Experimental investigation of the relationship between strain and scalar dissipation in gas-phase turbulent jets

A study is described that is aimed at investigating the strain/scalar dissipation layer relationship in unity Schmidt number turbulent flows. This analysis makes use of simultaneous PIV/acetone PLIF data that were acquired in a previous study of turbulent planar nonreacting jets. In particular, we seek to investigate the extent to which the measured strain field can be used to predict the structure of the measured scalar dissipation layers. A comparison of the strain/dissipation layer relationship with the theoretical, 1-D opposed flow solution corresponding to a steady uniform strain field was made, and the results suggest that it is not possible to correctly predict dissipative layer length scales based on this simplified theory. Several different reasons for the lack of agreement with the simple theory are considered, but we believe that unsteady effects are the dominant reason. To investigate unsteady effects, the unsteady scalar transport equation was solved numerically, where a uniform strain field was imposed that varied sinusoidally in time. The results of this simplified model appear to capture the qualitative trends seen in the measured data.