View article

The primary goal of the present effort is to enhance the current understanding of inner-outer interactions in rough-wall turbulent boundary layers. These interactions were recently established over smooth-wall turbulent boundary layers as modulating interactions, where the outer layer large scales amplitude and frequency modulate the near-wall small scales. Given that the outer layer dynamics responsible for these modulations are identical in most high-Reynolds-number (Re) rough-wall flows as well, similar modulation interactions are are explored to identify the similarities and differences of these interactions and establish a spatio-temporal description of the same. This is particularly important given the engineering significance of the flows over rough walls. This work was performed as two parts. In the first part, high temporal-resolution boundary layer hot-wire measurements were made in a wind tunnel, that fully resolved all dynamical scales temporally at fixed points in the flow. Flows over smooth and rough walls were investigated, with the latter being a complex topography indicative of a realistic roughness commonly encountered in engineering applications. Single-and two-probe measurements provided a dual perspective on the large scales, and enabled analysis of analytical techniques commonly employed. With these measurements, it was found that the nature of amplitude and frequency modulation occur even over this complex topography, and that the structure is very similar to that observed in smooth-wall flow. Further, the simultaneous two-probe measurements enabled the investigation of predictive models, which interestingly …