Coherent structures in a turbulent mixing layer: a comparison between direct numerical simulations and experiments.

An eduction scheme was developed in an attempt to determine the characteristics of large scale vortical structures in a turbulent mixing layer. This analysis scheme was applied to a set of experimental data taken in a new, larger mixing layer facility designed to minimize boundary and resonance effects. A similar scheme was developed to apply to the results of a direct numerical simulation of a temporally growing mixing layer. A comparison of the two approaches shows important similarities in the coherent structures. The numerical simulations indicate that low levels of coherent forcing can dramatically change the evolution of the mixing layer. In the absence of such forcing, the numerical simulations and experiments show a lack of regularity in the transverse position, spacing, amplitude, shape and spanwise coherence of the large scale vortical structures. (A)