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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...
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This paper describes the numerical solution of flow analysis in a two-dimensional combustion chamber with two parallel inlets aided for propellants entrance, addressing a number of different problems that depend on each other: the flow affected by a discrete point in-cell vortex, the velocity affected by the flow regime in the cell, and the combust...
Citations
... Mathematical equations are applied to describe the fluid motion by physical characterization, usually in partial differential form, called governing equations. These applications encompass performance assessment, behavioral predictions, and the substitution of impractical tests, such as those involving fire dynamics [65][66][67][68], chemical mechanisms and transportation of soot particles [69][70][71][72][73], contribution toward numerical database for fire safety standards [74][75][76][77][78][79], etc. Therefore, understanding the fundamental thermal degradation kinetics will contribute to thermal runaway analysis in the battery-CFD modelling framework. ...
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.
... The chemical reaction is described by a preassumed probability density function (pre-PDF) with two variables, namely the mixture fraction (f) and scalar dissipation (ṽ). The mixture fraction controls the portion of the fuel in a control volume, and the scalar dissipation governs the strain and suppression of the flame by reflecting the degree of flame departures from its chemical equilibrium [44]. To accurately model the combustion of methane, GRI-MECH 3.0 mechanism including 325 reaction steps and 53 chemical species was employed to calculate the flamelet library [45]. ...
A new predictive fire suppression model has been developed and applied to a compartment room environment with various fire locations to clarify the suppression mechanisms of water mist and sprinkler systems. To effectively mitigate the combustion process, an in-depth framework has been developed, which includes the thermal fluidic interactions and utilizes statistical approaches for water droplets characterization. Efficiencies and effectiveness of both systems under different operating conditions were investigated with a multi-parametric approach that uniquely traces the accumulative mass fluxes, penetrability and number counts of droplets. Different fire suppression scenarios were identified based on combustion behaviors, and the suppression systems’ performance was evaluated based on spray coverage, penetrability, water utilization rate and potential water damage. The current study finds that water mist systems significantly outperform sprinkler systems in suppressing centered fires from both time (within 0.55 s) and utilization rate (up to 6.78%) perspective, while sprinkler systems can effectively suppress fires within a larger area, but their water utilization rate is as low as 0.07%. For water mist systems, although the water utilization rate can be 37 times higher than sprinkler systems, their effective suppression coverage area is small, which provided directions for future improvement.
... In order to further investigate the performance of polymer composite material, PyroPolis (Snegirev et al., 2013) was later proposed after overcoming the drawback of previous models, including simple single-step kinetics and treatments to both homogeneous and inhomogeneous composite materials. In the past decade, computational fluid dynamics (CFD) have also been widely applied to studies in fire engineering to predict the pyrolysis process of solid materials Lin et al., 2021), fire propagation (Mallet et al., 2009;Rochoux et al., 2013;Chen et al., 2018b), fire suppression (Liu et al., 2020, soot formation (Yuen et al., 2017;Wang et al., 2020a), and other fire phenomena (Sasaki et al., 2018;Yuen et al., 2018b;Wang et al., 2020b). Large eddy simulation (LES)-based fire field modelling has become the most dominant in numerical studies with popular fire codes such as Fire Dynamics Simulator (FDS) (McGrattan et al., 2013) and FireFOAM (Ding et al., 2015). ...
In this study, a multiphase pyrolysis model has been proposed under the large eddy simulation (LES) framework incorporating moving boundary surface tracking, char formation, and detailed chemical kinetics combustion modelling. The proposed numerical model was applied to simulate the cone calorimeter test of two kinds of materials: (i) pinewood (charring) and (ii) low-density polyethylene (non-charring). Using a cone calorimeter setup, good agreement has been achieved between the computational and the experimental results. The model is capable of predicting the formation of the char layer and thus replicating the flame suppressing thermal and barrier effects. Furthermore, with the application of detailed chemical kinetics, the fire model was able to aptly predict the generation of asphyxiant gas such as CO/CO2 during the burning process. However, the pinewood experiments showed significant CO/CO2 emissions post flame extinguishment attributed to char oxidation effects, which were not considered by the fire model. Despite the limitation, the fully coupled LES model proposed in this study was capable of predicting the fluid mechanics and heat transfer for the turbulent reacting flow, solid-phase decomposition, and gaseous products under flaming conditions. In the future, it can be further extended to include char oxidation mechanisms to improve predictions for charring materials.
