Wind tunnel simulation of the three‐dimensional airflow patterns around shrubs

Dunes formed around vegetation such as shrubs are common in arid and semiarid regions and some coastal regions. Understanding their dynamics requires insights into the airflow patterns around shrubs. Thus, we analyzed the horizontal and vertical flow patterns around model shrubs using wind measurements obtained by particle image velocimetry in a scaled wind tunnel simulation. Flow patterns around shrubs were complicated by the presence of bleed flows and displaced flows. Below a critical shrub density (between 0.05 and 0.08), bleed flow is dominant. The flows separate in both horizontal and vertical planes when the shrub density equals or exceeds this critical density, resulting in reverse cells in the lee of shrubs. The horizontal reverse cells are characterized by two symmetrical, opposing reverse eddies, whereas the vertical reverse cells form a single eddy. The positions of the reverse cells shift in response to changes in shrub density, reflecting the interaction between bleed flow and reverse flow. The parameters of horizontal reverse cells are functions of shrub density and wind velocity. Parameters of vertical reverse cells change mainly with respect to shrub density and vary only slightly with wind velocity. The lengths of the horizontal and vertical reverse cells are correlated, reflecting interactions between them. Field experiments on dune morphology will be required to relate these airflow patterns to dune development.