Investigation of inner-outer interactions in a turbulent boundary layer using time-resolved PIV

Experiments were performed in a refractive-index-matching (RIM) flow facility to investigate inner-outer interactions over smooth and rough walls using time-resolved PIV. Lack of nearwall reflections due to RIM enabled measurements very close to the smooth and rough surfaces using PIV. Two cameras, with different fields of view and spatial resolutions, were used to view the streamwise-wall normal plane. Measurements of the smooth-wall boundary layer display amplitude and frequency modulations similar to those reported in the literature. Further, conditional averages were used to evaluate the spatio-temporal evolution of the largescale influences on the small scales, and their influences on energy distributions of the small-scale turbulence. The observations from the conditional averages yielded a picture consistent with the hotwire measurements reported in the literature. The smooth-wall measurements and analysis described in the current work established the phenomena and analytical tools to extend the current techniques to better understand roughness effects.