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Numerical studies on two large-scale compartment buoyant fires were performed utilizing a fully coupled Large Eddy Simulation (LES) and strained laminar flamelet combustion model, extended from single-step to multistep chemical reaction. Two Subgrid-Scaled (SGS) turbulent models, Smagorinsky and WALE, were examined for center and corner fires. Comp...
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Context 1
... atrium compartment fire case study conducted by Gutiérrez-Montes et al. [48] demonstrated that 1=10 R Ã 1=15 would successfully predict not only the flame properties but also the overall gas temperature field. Details of different mesh systems are investigated in Table 1, which have been constructed based on the resolution criteria in which coarse and medium mesh systems satisfy 1=10 R Ã 1=5 whereas fine mesh systems satisfy 1=10 R Ã 1=15. ...
Context 2
... sensitivity and time step. To determine the appropriate mesh for this study, grid convergence study is performed using different grid resolutions and the assessment is presented in Table 1 in terms of average grid size in meters. The mesh sensitivity results for the Smagorinsky-Lilly LES model and the single-step chemical reaction are illustrated in Figure 2. As can be seen in the figure, there is sig- nificant improvement from the coarse mesh to the medium mesh whereas there is in appreciable difference for the results between the medium mesh and the fine mesh. ...
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Citations
... where q represents the heat generation rate per unit volume of a single battery, and the subscript b denotes the battery cell. Moreover, the CFD methodology provides a numerical solution for turbulence flow [86][87][88][89]. The shear-stress transport k-ω model simulates the turbulence flow during the battery pack cooling process. ...
Given the growing demand for increased energy capacity and power density in battery systems, ensuring thermal safety in lithium-ion batteries has become a significant challenge for the coming decade. Effective thermal management plays a crucial role in battery design optimization. Air-cooling temperatures in vehicles often vary from ambient due to internal ventilation, with external air potentially overheating due to vehicle malfunctions. This article highlights the efficiency of lateral side air cooling in battery packs, suggesting a need for further exploration beyond traditional front side methods. In this study, we examine the impact of three different temperature levels and two distinct air-cooling directions on the performance of an air-cooling system. Our results reveal that the air-cooling direction has a more pronounced influence compared with the air-cooling temperature. By employing an optimal air-cooling direction and ambient air-cooling temperature, it is possible to achieve a temperature reduction of approximately 5 K in the battery, which otherwise requires a 10 K decrease in the air-cooling temperature to achieve a similar effect. Therefore, we propose an empirical formula for air-cooling efficiency under various conditions, aiming to provide valuable insights into the factors affecting air-cooling systems for industrial applications toward enhancing the fire safety of battery energy storage systems.
... Pioneering studies were conducted with Spalding's conventional two-equations k − ε model [14] , which have shown to be reliable compared with other Reynold-Averaged Navier Stokes (RANS) models with better accuracy [15] . In recent years, Large-Eddy-Simulation (LES) based fire model has become the dominant approach in numerical fire studies [16][17][18] , and several LES based commercial/open-sourced codes are available, with Fire Dynamics Simulator (FDS) [19] from NIST and FireFOAM [20] by FM Global as the most famous two. With the ease of commercial software, a significant number of simulation studies were performed focusing on compartment fire dynamics [21] [22] , species generation and distributions [ 17 , 23-26 ]. ...
A set of numerical analyses was conducted to investigate the effect of fuel location of dual burners in an under-ventilated ISO9705 compartment room. Moreover, the influences of the burner separation displacement on the fire development, the evolution of thermal layers, the distribution of toxic gas species were comprehensively studied. The simulations were conducted using a novel in-house large eddy simulation (LES) based fire field model comprised of subgrid-scale (SGS) turbulence, detailed chemical kinetics of combustion, soot and radiation models. The first part of the simulation focused on 3 different fuel distributions: single centre burner (SCB), single rear burner (SRB) and two distributed burner (TDB). Alternative configurations were considered for dual burners with 4 different distances between the dual burners, to study the influence towards air flow at the doorway, internal temperature profile and major chemical species (i.e. CO/CO2) distributions. The numerical outcome states that fuel distribution has a minor effect on heat release rate and the total CO2 amount but noticeable differences in CO's generation and distribution. Overall, the temperature and gas field predictions were almost identical for all dual burner cases, while significant differences were observed at the rear section of the compartment, especially temperature, CO/CO2vol fraction and soot concentration.
... The WALE model is developed by Nicoud and Ducros [29]. It works particularly well at near-wall conditions and at the transitional flow from laminar to turbulent [30]. ...
... The WALE model's constant, C w , is defined as 0.5. The WALE model detects the turbulent structure and turbulence viscosity by either strain rate, rotation rate, or combined [29]. ...
... Heskestad [43] and Thomas [29] experimental correlations have been used to compare the simulation results of the fire height, according to Eqs. (17) and (18). ...
