X. Wu ^a,b,c,*, X. Zou ^a, Z.C. Zheng ^a,d, C. Zhang ^a,e

a State Key Laboratory of Earth Surface Processes and Resource Ecology, MOE Engineering Center of Desertification and Blown-sand Control, Beijing Normal University, Beijing 100875, China

b  Department of Mechanical Engineering, Kansas State University, Manhattan, KS 66502, USA

c  College of Global Change and Earth System Science, Beijing Normal University, Beijing 100875, China

d  Aerospace Engineering Department, University of Kansas, Lawrence 66045, USA

e  Engineering & Wind Erosion Research Unit, USDA-ARS, Manhattan, KS 66502, USA

Abstract: Airflow is measured over a barchan dune in the field and over a scaled-down model in a wind tunnel. The change of the flow speed over the stoss side is represented by the change of speed-up ratio. According to the field measurement, the wind profiles within 0-3m above the stoss can be divided into two segments. The lower segment, about 0.66 m thick, is the inner-boundary layer, within which the friction velocities derived from the wind profiles increase from the upwind inter-dune region to the upper stoss, and then decrease near the dune top. This change, together with the changes of airflow field, speed-up ratio and sand flux, is related to the morphological change and contributes to the stable shape and height of a barchan dune. In the wind tunnel, airflow varies in a similar way as in the field, with the speed-up ratios constantly higher than 1.0 and increasing along the stoss slope. While the segmentation of wind profiles also occurs in the wind tunnel, friction velocities derived from the wind profiles decrease along the stoss, indicating a very thin inner-boundary layer above the wind tunnel model where the detailed wind-speed change becomes difficult to measure using the present instruments.

Keyword: Barchan dune; Field measurement; Wind profile; Wind-tunnel simulation