Wrinkling Scales of Turbulent Premixed Propagating Flame Fronts Obtained From LIF-OH Imaging

A key outstanding issue with turbulent premixed flames lies in modeling the burning rate which may be related to the flame surface density if the laminar flamelet assumption applies. Although it is generally accepted that, in the flamelet regimes, higher turbulence levels increases flame wrinkling and hence its surface density, recent imaging experiments are not consistent making this a controversial issue. More measurements of flame surface density and wrinkling scales with varying turbulence levels are, therefore, needed. This paper presents images of OH made using Laser Induced Fluorescence (LIF) in flames propagating from rest in a chamber where a series of baffles plates and obstacles are positioned in its path. From the OH images, a twodimensional flame surface contour is interpreted along the sharply defined edge between the burnt and un-burn region of the transient flow. Using the first derivative of this contour wrinkling scale and the degree of flame front contortion can be calculated and used in a qualitative capacity for describing the instantaneous flame front structure. For this study, the effects of obstacle geometry and hence turbulence levels on the structure of a premixed flame in a rectangular explosion vessel is examined. The wrinkling scales obtained here will also be relevant in the Large Eddy Simulation of these flows.