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Turbulent flame propagation in large unconfined H2/O2/N2 clouds

Turbulent flame propagation in large unconfined H2/O2/N2 clouds Jérôme Daubech a , Christophe Proust a,b , Guillaume Lecocq a E-mail: jerome.daubech@ineris.fr a INERIS, Verneuil en Halatte, France b UTC, Compiègne, France. Context.

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Turbulent flame propagation in large unconfined H2/O2/N2 clouds

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  1. Turbulent flame propagation in large unconfined H2/O2/N2 clouds Jérôme Daubecha, Christophe Prousta,b, Guillaume Lecocqa E-mail: jerome.daubech@ineris.fr a INERIS, Verneuil en Halatte, France b UTC, Compiègne, France

  2. 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 • Link between flame and turbulence Turbulent flow field Laminar flame

  3. 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

  4. 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

  5. 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

  6. 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

  7. Simulation of this flow field with PIMPLEFOAM Solver (RANS Solver) • Good agreement with the experimental measures 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 fieldwith PIMPLEFOAM Solver • Good agreement witjexperimentalmeasures Turbulent intensity : 5 m/s Turbulence lengthscale : 0.15 m • Simulation of experimental situation • Turbulent intensity : 1.5 m/s • Mean turbulent lengthscale : 0.16 m

  8. Flammable mixtures • Stoichiometric hydrogen/oxygen diluted with nitrogen

  9. Explosion in 25 i/s camera

  10. Quiescent stoichiometric H2/O2 mixture diluted with N2 Mixture 1 : 40 % H2, 20 % O2, 40 % N2 • Burnt gas overpressure and overpressure at 10 m • Maximum overpressure : 250 mbar at 36 ms Fast camera

  11. Flame trajectory and flame velocity Maximum overpressure : 250 mbar at 36 ms Quiescent stoichiometric H2/O2 mixture diluted with N2 Mixture 1 : 40 % H2, 20 % O2, 40 % N2 Part 1 Flamevelocity ~50 m/s Part 2 Flame velocity Increase by 50 to 115 m/s Flame velocity vs distance, spherical explosion of stoichiometric hydrogen-air mixtures – DRENCKHAHN ET AL, 1985 Fast camera Expansion ratio E : 7.5 Laminarflame speed Slad : 3.5 m/s E.Slad = 26 m/s -> Ratio ~2 betweenmeasured and theoreticalflamevelocity Creation of a turbulent/shear flow between the flame front and the plastic envelope Experimental observation consistent with previous works Hydrodynamic instability = self-acceleration of flame Motion of plastic sheetat 22 ms Two distincts part in flame trajectory

  12. Comparison between quiescent and turbulent mixture Mixture 1 : 40 % H2, 20 % O2, 40 % N2 • 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

  13. Comparison between quiescent and turbulent mixture Mixture 1 : 40 % H2, 20 % O2, 40 % N2 • Quiescent mixture – Average flame velocity = 50 m/s • Turburlent mixture – Average flame velocity = 85 m/s x 1.5 Turbulent flamevelocity = 11 m/s

  14. Comparison between quiescent and turbulent mixture Mixture 1 : 40 % H2, 20 % O2, 40 % N2 • Intercomparison between different correlations : • Bray correlation : • Shy correlation : • Gülder correlation : u’ - turbulent intensity, Lt – turbulent length scale, η – flame thickness, K – Karlovitz number Gülder correlation gives the best result and confirms the past INERIS choice to estimate the flame turbulent velocity

  15. Thank you for your attention

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