The identification of the type of regime has an essential effect on the selection of sub-grid scale and discretization methods, regarding the accuracy and computational time. In order to investigate the role of sub-grid scale and time discretization method in a pool fire modeling by the Large Eddy Simulation (LES), three sub-grid scales Smagorinsky, one-equation and Wall-Adapting Local Eddy-Viscosity (WALE) and three time discretization methods of first-order Euler method, second-order Crank Nicolson and backward second-order were investigated. The results indicate that WALE and one-equation sub-grid scale have an acceptable prediction, while Smagorinsky has a significant error with the experimental results. Different time discretization methods have little effects on the results of mean velocity and mean turbulent parameters of the pool fire. By considering the instantaneous distribution of parameters, all three methods perform similar results where the kinetic energy is less than 5 m²/s². In areas where the perturbation is aggravated, the two second-order discretization methods have the same error with a little difference by the first-order Euler method. The accuracies of second-order methods are about 10% for the velocity prediction, compared to the experimental results, while the error of the Euler method is 15%.
... In Eqs. (2) to (4), viscous stress tensor, species di usion vector, and heat ux vector are modeled using the Newton, Fourier and Fick rules, respectively [26]. In this simulation, Smagorinsky [27] and oneequation models [28] are used as SGS. ...
... It was found that the temperature and flow field predictions were accurate, so they suggested the Large Eddy Simulation (LES) for compartment fire simulation. They also examined the LES model in other scenarios, such as scaled compartment [23], and concluded that CFD with LES and flamelet combustion model can model the species with more details, higher accuracy, and lower computational cost. ...
... The relative error of the prediction in CO 2 concentration is higher than CO concentration. However, according to the previous simulations in the same scenario [23], this error is acceptable and has more accurate result. upward toward the ceiling. ...
Compartment fire is a hazardous phenomenon because of the generated poisonous and high-temperature gases. Air curtain systems can be used in order to control the fire spread. This paper examines the numerical simulation method with a focus on the combustion model which can model the poisonous gases and investigates the effect of air curtain on fire. The results of the flamelet generated manifold (FGM) combustion model, which considers all of the poisonous species with detail, in compartment fire with single and multi-floor building have been verified. A three-floor compartment fire scenario with methane as a fuel of 62.9, 500, and 5000 kW heat release rate, which represents over to under-ventilation, was selected as a test case. The impact of air curtains with various supply angles, velocity, and ventilation on pollutants and temperature distribution was examined. The mass fraction of CO and CO2 species reached near zero at angles of 12 and 24, at the over-ventilated case when using air curtain. Therefore, there is no hazard for the upper floors in case of using air curtain. However, in the under-ventilated case, it is necessary to improve the efficiency of air curtain by using ventilation in the fire room and increasing the exhaust velocity of the air curtain.
... devoted to the simulations of turbulent buoyant fire plumes and, more generally, flows encountered in fire safety applications are based on low Mach number variable-density Navier-Stokes solvers (FireFoam n.d.; McGrattan et al., 2014). These mathematical approaches represent the basis of the CFD code and physical sub-models for turbulence, combustion and radiationare then implemented to achieve numerical simulations of practical problems(Yuen et al., 2015;Yuen et al., 2016). An important step in the development of a CFD code is the verification and validation processes which establish the degree of confidence in a computational model for specific applications(Oberkampf and Trucano, 2002;Shunn et al., 2012;Mullyadzhanov et al., 2016). ...
This study reports the development of a LES-based numerical model dedicated to the simulation of well-ventilated and under-ventilated purely buoyant fire plumes. A new second-order low-Mach number variable-density flow solver was developed and verified in order to describe accurately the strong unsteady processes related to the purely buoyant nature of the flow. State-of-the art subgrid-scale turbulence, combustion and radiation models were specifically developed, including the non-adiabatic SLF (steady laminar flamelet) and FPV (flamelet/progress variable models). The RCFSK was considered as reference radiative property model whereas the performance of simpler models, including non-grey and grey versions of the weighted-sum-of-grey gases was assessed. The numerical model was exhaustively validated by simulating several well-documented non-reactive and reactive buoyant fire plumes. It was found capable to reproduce with high fidelity the dynamic and radiative structures of non-luminous fire plumes in both ventilated and under-ventilated configurations without adjusting any model parameters. In particular, the FPV allows addressing oxygen-diluted oxidizer conditions close to extinction. Several specific modelling issues were also investigated during the course of this work. The importance of resolving the laminar instabilities, which form periodically at the base of purely buoyant fire plumes and grow to generate energy containing structures that govern the mixing process, was demonstrated. The formation and growth of these instabilities are significantly affected by the burner geometry that has to be scrupulously consistent with the experiments to achieve an accurate description of the fire plume dynamics. The grey version of the weighted-sum-of-grey gases models have to be avoided whereas the non-grey versions can be a reasonable alternative for non-sooting pool fires. Finally, neglecting subgrid-scale turbulence-radiation interaction affects significantly the predictions of the fire plume structure and radiative heat flux even for lab-scale pool fires.
