Experimental data obtained via particle image velocimetry are used to investigate the self-wrinkling of premixed flame fronts induced by Darrieus-Landau (DL) instability and its interaction with turbulence from low to moderately high Reynolds numbers in a Bunsen configuration. At low Reynolds, hence in quasilaminar conditions, the DL instability is experimentally triggered by varying the mixture ratio. Conversely, in turbulent cases, the DL instability is triggered by varying the Bunsen nozzle diameter so that flames can be compared at the same equivalence ratio and jet Reynolds numbers. The differences between stable and unstable Bunsen flames at low Reynolds number are discussed in terms of vorticity generation downstream in the flame as well as total flame strain and its normal and tangential components. The straining pattern of a single DL cusp is calculated along the flame front to create a reference case for higher turbulence intensity cases and assess the influence of self-wrinkling of the flame front on the reactant flow field, i.e., the channeling effect. The results obtained are consistent with recent direct numerical simulations of single DL-cusp propagating in a quiescent environment. In addition, inspection of strain-curvature joint probability density function, curvature correlation coefficient and crossing length statistics will show that, even from the intermediate Reynolds numbers explored, unstable flames under the influence of self-wrinkling effects possess the statistical characteristics that stable flames gain only at high turbulence levels, where a unified and turbulence dominated regime is likely to be reached, although with the persistence of some residual differences.

Self-wrinkling induced by Darrieus-Landau instability in turbulent premixed Bunsen flames from low to moderately high Reynolds numbers

Troiani, G.;
2022-01-01

Abstract

Experimental data obtained via particle image velocimetry are used to investigate the self-wrinkling of premixed flame fronts induced by Darrieus-Landau (DL) instability and its interaction with turbulence from low to moderately high Reynolds numbers in a Bunsen configuration. At low Reynolds, hence in quasilaminar conditions, the DL instability is experimentally triggered by varying the mixture ratio. Conversely, in turbulent cases, the DL instability is triggered by varying the Bunsen nozzle diameter so that flames can be compared at the same equivalence ratio and jet Reynolds numbers. The differences between stable and unstable Bunsen flames at low Reynolds number are discussed in terms of vorticity generation downstream in the flame as well as total flame strain and its normal and tangential components. The straining pattern of a single DL cusp is calculated along the flame front to create a reference case for higher turbulence intensity cases and assess the influence of self-wrinkling of the flame front on the reactant flow field, i.e., the channeling effect. The results obtained are consistent with recent direct numerical simulations of single DL-cusp propagating in a quiescent environment. In addition, inspection of strain-curvature joint probability density function, curvature correlation coefficient and crossing length statistics will show that, even from the intermediate Reynolds numbers explored, unstable flames under the influence of self-wrinkling effects possess the statistical characteristics that stable flames gain only at high turbulence levels, where a unified and turbulence dominated regime is likely to be reached, although with the persistence of some residual differences.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12079/70509
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