The structure of dissipative scales in axisymmetric turbulent gas-phase jets

Abstract

Results are reported for an experimental study directed at investigating the fine scale structure of turbulent jet flows using the simultaneous imaging of the concentration and velocity fields. The measurements are obtained in an axisymmetric coflowing jet using particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) imaging of acetone vapor seeded into the jet gas. The measurements resolve the Kolmogorov scale, η, of the flow. These measurements are used to investigate the relationships among the vorticity, strain rate, kinetic energy dissipation, and scalar dissipation fields. The data are also used to analyze the physical size of the structures in the scalar and kinetic energy dissipation fields. The results show good correlation between regions of high compressive principal strain, scalar dissipation, and kinetic energy dissipation. Structures in the scalar dissipation field are seen to be sheet-like with thicknesses ranging between 1η and 6η, while those in the kinetic energy dissipation field are more topologically complex and range in scale from 1η to 10η. The mean sizes of scalar and kinetic energy dissipative structures are 3η and 4η, respectively. The constant Λ relating mean scalar dissipative structure size to outer scale variables () is measured to be 7.8. These results indicate that scalar dissipative structures are approximately a factor of two smaller than has been suggested in previous studies.

On the effect of heat release in turbulence spectra of non-premixed reacting shear layers

“…In reacting flows D can vary substantially in different regions of the flow owing to its dependence on temperature. Experimental investigations of the behaviour of the statistics of χ include, for example, Namazian, Schefer & Kelly (1988); Gladnick, LaRue & Samuelsen (1990); Boyer & Queiroz (1991) ;Nandula, Brown & Pitz (1994); Everest et al (1995); Chen & Mansour (1996); Buch & Dahm (1998) ;Fielding, Schaffer & Long (1998); Karpetis & Barlow (2002); Tsurikov & Clemens (2002) ;Su & Clemens (2003); Barlow & Karpetis (2004); Noda et al (2005); Wang, Clemens & Varghese (2005); and Markides & Mastorakos (2006). Complementary numerical studies, primarily using direct numerical simulations (DNS), have also verified some of the experimental findings, e.g.…”

Development of macro- and micromixing in confined flows of reactive fluids

“…As mentioned above, the reaction is possible between the lamellae of the acid and base only within thin diffusion layers that occupied a small vortex volume. The thickness of the scalar dissipation layers ranged from one to 6k K at Sc $ 1.5 [26], and it is obviously smaller at Sc ) 1. Therefore, only a small portion of the available acid fraction captured by the vortex was consumed in the reaction.…”

Ignition, flame structure and near-wall burning in transverse hydrogen jets in supersonic crossflow

“…We were able to carry out this analysis only on the J = 5.0 case because we did not have sufficient samples for other (lower-J) cases or the reacting shear layer was absent (for the J = 0.3 case). In particular, the OH layers in the shear layer were extracted using an algorithm based on the one by Tsurikov (Tsurikov 2002;Tsurikov & Clemens 2002). The algorithm first identifies and classifies the layer, then finds its centreline, thus its direction, and finally defines the layer profile along a line perpendicular to the local direction of the layer.…”