... In most fire simulations performed by the LES method [11,12], the second-order central method is typically used for the convection term. Higher-order methods, such as fourth-order central method, are also sometimes employed [13,14]. However, the effect of discretization method has not been investigated in any of these studies. ...
Using discretization technique is one of the challenges associated with numerical modeling. In the Large Eddy Simulation (LES) method, this issue becomes more critical because it affects the sub-grid scale (SGS) model and creates errors. Using an LES method, we investigated the numerical errors and compatibility of different discretization methods with SGS in pool fire modeling. First-order, central, and second-order upwind and linear upwind stabilized transport (LUST) schemes were examined in Smagorinsky (S_SGS) and k-equation (K_SGS) sub-grid scales. First-order upwind and second-order upwind methods estimated the velocity field, temperature, and perturbation with a significant error, so that in the plume area, there was 90% error with the first-order upwind and 50% error with the second-order upwind concerning the results of the mean square horizontal velocity perturbation. With an error of 20%, the LUST method had a better agreement with the experimental results. Besides, SGS did not have a significant effect on the results of this method. However, the second-order upwind method was more consistent with the S_SGS model. To improve the results of upwind methods, Quadratic Upstream Interpolation for Convective Kinematics and Monotonic Upwind Scheme for Conservation Laws discretization methods are recommended.
... In essence, the mixture fraction governs the amount of the fuel mixture in each control volume element in the simulation domain. The scalar dissipation is a term introduced to describe the strain and extinction of the flame, in which the larger this quantity depicts its departure from its chemical equilibrium [55]. It should be noted that, in the present work, the GRI-MECH 3.0 detailed chemical reaction mechanisms, with includes 325 reaction steps and 53 chemical species [56], was implemented to formulate the flamelet library for the strained laminar flamelet model, with ethylene (C H ) selected as parental fuel. ...
A numerical study of the fire whirl formation under symmetrical and asymmetrical entraining configuration is presented. This work aims to assess the effect of eddy-generation configuration on the evolution of the intriguing phenomenon coupled with both flow dynamics and combustion. The numerical framework implements large-eddy simulation, detailed chemistry to capture the sophisticated turbulence-chemistry interaction under reasonable computational cost. It also adopts liquid-based clean fuel with fixed injection rate and uniformed discretisation scheme to eliminate potential interference introduced by various aspects of uncertainties. The result reveals that the nascent fire whirl formulates significantly rapidly under the symmetrical two-slit configuration, with extended flame height and constrained vortex structure, compared with the asymmetrical baseline. However, its revolution orbit gradually diverges from domain centreline and eventually stabilises with a large radius of rotation, whereas the revolution pattern of that from the baseline case is relatively unchanged from the inception of nascent fire whirl. Through the analysis, the observed difference in evaluation pathway could be explained using the concept of circular motion with constant centripetal force. This methodology showcases its feasibility to reveal and visualise the fundamental insight and facilitate profound understanding of the flaming behaviour to benefit both research and industrial sectors.
... Large eddies are directly resolved while eddies that are smaller than the length scale are predicted by the SGS turbulence model [41]. In this study, the classical Smagorinsky model was employed to resolve the SGS eddies while a modelling constant of 0.2 was utilised, where this value has been previously validated for various full-scale compartment fire case studies [32,43,44]. It is associated with a wall-damping function which considered the decay of Reynolds Stresses approaching near a wall. ...
... Essentially, the mixture fraction governs the proportion of the fuel mixture in each control volume element in the discretised domain, and the first two moments of the mixture fraction, namely the mean mixture fraction, f , and the mixture fraction variance, g, are evaluated by resolving their conservation equations, respectively. Scalar dissipation is introduced to describe the strain and extinction of the flame, in which larger values of this quantity depict its departure from chemical equilibrium [49]. The scalar dissipation across the flamelet is determined based on the mean scalar dissipation of the flamelets embedded in turbulent flames at the position where f = f st , as well as the ratio of the function of the mixture fraction and density at the point of interest and at the position where f is stoichiometric. ...
This paper numerically examines the characterisation of fire whirl formulated under various entrainment conditions in an enclosed configuration. The numerical framework, integrating large eddy simulation and detailed chemistry, is constructed to assess the whirling flame behaviours. The proposed model constraints the convoluted coupling effects, e.g., the interrelation between combustion, flow dynamics and radiative feedback, thus focuses on assessing the impact on flame structure and flow behaviour solely attribute to the eddy-generation mechanisms. The baseline model is validated well against the experimental data. The data of the comparison case, with the introduction of additional flow channelling slit, is subsequently generated for comparison. The result suggests that, with the intensified circulation, the generated fire whirl increased by 9.42 % in peak flame temperature, 84.38 % in visible flame height, 6.81 % in axial velocity, and 46.14 % in velocity dominant region. The fire whirl core radius of the comparison case was well constrained within all monitored heights, whereas that of the baseline tended to disperse at 0.5 m height-above-burner. This study demonstrates that amplified eddy generation via the additional flow channelling slit enhances the mixing of all reactant species and intensifies the combustion process, resulting in an elongated and converging whirling core of the reacting flow.
