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 their flow-parallel bed profile compared to mature dunes. Flow associated with the development of these “protodunes,” wherein the crest gradually shifts downstream towards its mature state, was investigated by studying the perturbation of the turbulent boundary layer over a succession of representative bedforms. Rigid, three-dimensional models were studied in a refractive-index-matched experimental flume that enabled near-surface quantification of mean velocities and Reynolds stresses using particle-image velocimetry in wall-normal and wall-parallel measurement planes. Data indicate strong, topographically induced flow perturbations over the protodunes, to a similar relative degree to that found over mature dunes, despite their low-angled slopes. The shape of the crest is found to be an important factor in the development of flow perturbations, and only in the case with the flattest crest was maximal speed-up of flow, and reduction in turbulent stresses, found to occur upstream of the crest. Investigation of the log-linearity of the boundary layer profile over the stoss sides showed that, although the profile is strongly perturbed, a log-linear region exists, but is shifted vertically. A streamwise trend in friction velocity is thus present, showing a behavior similar to the trends in mean velocity. Analysis of the growth of the internal boundary layer on the dune stoss sides, beginning at the toe region, reveals a similar development for all dune shapes, despite clear differences in mean velocity and turbulent stress perturbations in their toe regions. The data presented herein provide the first documentation of flow over morphologies broadly characteristic of subtle, low-angle, aeolian protodunes, and indicate key areas where further study is required to yield a more complete quantitative understanding of flow–form–transport couplings that govern their morphodynamics.
National Science Foundation, USA (NE/R010196NSFGEONERC, NSFGEO1829541 and NSFGEO1829513)
NSFGEO-NERC: The Origin of Aeolian Dunes (TOAD)
Natural Environment Research CouncilFind out more...
- Social Sciences and Humanities
- Geography and Environment
Published inEarth Surface Processes and Landforms
Pages1439 - 1454
- AM (Accepted Manuscript)
Rights holder© John Wiley & Sons, Ltd
Publisher statementThis is the peer reviewed version of the following article: Bristow, N.R. ... et al. (2022). Topographic perturbation of turbulent boundary layers by low-angle, early-stage aeolian dunes. Earth Surface Processes and Landforms, 47 (6), 1439-1454, which has been published in final form at https://doi.org/10.1002/esp.5326. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.