Turbulent flame propagation in large unconfined H 2O
Turbulent flame propagation in large unconfined H 2/O 2/N 2 clouds Jérôme Daubecha, Christophe Prousta, b, Guillaume Lecocqa E-mail: jerome. daubech@ineris. fr a INERIS, Verneuil en Halatte, France b UTC, Compiègne, France
Context BARPPRO french R&D project – Protection of industrial facilities against explosion blast wave Turbulent flame velocity – Key aspect to evaluate unconfined explosion consequences The intensity of flow velocity fluctuations u’ The characteristic length of vortices Lt The laminar burning velocity Slad Turbulent flow field Laminar flame Link between flame and turbulence ICHS 2015, Yokohama – October 2015
Context Purposes of this presentation : § Presentation of the experimental device § Presentation of the overpressurse and the flame velocities for quiescent and turbulent mixtures § Discussion about flame behavior ICHS 2015, Yokohama – October 2015
Experimental Conditions Test plateform Metallic structure in 3. 5 cm thich IPN structure coverd with a 5 mm metal plate 1. 5 m hemispheric frame formed with 8 flexible plastic tube 150 µm plastic sheet covers the dome ICHS 2015, Yokohama – October 2015
Experimental Conditions Mixture preparation Injection of gas thanks to 4 jetflows (coanda effect) § Placed at 0. 9 m from center of the plateform § Homogeneous mixture § Creation of turbulent motion ICHS 2015, Yokohama – October 2015
Experimental conditions Instrumentation Concentration and homogeneity : § Controlled in 2 points at 0. 1 m and 1. 4 m from the test plateform Ignition source : § Pyrotechnical match at the center of the hemisphere on the floor Two pressure gauges Kistler 0 -10 bar § At the center of the hemisphere -> Overpressure in the burnt gases § At 10 m from the center of the hemisphere -> Pressure wave ICHS 2015, Yokohama – October 2015
Experimental conditions Characterization of turbulence in the dome Measurement of turbulence with 3 pitot probes in earlier version of test plateform : Simulation of this flow field with PIMPLEFOAM (RANS Solver) Turbulent intensity : 5 Solver m/s length scale : 0. 15 m § Good agreement with the. Turbulence experimental measures Simulation of experimental situation § Turbulent intensity : 1. 5 m/s § Mean turbulent length scale : 0. 16 m ICHS 2015, Yokohama – October 2015
Flammable mixtures Stoichiometric hydrogen/oxygen diluted with nitrogen % H 2 % O 2 % N 2 Laminar flame speed Slad (m/s) Expansion ratio E ICHS 2015, Yokohama – October 2015 Mixture 1 40 20 40 Mixture 2 45 22. 5 3. 5 4. 2 7. 5 8
Explosion in 25 i/s camera ICHS 2015, Yokohama – October 2015
Quiescent stoichiometric H 2/O 2 mixture diluted with N 2 Mixture 1 : 40 % H 2, 20 % O 2, 40 % N 2 Burnt gas overpressure and overpressure at 10 m Fast camera Maximum overpressure : 250 mbar at 36 ms ICHS 2015, Yokohama – October 2015
Quiescent stoichiometric H 2/O 2 mixture diluted with N 2 Mixture 1 : 40 % H 2, 20 % O 2, 40 % N 2 Flame trajectory and flame velocity Part 1 Flame velocity ~50 m/s Part 2 Flame velocity Increase by 50 to 115 m/s Flame velocity vs distance, spherical explosion of stoichiometric hydrogen-air Fast camera mixtures – DRENCKHAHN ET AL, 1985 Maximum overpressure mbar at 36 ms Expansion ratio E : 7. 5 Motion of plastic sheet at: 250 22 ms Creation Experimental of a turbulent/shear observation consistent flow between with previous the flame Two distincts in flame trajectory Laminar speed Slad : 3. 5 m/s works front andflame thepart plastic envelope E. Slad = 26 m/sinstability -> Ratio =~2 self-acceleration between measured and Hydrodynamic of flame theoretical flame velocity ICHS 2015, Yokohama – October 2015
Comparison between quiescent and turbulent mixture Mixture 1 : 40 % H 2, 20 % O 2, 40 % N 2 Turbulence created during gas injection by the 4 jetflows Burnt gas overpressures for the quiescent and the turbulent mixtures Quiescent/Turbulent mixtures : § Two parts in pressure signals § Strong pressure rise up linked to the motion of plastic sheet ICHS 2015, Yokohama – October 2015
Comparison between quiescent and turbulent mixture Mixture 1 : 40 % H 2, 20 % O 2, 40 % N 2 Quiescent mixture – Average flame velocity = 50 m/s Turburlent mixture – Average flame velocity = 85 m/s ICHS 2015, Yokohama – October 2015 Turbulent flame velocity = 11 m/s x 1. 5
Comparison between quiescent and turbulent mixture Mixture 1 : 40 % H 2, 20 % O 2, 40 % N 2 Intercomparison between different correlations : u’ - turbulent intensity, Bray correlation : Lt – turbulent length scale, Shy correlation : η – flame thickness, Gülder correlation : K – Karlovitz number Experiment Bray 11 25 Shy Gülder 33 14 Gülder correlation gives the best result and confirms the past INERIS choice to estimate the flame turbulent velocity ICHS 2015, Yokohama – October 2015
Thank you for your attention
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