Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Effects of hydrodynamic and thermo-diffusive instabilities in the local burning rate of lean premixed hydrogen/air laminar flames
Submission Author:
Rafael Meier , SC
Co-Authors:
Rafael Meier, Amir Antonio Martins Oliveira
Presenter: Rafael Meier
doi://10.26678/ABCM.COBEM2021.COB2021-2210
Abstract
Flame surface instability is present in turbulent premixed flame propagation in the flamelet and corrugated flamelet regimes, strongly affecting the turbulent flame speed. In this work, direct numerical simulations are used to evaluate the linear and non-linear growth of instabilities caused by initial perturbations in lean hydrogen/air premixed flames. The numerical simulations employ multi-step chemistry and detailed transport in a two-dimensional channel with periodic boundary conditions along the vertical boundaries. These flames present Lewis numbers smaller than the unit, and flame propagation is affected by both hydrodynamic and thermo-diffusive instabilities. A dispersion relation diagram mapping the perturbation growth rates and wavenumbers is compared to the literature data, validating the predictions. The stretch rate and thermo-diffusive instabilities in a Bunsen flame and a planar flame are compared. Then, the growth rates’ effect on the local burning rate at the flame front are assessed and compared to steady-state stretch rates. The comparison reveals that, in regions where the stretch is weaker, the spectrum of curvature and wavelengths tends to keep the relation of flame speed and curvature as predicted by the linear theory despite the chaotic behavior of the wrinkled front. On the other hand, when the flame front curvature grows towards high negative values, the results increase the deviation from the linear model.
Keywords
Direct numerical simulations, hydrodynamic and thermodiffusive instabilities, lean hydrogen/air premixed flames
