The Association of Scalar Dissipation Rate Layers and OH Zones with Strain, Vorticity, and 2-D Dilatation Fields in Turbulent Nonpremixed Jets and Jet Flames

Simultaneous PIV and PLIF methods were used to investigate the relationship between vorticity, principal strain rates, and 2-D dilatation on reaction surfaces in nonpremixed planar jet flames and on 2-D scalar dissipation rate layers and iso-scalar surfaces in nonreacting planar jets. Examination of simultaneous vorticity (ω z) contours and PLIF images in unsteady laminar and turbulent flames suggest that the reaction zone is associated with long correlated regions of high vorticity several times the outer-scale frequency, as well as high values of principal compressive strain (σmin) oriented at 45° to the flow direction and low values of negative 2-D dilatation. Compared to the simultaneous nonreacting flow measurements, the association of high σmin and negative 2-D dilatation on isoscalar surfaces is similar to the trends observed in the reaction zones of flames. However, significant differences exist in the relationship of σmin direction relative to surface orientation and ω z and surface location. These trends are quantified with PDFs and show that ωz is most likely to have a magnitude near the outer-scale frequency within the reaction zone, while zero ω z is likeliest on the nonreacting iso-scalar surfaces. In addition, it is observed that σmin orientation to the iso-scalar surfaces tends to align normal to the surface in nonreacting flows, but this trend is somewhat altered in the reacting cases. In all cases, the minimum principal strain is compressive over 80% of the time, suggesting a predominately sheet-like topology for both the OH layers and nonreacting scalar dissipation layers. In addition, joint PDFs on the layer surfaces indicate that the relationships between 2-D dilation and σmin remain relatively unchanged in the presence of heat release, but the association of ω z and σmin is significantly altered.