Final Report Summary - FLAME SPREAD (Fully Coupled Fluid-Solid Simulation of Upward Flame Spread and Fire Growth)
The project has encompassed a multitude of modelling and simulation techniques, that complement each other, bringing together fluid simulation, conjugate heat transfer, material flammability, pyrolysis, combustion, materials property and analytical methods spanning across a variety of disciplines in order to exploit the Fellow’s expertise in computational fluid dynamics (CFD), combustion, chemistry and numerical analysis to a basic and yet very important engineering problem that underpins the fire safety in the built environment and transport systems. The Fellow has integrated the different modelling techniques to capture the complex physics and chemistry that underpins the complex processes of flame spread and fire growth. He has also made full use of his analytical ability to critically assess the experimental data which is abundant in quantity but presenting conflicting results, in some cases; and on this basis, select appropriate data for model validation. The Fellow has delivered a validated flame spread model within the frame of the open source CFD code OpenFOAM; that is capable of predicting upward flame spread in different geometric configurations and complexities. He has also demonstrated the use of the powerful-state of the art predictive tool to attack flame spread in realistic fire scenarios. The Fellow, through regular seminars, workshops and other dissemination activities, has also transfered knowledge directly to the European academic and engineering community as well as the industry community that is charged with the responsibility of fire safety for European citizens and business.
The scientific achievements, in particular, include the following:
A fully coupled fluid-solid approach has been developed within FireFOAM [1], a Large Eddy Simulation (LES) based fire simulation solver within the OpenFOAM® toolbox [2]. Due consideration has been given to couple the radiative heat transfer and soot treatment with pyrolysis calculations. using the newly extended eddy dissipation concept (EDC) for multi-component fuels [3] and a laminar smoke point concept based soot model extended to turbulent fires using the partially stirred reactor (PaSR) concept [4,5]. For radiative heat transfer, the finite volume discrete ordinate method (FVDOM) is used with the weighted sum of grey gases model (WSGGM) [6]. In the solid region, the 1-D diffusion equation for sensible enthalpy with the Arrhenius type pyrolysis model developed by Chaos et al. [7] in FireFOAM is solved. The effect of in-depth radiation is taken into account using the relatively simple Beer’s law [8]. The surface regression model is based on that of Pizzo [9] which is considered based on the local pyrolysis rate.
In the pyrolysis model validation based on the test of Pizzo et al. [9] which excluded gases combustion, the model captured well the rate of surface regression and the time reaching the pyrolysis temperature, demonstrating that it is capable of predicting the temperature rise in flame spread condition with reasonable accuracy.
For the small scale wall fire case of Singh and Gollner [11], the predicted local pyrolysis rates are close to the measurements between 14 to 24.5 kW/m2 wall heat flux. The predicted convective, radiative, and re-radiative heat fluxes are in reasonably good agreement with the measurements; and the inclusion of the leading edge effect was found to improve the accuracy in the convective heat flux predictions near the edge of the PMMA sample.
The predicted trend and peak soot volume fractions are found to be close to the measurements of Hebert et al. [10] .
The model was also found to predict the pyrolysis and flame height with reasonably good accuracy in comparison with the large scale flame spread measurement of Liang et al. [12]. It also captured well the two stages in the development of flame height and heat release rate and the experimentally identified threshold of 25 kW/m2. The predicted total heat flux was found to follow well the universal total heat flux distribution identified by Quintiere et al. [13].
The validated model has then been used to conduct flame spread at different angles of inclinations as well as predicting upward flame spread representative of large scale fires.
The project extended the long term collaboration between the PI and FM Global into a new domain. The PDRA gained new knowledge and training. The new development in FireFOAM will eventually be openly released on the internet to the international research community for free downloading once gone through careful validation and separate check by FM Global.
A fully coupled fluid-solid approach for upward flame spread has been developed on the basis of FireFOAM. The radiative heat transfer and soot treatment are fully coupled with the pyrolysis calculations; and appropriate adjustment has been made to the calculation of the reaction time scale for laminar combustion and the calculations of SGS turbulent kinetic energy.
