FLAME FRONT CURVATURE DISTRIBUTIONS IN A TURBULENT PREMIXED FLAME ZONE

Distributions of flame front curvature obtained by laser sheet tomogra phy agree with those derived from numerical simulations of passive fla me propagation within three-dimensional Navier-Stokes turbulence. The experimental configuration is that of grid turbulence impinging upon a plate which stabilizes a premixed methane/air flame, planar images of the flame allow construction of flame curvature as a function of flam e location within the spatial zone that contains products and reactant s. In the simulations the flame burning velocity is twice the turbulen ce intensity and the Reynolds number based on the computed Taylor leng th scale is approximately 55. The computed flame geometry and flame st rain rate are obtained as a function of location based on the mean pro gress variable (defined by the passive surface displacement or by the scalar fluctuations defined over transverse planes). The shape of the mean progress variable profile compares well with experiment and with two reaction-diffusion models of propagation (KPP and an independent G aussian model). From the simulations planar slices are created in orde r to provide curvature information which is directly comparable to the experimental data. Distributions of curvature, based on planar inform ation, exhibit a change with location in the turbulent flame zone: an overall positive curvature (convex to the reactants) at the front to a negative value at the rear. however, this behavior is composed of pos itive curvature (which by itself has an average value with no spatial variation) and negative curvature (which increases in magnitude with d istance from the front). A single length scale allows a good match bet ween experimental and computed curvature throughout;he flame zone. The passive flame simulations show the most probable flame shape to be cy lindrical, and this feature, allows the planar information to be scale d in order to match the curvature distributions based on three dimensi onal information. The scaling factor is obtained by observing a cylind er with planar slices at all possible angles.