particular emphasis is given to the effect of impingement of droplets to account for the effect of splashing in the impact region. The study involves developing robust and accurate modelling approaches for the instabilities and aerodynamic breakup in the cascade which contribute to the formation of the cloud, air entrainment and fuel impingement on deflector plates. Suitable sub-models have been implemented in OpenFOAM® to facilitate the study. The predictions are compared with the experimental measurements and CFD predictions previously conducted by Atkinson and Coldrick [3] from the Health and Safety Laboratory (HSL), an agency of the Health and Safety Executive (HSE). The present predictions are found to better capture the interaction between the droplets and the gas phase. Improved agreement with the experimental measurements in the gasoline fuel cascades has also been achieved.
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