Unlike previous flame spread studies which were largely limited to one or two dimensional simulations and used off the shelf commercial CFD software and constrained by the available sub-models which only have limited representations of the flame spread scenarios, the present study has been based on the latest developed combustion and soot models for fire simulations by the host group as well as the newly implemented weighted sum of gray gas models for gaseous radiation properties.
The systematically validation studies support that the modelling approach developed can be used to predict upward flame spread scenarios with reasonable accuracy. In order to mimic the experimental conditions, gaseous combustion in the precursor burner was also simulated wherever relevant.
References
1 FM Global, FireFOAM, Available from: https://github.com/fireFoam-dev/
2 OpenFOAM Ltd., OpenFOAM, Avaiable from: http://www.openfoam.com/
3 Z. Chen, J. Wen, B. Xu, S. Dembele, Fire Safety Journal 64 (2014) 12-26.
4 Z. Chen, J. Wen, B. Xu, S. Dembele, Int. J Heat and Mass Transfer, Vol. 70, March 2014, pp. 389-408.
5 C. J. Wang, J. X. Wen, Y. M. Ding, Q. Z. He, S.X. Lu, EDC and PaSR based Soot Models in FireFOAM, FM Global, 6th FM Global Open Source CFD Fire Modelling Workshop May 15-16 2014, Norwood, Massachusetts.
6 T. F. Smith, Z. F. Shen, J. N. Frledman, Journal of Heat Transfer 104 (4) (1982) 602-608.
7 M. Chaos, M. M. Khan, N. Krishnamoorthy, J. L. De Ris, S. B. Dorofeev, Proceedings of the Combustion Institute 33 (2) (2011) 2599-2606.
8 F. Jiang, J. L. De Ris, M. M. Khan, Fire Safety Journal 44 (1) (2009) 106-112.
9 Y. Pizzo, C. Lallemand, A. Kacem, A. Kaiss, J. Gerardin, A. Acem, P. Boulet, B. Porterie, Combustion and Flame 162 (1) (2015) 226-236.
10 D. Hebert, A. Coppalle, M. Talbaut, 2d Soot Concentration and Burning Rate of a Vertical PMMA Slab using Laser-induced Incandescence, Proc. Combust. Inst. 34 (2) (2013) 2575-2582.
11 A. V. Singh, M. J. Gollner, Combust. Flame 162 (5) (2015) 2214-2230.
12 C. Liang, X. Cheng, H. Yang, H. Zhang, K. K. Yuen, Experimental Study of Vertically Upward Flame Spread over Polymethyl Methacrylate Slabs at Different Altitudes, Fire and Materials (2015) doi: 10.1002/fam.2304.
13 J. Quintiere, M. Harkleroad, Y. Hasemi, Combustion Science and Technology 48 (3-4) (1986) 191-222.
The scientific achievements, in particular, include the following:
A fully coupled fluid-solid approach has been developed within FireFOAM [1], a Large Eddy Simulation (LES) based fire simulation solver within the OpenFOAM® toolbox [2]. Due consideration has been given to couple the radiative heat transfer and soot treatment with pyrolysis calculations. using the newly extended eddy dissipation concept (EDC) for multi-component fuels [3] and a laminar smoke point concept based soot model extended to turbulent fires using the partially stirred reactor (PaSR) concept [4,5]. For radiative heat transfer, the finite volume discrete ordinate method (FVDOM) is used with the weighted sum of grey gases model (WSGGM) [6]. In the solid region, the 1-D diffusion equation for sensible enthalpy with the Arrhenius type pyrolysis model developed by Chaos et al. [7] in FireFOAM is solved. The effect of in-depth radiation is taken into account using the relatively simple Beer’s law [8]. The surface regression model is based on that of Pizzo [9] which is considered based on the local pyrolysis rate.
In the pyrolysis model validation based on the test of Pizzo et al. [9] which excluded gases combustion, the model captured well the rate of surface regression and the time reaching the pyrolysis temperature, demonstrating that it is capable of predicting the temperature rise in flame spread condition with reasonable accuracy.
