On the Hydrodynamic Stability of Flat-burner Flames

Abstract

We study wrinkled premixed flames held off a flat burner at much greater distances than the front thickness. We first show that the Landau-Darrieus hydrodynamic instability is weaker than for free flames. Using the weak-thermal-expansion method. we then build a non-linear evolut ion for the flame dynamics. which includes gravity effects and the curvature-induced local changes in burning speed in addition to the burner-affected hydrodynamic instability. This equation gives a means to compute the stand-off distance of the wrinkled flame and its shape in terms of the inlet flow rate and the wrinkle wavelength ; hence multiple solutions are predicted. and a selection mechanism is proposed. Finally, the hydrodynamic perturbations inside the burner are included, and are shown to be destabilizing.