Concurrent scale interactions in the far-field of a turbulent mixing layer

Abstract

The interaction between large-and small-scale fluctuations in turbulent flow is not only of great fundamental interest but an understanding of these interactions is fundamental to the modelling of the sub-grid scale (SGS) stresses in a large eddy simulation (LES). Particle image velocimetry (PIV) data is acquired with two different spatial resolutions, simultaneously, in the self-similar region of a turbulent planar mixing layer. The SGS activity is observed to be amplified by concurrent large-scale low momentum fluctuations and attenuated by high momentum fluctuations with both the sign and magnitude of the large-scale fluctuations being of significance. Further, regions in which the orientation of the large-scale Reynolds stress tensor is aligned perpendicularly to the direction of the mean shear of the flow are shown to lead to an increased level of small-scale activity.