For the small scale wall fire case of Singh and Gollner [11], the predicted local pyrolysis rates are close to the measurements between 14 to 24.5 kW/m2 wall heat flux. The predicted convective, radiative, and re-radiative heat fluxes are in reasonably good agreement with the measurements; and the inclusion of the leading edge effect was found to improve the accuracy in the convective heat flux predictions near the edge of the PMMA sample.
The predicted trend and peak soot volume fractions are found to be close to the measurements of Hebert et al. [10] .
The model was also found to predict the pyrolysis and flame height with reasonably good accuracy in comparison with the large scale flame spread measurement of Liang et al. [12]. It also captured well the two stages in the development of flame height and heat release rate and the experimentally identified threshold of 25 kW/m2. The predicted total heat flux was found to follow well the universal total heat flux distribution identified by Quintiere et al. [13].
The validated model has then been used to conduct flame spread at different angles of inclinations as well as predicting upward flame spread representative of large scale fires.
The project extended the long term collaboration between the PI and FM Global into a new domain. The PDRA gained new knowledge and training. The new development in FireFOAM will eventually be openly released on the internet to the international research community for free downloading once gone through careful validation and separate check by FM Global.
A fully coupled fluid-solid approach for upward flame spread has been developed on the basis of FireFOAM. The radiative heat transfer and soot treatment are fully coupled with the pyrolysis calculations; and appropriate adjustment has been made to the calculation of the reaction time scale for laminar combustion and the calculations of SGS turbulent kinetic energy.
Unlike previous flame spread studies which were largely limited to one or two dimensional simulations and used off the shelf commercial CFD software and constrained by the available sub-models which only have limited representations of the flame spread scenarios, the present study has been based on the latest developed combustion and soot models for fire simulations by the host group as well as the newly implemented weighted sum of gray gas models for gaseous radiation properties.
The systematically validation studies support that the modelling approach developed can be used to predict upward flame spread scenarios with reasonable accuracy. In order to mimic the experimental conditions, gaseous combustion in the precursor burner was also simulated wherever relevant.
References
1 FM Global, FireFOAM, Available from: https://github.com/fireFoam-dev/
2 OpenFOAM Ltd., OpenFOAM, Avaiable from: http://www.openfoam.com/
3 Z. Chen, J. Wen, B. Xu, S. Dembele, Fire Safety Journal 64 (2014) 12-26.
4 Z. Chen, J. Wen, B. Xu, S. Dembele, Int. J Heat and Mass Transfer, Vol. 70, March 2014, pp. 389-408.
5 C. J. Wang, J. X. Wen, Y. M. Ding, Q. Z. He, S.X. Lu, EDC and PaSR based Soot Models in FireFOAM, FM Global, 6th FM Global Open Source CFD Fire Modelling Workshop May 15-16 2014, Norwood, Massachusetts.
6 T. F. Smith, Z. F. Shen, J. N. Frledman, Journal of Heat Transfer 104 (4) (1982) 602-608.
7 M. Chaos, M. M. Khan, N. Krishnamoorthy, J. L. De Ris, S. B. Dorofeev, Proceedings of the Combustion Institute 33 (2) (2011) 2599-2606.
8 F. Jiang, J. L. De Ris, M. M. Khan, Fire Safety Journal 44 (1) (2009) 106-112.
9 Y. Pizzo, C. Lallemand, A. Kacem, A. Kaiss, J. Gerardin, A. Acem, P. Boulet, B. Porterie, Combustion and Flame 162 (1) (2015) 226-236.
10 D. Hebert, A. Coppalle, M. Talbaut, 2d Soot Concentration and Burning Rate of a Vertical PMMA Slab using Laser-induced Incandescence, Proc. Combust. Inst. 34 (2) (2013) 2575-2582.
11 A. V. Singh, M. J. Gollner, Combust. Flame 162 (5) (2015) 2214-2230.
12 C. Liang, X. Cheng, H. Yang, H. Zhang, K. K. Yuen, Experimental Study of Vertically Upward Flame Spread over Polymethyl Methacrylate Slabs at Different Altitudes, Fire and Materials (2015) doi: 10.1002/fam.2304.
13 J. Quintiere, M. Harkleroad, Y. Hasemi, Combustion Science and Technology 48 (3-4) (1986) 191-222.