CHEMICAL ENGINEERING TRANSACTIONS VOL. 67, 2018 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Valerio Cozzani, Bruno Fabiano, Davide Manca Copyright © 2018, AIDIC Servizi S.r.l. I SBN 978-88-95608-64-8; I SSN 2283-9216 Practical LES Modelling of Jet Fires: Issues and Challenges Simone Favrin, Valentina Busini, Renato Rota, Marco Derudi* Politecnico di Milano, Dip. di Chimica, Materiali e Ingegneria Chimica “G. Natta”, Via Mancinelli 7 - 20131 Milano – Italy marco.derudi@polimi.it Jet fires represent a major risk in the process industry and it is a growing trend to use Computational Fluid Dynamics (CFD) models to achieve a better description in realistic scenarios. In this work, a process of validation was undertaken to investigate the capabilities of Fire Dynamic Simulator (FDS) in representing a jet fire. In particular, a medium scale subsonic propane jet fire was simulated with the purpose of analysing two main parameters (mesh dependency and initial unmixed fraction of the reactants). Results of different simulations were compared with the experimental data to highlight model performance and limitations. 1. Background A jet fire in a congested environment can rapidly lead to major consequences; even short time exposures to jet fire effects can generate catastrophic outcomes due to the high temperatures and heat transfer rates which can easily lead to the failure of other vessels or equipment. Jet fire research is still an open problem because even if a certain number of correlations are available in literature (Lees, 2004), better estimations are always required for different aspects. An example is represented by Boot (2016), who found radiation correlations still requiring improvements and validation. One of the fundamental aspects to consider when evaluating a jet fire is the impinging phenomenon, which consists of the modification of the free flame behavior due to the interaction with obstacles, barriers, or equipment (Casal et al., 2012). That said, flame impingement is strongly affected by environmental conditions, plant layout and geometric factors. Consequently, to perform a correct risk assessment in real scenarios neither semi-empirical correlations nor integral models are sufficient because they refer to non-impinged conditions. Therefore, CFD modelling is a suitable tool to be used in the decision-making procedure for loss prevention when jet fires are involved. 1.1 FDS development and extended applications In the last years, FDS has been increasingly used as a fire engineering tool. In parallel with the spreading of the software, a deep knowledge of the physical behaviour of fire and smoke and of its computational limits is required (Tavelli et al., 2013; Johansson & Ekholm, 2018). As a direct consequence of this, before it is possible to use FSD to model new phenomena (such as jet fires), it is necessary to perform a specific validation of the software. Validation and extension of the fields of applicability of FDS has been addressed in recent works such the one of Sellamy et al. (2018) in which a modelling of BLEVE phenomena is proposed, or by Sun et al. (2017) who performed a preliminary validation of FDS for impinging jet fires. Different aspects concur in the simulation of jet fires; first of all, the combustion model, even if extremely simplified needs to be adequate to the purpose of describing the combustion in the flame region. Maragkos & Merci (2017) reported the good agreement achieved using FDS in modelling the combustion of a fire plume. Other critical aspects are related to the description of high momentum jets, but as reported in Ferreira & Vianna (2016) FDS appears to be able to deal with high velocity gaseous dispersions and good agreement can be expected. Several studies have been performed to understand high velocity jet flames but usually they present two main limitations: steady state conditions and low dimensions of the domain. Simulating a stationary flame is a limitation because change in shape can happen rapidly and can be not well described by a steady solution: the case of vortexes or periodically steady solutions is representative of this limitation. Low dimensions of the domain are the price payed to implement a detailed combustion model. Unfortunately, the DOI: 10.3303/CET1867044 Please cite this article as: Favrin S., Busini V., Rota R., Derudi M., 2018, Practical les modelling of jet fires: issues and challenges, Chemical Engineering Transactions, 67, 259-264 DOI: 10.3303/CET1867044 259