On the identification of intense Reynolds stress structures in wall-bounded flows using information-limited two-dimensional planar data

Abstract

Historically the majority of investigations into the transfer of momentum have been focused on the classification and statistical analysis of single points of above average Reynolds stress. These regions of intense Reynolds stress are responsible for the majority of the wall-normal transfer of momentum and most of the production of turbulent kinetic energy. Single point hot-wire measurements were critical in understanding the roll of the regions of intense Reynolds stress, but provide no information about their formation, spatial extent, orientation, nor their position relative to other types of coherent structures. DNS of turbulent wall-bounded shear flows overcomes this information-limit by providing the full three-dimensional (3D) volumetric flow field information, albeit limited to low Reynolds numbers. Advancements in particle image velocimetry (PIV) have enabled the measurement of High Reynolds number turbulent wall-bounded shear flows, with measurements of two instantaneous velocity components in a single two-dimensional (2D) plane (e.g. streamwise wall-normal plane). However, the deductions and conclusions based on these information limited 2D measurements may be detrimentally affected by the lack of information from the third dimension. This study aims to address this issue by using DNS from a turbulent channel flow at Reτ=945 and comparing the geometric characterisation of intense Reynolds stress objects computed from the full 3D flow fields with those computed from the information-limited 2D flow fields that span streamwise wall-normal planes.