Airflow Dynamics Over Unvegetated and Vegetated Dunes

Notable progress has been made in the 80 years following Bagnold's (1941) seminal work on the physics of windblown sand and desert dunes, yet a range of challenges remain for quantifying and modelling wind flow and eolian sand transport over complex dune terrain. These challenges arise from fundamental differences in airflow dynamics over topographically complex surfaces that limit the applicability of conventional boundary layer theory, as well as from a multitude of interactions between dune form, wind flow, sediment transport, and roughness elements, including vegetation, that vary over space and time. In recent decades, significant advances have been made using wind tunnel simulations, detailed field experiments using three-dimensional ultrasonic anemometry, and numerical flow field simulations that, combined, have improved our ability to more accurately model and characterize dune morphodynamics. This chapter provides a comprehensive review of both the fundamentals and recent advances in our understanding of airflow dynamics over a wide range of dune terrain from relatively simple transverse dunes to more complex vegetated dunes such as nebkha and coastal foredunes. New insights from computational fluid dynamics (CFD) modelling approaches are also presented. The review identifies persistent knowledge gaps and opportunities for further research on the measurement and modelling of airflow and sand transport patterns that maintain dune form and function.