The effects of heat release on turbulent nonpremixed planar jet flames

The aim of this work is to address the issue of how high heat release resulting from exothermic reactions affects the structure of transitional and turbulent nonpremixed planar jet flames. The approach taken was to conduct a thorough comparative study of planar jet flames and nonreacting planar jets where global differences between the two types of flows were accounted for. A particular emphasis was placed on studying jet flames and nonreacting jets with approximately matched local Reynolds numbers and under momentum-dominated conditions. The diagnostic techniques used included particle image velocimetry (PIV), planar laser-induced fluorescence (PLIF), and planar laser Mie scattering (PLMS).; The PLMS measurements show that the jet flames and nonreacting jets exhibit a significantly different turbulent large-scale structure. In particular, the presence of the flame seems to suppress the large-scale coherent structures that are present in the nonreacting jets. This difference does not appear to be due to global Reynolds number effects or global density differences resulting from heat release. PIV and PLIF measurements were used to investigate the relationships among vorticity, shear, principal strain rates, 2-D dilatation, and other kinematic quantities on OH surfaces in jet flames and on 2-D scalar dissipation rate layers and iso-scalar surfaces in nonreacting planar jets. Simultaneous vorticity ($wz$) contours and OH PLIF images in turbulent jet flames suggest that the reaction zones are strongly correlated with high vorticity. The high vorticity is apparently due to the large shear that is associated with the reaction zones. This shear causes the principal compressive strain ($S\prime min$) field to be predominately oriented at 45° to the flow direction. For the moderate Reynolds number flame, thin OH zones tend to be associated with high compressive strain and to align normal to the preferred direction of strain; however, such an alignment does not occur for the lowest Reynolds number flame. In contrast, the nonreacting jet dissipation layers and iso-scalar surfaces are not strongly correlated with vorticity and the underlying strain field does not exhibit a preferred direction.; These trends were investigated with a statistical analysis. (Abstract shortened by UMI.)...