Phase relationships in presence of a synthetic large-scale in a turbulent boundary layer

A synthetic spanwise-constant spatio-temporal mode is excited in a flat plate turbulent boundary layer through a spatially impulsive patch of dynamic wall-roughness. The streamwise wavelength of the synthetic mode approximately corresponds to the very large-scale motions present in high Reynolds number wall turbulence. Hot wire anemometer measurements made downstream of the roughness forcing reveal the nature of the two dimensional synthetic large-scale and its influence on the small-scale turbulence. A clear phase organizing effect on the small-scales is noticed in presence of the synthetic large-scale. A thorough understanding of these phase relations lays the foundation for a framework that allows for practical manipulation of energetic small-scale turbulence through large-scale inputs by utilizing the inherent non-linear coupling present in the governing Navier-Stokes equations.