... Computational fluid dynamic (CFD) modelling on building fires has been rapidly developing benefited by the advancements of numerical methodologies and computational power. [16][17][18] Temperature and velocity can be predicted by solving partial differential equations, and soot and flame can also be visualized. However, CFD modelling must be validated with experiments in each simulation. ...
A high-performance smoke exhaust system is vital for maintaining a tenable environment during fire accidents evacuation. This study proposes a novel vortex flow driven smoke exhaust system to delay the smoke filling process during the atrium fire accident. The complex fluid movement and combustion reactions were predicted using Fire Dynamics Simulator, and the predicted smoke filling process was identified by the least-square method. Good agreements between numerical predictions and experimental measurements for vertical temperature, tangential velocity profile and smoke interface height were achieved. The numerical outcomes revealed that the amount of fresh air supplied, heat release rate and exhaust fan's rate determined the smoke interface's final height. A parametric study was also carried out to investigate the dominating factor in maintaining a stable vortex flow to maximize the smoke exhaust efficiency. Numerical results showed that the vortex flow smoke exhaust system could slow down the smoke filling, and the stability of the swirling fire is crucial for the system's performance.
... This book includes a series of seventeen research studies that reveal new knowledge about combustion and its application. The topics covered span many diverse areas associated with combustion including: fires [1][2][3], engines and applications [4][5][6][7][8][9][10][11][12][13][14][15], and acoustics [16,17]. ...
The role that combustion plays in energy systems remains crucial in supplying the world’s ever-increasing power demands [...]
Buildings with large internal spaces, such as vertical shafts or atria, are widespread nowadays. In the case of fire, internal air currents may generate devastating fire whirls that can cause severe damage due to intensive heat release rate (HRR) and temperatures. This work presents the generation and evolution of fire whirls in a full-scale atrium experiment and their comparison with a numerical approach. A set of numerical models using FDS 6.7.5 are tested to assess the influence of the HRR curve and the impact of intrusive methods of temperature measurements on the prediction of whirls. The results show that the Burgers vortex model is well reproduced, although the continuous flame and plume regions can only be distinguished with fine grids. However, the periodic evolution of the whirls is better predicted with a time-averaged HRR curve, showing its influence on the flame height. The use of the experimental HRR curve presents more accurate results only in the temperatures far from the flame, with errors lower than 8.5% even for coarse grids. In addition, a small obstacle above the flame is observed to affect the formation of the whirls, which consequently impacts the grid sensitivity and computational cost.
Purpose
The purpose of this paper is to investigate the development process of the fire whirl in the fixed-frame facility and focus on the impacts of the fire whirl’s vortex core on the formation and flame structure of the fire whirl.
Design/methodology/approach
The complex turbulent reacting flame surface is captured by the large eddy simulation turbulence closure coupled with two sub-grid scale (SGS) kinetic schemes (i.e. the chemistry equilibrium and steady diffusion flamelet). Numerical predictions are validated thoroughly against the measurements by Lei et al. (2015) with excellent agreements. A double maximum tangential velocity refinement approach is proposed to quantify the vortex cores’ instantaneous location and region, addressing the missing definition in other studies.
Findings
The numerical results show that the transition process of the fire whirl is dominated by the vortex core movement, which is related to the centripetal force. The unsteadiness of the fully developed fire whirl was found depending on the instantaneous fluctuation of heat release rate. The steady diffusion flamelet scheme is essential to capture the instantaneous fluctuation. Furthermore, the axial velocity inside the vortex core is the key to determining the state of fire whirl.
Practical implications
Due to intensive interactions between buoyant fires and ambient rotating flow, the on-set and formation of fire whirl still remain largely elusive. This paper focused on the transition process of fire whirl between different development stages. This paper provides insights into the transition process from the inclined flame to the fire whirls based on the centripetal force.
Originality/value
This paper presented and compared two SGS kinetic schemes to resolve the fire whirl development process and the unsteadiness of its vortical structures. The modelling framework addresses the shortcoming of previous numerical studies where RANS turbulence closure and simplified combustion kinetics was adopted. Numerical results also revealed the fire whirl transition process and its relationship to centripetal force.
