FLAME CURVATURE STATISTICS IN AXISYMMETRICAL TURBULENT JET FLAMES

Flame curvature in axisymmetric turbulent jet flames are obtained expe rimentally for u'/S-L from 0.8-1.5. The measurements indicate that the flame curvature statistics exhibit a substantial change as a function of the axial location in turbulent jet flames primarily due to the ev olution of flame wrinkle structures. In particular, it is found that t he flame curvature tends to be very small near the burner exit, while development of the flame wrinkle structures further from the burner ex it results in an increase in magnitude and asymmetry in flame curvatur e probability density functions (pdf's). The mean flame curvature in t he vertical plane is close to zero in spite of the asymmetry in the fl ame curvature pdf's except near the flame tip where the mean flame cur vature becomes negative due to the frequent occurrences of cusps. In c ontrast, the flame curvature in the horizontal plane are strongly affe cted by the burner dimension and geometry in that the magnitude of bot h positive and negative fame curvatures are increased by the finite cu rvature of the conical jet flame shape in the mean. The mean flame cur vature in the horizontal plane tends to be of the order of the burner radius. The flame orientation statistics of turbulent jet flames have also been obtained, which show a similar evolution as a function of th e distance from the burner exit.