Inner-Outer Interactions in a Turbulent Boundary Layer Overlying Complex Roughness

Abstract eng:
Experiments were performed to investigate the modulating influences of the inertial-region large-scale structures, on the small scales near the wall in a turbulent boundary layer. Hot-wire measurements were made in flow over a smooth- and a rough-wall (a multiscale topography), in light of recent studies establishing the phenomena in flows over smooth walls. One-probe measurements capture the streamwise turbulent kinetic energy distribution among various scales and local large-scale–small-scale interactions across the flow. Twoprobe measurements, measuring the large scales in the inertial region and small scales in the near-wall region simultaneously, were then performed to investigate the modulation influences. Amplitude (AM) and frequency modulation (FM) were observed in rough-wall flow, similar in structure to that of the smooth-wall flow. Further, among different spanwise locations investigated in flow over the roughness, it was found that the subtle differences in interactions exist between regions of low-momentum pathways (LMPs) and high-momentum counter parts (HMPs).

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