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Povzetek: Large eddy simulations of ventilation-controlled compartment fire scenarios conducted with FDS and new dynamic extinction and re-ignition models are presented. Flame extinction is modelled considering an enthalpy balance, based on a critical flame temperature, while re-ignition is allowed if the local resolved temperature exceeds a given re-ignition temperature. The re-ignition temperatures are estimated on the basis of counterflow simulations with hot oxidizers at different strain rates. The determination of the critical flame temperatures is made through well-stirred reactor simulations under different residence times and diluent types/concentrations. The new models are applied in reduced-scale ventilation-limited compartment fire scenarios with variable heat release rate. Comparison against the original model of FDS, relying on constant critical flame and re-ignition temperatures, are made. Overall, the predictions with the new dynamic models agree both qualitatively and quantitatively with the experiments. By considering the local properties of the flow, the new models bring some improvements, compared to the original models of FDS, in particular for the O concentrations inside the compartment in ventilation-controlled conditions.
Ključne besede: flame extinction, flame re-ignition, under-ventilated conditions, CFD modelling, FDS
Objavljeno v DiRROS: 17.07.2026; Ogledov: 191; Prenosov: 115
Celotno besedilo (5,70 MB)
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Ključne besede: numerična simulacija CFD, NTM diagram, mehanski preračun nosilnosti, tekoči trak, ekstruzija filamenta, zračno hlajenje, CAD, vodenje tekočega traku, diplomsko delo
Objavljeno v DiRROS: 09.04.2025; Ogledov: 915; Prenosov: 363
Celotno besedilo (2,52 MB)

Povzetek: Data from thermocouple (TC) measurements play a pivotal role in fire safety science and engineering studies. It is well-known that there are deviations from the actual local gas temperature and many studies have led to the development of correction factors. The present study focuses on these deviations inside compartments through a systematic series of CFD simulations, performed with Fire Dynamics Simulator (FDS), version 6.8.0. A canonical cubic box is used as geometry. This allows for the demonstration of the impact of the presence of smoke, with variable optical thickness, on the TC data as retrieved from FDS. Significant differences are observed between TC measurements and local gas temperatures. Corrections as developed for TC measurements in open atmospheres cannot be readily applied in compartment configurations, where smoke properties change both spatially and temporally.
Ključne besede: thermocouple measurements, CFD simulations, heat transfer, compartment fires, cooling, fire dynamics, FDS
Objavljeno v DiRROS: 28.10.2024; Ogledov: 1277; Prenosov: 508
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Povzetek: Purpose – This study aims to develop an experimentally validated three-dimensional numerical model for predicting different flow patterns produced with a gas dynamic virtual nozzle (GDVN). Design/methodology/approach – The physical model is posed in the mixture formulation and copes with the unsteady, incompressible, isothermal, Newtonian, low turbulent two-phase flow. The computational fluid dynamics numerical solution is based on the half-space finite volume discretisation. The geo-reconstruct volume-of-fluid scheme tracks the interphase boundary between the gas and the liquid. To ensure numerical stability in the transition regime and adequately account for turbulent behaviour, the k-v shear stress transport turbulence model is used. The model is validated by comparison with the experimental measurements on a vertical, downward-positioned GDVN configuration. Three different combinations of air and water volumetric flow rates have been solved numerically in the range of Reynolds numbers for airflow 1,009–2,596 and water 61–133, respectively, at Weber numbers 1.2–6.2. Findings – The half-space symmetry allows the numerical reconstruction of the dripping, jetting and indication of the whipping mode. The kinetic energy transfer from the gas to the liquid is analysed, and locations with locally increased gas kinetic energy are observed. The calculated jet shapes reasonably well match the experimentally obtained high-speed camera videos. Practical implications – The model is used for the virtual studies of new GDVN nozzle designs and optimisation of their operation. Originality/value – To the best of the authors’ knowledge, the developed model numerically reconstructs all three GDVN flow regimes for the first time.
Ključne besede: flow-focusing, dripping, jetting, whipping, gas dynamic virtual nozzle, CFD
Objavljeno v DiRROS: 28.02.2024; Ogledov: 927; Prenosov: 704
Celotno besedilo (4,19 MB)
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