Topographic perturbation of turbulent boundary layers by low‐angle, early‐stage aeolian dunes

Decimeter-scale early-stage aeolian bedforms represent topographic features that differ notably from their mature dune counterparts, with nascent forms exhibiting more gently sloping lee sides and a reverse asymmetry in flow-parallel bed profile compared to dunes. Flow associated the development of these “protodunes,” wherein crest gradually shifts downstream towards its state, was investigated by studying perturbation turbulent boundary layer over succession representative bedforms. Rigid, three-dimensional models were studied refractive-index-matched experimental flume enabled near-surface quantification mean velocities Reynolds stresses using particle-image velocimetry wall-normal wall-parallel measurement planes. Data indicate strong, topographically induced flow perturbations protodunes, similar relative degree found dunes, despite low-angled slopes. The shape is be an important factor perturbations, only case flattest maximal speed-up flow, reduction stresses, occur upstream crest. Investigation log-linearity stoss showed that, although strongly perturbed, log-linear region exists, but shifted vertically. A streamwise trend friction velocity thus present, showing behavior trends velocity. Analysis growth internal on sides, beginning at toe region, reveals for all shapes, clear differences stress regions. data presented herein provide first documentation morphologies broadly characteristic subtle, low-angle, key areas where further study required yield complete quantitative understanding flow–form–transport couplings govern morphodynamics.