Stability of a Premixed Laminar V-Shaped Flame

Abstract

This paper examines the stability of a premixed hydrogen-air flame that is perturbed by a rod set upstream in the flow. Depending on the diameter of the rod, the scales of the vortices are of different magnitudes compared with the thickness of the flame front. Comparisons were made between a vortex street generated by a rod with and without natural vibrations, using identical upstream conditions (the same Reynolds number) but with different amplitude oscillations and wavelengths. Several cases were investigated using laser-Doppler velocimetry to measure the axial and transverse velocity field of the vortex street. Also, tomography was used to visualize the effect of the velocity field on the shape of the flame front. Thus, we were able to measure wavelengths and growth of perturbations in this flowfield. When the amplitude of the oscillations produced by the vortex street were less than the flame front thickness, the flame develops a particular pattern that seems to trigger a transition phenomenon between stable and unstable states. When the initial disturbance was much larger than the flame front thickness, the perturbations grew and a distorsion of the vortex structures was observed.