Turbulence fields in the lee of two-dimensional transverse dunes simulated in a wind tunnel

The turbulence field of airflow in the lee of a dune has significant impacts on dune dynamics and related processes. We used particle image velocimetry in a wind tunnel simulation to obtain detailed velocity measurements in the lee of two-dimensional transverse dune models, then used the results to analyse their turbulence fields. The dune models used in this study had a single lee angle of 30 degrees, and a total of six stoss angles: 3 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees and 25 degrees. We used vorticity, turbulence intensity, Reynolds stress and turbulent kinetic energy to characterize the turbulence fields. These parameters were functions of stoss angle, wind velocity, distance from the dune crest and height above the ground surface. The stoss angles could generally be divided into two groups based on the profiles of mean velocity, turbulence and Reynolds stress. Stoss angles of 3 degrees and 5 degrees usually had similar profiles, and angles of 15 degrees, 20 degrees and 25 degrees formed a second group with similar profiles. The profiles for the stoss angle of 10 degrees were usually transitional and were intermediate between the two groups. Vorticity, Reynolds stress and turbulent kinetic energy increased monotonically with increasing free-stream wind velocity, but their variations with respect to the stoss angle were complex. The stoss angles of 15 degrees and 20 degrees had the maximum values of these three parameters, thus these angles may have special significance in dune development given the characteristics of the mean velocity fields and turbulence fields they produce within the lee airflow. It is the streamwise velocity component and its turbulence that determine the surface shear stress. Copyright (C) 2008 John Wiley & Sons, Ltd.